SALICYLAMIDE-LANTHANIDE COMPLEXES FOR USE AS LUMINESCENT MARKERS

Abstract: The present invention provides luminescent lanthanide metal chelates comprising a metal ion of the lanthanide series and a complexing agent comprising at least one salicylamidyl moiety. Also provided are probes incorporating the salicylamidyl ligands of the invention and methods utilizing the ligands of the invention and probes comprising the ligands of the invention.

Description: SALICYLAMIDE-LANTHANIDE COMPLEXES FOR USE AS LUMINESCENT MARKERS CROSS-REFERENCES TO RELATED APPLICATIONS This application claims priority to United States Provisional Patent Application Serial No. 60/120,600, filed on February 18, 1999. This application is also related to United States Provisional Patent Application Serial No. 60/120,881 filed on February 18, 1999 and United States Patent Application Serial No. . bearing attorney Docket No. 02307V-093410US, and filed on an even date herewith. Each of these documents are incorporated herein by reference in their entirety for all purposes. STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT This work was partially supported by grants from the National Institutes of Health (DK32999) and the United States Department of Energy (DEAC0376F00098). The Government may have rights in the subject matter disclosed herein. BACKGROUND OF THE INVENTION There is a continuous and expanding need for rapid, highly specific methods of detecting and quantifying chemical, biochemical and biological substances as analytes in research and diagnostic mixtures. Of particular value are methods for measuring small quantities of nucleic acids, peptides, pharmaceuticals, metabolites, microorganisms and other materials of diagnostic value. Examples of such materials include small molecular bioactive materials (e.g., narcotics and poisons, drugs administered for therapeutic purposes, hormones), pathogenic microorganisms and viruses, antibodies, and enzymes and nucleic acids, particularly those implicated in disease states. The presence of a particular analyte can often be determined by binding methods that exploit the high degree of specificity, which characterizes many biochemical and biological systems. Frequently used methods are based on, for example, antigen- antibody systems, nucleic acid hybridization techniques, and protein-ligand systems. In these methods, the existence of a complex of diagnostic value is typically indicated by the presence or absence of an observable "label" which has been attached to one or more of the interacting materials. The specific labeling method chosen often dictates the usefulness and versatility of a particular system for detecting an analyte of interest. Preferred labels are inexpensive, safe, and capable of being attached efficiently to a wide variety of chemical, biochemical, and biological materials without significantly altering the important binding characteristics of those materials. The label should give a highly characteristic signal, and should be rarely, and preferably never, found in nature. The label should be stable and detectable in aqueous systems over periods of time ranging up to months. Detection of the label is preferably rapid, sensitive, and reproducible without the need for expensive, specialized facilities or the need for special precautions to protect personnel. Quantification of the label is preferably relatively independent of variables such as temperature and the composition of the mixture to be assayed. A wide variety of labels have been developed, each with particular advantages and disadvantages. For example, radioactive labels are quite versatile, and can be detected at very low concentrations, such labels are, however, expensive, hazardous, and their use requires sophisticated equipment and trained personnel. Thus, there is wide interest in non-radioactive labels, particularly in labels that are observable by spectrophotometric, spin resonance, and luminescence techniques, and reactive materials, such as enzymes that produce such molecules. Labels that are detectable using fluorescence spectroscopy are of particular interest, because of the large number of such labels that are known in the art. Moreover, the literature is replete with syntheses of fluorescent labels that are derivatized to allow their facile attachment to other molecules, and many such fluorescent labels are commercially available. In addition to being directly detected, many fluorescent labels operate to quench the fluorescence of an adjacent second fluorescent label. Because of its dependence on the distance and the magnitude of the interaction between the quencher and the fluorophore, the quenching of a fluorescent species provides a sensitive probe of molecular conformation and binding, or other, interactions. An excellent example of the use of fluorescent reporter quencher pairs is found in the detection and analysis of nucleic acids. An alternative detection scheme, which is theoretically more sensitive than autoradiography, is time-resolved fluorimetry. According to this method, a chelated lanthanide metal with a long radiative lifetime is attached to a molecule of interest. Pulsed excitation combined with a gated detection system allows for effective discrimination against short-lived background emission. For example, using this approach, the detection and quantification of DNA hybrids via an europium-labeled antibody has been demonstrated (Syvanen et al, Nucleic Acids Research 14: 1017-1028 (1986)). In addition, biotinylated DNA was measured in microtiter wells using Eu- labeled strepavidin (Dahlen, Anal. Biochem, 164: 78-83 (1982)). A disadvantage, however, of these types of assays is that the label must be washed from the probe and its fluorescence developed in an enhancement solution. A further drawback has been the fact that the fluorescence produced has only been in the nanosecond (ns) range, a generally unacceptably short period for adequate detection of the labeled molecules and for discrimination from background fluorescence. In view of the predictable practical advantages it has been generally desired that the lanthanide chelates employed should exhibit a delayed fluorescence with decay times of more than 10 μs. The fluorescence of many of the known fluorescent chelates tends to be inhibited by water. As water is generally present in an assay, particularly an immunoassay system, lanthanide complexes that undergo inhibition of fluorescence in the presence of water are viewed as somewhat unfavorable or impractical for many applications. Moreover, the short fluorescence decay times is considered a disadvantage of these compounds. This inhibition is due to the affinity of the lanthanide ions for coordinating water molecules. When the lanthanide ion has coordinated water molecules, the absorbed light energy (excitation energy) is transferred from the complex to the solvent rather than being emitted as fluorescence. Thus, lanthanide chelates, particularly coordinatively saturated chelates having excellent fluorescence properties are highly desirable. In the alternative, coordinatively unsaturated lanthanide chelates that exhibit acceptable fluorescence in the presence of water are also advantageous. Such chelates that are derivatized to allow their conjugation to one or more components of an assay, find use in a range of different assay formats. The present invention provides these and other such compounds and assays using these compounds. SUMMARY OF THE INVENTION Luminescent (including fluorescent and phosphorescent) markers find a wide variety of applications in science, medicine and engineering. In many situations, these markers provide competitive replacements for radiolabels, chromogens, radiation- dense dyes. etc. Moreover, improvements in fluorimetric instrumentation have increased attainable sensitivities and permitted quantitative analysis. Lanthanide chelates in combination with time-resolved fluorescent spectroscopy is a generally accepted immunochemical tool. Presently preferred lanthanide ions include, Dy " , Sm" τ , Tb ~ + , Ev ' ~ and Eu", ΗάH Yb "~ . Other lanthanide ions, such as La "" \ Gd ~+ and Lu" + are useful, but generally less preferred. The present invention provides lanthanide complexes that are extremely luminescent and possess many features desired for fluorescent markers and probes of use in fluorescent assay systems. Among these advantages are: 1) ligands acting as both chelators and chromophore/energy transfer devices; 2) very high quantum yields of lanthanide ion fluorescence of the present complexes in water without external augmentation, such as by micelles or fluoride; 3) high stability and solubility of these complexes in water; 4) an extremely easy synthesis that employs inexpensive starting materials; and 5) facile access to many derivatives for linking these luminescent probes to, for example, an immunoreactive agent or solid support (e.g., polymer). The present invention provides a new class of lanfhanide-complexing ligands that incorporate salicylamide moieties within their structures and luminescent metal complexes of these ligands. The compounds of the invention include salicylylamide-based bidentate, tetradentate and other higher polydentate ligands. The compounds of the invention are easily prepared in good yields. Thus, in a first aspect, the present invention provides a luminescent lanthanide metal chelate comprising a metal ion of the lanthanide series and a complexing agent comprising at least one salicylamidyl moiety. In a second aspect, the invention provides a compound having a structure according to Formula I: In Formula I. R 1 and R 2 are members independently selected from the group consisting of alkyl. substituted alkyl, halogen and — OR 6 , wherein R 6 is a member selected from the group consisting of H, alkyl. substituted alkyl groups and a single negative charge. R 4 , R\ R 7 , R 10 and R 20 are members independently selected from the group consisting of H, alkyl and substituted alkyl groups. R\ R and R are members independently selected from the group consisting of alkyl and substituted alkyl groups. R 1 1 , R 12 , R 13 , R 21 , R 22 and R 23 are members independently selected from alkyl. substituted alkyl, H, — NR 14 R 15 , — NO 2; — OR 16 , — OOR 17 , wherein, R 14 , R 15 , R 16 and R 17 are members independently selected from the group consisting of H, alkyl and substituted alkyl, wherein R 17 can optionally form a ring with R 1 1 , R1 ^ or both, and R 7 " ) can optionally form a ring with R , R" " or both. The rings are members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocyclyl and saturated heterocyclyl ring systems. Q 1 is — OR 18 and Q 2 is — OR 19 , wherein R 18 and R 19 are members independently selected from H, an enzymatically labile group, a hydrolytically labile group and a single negative charge. The letters a and z are independently selected from the group consisting of 0 and 1, with the proviso that when a is 0, N 1 is covalently attached directly to carbonyl 1 ', and when z is 0, N 2 is covalently attached directly to carbonyl group 2'. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exemplary synthetic scheme for the preparation of the TRENSAM ligand of the invention. FIG. 2 is an overlay plot of spectra obtained from the batch spectrophotometric titration of the ligand TRENSAM by TbCl 3 in MeOH. FIG. 3 is an overlay plot of a calculated spectrum of M^ and an observed spectrum for TRENSAM. FIG. 4 (A-B) are views of the x-ray crystal structure of Tb[TRENSAM] 2 * : (A) Full (top) view; and (B) partial (bottom) view. FIG. 5 is a view of the polyhedron coordination around Tb 3+ in Tb[TRENSAM] 2 + . FIG. 6 (A-B) are structural Formulae of representative dendrimers of use in the present invention. FIG. 7 is a synthetic scheme leading to a versatile intermediate for the synthesis of ligands of the invention. FIG. 8 is a synthetic scheme leading to ligands of the invention having backbones of variable length. FIG. 9 is a schematic diagram if a multiplex assay of the invention. FIG. 10 is a table of representative structures for exemplary compounds of the invention. DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS Abreviations As used herein, "SL," refers to the salicylamidyl derived ligands of the invention. "SL" encompasses the ligands of the invention in both their free state and when they have complexed one or more metal ions. Moreover, "SL" encompasses ligands that include one or more salicylamidyl groups in combination with one or more phthamidyl groups ("SPL"). Definitions Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Generally, the nomenclature used herein and the laboratory procedures in molecular biology, organic chemistry and nucleic acid chemistry and hybridization described below are those well known and commonly employed in the art. Standard techniques are used for nucleic acid and peptide synthesis. Generally, enzymatic reactions and purification steps are performed according to the manufacturer's specifications. The techniques and procedures are generally performed according to conventional methods in the art and various general references (see generally, Sambrook et al. MOLECULAR CLONING: A LABORATORY MANUAL, 2d ed. (1989) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., which is incorporated herein by reference), which are provided throughout this document. The nomenclature used herein and the laboratory procedures in analytical chemistry, and organic synthetic described below are those known and employed in the art. Standard techniques, or modifications thereof, are used for chemical syntheses and chemical analyses. "Analyte", as used herein, means any compound or molecule of interest for which a diagnostic test is performed, such as a biopolymer or a small molecular bioactive material. An analyte can be, for example, a protein, peptide, carbohydrate, polysaccharide, glycoprotein, hormone, receptor, antigen, antibody, virus, substrate, metabolite, transition state analog, cofactor. inhibitor, drug, dye, nutrient, growth factor, etc., without limitation. As used herein, "energy transfer" refers to the process by which the fluorescence emission of a fluorescent group is altered by a fluorescence-modifying group. If the fluorescence-modifying group is a quenching group, then the fluorescence emission from the fluorescent group is attenuated (quenched). Energy transfer can occur through fluorescence resonance energy transfer, or through direct energy transfer. The exact energy transfer mechanisms in these two cases are different. It is to be understood that any reference to energy transfer in the instant application encompasses all of these mechanistically-distinct phenomena. As used herein, "energy transfer pair" refers to any two molecules that participate in energy transfer. Typically, one of the molecules acts as a fluorescent group, and the other acts as a fluorescence-modifying group. The preferred energy transfer pair of the instant invention comprises a fluorescent group and a quenching group of the invention. There is no limitation on the identity of the individual members of the energy transfer pair in this application. All that is required is that the spectroscopic properties of the energy transfer pair as a whole change in some measurable way if the distance between the individual members is altered by some critical amount. "Energy transfer pair" is used to refer to a group of molecules that form a single complex within which energy transfer occurs. Such complexes may comprise, for example, two fluorescent groups, which may be different from one another and one quenching group, two quenching groups and one fluorescent group, or multiple fluorescent groups and multiple quenching groups. In cases where there are multiple fluorescent groups and/or multiple quenching groups, the individual groups may be different from one another. As used herein, "fluorescence-modifying group" refers to a molecule of the invention that can alter in any way the fluorescence emission from a fluorescent group. A fluorescence-modifying group generally accomplishes this through an energy transfer mechanism. Depending on the identity of the fluorescence-modifying group, the fluorescence emission can undergo a number of alterations, including, but not limited to, attenuation, complete quenching, enhancement, a shift in wavelength, a shift in polarity, and a change in fluorescence lifetime. One example of a fluorescence-modifying group is a quenching group. "Fluorescence resonance energy transfer" or "FRET" is used interchangeably with FET, and refers to an energy transfer phenomenon in which the light emitted by the excited fluorescent group is absorbed at least partially by a fluorescence- modifying group of the invention. If the fluorescence-modifying group is a quenching group, then that group will preferably not radiate a substantial fraction of the absorbed light as light of a different wavelength, and will preferably dissipate it as heat. FRET depends on an overlap between the emission spectrum of the fluorescent group and the absorption spectrum of the quenching group. FRET also depends on the distance between the quenching group and the fluorescent group. "Moiety" refers to the radical of a molecule that is attached to another moiety. As used herein, "nucleic acid" means DNA, RNA, single-stranded, double- stranded, or more highly aggregated hybridization motifs, and any chemical modifications thereof. Modifications include, but are not limited to, those providing chemical groups that incorporate additional charge, polarizability, hydrogen bonding, electrostatic interaction, and fluxionality to the nucleic acid ligand bases or to the nucleic acid ligand as a whole. Such modifications include, but are not limited to, peptide nucleic acids, phosphodiester group modifications (e.g., phosphorothioates, methylphosphonates), 2'- position sugar modifications, 5-position pyrimidine modifications, 8-position purine modifications, modifications at exocyclic amines, substitution of 4-thiouridine, substitution of 5-bromo or 5-iodo-uracil; backbone modifications, methylations, unusual base-pairing combinations such as the isobases, isocytidine and isoguanidine and the like. Modifications can also include 3' and 5' modifications such as capping with a SL, a fluorophore or another moiety. As used herein, "quenching group" refers to any fluorescence-modifying group of the invention that can attenuate at least partly the light emitted by a fluorescent group. This attenuation is referred to herein as "quenching". Hence, illumination of the fluorescent group in the presence of the quenching group leads to an emission signal that is less intense than expected, or even completely absent. Quenching typically occurs through energy transfer between the fluorescent group and the quenching group. "Peptide" refers to a polymer in which the monomers are amino acids and are joined together through amide bonds, alternatively referred to as a polypeptide. When the amino acids are α-amino acids, either the L-optical isomer or the D-optical isomer can be used. Additionally, unnatural amino acids, for example, β-alanine, phenylglycine and homoarginine are also included. Commonly encountered amino acids that are not gene- encoded may also be used in the present invention. All of the amino acids used in the present invention may be either the D - or L -isomer. The L -isomers are generally preferred. In addition, other peptidomimetics are also useful in the present invention. For a general review, see, Spatola, A. F., in CHEMISTRY AND BIOCHEMISTRY OF AMINO ACIDS, PEPTIDES AND PROTEINS, B. Weinstein, eds., Marcel Dekker, New York, p. 267 (1983). The term "alkyl" is used herein to refer to a branched or unbranched, saturated or unsaturated, monovalent hydrocarbon radical, generally having from about 1- 30 carbons and preferably, from 4-20 carbons and more preferably from 6-18 carbons. When the alkyl group has from 1-6 carbon atoms, it is referred to as a "lower alkyl." Suitable alkyl radicals include, for example, structures containing one or more methylene, methine and/or methyne groups. Branched structures have a branching motif similar to i- propyl, t-butyl, i-butyl, 2-ethylpropyl, etc. As used herein, the term encompasses "substituted alkyls," and "cyclic alkyl." "Substituted alkyl" refers to alkyl as just described including one or more substituents such as lower alkyl, aryl, acyl, halogen (i.e., alkylhalos, e.g., CF . ,), hydroxy, amino, alkoxy, alkylamino, acylamino, thioamido, acyloxy, aryloxy, aryloxyalkyl, mercapto, thia, aza, oxo, both saturated and unsaturated cyclic hydrocarbons, heterocycles and the like. These groups may be attached to any carbon or substituent of the alkyl moiety. Additionally, these groups may be pendent from, or integral to, the alkyl chain. The term "aryl" is used herein to refer to an aromatic substituent, which may be a single aromatic ring or multiple aromatic rings which are fused together, linked covalently, or linked to a common group such as a methylene or ethylene moiety. The common linking group may also be a carbonyl as in benzophenone. The aromatic ring(s) may include phenyl, naphthyl, biphenyl, diphenylmethyl and benzophenone among others. The term "aryl" encompasses "arylalkyl" and "substituted aryl." "Substituted aryl" refers to aryl as just described including one or more functional groups such as lower alkyl, acyl, halogen, alkylhalos (e.g. CF ), hydroxy, amino. alkoxy. alkylamino, acylamino, acyloxy, phenoxy, mercapto and both saturated and unsaturated cyclic hydrocarbons which are fused to the aromatic ring(s), linked covalently or linked to a common group such as a methylene or ethylene moiety. The linking group may also be a carbonyl such as in cyclohexyl phenyl ketone. The term "substituted aryl" encompasses "substituted arylalkyl." The term "arylalkyl" is used herein to refer to a subset of "aryl" in which the aryl group is attached to another group by an alkyl group as defined herein. "Substituted arylalkyl" defines a subset of "substituted aryl" wherein the substituted aryl group is attached to another group by an alkyl group as defined herein. The term "acyl" is used to describe a ketone substituent, — C(O)R, where R is alkyl or substituted alkyl, aryl or substituted aryl as defined herein. The term "halogen" is used herein to refer to fluorine, bromine, chlorine and iodine atoms. The term "hydroxy" is used herein to refer to the group — OH. The term "amino" is used to — NRR', wherein R and R' are independently H, alkyl, aryl or substituted analogues thereof. "Amino" encompasses "alkylamino" denoting secondary and tertiary amines and "acylamino" describing the group RC(O)NR' . The term "alkoxy" is used herein to refer to the — OR group, where R is alkyl, or a substituted analogue thereof. Suitable alkoxy radicals include, for example, methoxy, ethoxy, t-butoxy, etc. As used herein, the term "aryloxy" denotes aromatic groups that are linked to another group directly through an oxygen atom. This term encompasses "substituted aryloxy" moieties in which the aromatic group is substituted as described above for "substituted aryl. " Exemplary aryloxy moieties include phenoxy, substituted phenoxy, benzyloxy, phenethyloxy, etc. As used herein "aryloxy alkyl" defines aromatic groups attached, through an oxygen atom to an alkyl group, as defined herein. The term "aryloxy alkyl" encompasses "substituted aryloxyalkyl" moieties in which the aromatic group is substituted as described for "substituted aryl. " As used herein, the term "mercapto" defines moieties of the general structure — S — R wherein R is H, alkyl, aryl or heterocyclic as described herein. The term "saturated cyclic hydrocarbon" denotes groups such as the cyclopropyl. cyclobutyl, cyclopentyl, etc.. and substituted analogues of these structures. These cyclic hydrocarbons can be single- or multi-ring structures. The term "unsaturated cyclic hydrocarbon" is used to describe a monovalent non-aromatic group with at least one double bond, such as cyclopentene, cyclohexene, etc. and substituted analogues thereof. These cyclic hydrocarbons can be single- or multi-ring structures. The term "heteroaryl" as used herein refers to aromatic rings in which one or more carbon atoms of the aromatic ring(s) are replaced by a heteroatom such as nitrogen, oxygen or sulfur. Heteroaryl refers to structures that may be a single aromatic ring, multiple aromatic ring(s), or one or more aromatic rings coupled to one or more non-aromatic ring(s). In structures having multiple rings, the rings can be fused together, linked covalently, or linked to a common group such as a methylene or ethylene moiety. The common linking group may also be a carbonyl as in phenyl pyridyl ketone. As used herein, rings such as thiophene, pyridine, isoxazole, phthalimide, pyrazole, indole, furan, etc. or benzo-fused analogues of these rings are defined by the term "heteroaryl. " "Heteroarylalkyl" defines a subset of "heteroaryl" wherein an alkyl group, as defined herein, links the heteroaryl group to another group. "Substituted heteroaryl" refers to heteroaryl as just described wherein the heteroaryl nucleus is substituted with one or more functional groups such as lower alkyl, acyl, halogen, alkylhalos (e.g. CF 3 ), hydroxy, amino, alkoxy, alkylamino, acylamino, acyloxy, mercapto, etc. Thus, substituted analogues of heteroaromatic rings such as thiophene, pyridine, isoxazole, phthalimide, pyrazole, indole, furan, etc. or benzo-fused analogues of these rings are defined by the term "substimted heteroaryl. " "Substituted heteroarylalkyl" refers to a subset of "substituted heteroaryl" as described above in which an alkyl group, as defined herein, links the heteroaryl group to another group. The term "heterocyclic" is used herein to describe a monovalent saturated or unsaturated non-aromatic group having a single ring or multiple condensed rings from 1-12 carbon atoms and from 1-4 heteroatoms selected from nitrogen, sulfur or oxygen within the ring. Such heterocycles are. for example, tetrahydrofuran, morpholine. piperidine, pyrrolidine, etc. The term "substituted heterocyclic" as used herein describes a subset of "heterocyclic" wherein the heterocycle nucleus is substituted with one or more functional groups such as lower alkyl, acyl, halogen, alkylhalos {e.g. CF 3 ), hydroxy, amino, alkoxy, alkylamino, acylamino, acyloxy, mercapto, etc. The term "heterocyclicalkyl" defines a subset of "heterocyclic" wherein an alkyl group, as defined herein, links the heterocyclic group to another group. Introduction The present invention provides a class of luminescent probes that are based on metal chelates of salicylamidyl-based ligands ("SL"), particularly chelates of the lanthanide series. Other compounds of the invention include both salicylamidyl and phthamidyl moieties in a single ligand ("SPL"). The compounds of the invention emit light or they can be used to absorb light emitted by a reporter fluorophore. The fluorophores of the invention can be used as small molecules in solution assays or they can be utilized as a label that is attached to an analyte or a species that interacts with, and allows detection and/or quantification of an analyte. Fluorescent labels have the advantage of requiring few precautions in their handling, and being amenable to high-throughput visualization techniques (optical analysis including digitization of the image for analysis in an integrated system comprising a computer). Preferred labels are typically characterized by one or more of the following: high sensitivity, high stability, low background, long lifetimes, low environmental sensitivity and high specificity in labeling. The fluorophores of the invention can be used with other fluorophores or quenchers as components of energy transfer probes. Many fluorescent labels are useful in combination with the SL and SPL of the invention. Many such labels are commercially available from, for example, the SIGMA chemical company (Saint Louis, MO), Molecular Probes (Eugene, OR), R&D systems (Minneapolis, MN), Pharmacia LKB Biotechnology (Piscataway, NJ), CLONTECH Laboratories, Inc. (Palo Alto, CA), Chem Genes Corp., Aldrich Chemical Company (Milwaukee, WI), Glen Research, Inc., GIBCO BRL Life Technologies, Inc. (Gaithersburg, MD), Fluka Chemica- Biochemika Analytika (Fluka Chemie AG, Buchs, Switzerland), and Applied Biosystems (Foster City, CA), as well as many other commercial sources known to one of skill. Furthermore, those of skill in the art will recognize how to select an appropriate fluorophore for a particular application and, if it not readily available commercially, will be able to synthesize the necessary fluorophore de novo or synthetically modify commercially available fluorescent compounds to arrive at the desired fluorescent label. In addition to small molecule fluorophores. naturally occurring fluorescent proteins and engineered analogues of such proteins are useful with the SLs and SPLs of the present invention. Such proteins include, for example, green fluorescent proteins of cnidarians (Ward et al., Photochem. Photobiol. 35:803-808 (1982); Levine et al.. Comp. Biochem. PhysioL, 72B:77-85 (1982)), yellow fluorescent protein from Vibrio ./..scber. strain (Baldwin et al.. Biochemistry 29:5509-15 (1990)), Peridinin-chlorophyll from the dinoflagellate Symbiodinium sp. (Morris et ah. Plant Molecular Biology! 24:673:77 (1994)), phycobiliproteins from marine cyanobacteria, such as Synechococcus, e.g., phycoerythrin and phycocyanin (Wilbanks et al, J. Biol. Chem. 268:1226-35 (1993)), and the like. The compounds of the invention can be used as probes, as tools for separating particular ions from other solutes, as probes in microscopy, enzymology, clinical chemistry, molecular biology and medicine. The compounds of the invention are also useful as therapeutic agents in modalities, such as photodynamic therapy and as diagnostic agents in imaging methods, such as magnetic resonance imaging. Moreover, the compounds of the invention are useful as components of optical amplifiers of light, waveguides and the like. Furthermore, the compounds of the invention can be incorporated into inks and dyes, such as those used in the printing of currency or other negotiable instruments. The compounds of the invention can be made to luminesce by exciting them in any manner known in the art, including, for example, with light or electrochemical energy (see, for example, Kulmala et al, Analytica Chimica Ada 386: 1 (1999)). The luminescence can, in the case of chiral compounds of the invention, be circularly polarized (see, for example, Riehl et al, Chem. Rev. 86: 1 (1986)). The compounds, probes and methods discussed in the following sections are generally representative of the compositions of the invention and the methods in which such compositions can be used. The following discussion is intended as illustrative of selected aspects and embodiments of the present invention and it should not be interpreted as limiting the scope of the present invention. The Compounds The present invention provides an array of salicylamidyl-based metal chelating ligands ("SL") that comprise at least one salicylamidyl moiety within their framework. The SL compounds can also include one or more phthalamidyl moiety within their framework in combination with the one or more salicylamidyl moiety ("SPL"). In one aspect, the invention provides a luminescent lanthanide ion complex. The chelating group comprises at least one salicylamidyl group, preferably between 2 and 100 salicylamidyl groups, more preferably between 3 and 75 salicylamidyl groups, even more preferably between 4 and 50 salicylamidyl groups and more preferably still, between 5 and 25 salicylamidyl groups. The complex also, preferably has a quantum yield of at least about 0.1. Even more preferably, the lanthanide ion of the complex is a member selected from europium, terbium and combinations thereof. The at least one salicylamidyl group of the chelating group can be substituted with one or more electron withdrawing and/or electron donating group. Those of skill in the art will understand which substituents, when appended to an aromatic ring will exhibit electron withdrawing or electron donating properties. Tables of substituents that are appropriate for inclusion in the SLs of the invention can be found in the literature. See, for example, Hammett, J. Am. Chem. Soc. 59: 96 (1937); Johnson, THE HAMMETT EQUATION, Cambridge University Press, New York, 1973; Hansch et al, J. Med. Chem. 16: 1207 (1973); and Hansch et al, SUBSTITUENT CONSTANTS FOR CORRELATION ANALYSIS IN CHEMISTRY AND BIOLOGY, Wiley, New York, 1979. Moreover, the salicylamidyl groups of the complex can be connected by a backbone of substantially any length and chemical composition, with the proviso that the backbone should orient the salicylamidyl and other rings in a manner that is conducive to their complexation of the desired metal ion. That the backbone be stable to the conditions in which the complex is used is also generally preferred. As such, representative backbones include, for example, alkyl groups, substituted alkyl groups, conjugated unsaturated systems, aryl groups, heteroaryl groups, dendrimers, polyethers, polyamides, polyimines, biopolymers and backbones that are a combination of more than one of these groups. Other useful backbone systems will be apparent to those of skill in the art. In a second aspect, the invention provides a compound having a structure according to Formula I: In Formula I, R 1 and R 2 are members independently selected from the group consisting of alkyl, substituted alkyl, halogen and — OR 6 , wherein R 6 is a member selected from the group consisting of H, alkyl, substituted alkyl groups and a single negative charge. R 4 , R 5 , R 7 , R 10 and R 20 are members independently selected from the group consisting of H, alkyl and substituted alkyl groups. R 3 , R 8 and R 9 are members independently selected from the group consisting of alkyl and substituted alkyl groups. R π , R 12 , R 13 , R 2 '. R 22 and R 3 are members independently selected from alkyl, substituted alkyl, H, — NR 14 R 15 , — NO 2 , —OR 16 , — COOR 17 , wherein, R 14 , R 15 , R 16 and R 17 are members independently selected from the group consisting of H, alkyl and substituted alkyl, wherein R 12 can optionally form a πng with R , R or both, and R ' can optionally form a πng with R , R 23 or both. The rings are members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocyclyl and saturated heterocyclyl ring systems. Q 1 is — OR 18 and Q ^' is — OR 1 Q , wherein R 1 and R 10 are members independently selected from H, an enzymatically labile group, a hydrolytically labile group and a single negative charge. The letters a and z are independently selected from the group consisting of 0 and 1, with the proviso that when a is 0, N 1 is covalently attached directly to carbonyl 1 ', and when z is 0, N is covalently attached directly to carbonyl group 2'. In another preferred embodiment, the present invention provides a compound according to Formula I, wherein R 8 is (CH 2 ) P and P is an integer between 1 and 5, inclusive. R 4 is an alkyl group substituted with a moiety having a structure according to Formula IV: In Formula IV. R 29 is a member selected from the group consisting of alkyl, substituted alkyl, aryl, substituted aryl, halogen and — OR 7 , wherein R 7 is a member selected from the group consisting of H, alkyl, substituted alkyl groups, heteroaryl groups, heterocyclic groups and a single negative charge. R 46 is a member selected from H, alkyl and substituted alkyl. R 31 , R 32 and R 33 are members independently selected from alkyl, substituted alkyl, H, — NR 24 R 25 , — NO 2 , —OR 26 , — COOR 27 , wherein, R' 4 , R 25 , R 26 and R" 7 are members independently selected from the group consisting of H, alkyl and substituted alkyl, wherein R 32 can optionally form a ring with R ', R or both. The rings being members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocyclyl and saturated heterocyclyl ring systems. R is (CH 2 ) X and X is an integer between 1 and 5, inclusive. Q — OR " , wherein R is a member selected from H, an enzymatically labile group, a hydrolytically labile group and a single negative charge; In further preferred embodiment, the invention provides a compound having a structure according to Formula V: In yet another preferred embodiment, the invention provides a compound according to Formulae I and IV in combination, wherein R 4 is an alkyl group substituted with a group having a structure according to Formula IV and R" is an alkyl group substituted with a moiety having a structure according to Formula VI: In Formula VI, R j9 is a member selected from the group consisting of alkyl, substituted alkyl, halogen and — OR ' , wherein R 7 is a member selected from the group consisting of H, alkyl, substituted alkyl groups and a single negative charge. R is a member selected from alkyl and substituted alkyl. R 41 , R 42 and R 43 are members independently selected from alkyl, substituted alkyl, H, — NR 34 R 35 , — NO?, — OR 36 , — COOR 37 , wherein, R 34 , R 35 , R 36 and R 3"7 are members independently selected from the group consisting of H, alkyl and substituted alkyl, wherein R 42 can optionally form a ring with R 41 , R 43 or both. The rings are members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocyclyl and saturated heterocyclyl ring systems. In yet another preferred embodiment, the invention provides a compound having a structure according to Formula VII: In Formula VII, M, N, P and Z are members independently selected from the group consisting of the integers between 1 and 5, inclusive. R Groups For clarity of illustration, the discussion of the identities of the various R groups {e.g., R 1 . R\ R\ etc.) set forth in the formulae above is collected together in this section. This discussion is equally applicable to each of the formulae set forth herein. Moreover, although the discussion focuses on certain representative formulae, it is to be understood that this is a device used to simplify the discussion of the R groups and that it does not serve to limit the scope of the R groups. Referring to Formulae I and II in combination and the resulting complexing agent with three salicylamidyl rings, the following discussion is generally relevant to any compound of the invention. It will be apparent to those of skill in the art that when additional salicylamidyl rings, linker groups and backbones are included in a compound of the invention, the following discussion is equally relevant to them. Throughout the range of compounds of the invention, the substituents on the non-amidyl carbonyl carbons (e.g., R 1 , R") are preferably selected from the group consisting of alkyl, substituted alkyl, aryl, substituted aryl, halogen and alkoxy and aryloxy moieties of the general structure — OR 7 , wherein R 7 is preferably a member selected from the group consisting of H, alkyl, substituted alkyl groups, aryl, substituted aryl, heteroaryl, heterocyclyl and a single negative charge In one preferred embodiment, one or more of the above-recited R groups is a member independently selected from the group consisting of H, Ci to Cio alkyl and Ci to Cio substituted alkyl, and more preferably members independently selected from the group consisting of H, C 2 to C 6 alkyl and C 2 to C 6 substituted alkyl. In another preferred embodiment, one or more of the above-recited R groups is a member independently selected from the group consisting of H, aryl, substituted aryl and combinations thereof. In a further preferred embodiment, one or more of the above-recited R groups is a member independently selected from the group consisting of H and alkyl substituted with polycyclic aryl groups, preferably napthyl groups. In yet another preferred embodiment, one or more of the above-recited R groups is a member selected from the group consisting of H and a primary alkyl amine, preferably a C| to C alkyl chain bearing an amine moiety at the ω-position, more preferably a C 2 to H alkyl chain bearing an amine moiety at the ω-position. In a still further preferred embodiment, one or more of the above-recited R groups is a polyether, preferably a member selected from ethylene glycol, ethylene glycol oligomers and combinations thereof, having a molecular weight of from about 60 dahons to about 10,000 da ons, and more preferably of from about 100 daltons to about 1.000 daltons. Representative polyether-based substituents include, but are not limited to, the following structures: in which j is a number from 1 to 100, inclusive. Other functionalized polyethers are known to those of skill in the art, and many are commercially available from, for example, Shearwater Polymers, Inc. (Alabama). In another preferred embodiment, one or more of the above-recited R groups comprise a reactive group for conjugating said compound to a member selected from the group consisting of molecules and surfaces. Representative useful reactive groups are discussed in greater detail in the succeeding section. Additional information on useful reactive groups is known to those of skill in the art. See, for example, Hermanson, BIOCONJUGATE TECHNIQUES, Academic Press, San Diego. 1996. In a preferred embodiment, one or more of the above-recited R groups is a member selected from ω-carboxyl alkyl groups, ω-carboxyl substituted alkyl groups and combinations thereof, more preferably the R group has a structure according to Formula II: In Formula II, X is a member selected from O, S and NR 50 . R i is preferably a member selected from H, alkyl and substituted alkyl. Y is preferably a member selected from H and a single negative charge; and j and k are preferably members independently selected from the group consisting of integers from 1 to 18. In a further preferred embodiment, one or more of the above-recited R groups has a structure according to Formula III: in which Y is substantially as recited above for Formula II. In yet another preferred embodiment, one or more of the R groups can combine characteristics of one or more of the above-recited groups. For example, one preferred R group combines both the attributes of a polyether and a reactive group: in which j is an integer between 1 and 100, inclusive. Other such "chimeric" R groups include, but are not limited to, moieties such as sugars (e.g., polyol with reactive hydroxyl), amino acids, amino alcohols, carboxy alcohols, amino thiols, and the like. In a still further preferred embodiment, the compounds of the invention have more than one type of R group on a single molecule. For example a single molecule can include an R group that is a polyether and an R group that is an amine. Many other such combinations of different substituents will be apparent to those of skill in the art. Representative structures according to this embodiment are set forth below: wherein, n is an integer between 0 and 6, and preferably between 1 and 3 and at least one X' is not a nitrogen or substituted nitrogen Preferred identities for X', include, for example, CH , O and S Exemplary lanthanide chelates of the invention have a structure according to Structure 1 Preferred metal chelates have the structure where n is between 1 and 5, R is an amide and R', R", R'" and R"" are members independently selected from the group consisting of H, OH, alkyl and halogen Exemplary compounds according to the structure above are set forth in Table 1 Table 3Li = 1,3-diaminopropane; 4Li - 1,4-diaminopropane; TREN = tris(2-aminoethyl)amine; Am32 = poly(proyleneimine) dendrimer, 4 th generation. In yet another preferred embodiment, the compounds of the invention are associated with another molecule by a weak interaction (e.g. van der Waals) to form a species, such as, for example, and inclusion complex. Preferred molecules interacting with the PLs include, but are not limited to dendrimers, macrocycles, cyclodextrins, and the like. Reactive Functional Groups Certain of the compounds of the invention bear a reactive functional group, such as a component of a linker arm, which can be located at any position on any aryl nucleus or on a chain, such as an alkyl chain, attached to an aryl nucleus, or on the backbone of the chelating agent. These compounds are referred to herein as "reactive ligands." When the reactive group is attached to an alkyl, or substituted alkyl chain tethered to an aryl nucleus, the reactive group is preferably located at a terminal position of an alkyl chain. Reactive groups and classes of reactions useful in practicing the present invention are generally those that are well known in the art of bioconjugate chemistry. Currently favored classes of reactions available with reactive ligands of the invention are those which proceed under relatively mild conditions. These include, but are not limited to nucleophilic substitutions (e.g., reactions of amines and alcohols with acyl halides, active esters), electrophilic substitutions (e.g., enamine reactions) and additions to carbon-carbon and carbon-heteroatom multiple bonds {e.g.. Michael reaction. Diels-Alder addition). These and other useful reactions are discussed in, for example. March, ADVANCED ORGANIC CHEMISTRY. 3rd Ed., John Wiley & Sons. New York. 1985: Hermanson. BIOCONJUGATE TECHNIQUES, Academic Press, San Diego. 1996; and Feeney et al. MODIFICATION OF PROTEINS; Advances in Chemistry Series, Vol. 198, American Chemical Society, Washington, D.C., 1982. Useful reactive functional groups include, for example: (a) carboxyl groups and various derivatives thereof including, but not limited to. N-hydroxysuccinimide esters, N-hydroxybenztriazole esters, acid halides. acyl imidazoles, thioesters, p-nitrophenyl esters, alkyl, alkenyl, alkynyl and aromatic esters; (b) hydroxyl groups, which can be converted to esters, ethers, aldehydes, etc. (c) haloalkyl groups, wherein the halide can be later displaced with a nucleophilic group such as, for example, an amine, a carboxylate anion. thiol anion, carbanion, or an alkoxide ion, thereby resulting in the covalent attachment of a new group at the site of the halogen atom; (d) dienophile groups, which are capable of participating in Diels-Alder reactions such as, for example, maleimido groups; (e) aldehyde or ketone groups, such that subsequent derivatization is possible via formation of carbonyl derivatives such as, for example, imines, hydrazones, semicarbazones or oximes, or via such mechanisms as Grignard addition or alkyllithium addition; (f) sulfonyl halide groups for subsequent reaction with amines, for example, to form sulfonamides; (g) thiol groups, which can be converted to disulfides or reacted with acyl halides; (h) amine or sulfhydryl groups, which can be, for example, acylated, alkylated or oxidized; (i) alkenes, which can undergo, for example, cycloadditions, acylation, Michael addition, etc; j) epoxides, which can react with, for example, amines and hydroxyl compounds; and (k) phosphoramidites and other standard functional groups useful in nucleic acid synthesis. The reactive functional groups can be chosen such that they do not participate in, or interfere with, the reactions necessary to assemble the reactive ligand. Alternatively, a reactive functional group can be protected from participating in the reaction by the presence of a protecting group. Those of skill in the art understand how to protect a particular functional group such that it does not interfere with a chosen set of reaction conditions. For examples of useful protecting groups, see, for example, Greene et al, PROTECTIVE GROUPS IN ORGANIC SYNTHESIS, John Wiley & Sons, New York, 1991. Donor and Acceptor Moieties One of the advantages of the compounds of the invention is that they can be used with a wide range of energy donor and acceptor molecules to construct fluorescence energy transfer probes. A vast array of fluorophores useful in conjunction with the SLs are known to those of skill in the art. See, for example, Cardullo et al, Proc. Natl. Acad. Sci. USA 85: 8790-8794 (1988); Dexter, D.L., J of Chemical Physics 21 : 836- 850 (1953); Hochstrasser et al, Biophysical Chemistry 45: 133-141 (1992); Selvin, P., Methods in Enzymology 246: 300-334 (1995); Steinberg, I. Ann. Rev. Biochem., 40: 83- 1 14 (1971 ); Stryer, L. Ann. Rev. Biochem., 47: 819-846 (1978); Wang et al, Tetrahedron Letters 31 : 6493-6496 (1990); Wang et al, Anal. Chem. 67: 1197- 1203 (1995). A non-limiting list of exemplary donors that can be used in conjunction with the quenchers of the invention is provided in Table 2. TABLE 2 Suitable moieties that can be selected as donors or acceptors in FET pairs 4-acetamιdo-4'-ιsothιocyanatostιlbene-2,2'dιsulfomc acid acπdine and deπvatives: acπdine acπdine lsothiocyanate 5-(2'-amιnoet y])amιnonaphthalene-l -sulfonic acid (EDANS) 4-amιno-N-[3-vιnylsulfonyl)phenyl]naphthahmιde-3,5 disulfonate N-(4-amhno- 1 -naphthy l)maleιmιde anthramlamide BODIPY TABLE 2 (co .) Suitable moieties that can be selected as donors or acceptors in FET pairs Brilliant Yellow coumaπn and derivatives coumaπn 7-amιno-4-methylcoumarm (AMC. Coumaπn 120) 7-amιno-4-rπfluoromethylcouluarm (Coumaran 151 ) cyanine dyes cyanos e 4\6-dιam-nιdιno-2-phenyhndole (DAPI) 5', 5"-dιbromopyrogallol-sulfonaphthalem (Bromopyrogallol Red) 7-dιethylamιno-3-(4'-ιsothιocyanatophenyl)-4-methylcoumarιn diethylenetπamine pentaacetate 4,4'-dπsothιocyanatodιhydro-stιlbene-2.2'-dιsulfomc acid 4,4'-dιιsothιocyanatostιlbene-2,2'-dιsulfomc acid 5-[dιmethylamιno]naphthalene-l-sulfonyl chloride (DNS, dansylchionde) 4-(4'-dιmethylamιnophenylazo)benzoιc acid (DABCYL) 4-dιmethylamιnophenylazopheny 1-4 '-isothiocyanate (DABITC) eosin and derivatives eosin eosin isothiocyanate erythrosin and derivatives erythrosin B erythrosin isothiocyanate ethidium fluorescein and derivatives 5-carboxyfluoresceιn (FAM) 5-(4,6-dιchloromazιn-2-yl)amιnofluoresceιn (DTAF) 2 ' ,7 '-dιmethoxy-4 ' 5 '-dιchloro-6-carboxyfluoresceιn (JOE) fluorescein fluorescein isothiocyanate QFITC (XRITC) fluorescamine IR144 IR1446 Malachite Green isothiocyanate 4-methylumbelhferone ortho cresolphthalem nitrotyrosrne pararosaniline Phenol Red B-phycoerythπn o-phthaldialdehyde pyrene and derivatives pyrene pyrene butyrate succimmidyl 1 -pyrene butyrate quantum dots Reactive Red 4 (Cibacron™ Brilliant Red 3B-A) rhodamine and derivatives 6-carboxy-X-rhodamιne (ROX) 6-carboxyrhodamme (R6G) hssamine rhodamine B sulfonyl chloride rhodamine (Rhod) rhodamine B rhodamine 123 TABLE 2 (co .) Suitable moieties that can be selected as donors or acceptors in FET pairs rhodamine X isothiocyanate sulforhodamme B sulforhodamine 101 sulfonyl chloride derivative of sulforhodamine 101 (Texas Red) NN,N ' ,N ' -tetramethyl-6-carboxyrhodamine (TAMRA ) tetramethyl rhodamine tetramethyl rhodamine isothiocyanate (TRITC) riboflavin rosolic acid lanthanide chelate derivatives There is a great deal of practical guidance available in the literature for selecting appropriate donor-acceptor pairs for particular probes, as exemplified by the following references: Pesce et al, Eds., FLUORESCENCE SPECTROSCOPY (Marcel Dekker, New York, 1971); White et al, FLUORESCENCE ANALYSIS: A PRACTICAL APPROACH (Marcel Dekker, New York, 1970); and the like. The literature also includes references providing exhaustive lists of fluorescent and chromogenic molecules and their relevant optical properties, for choosing reporter-quencher pairs (see, for example, Berlman, HANDBOOK OF FLUORESCENCE SPECTRA OF AROMATIC MOLECULES, 2nd Edition (Academic Press, New York, 1971); Griffiths, COLOUR AND CONSTITUTION OF ORGANIC MOLECULES (Academic Press, New York, 1976); Bishop, Ed., INDICATORS (Pergamon Press, Oxford, 1972); Haugland, HANDBOOK OF FLUORESCENT PROBES AND RESEARCH CHEMICALS (Molecular Probes, Eugene, 1992) Pringsheim, FLUORESCENCE AND PHOSPHORESCENCE (Interscience Publishers, New York, 1949); and the like. Further, there is extensive guidance in the literature for derivatizing reporter and quencher molecules for covalent attachment via readily available reactive groups that can be added to a molecule. The diversity and utility of chemistries available for conjugating fluorophores to other molecules and surfaces is exemplified by the extensive body of litereature on preparing nucleic acids derivatized with fluorophores. See, for example, Haugland (supra); Ullman et al, U.S. Pat. No. 3,996,345; Khanna et al, U.S. Pat. No. 4,351,760. Thus, it is well within the abilities of those of skill in the art to choose an energy exchange pair for a particular application and to conjugate the members of this pair to a probe molecule, such as for example, a small molecular bioacm e mateπal nucleic acid, peptide or other polymer In a FET pair, it is generally preferred that an absorbance band of the acceptor substantially overlap a fluorescence emission band of the donor When the donor (fluorophore) is a component of a probe that utilizes fluorescence resonance energ> transfer (FRET), the donor fluorescent moiety and the quencher (acceptor) of the invention are preferably selected so that the donor and acceptor moieties exhibit fluorescence resonance energ\ transfer when the donor is excited One factor to be considered in choosing the fluorophore-quencher pair is the efficiency of fluorescence resonance energy transfer een them Preferably, the efficiency of FRET between the donor and acceptor moieties is at least 10%, more preferably at least 50% and even more preferably at least 80% The efficiency of FRET can easily be empiπcally tested using the methods both descπbed herein and known in the art The efficiency of FRET between the donor-acceptor pair can also be adjusted by changing ability of the donor and acceptor to dimeπze or closely associate If the donor and acceptor moieties are known or determined to closely associate, an increase or decrease in association can be promoted by adjusting the length of a linker moiety, or of the probe itself, between the two fluorescent proteins The ability of donor- acceptor pair to associate can be increased or decreased by tuning the hydrophobic or ionic interactions, or the steπc repulsions in the probe construct Thus, intramolecular interactions responsible for the association of the donor-acceptor pair can be enhanced or attenuated Thus, for example, the association between the donor-acceptor pair can be increased by, for example, utilizing a donor beaπng an overall negativ e charge and an acceptor with an overall positive charge In addition to fluorophores that are attached directly to a probe, the fluorophores can also be attached by indirect means In this embodiment, a ligand molecule (e g , biotin) is preferably covalently bound to the probe species The ligand then binds to another molecules (e g , streptavidin) molecule, which is either lnherent detectable or covalently bound to a signal system, such as a fluorescent compound of the invention, or an enzyme that produces a fluorescent compound by conv ersion of a non- fluorescent compound Useful enzymes of interest as labels include, for example, hydrolases, particularly phosphatases, esterases and glycosidases, or oxidotases, particularly peroxidases Fluorescent compounds include fluorescein and its deπvatives, rhodamine and its deπvatives, dansyl, umbelhferone, etc , as discussed above For a review of various labeling or signal producing systems that can be used. see. U.S. Patent No. 4,391,904. Presently preferred fluorophores of use in conjunction with the complexes of the invention, include, for example, xanthene dyes, including fluoresceins, and rhodamine dyes. Many suitable forms of these compounds are widely available commercially with substituents on their phenyl moieties, which can be used as the site for bonding or as the bonding functionality for attachment to an nucleic acid. Another group of preferred fluorescent compounds are the naphthylamines. having an amino group in the alpha or beta position. Included among such naphthylamino compounds are 1 - dimethylaminonaphthyl-5-sulfonate, l-anilino-8-naphthalene sulfonate and 2-p-touidinyl- 6-naphthalene sulfonate. Other donors include 3-phenyl-7-isocyanatocoumarin, acridines, such as 9-isothiocyanatoacridine and acridine orange; N-(p-(2- benzoxazolyl)phenyl)maleimide; benzoxadiazoles, stilbenes, pyrenes, and the like. For clarity of illustration, the discussion below focuses on attaching the complexes of the invention and other fluorophores to nucleic acids. The focus on nucleic acid probes is not intended to limit the scope of probe molecules to which the complexes of the invention can be attached. Those of skill in the art will appreciate that the complexes of the invention can also be attached to small molecules (e.g., small molecular bioactive agents), proteins, peptides, synthetic polymers, solid supports and the like using standard synthetic chemistry or modifications thereof. In an exemplary embodiment, in which the probe is a nucleic acid probe, the acceptor molecule is a rhodamine dye. The rhodamine moiety is preferably attached to either the 3'- or the 5'-terminus of the nucleic acid, although internal sites are also accessible for derivitization of SLs and have utility for selected purposes. Whichever terminus the rhodamine derivative is attached to, the complex of the invention will generally be attached to its antipode, or at a position internal to the nucleic acid chain. The rhodamine acceptor is preferably introduced using a commercially available amidite. Different donor groups of the invention are also preferably introduced using a reactive derivative (e.g., amidite) of the donor. Alternatively, donor groups comprising reactive groups (e.g., isothiocyanates, active esters, etc.) can be introduced via reaction with a reactive moiety on a tether or linker arm attached to the nucleic acid (e.g., hexylamine). In yet another preferred embodiment, the donor moiety can be attached at the 3 '-terminus of a nucleic acid by the use of a derivatized synthesis support. For example, a complexing agent of the invention is tethered to a solid support that is derivatized with an analogue of the complex. Such derivatized supports are well known in the art and are exemplified by a TAMRA (tetramethylrhodamine carboxylic acid) derivative that is attached to a nucleic acid 3 '-terminus using a commercially available solid support that is derivatized with an analogue of the TAMRA fluorophore (Biosearch Technologies, Inc.) In view of the well-developed body of literature concerning the conjugation of small molecules to nucleic acids, many other methods of attaching donor/ acceptor pairs to nucleic acids will be apparent to those of skill in the art. For example, rhodamine and fluorescein dyes are conveniently attached to the 5 '-hydroxyl of an nucleic acid at the conclusion of solid phase synthesis by way of dyes derivatized with a phosphoramidite moiety (see, for example, Woo et al, U.S. Pat. No. 5,231,191 ; and Hobbs, Jr., U.S. Pat. No. 4,997,928). More specifically, there are many linking moieties and methodologies for attaching groups to the 5'- or 3'-termini of nucleic acids, as exemplified by the following references: Eckstein, editor, Nucleic Acids and Analogues: A Practical Approach (IRL Press, Oxford, 1991); Zuckerman et al, Nucleic Acids Research, 15: 5305-5321 (1987) (3'-thiol group on nucleic acid); Sharma et al, Nucleic Acids Research, 19: 3019 (1991) (3'-sulfhydryl); Giusti et al, PCR Methods and Applications, 2: 223-227 (1993) and Fung et al, U.S. Pat. No. 4, 757,141 (5'-phosphoamino group via Aminolink TM II available from P.E. Biosystems, CA.) Stabinsky, U.S. Pat. No. 4,739,044 (3-aminoalkylphosphoryl group); Agrawal et al, Tetrahedron Letters, 31 : 1543-1546 (1990) (attachment via phosphoramidate linkages); Sproat et al, Nucleic Acids Research, 15: 4837 (1987) (5- mercapto group); Nelson et al, Nucleic Acids Research, 17: 7187-7194 (1989) (3'-amino group), and the like. Means of detecting fluorescent labels are well known to those of skill in the art. Thus, for example, fluorescent labels can be detected by exciting the fluorophore with the appropriate wavelength of light and detecting the resulting fluorescence. The fluorescence can be detected visually, by means of photographic film, by the use of electronic detectors such as charge coupled devices (CCDs) or photomultipliers and the like. Similarly, enzymatic labels may be detected by providing the appropriate substrates for the enzyme and detecting the resulting reaction product. Synthesis The compounds of the invention are synthesized by an appropriate combination of generally well-known synthetic methods. Techniques useful in synthesizing the compounds of the invention are both readily apparent and accessible to those of skill in the relevant art. The discussion below is offered to illustrate certain of the diverse methods available for use in assembling the compounds of the invention, it is not intended to limit the scope of reactions or reaction sequences that are useful in preparing the compounds of the present invention. The compounds of the invention can be prepared as a single stereoisomer or as a mixture of stereoisomers. In a preferred embodiment, the compounds are prepared as substantially a single isomer. Isomerically pure compounds are prepared by using synthetic intermediates that are isomerically pure in combination with reactions that either leave the stereochemistry at a chiral center unchanged or result in its complete inversion. Alternatively, the final product or intermediates along the synthetic route can be resolved into a single stereoisomer. Techniques for inverting or leaving unchanged a particular stereocenter, and those for resolving mixtures of stereoisomers are well known in the art and it is well within the ability of one of skill in the art to choose an appropriate method for a particular situation. See, generally, Furniss et al. (eds.)NOGEL'S ENCYCLOPEDIA OF PRACTICAL ORGANIC CHEMISTRY 5 TH ED., Longman Scientific and Technical Ltd., Essex, 1991, pp. 809-816; and Heller, Ace. Chem. Res. 23: 128 (1990). An exemplary synthetic scheme leading to a complexing agent of the invention is set forth in Scheme 1 (Fig. 1). Methyl salicylate is mixed with tris(2- aminoethyl)amine and heated to afford ligand 1. An exemplary synthetic route to a versatile activated salicylic acid starting material is set forth in Scheme 2 (Fig. 7). 3-Methylsalicylic acid is converted to compound 2, in which the carboxylic acid is converted to the corresponding methyl ester and the phenolic hydroxide is converted to the corresponding methyl ether. The methyl ester is saponified under basic conditions, affording compound 3. The methyl substituent on the phenyl ring is oxidized with permanganate to the corresponding carboxylic acid, 4. Compound 4 is subsequently converted to the bis-methyl ester, 5 and one of the ester groups is saponified, using one equivalent of base to produce compound 6. The resulting carboxylic acid is converted to an acid chloride, 7, which is reacted with 2- mercaptothiazoline to produce compound 8. Several representative ligands of the invention are prepared as set forth in Scheme 3 (FIG. 8). The compounds set forth in Scheme 3 have backbones of varying length. Thus, compound 8 is added to an amine with four primary amine moieties and a backbone of a selected length to afford compounds 9 (n =1 ), 10 (n =2) and 11 (n=3). Compounds 9-11 are deprotected by treatment with BBr : , to afford ligands 12, 13 and 14. The above-recited synthetic schemes are intended to be exemplary of certain embodiments of the invention, those of skill in the art will recognize that many other synthetic strategies for producing the ligands of the invention are available without resort to undue experimentation. The substituents on the salicylamidyl group and the on the backbone joining the salicylamidyl groups can themselves comprise chelating agents other than a salicylamidyl group. Preferably, these chelators comprise a plurality of anionic groups such as carboxylate or phosphonate groups. In a preferred embodiment, these non-SL chelating agents are selected from compounds which themselves are capable of functioning as lanthanide chelators. In another preferred embodiment, the chelators are aminocarboylates (i.e. EDTA, DTP A, DOTA, NTA, HDTA, etc. and their phosphonate analogs such as DTPP, EDTP, HDTP, NTP, etc). Many useful chelating groups, crown ethers, cryptands and the like are known in the art and can be incorporated into the compounds of the invention. See, for example, Pitt et al, "The Design of Chelating Agents for the Treatment of Iron Overload," In, INORGANIC CHEMISTRY IN BIOLOGY AND MEDICINE; Martell, Ed.; American Chemical Society, Washington, D.C., 1980, pp. 279-312; Lindoy, THE CHEMISTRY OF MACROCYCLIC LIGAND COMPLEXES; Cambridge University Press, Cambridge, 1989; Dugas, BIOORGANIC CHEMISTRY; Springer-Verlag, New York, 1989. and references contained therein. Additionally, a manifold of routes allowing the attachment of chelating agents, crown ethers and cyclodextrins to other molecules is available to those of skill in the art. See, for example, Meares et al, "Properties of In Vivo Chelate-Tagged Proteins and Polypeptides." In, MODIFICATION OF PROTEINS: FOOD, NUTRITIONAL, AND PHARMACOLOGICAL ASPECTS;" Feeney, et al, Eds., American Chemical Society, Washington, D.C., 1982, pp. 370-387; Kasina et al, Bioconjugate Chem., 9: 108-117 (1998); Song et al, Bioconjugate Chem., 8: 249-255 (1997). In other embodiments substituents on the salicylamidyl group or on the backbone are fluorescence sensitizers. Exemplary sensitizers include rhodamine 560. 575 and 590 fluoresceins, 2- or 4-quinolones, 2 or 4- coumarins, or derivatives thereof e.g. coumarin 445, 450, 490, 500 and 503, 4-trifluoromethylcoumarin (TFC), 7-diethyl- amino-cumarin-3-carbohyddzide, etc., and especially carbostyril 124 (7-amino-4-methyl- 2-quinolone), coumarin 120 (7-amino-4-methyl-2-coumarin), coumarin 124 (7-amino-4- (trifluoromethyl)-2-coumarin), aminomethyltrimethylpsoralen, napthalene and the like. In a preferred embodiment, the sensitizer is a moiety that comprises a napthyl moiety. After the SL is formed and purified, the fluorescent lanthanide complex is synthesized by any of a wide range of art-recognized methods, including, for example, by incubating a salt of the chelate with a lanthanide salt such as the lanthanide trihalide, triacetate, and the like. The compounds of the invention, in their unconjugated form are useful as probes, indicators, separation media, and the like. Moreover, the compounds of the invention can be conjugated to a wide variety of compounds to create specific labels, probes, diagnostic and/or therapeutic reagents, etc. Examples of species to which the compounds of the invention can be conjugated include, for example, biomolecules such as proteins (e.g., antibodies, enzymes, receptors, etc.), nucleic acids (e.g., RNA, DNA, etc.), bioactive molecules (e.g., drugs, toxins, etc.); solid substrates such as glass or polymeric beads, sheets, fibers, membranes (e.g. nylon, nitrocellulose), slides (e.g. glass, quartz) and probes; etc. In a preferred embodiment, the species to which the compound is conjugated is a biomolecule. Preferred biomolecules are those selected from the group consisting of antibodies, nucleic acids, enzymes, haptens, carbohydrates and antigens. Assays and SL-Bearing Probes In another preferred embodiment, the present invention provides a SL that is tethered to another molecule, such as a probe molecule and assays using these probes. Assays The following discussion is generally relevant to the assays described herein. This discussion is intended to illustrate the invention by reference to certain preferred embodiments and should not be inteφreted as limiting the scope of probes and assay types in which the compounds of the invention find use. Other assay formats utilizing the compounds of the invention will be apparent to those of skill in the art. Assays based on specific binding reactions are used for detecting a wide variety of substances such as drugs, hormones, enzymes, proteins, antibodies, and infectious agents in various biological fluids and tissue samples. In general, the assays consist of an analyte, a recognition moiety for the analyte. and a detectable label. Competitive assay modalities generally utilize a binding partner in addition to these components. In an exemplary embodiment, the binding partner is a molecule that interacts with a recognition moiety to form a complex that is inherently less stable than a similar complex formed between the recognition moiety and the analyte, and is subsequently displaced by the incoming analyte. Because the results of specific binding interactions are frequently not directly observable, a variety of fluorescent labels have been devised for determining the presence of an interaction. The fluorophores of the invention are detected by use of fluorescence spectroscopy or by the naked eye. An introduction to labels, labeling procedures and detection of labels, such as are useful in practicing the present invention, is found in Polak et al. INTRODUCTION TO IMMUNΌCYTOCHEMISTRY, 2 nd Ed., Springer Verlag, NY, (1977), and in Haugland, HANDBOOK OF FLUORESCENT PROBES AND RESEARCH CHEMICALS, a combined handbook and catalogue Published by Molecular Probes, Inc., Eugene, OR.(1996) In certain embodiments, the assay is a competitive assay. In practice, the components of the assay (i.e., recognition moiety, binding partner and analyte) can have substantially any chemical structure, however in a preferred embodiment, the recognition moiety, the binding partner and the analyte are members independently selected from the group consisting of small molecular bioactive agents, biomolecules and combinations thereof. When a component of the assay is a biomolecule, the biomolecule is preferably a member selected from the group consisting of haptens, antibodies, antigens, carbohydrates, nucleic acids, peptides, enzymes and receptors. In a competitive assay format, one or more than one of the components is labeled with a compound of the invention. For example, in one embodiment, the binding partner is labeled with a compound of the invention and its displacement from an immobilized recognition moiety is detected by the appearance of fluorescence in a liquid phase of the assay. In another competitive assay format, an immobilized enzyme is complexed with a substrate conjugated to a compound of the invention. The complex is then contacted with a putative antagonist. The displacement of fluorescence from the immobilized enzyme into a liquid phase of the assay is indicative of displacement of the substrate by the putative antagonist. These embodiments are offered by way of example only and it will be plain to one of skill in the art that many other competitive assay formats can utilize and benefit from the compounds of the invention. In addition to ascertaining a binding event, it is frequently desired to quantitate the magnitude of the affinity between two or more binding partners. Thus, it is also within the scope of the present invention to utilize the compounds disclosed herein as a support for such assays. Most typically, the amount of analyte present is measured by quantitating the amount of label fixed to a binding partner, analyte or recognition moiety following a binding event. Means of detecting and quantitating fluorescent labels are well known to those of skill in the art. In another preferred embodiment, the affinity between twcor more assay constituents is measured by quantifying a population selected from the group consisting of the analyte-recognition moiety complex, free analyte, free binding partner, binding partner-recognition moiety complex and combinations thereof. The format of an assay for extracting affinity data for two molecules can be understood by reference to an embodiment in which a ligand that is known to bind to a receptor is displaced by an antagonist to that receptor. Other variations on this format will be apparent to those of skill in the art. The competitive format is well known to those of skill in the art. See, for example, U.S. Pat. Nos. 3,654,090 and 3,850,752. The binding of an antagonist to a receptor can be assayed by a competitive binding method using a ligand for that receptor and the antagonist. The binding assay can be performed, for example, in a 96-well filtration plate assembly (Millipore Coφoration, Bedford, Mass.). One of the three binding partners (i.e., the ligand, antagonist or receptor) is generally bound to the well or to a particulate material contained within the well. Competition binding data can be analyzed by a number of techniques, including nonlinear least-squares curve fitting procedure. When the ligand is an antagonist for the receptor, this method provides the IC50 of the antagonist (concentration of the antagonist which inhibits specific binding of the ligand by 50% at equilibrium). The IC50 is related to the equilibrium dissociation constant (Ki) of the antagonist based on the Cheng and Prusoff equation: Ki = IC50/(1 + L/Kd), where L is the concentration of the ligand used in the competitive binding assay, and Kd is the dissociation constant of the ligand as determined by Scatchard analysis. These assays are described, among other places, in Maddox et al, JE.xp Med., 158: 1211 (1983); Hampton et al. SEROLOGICAL METHODS, A LABORATORY MANUAL, APS Press, St. Paul. Minn.. 1990. The assays of the invention can be practiced with some or all components in solution. Alternatively, one or more components can be substantially insoluble in the assay medium. In a preferred embodiment, one or more members selected from the group consisting of the recognition moiety, the binding partner and the analyte are attached to a surface. Useful surface include, but are not limited to, glass or polymeric beads, sheets, fibers, membranes (e.g. nylon, nitrocellulose), slides (e.g. glass, quartz) and the like. The assay can be performed in a large variety of ways. It is within the abilities of one of skill in the art to choose, for example, when to form the fluorescent complex by chelating the lanthanide, which assay component the chelate should be attached to and the like. In a preferred embodiment, the fluorescent complex is formed prior to displacing the binding partner from the binding partner-recognition moiety complex. In another preferred embodiment, the fluorescent complex is formed after displacing the binding partner from the binding partner-recognition moiety complex. Following the displacement of the binding partner from the binding partner-recognition moiety complex, the remaining steps of the assay can be performed on the mixture that is formed by the displacement or one or more of the components of the mixture can be removed. In a preferred embodiment, the method further comprises separating the free binding partner from a member of the group consisting of the recognition-binding partner pair, the analyte-recognition moiety pair and combinations thereof. In a prefeπed embodiment, the assays of the invention are immunological assays. Immunological assays involve reactions between immunoglobulins (antibodies) which are capable of binding with specific antigenic determinants of various compounds and materials (antigens). Other types of reactions include binding between avidin and biotin, protein A and immunoglobulins, lectins and sugar moieties and the like. See, for example, U.S. Patent No. 4,313,734 , issued to Leuvering; U.S. Patent No. 4,435,504 . issued to Zuk; U.S. Patent Nos. 4,452,901 and 4,960,691, issued to Gordon; and U.S. Patent No. 3,893,808, issued to Campbell. These assay techniques provide the ability to detect both the presence and amount of small quantities of analytes and are useful in, for example medical diagnostics and forensic applications. In the methods of the present invention, the analyte or its binding to the recognition moiety is generally detected by the use of a fluorescent label according to the invention, Immunological assays are of three general types. In an exemplary competitive binding assays, labeled reagents and unlabeled analyte compounds compete for binding sites on a binding material. After an incubation period, unbound materials are washed off and the amount of labeled reagent bound to the site is compared to reference amounts for determination of the analyte concentration in the sample solution. A second type of immunological assay is known as a sandwich assay and generally involves contacting an analyte sample solution to a surface comprising a first binding material immunologically specific for that analyte. A second solution comprising a binding material bearing a compound of the invention of the same type (antigen or antibody) as the first binding material is then added to the assay. The labeled binding material will bind to any analyte which is bound to the first binding material. The assay system is then subjected to a wash step to remove labeled binding material which failed to bind with the analyte and the amount of labeled material remaining is ordinarily proportional to the amount of bound analyte. A third type of immunological assay technique involves agglutination reaction techniques and is exemplified by well-known assays for blood antigens and serum types. Immunological cross-reactivity between antibodies within serum and antigens presented on red blood cell surfaces is indicated by the formation of a three dimensional cross-linked network of red blood cells and antibodies. The agglutination of the serum/red blood cell mixture results in the formation of a pellet which can be visible to the naked eye, via the fluorescence of a compound of the invention attached to one or more components of the assay. These assay procedures, enumerated above, were originally performed according to liquid phase immunochemistry techniques wherein enzymes and radiolabeled reactions were carried out in liquid solution in apparatus such as microtiter plates. More recently, techniques and procedures have been adapted for carrying out "solid" phase assays wherein enzymatic and immunological reactions are carried out in solution on immobilizing substrates. These types of assays, generally designated immunochromatographic immunoassays, can be developed in any number of formats employing principals of competitive, sandwich, or agglutination types of assays. They can also involve either flow across or flow along the immobilizing substrate. In general, the sandwich assays have the greatest utility for detection of large protein analytes or antibodies. The flow across type of assays have been used most extensively in sandwich type assays. An exemplary immunochromatographic sandwich immunoassay procedure using the fluorescent agents of the invention employs a porous surface and an agent of the invention as a visual label attached to one member of a binding pair (e.g., antigen or antibody). The porous surface is generally a flat sheet and is usually comprised of either nylon, nitrocellulose, glass fiber, or the like. In a typical immunochromatographic format a region or small area of the porous surface becomes a solid phase capturing surface by immobilizing a member of a binding pair directly onto the surface of a porous membrane or by indirectly attaching the member onto capture particles (i.e., latex, glass,) which are immobilized on the surface of a porous membrane. Direct immobilization of the binding pair to a porous membrane or capture particles occur through electrostatic interaction, (i.e., differences in ionic charge), hydrophobic interaction, or covalent binding. Where capture particles are used, the immobilization of capture particles to porous membranes can also occur through the same phenomena or through size exclusion preventing migration of the particles through the pores or fibers of the membrane. Many other types of assays can be run utilizing the compounds of the invention. In a typical noncompetitive immunochromatographic assay, a test sample of a biological fluid such as blood, serum, plasma, saliva, urine, etc. must be in a sufficient volume and have a sufficient concentration of analyte to allow for sufficient interaction to occur between the analyte of interest, the labeled particles and the capturing solid phase. In order to increase the reaction kinetics, the concentration of particle labeled member of a binding pair and the concentration of binding pair at the surface of the porous membrane or capturing particles is optimized to produce as much specific binding as possible and at the same time minimize any nonspecific binding. The concentration of the particle labeled member must be of a concentration that does not produce prozone phenomena throughout the range of analyte concentrations that are of interest. Such concentration optimization is well within the abilities of one of skill. Immunochromatographic assays can be in the form of strips or layers of the multilayered materials of the invention employing a hydrophobic support (e.g., Mylar, polystyrene, polypropylene, glass, etc.) wherein one or more compounds of the invention or moieties functionalized with a compound of the invention is either fixed directly or indirectly with a binder such as glue to the support. If it is desired, hydrophobic supports and housings can be employed to reduce evaporation of the fluid phase while the immunoreactants are being brought into contact with each other. In an exemplary non-competitive assay in accordance with this aspect of the invention, an analyte is solubilized, deposited and bound onto the particulate material. The particulate material is then hydrated and sequentially exposed to primary antibodies and enzyme-conjugated secondary antibodies specific for the primary antibodies, with washing steps in between where appropriate. Enzyme levels are then determined by, for instance, substrate conversion protocols well known in the art, and the amount of primary antibodies can thus be measured by reference to a standard run in parallel. Additionally, a binding domain of a receptor, for example, can serve as the focal point for a drug discovery assay, where, for example, the receptor is-immobilized, and incubated both with agents (i.e., ligands) known to interact with the binding domain thereof, and a quantity of a particular drug or inhibitory agent under test. One of the incubation components is labeled with a compound of the invention. The extent to which the drug binds with the receptor and thereby inhibits receptor-ligand complex formation can then be measured. Such possibilities for drug discovery assays are contemplated herein and are considered within the scope of the present invention. Other focal points and appropriate assay formats will be apparent to those of skill in the art. The compounds and methods of the invention can also be used to sequence nucleic acids and peptides. Fluorescent-labeled oligonucleotide primers have been used in place of radiolabeled primers for sensitive detection of DNA fragments (U.S. Pat. No. 4,855,225 to Smith et al). Additionally, DNA sequencing products can be labeled with fluorescent dideoxynucleotides (U.S. Pat. No. 5,047,519 to Prober et al.) or by the direct incoφoration of a fluorescent labeled deoxynucleotide (Voss et al. Nucl Acids Res. 17:2517 (1989)). The compounds of the invention are useful in both of these formats. As currently practiced, fluorescent sequencing reactions circumvent many of the problems associated with the use of radionuclides. As discussed above, the fluorescent complex can be formed at substantially any step of the assay. This is equally true in those embodiments, wherein one or more components of the assay mixture are removed following the displacement of the binding partner. In a preferred embodiment, the fluorescent complex is formed following the separation. Compounds of the invention can be used to indicate the presence and amount of an enzyme in a mixture. For example, in certain embodiments, Q 1 is an enzymatically labile group and the presence of the labile group on the phenolic oxygen of the salicylamidyl group will prevent the formation of a stable complex of a lanthanide ion. This situation is reversed, and a stable lanthanide complex is formed, when the salicylamidyl chelate is contacted with an enzyme that is capable of cleaving the labile group, thus, freeing the phenolic oxygen anion. Similar to the embodiments discussed above, the assay mixture can be contacted with the enzyme at any time during the assay process. Additionally, if a component is separated from the reaction mixture (e.g., the liberated binding partner), the separated component and/or the remaining component can be contacted with the enzyme. In a prefeπed embodiment, wherein Q 1 is an enzymatically labile group, the method further includes contacting a member selected from the group consisting of the binding partner-recognition moiety complex, the free binding partner and combinations thereof with an enzyme, thereby removing the enzymatically labile group. An array of enzymatically removable groups is known in the art and it is within the abilities of one of skill in the art to select an appropriate enzymatically labile group for a particular application. In a preferred embodiment, the enzymatically labile group comprises a component of a member selected from the group consisting of phosphate, sulfate, acyl and glycoside groups. Enzymes capable of removing these groups include, for example, esterases, phosphatases, glycosidases and the like. In another preferred embodiment, the removal of the enzymatically labile group and the subsequent formation of a fluorescent complex is used to detect the presence of an enzyme capable of removing the enzymatically labile group. See, for example, Drevin et al, U.S. Patent No. 5252462, issued October 12, 1993. Although the compounds of the invention can be tethered to any component of the assay, they will most generally be attached to the binding partner. In this embodiment, the compounds of the invention can be attached to the binding partner through a reactive group on a salicylamidyl moiety, backbone or amide substitutent. Alternatively, they can be attached to the binding partner through a reactive group on the aromatic nucleus of one or more of the salicylamidyl, moieties of the compounds. As discussed above, many suitable reactive groups are known to those of skill in the art and one of skill will be able to both choose and prepare a salicylamidyl-chelate that is appropriately functionalized for a particular application. It will generally be preferred that the linkage between the salicylamidyl- chelates and the binding partner be stable under the conditions of the assay. Many stable linkages can be formed between the binding partner and the salicylamidyl chelate including, for example, amides, amines, ethers, ureas, and the like. In a preferred embodiment, the linkage between the binding partner and a compound of the invention is a member selected from the group consisting of amide, thioamide, thoiurea and carbamate linkages. Suitable reactive groups and linkages are discussed in greater detail above. In general, to determine the concentration of a target molecule, such as, for example, a nucleic acid, it is preferable to first obtain reference data in which constant amounts of probe and nucleic acid ligand are contacted with varying amounts of target. The fluorescence emission of each of the reference mixtures is used to derive a graph or table in which target concentration is compared to fluorescence emission. For example, a probe that: a) hybridizes to a target-free nucleic acid ligand; and b) has a stem-loop architecture with the 5' and 3' termini being the sites of fluorescent group and SL labeling, could be used to obtain such reference data. Such a probe gives a characteristic emission profile in which the fluorescence emission decreases as the target concentration increases in the presence of a constant amount of probe and nucleic acid ligand. Then, a test mixture with an unknown amount of target is contacted with the same amount of first nucleic acid ligand and second probe, and the fluorescence emission is determined. The value of the fluorescence emission is then compared with the reference data to obtain the concentration of the target in the test mixture. Multiplex Analyses In another preferred embodiment, the quenchers of the invention are utilized as a component of one or more probes used in an assay designed to detect multiple species in a mixture. An assays used to detect two or more species by using at least two probes bearing different fluorophores is refeπed to herein as a "multiplex analysis." A schematic diagram of such a multiplex analysis using a SL is set forth in FIG. 9. Probes that include the compounds of the invention are also useful in performing multiplex-type analyses and assays. In a typical multiplex analysis, two or more distinct species (or regions of one or more species) are detected using two or more probes, wherein each of the probes is labeled with a different fluorophore. Prefeπed multiplex analyses relying on fluorescent energy transfer ideally meet several criteria. The fluorescent species should be bright and spectrally well-resolved and the energy transfer between the fluorescent species and the acceptor should be efficient. Because of the ready availability of SLs of the invention having different emission characteristics, the compounds of the invention are particularly well suited for use in multiplex applications. Access to SLs having a range of absorbance characteristics allows for the design of FET probes in which the acceptor absorbance properties and the SL emission properties are matched, thereby providing a useful level of spectral overlap. The simultaneous use of two or more probes using FET is known in the art. For example, multiplex assays using nucleic acid probes with different sequence specificities have been described. Fluorescent probes have been used to determine whether an individual is homozygous wild-type, homozygous mutant or heterozygous for a particular mutation. For example, using one quenched-fluorescein molecular beacon that recognizes the wild-type sequence and another rhodamine-quenched molecular beacon that recognizes a mutant allele, it is possible to genotype individuals for the β- chemokine receptor (Kostrikis et al. Science 279:1228-1229 (1998)). The presence of only a fluorescein signal indicates that the individual is wild-type, and the presence of rhodamine signal only indicates that the individual is a homozygous mutant. The presence of both rhodamine and fluorescein signal is diagnostic of a heterozygote. Tyagi et al. Nature Biotechnology 16: 49-53 (1998)) have described the simultaneous use of four differently labeled molecular beacons for allele discrimination, and Lee et al, BioTechniques 27: 342-349 (1999) have described seven color homogenous detection of six PCR products. The SLs of the present invention can be used in multiplex assays designed to detect and/or quantify substantially any species, including, for example, whole cells, viruses, proteins (e.g., enzymes, antibodies, receptors), glycoproteins, lipoproteins, subcellular particles, organisms (e.g., Salmonella), nucleic acids (e.g., DNA, RNA, and analogues thereof), polysaccharides, lipopolysaccharides, lipids, fatty acids, non- biological polymers and small bioactive molecules (e.g., toxins, drugs, pesticides, metabolites, hormones, alkaloids, steroids). Recognition moieties As used herein, the term "recognition moiety" refers to molecules that can interact with an analyte via either attractive or repulsive mechanisms. In a prefeπed embodiment, a recognition moiety is conjugated to a compound of the invention. In another exemplary embodiment, the analyte and the recognition moiety form an intimately associated pair by, for example, covalent bonding, ionic bonding, ion pairing, van der Waals association and the like. In another exemplary embodiment, the analyte and recognition moiety interact by a repulsive mechanism such as incompatible steric characteristics, charge-charge repulsion, hydrophilic-hydrophobic interactions and the like. It is understood that there is overlap between the generic terms "recognition moiety" and "analyte." In a particular application, a species may be an analyte. while in a different application, the species serves as a recognition moiety. In certain embodiments, the compounds of the invention serve as recognition moieties (e.g., when the analyte is a metal ion). Recognition moieties can be selected from a wide range of small bioactive molecules (e.g., drugs, pesticides, toxins, etc.), organic functional groups (e.g., amines, carbonyls, carboxylates, etc.), biomolecules, metals, metal chelates and organometallic compounds. When the recognition moiety is an amine, in prefeπed embodiments, the recognition moiety will interact with a structure on the analyte which reacts by interacting (e.g., binding, complexing) with the amine (e.g., carbonyl groups, alkylhalo groups). In another prefeπed embodiment, the amine is protonated by an acidic moiety on the analyte of interest (e.g., carboxylic acid, sulfonic acid). In certain prefeπed embodiments, when the recognition moiety is a carboxylic acid, the recognition moiety will interact with the analyte by, for example, complexation (e.g., metal ions). In still other prefeπed embodiments, the carboxylic acid will protonate a basic group on the analyte (e.g. amine). In another prefeπed embodiment, the recognition moiety is a drug moiety. The drug moieties can be agents already accepted for clinical use or they can be drugs whose use is experimental, or whose activity or mechanism of action is under investigation. The drug moieties can have a proven action in a given disease state or can be only hypothesized to show desirable action in a given disease state. In a prefeπed embodiment, the drug moieties are compounds which are being screened for their ability to interact with an analyte of choice. As such, drug moieties which are useful as recognition moieties in the instant invention include drugs from a broad range of drug classes having a variety of pharmacological activities. Classes of useful agents include, for example, non-steroidal anti- inflammatory drugs (NSAIDS). The NSAIDS can, for example, be selected from the following categories: (e.g., propionic acid derivatives, acetic acid derivatives, fenamic acid derivatives, biphenylcarboxylic acid derivatives and oxicams); steroidal anti- inflammatory drugs including hydrocortisone and the like; antihistaminic drugs (e.g., chloφheniramine, triprolidine); antitussive drugs (e.g., dextromethoφhan. codeine, carmiphen and carbetapentane); antipruritic drugs (e.g., methidilizine and trimeprizine): anticholinergic drugs (e.g., scopolamine, atropine, homatropine, levodopa); anti-emetic and antinauseant drugs (e.g., cyclizine, meclizine, chloφromazine, buclizine); anorexic drugs (e.g., benzphetamine, phentermine, chloφhentermine, fenfluramine); central stimulant drugs (e.g., amphetamine, methamphetamine, dextroamphetamine and methylphenidate); antiarrhythmic drugs (e.g., propanolol, procainamide, disopyraminde, quinidine, encainide); β-adrenergic blocker drugs (e.g., metoprolol, acebutolol, betaxolol, labetalol and timolol); cardiotonic drugs (e.g., milrinone, amrinone and dobutamine); antihypertensive drugs (e.g., enalapril, clonidine, hydralazine, minoxidil, guanadrel, guanethidine);diuretic drugs (e.g., amiloride and hydrochlorothiazide); vasodilator drugs (e.g., diltazem, amiodarone, isosuprine, nylidrin, tolazoline and verapamil); vasoconstrictor drugs (e.g., dihydroergotamine, ergotamine and methylsergide); antiulcer drugs (e.g., ranitidine and cimetidine); anesthetic drugs (e.g., lidocaine, bupivacaine, chloφrocaine, dibucaine); antidepressant drugs (e.g., imipramine, desipramine, amitryptiline, nortryptiline); tranquilizer and sedative drugs (e.g., chlordiazepoxide, benacytyzine, benzquinamide, flurazapam, hydroxyzine, loxapine and promazine); antipsychotic drugs (e.g., chloφrothixene, fluphenazine, haloperidol, molindone, thioridazine and trifluoperazine); antimicrobial drugs (antibacterial, antifungal, antiprotozoal and antiviral drugs). Antimicrobial drugs which are preferred for incoφoration into the present composition include, for example, pharmaceutically acceptable salts of β-lactam drugs, quinolone drugs, ciprofloxacin, norfloxacin, tetracycline, erythromycin, amikacin, triclosan, doxycycline, capreomycin, chlorhexidine, chlortetracycline, oxytetracycline. clindamycin, ethambutol, hexamidine isothionate, metronidazole, pentamidine, gentamycin, kanamycin, lineomycin, methacycline, methenamine, minocycline, neomycin, netilmycin, paromomycin, streptomycin, tobramycin, miconazole and amanfadine. Other drug moieties of use in practicing the present invention include antineoplastic drugs (e.g., antiandrogens (e.g., leuprolide or flutamide), cytocidal agents (e.g., adriamycin, doxorubicin, taxol, cyclophosphamide, busulfan, cisplatin, α-2- interferon) anti-estrogens (e.g., tamoxifen , antimetabolites (e.g.. fluorouracil, methotrexate, mercaptopurine, thioguanine). The recognition moiety can also comprise hormones (e.g., medroxyprogesterone, estradiol, leuprolide, megestrol, octreotide or somatostatin); muscle relaxant drugs (e.g., cinnamedrine, cyclobenzaprine, flavoxate, oφhenadrine, papaverine, mebeverine, idaverine, ritodrine, dephenoxylate, dantrolene and azumolen); antispasmodic drugs; bone-active drugs (e.g., diphosphonate and phosphonoalkylphosphinate drug compounds); endocrine modulating drugs (e.g., contraceptives (e.g., ethinodiol, ethinyl estradiol, norethindrone. mestranol, desogestrel, medroxyprogesterone), modulators of diabetes (e.g., glyburide or chloφropamide), anabolics, such as testolactone or stanozolol, androgens (e.g., methyltestosterone, testosterone or fluoxymesterone), antidiuretics (e.g., desmopressin) and calcitonins). Also of use in the present invention are estrogens (e.g., diethylstilbesterol), glucocorticoids (e.g., triamcinolone, betamethasone, etc.) and progenstogens, such as norethindrone, ethynodiol, norethindrone, levonorgestrel; thyroid agents (e.g., liothyronine or levothyroxine) or anti-thyroid agents (e.g., methimazole); antihypeφrolactinemic drugs (e.g., cabergoline); hormone suppressors (e.g., danazol or goserelin), oxytocics (e.g., methylergonovine or oxytocin) and prostaglandins, such as mioprostol, alprostadil or dinoprostone, can also be employed. Other useful recognition moieties include immunomodulating drugs (e.g., antihistamines, mast cell stabilizers, such as lodoxamide and/or cromolyn, steroids (e.g., triamcinolone, beclomethazone, cortisone, dexamethasone, prednisolone, methylprednisolone, beclomethasone, or clobetasol), histamine H 2 antagonists (e.g., famotidine, cimetidine, ranitidine), immunosuppressants (e.g., azathioprine, cyclosporin), etc. Groups with anti-inflammatory activity, such as sulindac, etodolac, ketoprofen and ketorolac, are also of use. Other drugs of use in conjunction with the present invention will be apparent to those of skill in the art. The above enumerated, and other molecules, can be attached to the compounds of the invention, to solid substrates and the like by methods well-known to those of skill in the art. Ample guidance can be found in literature devoted to, for example, the fields of bioconjugate chemistry and drug delivery. For example, one of skill, faced with a drug comprising an available amine will be able to choose from among a variety of amine derivatizing reactions, locate an appropriately functionalized partner (e.g., a carboxylic acid terminated thiol) for the organic layer and react the partners under conditions chosen to effect the desired coupling (e.g., dehydrating agents, e.g., dicyclohexylcarbodiimide). See, for example, MODIFICATION OF PROTEINS: FOOD, NUTRITIONAL, AND PHARMACOLOGICAL ASPECTS, Feeney et al, Eds., American Chemical Society, Washington, D.C, 1982, pp. 370-387; POLYMERIC DRUGS AND DRUG DELIVERY SYSTEMS, Dunn et al, Eds., American Chemical Society, Washington, D.C. 1991. When the recognition moiety is a chelating agent, crown ether or cyclodextrin. host-guest chemistry will dominate the interaction between the recognition moiety and the analyte. The use of host-guest chemistry allows a great degree of recognition moiety-analyte specificity to be engineered into a compound or assay of the invention. The use of these compounds to bind to specific compounds is well known to those of skill in the art. See, for example, Pitt et al, "The Design of Chelating Agents for the Treatment of Iron Overload," In, INORGANIC CHEMISTRY IN BIOLOGY AND MEDICINE; Martell, Ed.; American Chemical Society, Washington, D.C, 1980, pp. 279-312; Lindoy, THE CHEMISTRY OF MACROCYCLIC LIGAND COMPLEXES; Cambridge University Press, Cambridge, 1989; Dugas, BIOORGANIC CHEMISTRY; Springer-Veriag, New York, 1989, and references contained therein. Additionally, a manifold of routes allowing the attachment of chelating agents, crown ethers and cyclodextrins to other molecules is available to those of skill in the art. See, for example, Meares et al, "Properties of In Vivo Chelate-Tagged Proteins and Polypeptides." In, MODIFICATION OF PROTEINS : FOOD, NUTRITIONAL, AND PHARMACOLOGICAL ASPECTS;" Feeney, et al, Eds., American Chemical Society, Washington, D.C, 1982, pp. 370-387; Kasina et al, Bioconjugate Chem., 9: 108-1 17 (1998); Song et al, Bioconjugate Chem., 8: 249-255 (1997). In another preferred embodiment, the recognition moiety forms an inclusion complex with the analyte of interest. In a particularly prefeπed embodiment, the recognition moiety is a cyclodextrin or modified cyclodextrin. Cyclodextrins are a group of cyclic oligosaccharides produced by numerous microorganisms. Cyclodextrins have a ring structure which has a basket-like shape. This shape allows cyclodextrins to include many kinds of molecules into their internal cavity. See, for example, Szejtli, CYCLODEXTRINS AND THEIR INCLUSION COMPLEXES: Akademiai Klado. Budapest. 1982: and Bender et al, CYCLODEXTRIN CHEMISTRY, Springer-Veriag, Berlin, 1978. Cyclodextrins are able to form inclusion complexes with an aπay of bioactive molecules including, for example, drugs, pesticides, herbicides and agents of war. See, Tenjaria et al, J. Pharm. Sci., 87: 425-429 (1998); Zughul et al, Pharm. Dex. Technol, 3: 43-53 (1998); and Albers et al, Crit. Rev. Ther. Drug Carrier Syst.. 12: 311- 337 (1995). Importantly, cyclodextrins are able to discriminate between enantiomers of compounds in their inclusion complexes. Thus, in one prefeπed embodiment, the invention provides for the detection of a particular enantiomer in a mixture of enantiomers. See, Koppenhoefer et al, J. Chromatogr., A 793: 153-164 (1998). The cyclodextrin or any other recognition moiety can be attached to a compound of the invention, solid support and the like either directly or through a spacer arm. See, Yamamoto et al, J. Phys. Chem. B, 101: 6855-6860 (1997). Methods to attach cyclodextrins to other molecules are well known to those of skill in the chromatographic and pharmaceutical arts. See, Sreenivasan, K. J., Appl. Polym. Sci., 60: 2245-2249 (1996). In another exemplary embodiment, the recognition moiety is a polyaminocarboxylate chelating agent such as ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTP A). These recognition moieties can be attached, for example, to any amine-terminated component of a compound of the invention, solid support or a spacer arm, for example, by utilizing the commercially available dianhydride (Aldrich Chemical Co., Milwaukee, WI). In still further prefeπed embodiments, the recognition moiety is a biomolecule such as a protein, nucleic acid, peptide or an antibody. Biomolecules useful in practicing the present invention can be derived from any source. The biomolecules can be isolated from natural sources or can be produced by synthetic methods. Proteins can be natural proteins or mutated proteins. Mutations can be effected by chemical mutagenesis, site-directed mutagenesis or other means of inducing mutations known to those of skill in the art. Proteins useful in practicing the instant invention include, for example, enzymes, antigens, antibodies and receptors. Antibodies can be either polyclonal or monoclonal. Peptides and nucleic acids can be isolated from natural sources or can be wholly or partially synthetic in origin. In those embodiments wherein the recognition moiety is a protein or antibody, the protein can be tethered to a compound of the invention, solid support or a crosshnkmg agent by any reactive peptide residue av ailable on the surface of the protein In prefeπed embodiments, the reactive groups are amines or carboxylates In particularh prefeπed embodiments, the reactive groups are the .-amine groups of lysme residues Recognition moieties which are antibodies can be used to recognize analytes which are proteins, peptides, nucleic acids, sacchaπdes or small bioactive mateπals, such as drugs, herbicides, pesticides, industπal chemicals and agents of war Methods of raising antibodies for specific molecules are well-known to those of skill in the art See, United States Patents No 5, 147,786, issued to Feng et al on September 15, 1992, No 5,334,528, issued to Stanker et al on August 2, 1994, No 5 686,237, issued to Al-Bayati, M A.S on November 1 1, 1997, and No 5,573,922, issued to Hoess et al on November 12, 1996 Methods for attaching antibodies agents to surfaces are also known in the art See, Delamarche et al Langmuir, 12: 1944-1946 (1996) A recognition moiety can be conjugated to a compound of the invention by any of a large number of art-known attachment methods, as discussed above In one embodiment, the recognition moiety is tethered directly to the salicylamidyl chelate through a group on the aromatic salicylamidyl nucleus, backbone or amide substituent In another exemplary embodiment, a reactive bifunctional crosshnkmg agent is attached reactive group on a SL and this conjugate is subsequently bound to the recognition moiety via the reactive group on the crosshnking component and a group of complementary reactivity on the recognition moiety Many useful crosshnking agents can be purchased commercially (Pierce Rockford, IL) or can be synthesized using techniques known in the art Alternatively, the recognition moiety and cross-linking agent are coupled pπor to attaching the salicylamidyl chelate to the recognition moiety Analytes The mateπals and methods of the present mvention can be used to detect any analyte, or class of analytes, which interact with a recognition moiety in a detectable manner. The interaction between the analyte and recognition moiety can be any physicochemical interaction, including covalent bonding, ionic bonding, hydrogen bonding, van der Waals interactions, repulsive electronic interactions, attractive electronic interactions and hydrophobic/hydrophihc interactions In a prefeπed embodiment, the interaction is an ionic interaction In this embodiment, an acid, base, metal ion or metal ion-binding ligand is the analyte In a still further preferred embodiment, the interaction is a hydrogen bonding interaction. In particularly prefeπed embodiments, the hybridization of a nucleic acid to a nucleic acid having a complementary sequence is detected. In another prefeπed embodiment, the interaction is between an enzyme or receptor and a small molecule or peptide which binds thereto. In another embodiment, the analyte competes for the recognition moiety with another agent which has been bound to the recognition moiety prior to introducing the analyte of interest. In this embodiment, it is the process or result of the analyte displacing the pre-bound agent which causes the detectable levels of fluorescence from the compound of the invention. Suitable combinations of recognition moieties and analytes will be apparent to those of skill in the art. In presently prefeπed embodiments, the analyte is a member selected from the group consisting of acids, bases, organic ions, inorganic ions, pharmaceuticals, herbicides, pesticides and biomolecules. Each of these agents, where practicable, can be detected as a vapor or a liquid. These agents can be present as components in mixtures of structurally unrelated compounds, racemic mixtures of stereoisomers, non-racemic mixtures of stereoisomers, mixtures of diastereomers, mixtures of positional isomers or as pure compounds. Within the scope of the invention is a device and a method to detect a particular analyte of interest without interference from other substances within a mixture. Organic ions which are substantially non-acidic and non-basic (e.g., quaternary alkylammonium salts) can be detected by a labeled recognition moiety of the invention. For example, a SL-labeled recognition moiety with ion exchange properties is useful in the present invention. A specific example is the exchange of a cation such as dodecyltrimethylammonium cation for a metal ion such as sodium. Recognition moieties that form inclusion complexes with organic ions are also of use. For example, crown ethers and cryptands can be used to form inclusion complexes with organic ions such as quaternary ammonium cations. Inorganic ions such as metal ions and complex ions (e.g., SO "2 , PO "3 ) can also be detected using the SLs and methods of the invention. Metal ions can be detected, for example, by their complexation or chelation by SLs or chelating agents bound to a compound of the invention. In this embodiment, the recognition moiety can be a simple monovalent moiety (e.g., carboxylate, amine, thiol) or can be a more structurally complex agent (e.g., ethylenediaminepentaacetic acid, crown ethers, aza crowns, thia crowns). Complex inorganic ions can be detected by their ability to compete with SLs for bound metal ions in ligand-metal complexes. When a ligand bound to a SL forms a metal-complex having a fhermodynamic stability constant which is less than that of the complex between the metal and the complex ion, the complex ion will cause the dissociation of the metal ion from the immobilized ligand. If the metal ion is the complexed lanthanide, the fluorescence will be decreased. Methods of determining stability constants for compounds formed between metal ions and ligands are well known to those of skill in the art. Using these stability constants, chelates that are specific for particular ions can be manufactured. See, Martell, A.E., Motekaitis, R.J., DETERMINATION AND USE OF STABILITY CONSTANTS, 2d Ed., VCH Publishers, New York 1992. In a prefeπed embodiment, the affinity of an analyte for a particular metal ion is exploited by using a compound of the invention that includes that particular metal ion. The metal ion generally must have available at least one empty coordination site to which the analyte can bind. Alternatively, at least one bond between the metal and the metal-immobilizing agent must be sufficiently labile in the presence of the analyte to allow the displacement of at least one bond of the immobilizing reagent by the analyte. The interaction between the analyte and the metal ion can be detected using a number of art-recognized techniques, including, for example, UV Vis and fluorescence spectroscopy. Other combinations of analytes and recognition moieties will be apparent to those of skill in the art. Probes The invention provides probes including SL moieties conjugated to, for example, a target species, a ligand for a target species (e.g., nucleic acid, peptide, etc.), a small molecule (e.g., drug, pesticide, etc.), and the like. Nucleic Acid Probes The SLs of the invention are useful in conjunction with nucleic-acid probes and they can be used as components of detection agents in a variety of DNA amplification/quantification strategies including, for example, 5'-nuclease assay, Strand Displacement Amplification (SDA), Nucleic Acid Sequence-Based Amplification (NASBA), Rolling Circle Amplification (RCA), as well as for direct detection of targets in solution phase or solid phase (e.g., aπay) assays. Furthermore, the SL-derivatized nucleic acids can be used in probes of substantially any format, including, for example, format selected from molecular beacons, scoφion probes, sunrise probes, conformationally assisted probes, light up probes and TaqMan™ probes. Thus in a further aspect, the present invention provides a method for detecting a nucleic acid target sequence. The method includes: (a) contacting the target sequence with a detector nucleic acid; (b) hybridizing the target binding sequence to the target sequence, thereby altering the conformation of the detector nucleic acid, causing a change in a fluorescence parameter; and (c) detecting the change in the fluorescence parameter, thereby detecting the nucleic acid target sequence. In the methods described herein, unless otherwise noted, a prefeπed detector nucleic acid includes a single-stranded target binding sequence. The binding sequence has linked thereto: i) a fluorophore; and ii) a SL of the invention. Moreover, prior to its hybridization to a complementary sequence, the detector nucleic acid is preferably in a conformation that allows fluorescence energy transfer between the fluorophore and the SL when the fluorophore is excited. Furthermore, in each of the methods described in this section, a change in fluorescence is detected as an indication of the presence of the target sequence, and that change in fluorescence is preferably detected in-real time. In another aspect, the invention provides a further method for detecting the presence of a nucleic acid target sequence. The method includes: (a) hybridizing to the target sequence a detector nucleic acid comprising a single-stranded target binding sequence and an intramolecularly associated secondary structure 5 ' to the target binding sequence, wherein at least a portion of the target sequence forms a single stranded tail which is available for hybridization to the target sequence; (b) in a primer extension reaction, synthesizing a complementary strand using the intramolecularly associated secondary structure as a template, thereby dissociating the intramolecularly associated secondary structure and producing a change in a fluorescence parameter; (c) detecting the change in the fluorescence parameter, thereby detecting the nucleic acid target sequence. In this method, and unless otherwise noted, the other methods described in this section, the detector nucleic acid can assume substantially any intramolecularly associated secondary structure, but this structure is preferably a member selected from haiφins. stem-loop structures, pseudoknots, triple helices and conformationally assisted structures. Moreover, the intramolecularly base-paired secondary structure preferably comprises a portion of the target binding sequence. Moreover, the intramolecularly associated secondary structure preferably includes a totally or partially single-stranded endonuclease recognition site. The complementary strand can be prepared by any art-recognized method for preparing such strands, but is preferably synthesized in a target amplification reaction, and more preferably by extension of the target sequence using the detector nucleic acid as a template. In another aspect, the invention provides a method for detecting amplification of a target sequence. The method includes the use of an amplification reaction including the following steps: (a) hybridizing the target sequence and a detector nucleic acid. The detector nucleic acid includes a single-stranded target binding sequence and an intramolecularly associated secondary structure 5' to the target binding sequence. At least a portion of the target sequence forms a single stranded tail which is available for hybridization to the target sequence; (b) extending the hybridized detector nucleic acid on the target sequence with a polymerase to produce a detector nucleic acid extension product and separating the detector nucleic acid extension product from the target sequence; (c) hybridizing a primer to the detector nucleic acid extension product and extending the primer with the polymerase, thereby linearizing the intramolecularly associated secondary structure and producing a change in a fluorescence parameter; and (d) detecting the change in the fluorescence parameter, thereby detecting the target sequence. In yet a further aspect, the invention provides a method of ascertaining whether a first nucleic acid and a second nucleic acid hybridize. In this method, the first nucleic acid includes a SL according to the invention. The method includes: (a) contacting the first nucleic acid with the second nucleic acid; (b) detecting an alteration in a fluorescent property of a member selected from the first nucleic acid, the second nucleic acid and a combination thereof, thereby ascertaining whether the hybridization occurs. A probe bearing both a SL and a fluorophore can be used or, alternatively, one or more of the nucleic acids can be singly labeled with a SL or fluorophore. When a nucleic acid singly labeled with a SL is the probe, the interaction between the first and second nucleic acids can be detected by observing the quenching of the native nucleic acid fluorescence or. more preferably, the quenching of the fluorescence of a fluorophore attached to the second nucleic acid. In addition to their general utility in species designed to probe nucleic acid amplification, detection and quantification, the present SLs can be used in substantially any nucleic acid probe format now known or later discovered. For example, the SLs of the invention can be mcoφorated into probe motifs, such as Taqman probes (Held et al. Genome Res. 6: 986-994 ( 1996), Holland et al, Proc. Nat. Acad. Sci. USA 88: 7276-7280 (1991 ), Lee et al, Nucleic Acids Res. 21 : 3761 -3766 (1993)), molecular beacons (Tyagi et al, Nature Biotechnology 14:303-308 (1996), Jayasena et al, U.S. Patent No. 5,989,823, issued November 23, 1999)) scoφion probes (Whitcomb et al, Nature Biotechnology 17: 804-807 (1999)), sunrise probes (Nazarenko et al, Nucleic Acids Res. 25: 2516-2521 (1997)), conformationally assisted probes (Cook, R., copending and commonly assigned U.S. Provisional Application 60/138,376, filed June 9, 1999), peptide nucleic acid (PNA)-based light up probes (Kubista et al, WO 97/45539, December 1997), double-strand specific DNA dyes (Higuchi et al, Bio/Technology 10: 413-417 (1992), Wittwer et al, BioTechniques 22: 130-138 (1997)) and the like. These and other probe motifs with which the present SLs can be used are reviewed in NONISOTOPIC DNA PROBE TECHNIQUES, Academic Press, Inc. 1992. The nucleic acids for use in the probes of the invention can be any suitable size, and are preferably in the range of from about 10 to about 100 nucleotides, more preferably from about 10 to about 80 nucleotides and more preferably still, from about 20 to about 40 nucleotides. The precise sequence and length of a nucleic acid probe of the invention depends in part on the nature of the target polynucleotide to which it binds. The binding location and length may be varied to achieve appropriate annealing and melting properties for a particular embodiment. Guidance for making such design choices can be found in many art-recognized references. Preferably, the 3'-terminal nucleotide of the nucleic acid probe is blocked or rendered incapable of extension by a nucleic acid polymerase. Such blocking is conveniently carried out by the attachment of a donor or acceptor molecule to the terminal 3'-position of the nucleic acid probe by a linking moiety. The nucleic acid can comprise DNA, RNA or chimeric mixtures or derivatives or modified versions thereof. Both the probe and target nucleic acid can be present as a single strand, duplex, triplex, etc. In addition to being labeled with an molecular energy transfer donor and a molecular energy transfer acceptor moiety, the nucleic acid can be modified at the base moiety, sugar moiety, or phosphate backbone with other groups such as radioactive labels, minor groove binders, intercalating agents an the like. For example, the nucleic acid can comprise at least one modified base moiety which is selected from the group including, but not limited to, 5-fluorouracil, 5- bromouracil, 5-chlorouracil, 5-iodouracil, hypoxanthine, xanthine, 4-acetylcytosine, 5- (carboxyhydroxylmethyl) uracil, 5-carboxymethylaminomethyl-2-thiouridine, 5- carboxymethylaminomethyluracil, dihydrouracil, beta-D-galactosylqueosine, inosine, N°- isopentenyladenine, 1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2- methyladenine, 2-methylguanine, 3-methylcytosine, 5-methylcytosine, N 6 -adenine, 7- methylguanine, 5-methylaminomethyluracil, 5-methoxyaminomethyl-2-thiouracil, beta- D-mannosylqueosine, 5'-methoxycarboxymethyluracil, 5-methoxyuracil, 2-methylthio- N°-isopentenyladenine, uracil-5-oxyacetic acid (v), wybutoxosine, pseudouracil, queosine, 2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil, uracil-5-oxyacetic acid methyl ester, uracil-5-oxyacetic acid (v), 5-methyl-2-thiouracil, 3- (3-amino-3-N-2-carboxypropyl) uracil, (acp3)w, and 2,6-diaminopurine. In another embodiment, the nucleic acid comprises at least one modified sugar moiety selected from the group including, but not limited to, arabinose, 2- fluoroarabinose, xylulose, and hexose. In yet another embodiment, the nucleic acid comprises at least one modified phosphate backbone selected from the group including, but not limited to, a phosphorothioate, a phosphorodithioate, a phosphoramidothioate, a phosphoramidate, a phosphordiamidate, a methylphosphonate, an alkyl phosphotriester, and a formacetal or analog thereof. Phosphodiester linked nucleic acids of the invention can be synthesized by standard methods known in the art, e.g. by use of an automated DNA synthesizer (such as are commercially available from P.E. Biosystems, etc.) using commercially available amidite chemistries. Nucleic acids bearing modified phosphodiester linking groups can be synthesized by methods known in the art. For example, phosphorothioate nucleic acids may be synthesized by the method of Stein et al. (Nucl. Acids Res. 16:3209 (1988)), methylphosphonate nucleic acids can be prepared by use of controlled pore glass polymer supports (Sarin et al, Proc. Natl. Acad. Sci. U.S.A. 85:7448-7451 (1988)). Other methods of synthesizing both phosphodiester- and modified phosphodiester-linked nucleic acids will be apparent to those of skill in the art. Nucleic acid probes of the invention can be synthesized by a number of approaches, e.g., Ozaki et al. Nucleic Acids Research. 20: 5205-5214 (1992); Agrawal et al, Nucleic Acids Research. 18: 5419-5423 (1990); or the like. The nucleic acid probes of the invention are conveniently synthesized on an automated DNA synthesizer, e.g., a P.E. Biosystems, Inc. (Foster City, Calif.) model 392 or 394 DNA/RNA Synthesizer, using standard chemistries, such as phosphoramidite chemistry (see, for example, disclosed in the following references: Beaucage et al, Tetrahedron, 48: 2223-231 1 (1992); Molko et al, U.S. Pat. No. 4,980,460; Koster et al., U.S. Pat. No. 4,725,677; Caruthers et al, U.S. Pat. Nos. 4,415,732; 4,458,066; and 4,973,679. Alternative chemistries resulting in non-natural backbone groups, such as phosphorothioate, phosphoramidate, and the like, can also be employed. When the nucleic acids are synthesized utilizing an automated nucleic acid synthesizer, the stabilizing moiety, energy transfer donor and energy transfer acceptor moieties are preferably introduced during automated synthesis. Alternatively, one or more of these moieties can be introduced either before or after the automated synthesis procedure has commenced. In another exemplary embodiment, one or more of these moieties is introduced after the automated synthesis is complete. The donor moiety is preferably separated from the SL by at least about 10 nucleotides, and more preferably by at least about 15 nucleotides. The donor moiety is preferably attached to either the 3'- or 5'-terminal nucleotides of the probe. The SL moiety is also preferably attached to either the 3 '- or 5 '-terminal nucleotides of the probe. More preferably, the donor and acceptor moieties are attached to the 3'- and 5 '- or 5'- and 3 '-terminal nucleotides of the probe, respectively. Once the desired nucleic acid is synthesized, it is preferably cleaved from the solid support on which it was synthesized and treated, by methods known in the art, to remove any protecting groups present (e.g., 60 °C, 5h, concentrated ammonia). In those embodiments in which a base-sensitive group is attached to the nucleic acids (e.g., TAMRA), the deprotection will preferably use milder conditions (e.g., butylamine: water 1 :3, 8 hours, 70 °C). Deprotection under these conditions is facilitated by the use of quick deprotect amidites (e.g., dC-acetyl, dG-dmf). Following cleavage from the support and deprotection, the nucleic acid is purified by any method known in the art, including chromatography, extraction and gel purification. In a prefeπed embodiment, the nucleic acid is purified using HPLC The concentration and purity of the isolated nucleic acid is preferably determined by measuring the optical density at 260 nm in a spectrophotometer. Peptide Probes Peptides, proteins and peptide nucleic acids that are labeled with a fluorophore and a SL of the invention can be used in both in vivo and in vitro enzymatic assays. Thus, in another aspect, the present invention provides a method for determining whether a sample contains an enzyme. The method comprises: (a) contacting the sample with a peptide construct; (b) exciting the fluorophore; and (c) determining a fluorescence property of the sample, wherein the presence of the enzyme in the sample results in a change in the fluorescence property. Peptide constructs useful in practicing the invention include those with the following features: i) a fluorophore; ii) a SL of the invention; and iii) a cleavage recognition site for the enzyme. Moreover, the peptide construct is preferably of a length and orientation and in a conformation allowing fluorescence energy transfer between the fluorophore and the SL when the fluorophore is excited. When the probe is used to detect an enzyme, such as a degradative enzyme (e.g., protease), and a degree of fluorescence resonance energy transfer that is lower than an expected amount is observed, this is generally indicative of the presence of an enzyme. The degree of fluorescence resonance energy transfer in the sample can be determined, for example, as a function of the amount of fluorescence from the donor moiety, the amount of fluorescence from the acceptor moiety, the ratio of the amount of fluorescence from the donor moiety to the amount of fluorescence from the acceptor moiety or the excitation state lifetime of the donor moiety. The assay also is useful for determining the amount of enzyme in a sample by determining the degree of fluorescence resonance energy transfer at a first and second time after contact between the enzyme and the tandem construct, and determining the difference in the degree of fluorescence resonance energy transfer. The difference in the degree of fluorescence resonance energy transfer reflects the amount of enzyme in the sample. The assay methods also can also be used to determine whether a compound alters the activity of an enzyme, i.e., screening assays. Thus, in a further aspect, the invention provides methods of determining the amount of activity of an enzyme in a sample from an organism. The method includes: (a) contacting a sample comprising the enzyme and the compound with a peptide construct comprising (b) exciting the fluorophore; and (c) determining a fluorescence property of the sample, wherein the activity of the enzyme in the sample results in a change in the fluorescence property. Peptide constructs useful in this aspect of the invention are substantially similar to those described immediately above. In a prefeπed embodiment, the amount of enzyme activity in the sample is determined as a function of the degree of fluorescence resonance energy transfer in the sample and the amount of activity in the sample is compared with a standard activity for the same amount of the enzyme. A difference between the amount of enzyme activity in the sample and the standard activity indicates that the compound alters the activity of the enzyme. Representative enzymes with which the present invention can be practiced include, for example, trypsin, enterokinase, HIV-1 protease, prohormone convertase, interleukin- lb-converting enzyme, adenovirus endopeptidase, cytomegalo virus assemblin, leishmanolysin, β-secretase for amyloid precursor protein, thrombin, renin, angiotensin-converting enzyme, cathepsin-D and a kininogenase, and proteases in general. Proteases play essential roles in many disease processes such as Alzheimer's, hypertension, inflammation, apoptosis, and AIDS. Compounds that block or enhance their activity have potential as therapeutic agents. Because the normal substrates of peptidases are linear peptides and because established procedures exist for making non-peptidic analogs, compounds that affect the activity of proteases are natural subjects of combinatorial chemistry. Screening compounds produced by combinatorial chemistry requires convenient enzymatic assays. The most convenient assays for proteases are based on fluorescence resonance energy transfer from a donor fluorophore to an acceptor placed at opposite ends of a short peptide chain containing the potential cleavage site (see, Knight C. G., Methods in Enzymol. 248: 18-34 (1995)). Proteolysis separates the fluorophore and acceptor, resulting in increased intensity in the emission of the donor fluorophore. Existing protease assays use short peptide substrates incoφorating unnatural chromophoric amino acids, assembled by solid phase peptide synthesis. Assays of the invention are also useful for determining and characterizing substrate cleavage sequences of proteases or for identifying proteases, such as oφhan proteases. In one embodiment the method involves the replacement of a defined linker moiety amino acid sequence with one that contains a randomized selection of amino acids. A library of fluorescent SL-bearing probes, wherein the fluorophore and the SL are linked by a randomized peptide linker moiety can be generated using recombinant engineering techniques or synthetic chemistry techniques. Screening the members of the library can be accomplished by measuring a signal related to cleavage, such as fluorescence energy transfer, after contacting the cleavage enzyme with each of the library members of the tandem fluorescent peptide construct. A degree of fluorescence resonance energy transfer that is lower than an expected amount indicates the presence of a linker sequence that is cleaved by the enzyme. The degree of fluorescence resonance energy transfer in the sample can be determined, for example, as a function of the amount of fluorescence from the donor moiety, the amount of fluorescence from the acceptor donor moiety, or the ratio of the amount of fluorescence from the donor moiety to the amount of fluorescence from the acceptor moiety or the excitation state lifetime of the donor moiety. In the tandem constructs of the invention, the donor and acceptor moieties are connected through a linker moiety. The linker moiety, preferably, includes a peptide moiety, but can be another organic molecular moiety, as well. In a preferred embodiment, the linker moiety includes a cleavage recognition site specific for an enzyme or other cleavage agent of interest. A cleavage site in the linker moiety is useful because when a tandem construct is mixed with the cleavage agent, the linker is a substrate for cleavage by the cleavage agent. Rupture of the linker moiety results in separation of the fluorophore and the SL of the invention. The separation is measurable as a change in FRET. When the cleavage agent of interest is a protease, the linker can comprise a peptide containing a cleavage recognition sequence for the protease. A cleavage recognition sequence for a protease is a specific amino acid sequence recognized by the protease during proteolytic cleavage. Many protease cleavage sites are known in the art, and these and other cleavage sites can be included in the linker moiety. See, e.g., Matayoshi et al. Science 247: 954 (1990); Dunn et al. Meth. Enzymol. 241 : 254 (1994); Seidah et al. Meth. Enzymol. 244: 175 (1994); Thornberry, Meth. Enzymol. 244: 615 (1994); Weber et al. Meth. Enzymol. 244: 595 (1994); Smith et al. Meth. Enzymol. 244: 412 (1994); Bouvier et al. Meth. Enzymol 248: 614 ( 1995). Hardy et al . in AMYLOID PROTEIN PRECURSOR IN DEVELOPMENT, AGING, AND ALZHEIMER'S DISEASE, ed. Masters et al pp. 190-198 (1994). Solid Support Immobilized SL Analogues The SLs of the invention can be immobilized on substantially any polymer, biomolecule, and solid or semi-solid material having any useful configuration. Moreover, any conjugate comprising one or more SLs can be similarly immobilized. When the support is a solid or semi-solid, examples of preferred types of supports for immobilization of the nucleic acid probe include, but are not limited to, controlled pore glass, glass plates, polystyrene, avidin coated polystyrene beads, cellulose, nylon, acrylamide gel and activated dextran. These solid supports are prefeπed because of their chemical stability, ease of functionalization and well-defined surface area. Solid supports such as, controlled pore glass (CPG, 500 A, 1000 A) and non-swelling high cross-linked polystyrene ( 1000 A) are particularly preferred. According to the present invention, the surface of a solid support is functionalized with a SL of the invention or a species including a SL of the invention. For clarity of illustration, the following discussion focuses on attaching a reactive SL to a solid support. The following discussion is also broadly relevant to attaching a species that includes within its structure a reactive SL to a solid support, and the attachment of such species and reactive SL analogues to other molecules and structures. The SLs are preferably attached to a solid support by forming a bond between a reactive group on the SL and a reactive group on the surface of the solid support or a linker attached to the solid support, thereby derivatizing the solid support with one or more SL analogues. The bond between the solid support and the SL is preferably a covalent bond, although ionic, dative and other such bonds are useful as well. Reactive groups which can be used in practicing the present invention are discussed in detail above and include, for example, amines, hydroxyl groups, carboxylic acids, carboxylic acid derivatives, alkenes, sulfhydryls, siloxanes, etc. A large number of solid supports appropriate for practicing the present invention are available commercially and include, for example, peptide synthesis resins, both with and without attached amino acids and/or peptides (e.g. , alkoxybenzyl alcohol resin, aminomethyl resin, aminopolystyrene resin, benzhydrylamine resin, etc. (Bachem)), functionalized controlled pore glass (BioSearch Technologies. Inc.), ion exchange media (Aldrich), functionalized membranes (e.g. , — COOH membranes; Asahi Chemical Co., Asahi Glass Co., and Tokuyama Soda Co.), and the like. Moreover, for applications in which an appropriate solid support is not commercially available, a wide variety of reaction types are available for the functionalization of a solid support surface. For example, supports constructed of a plastic such as polypropylene, can be surface derivatized by chromic acid oxidation, and subsequently converted to hydroxylated or aminomethylated surfaces. The functionalized support is then reacted with a SL of complementary reactivity, such as a SL active ester, acid chloride or sulfonate ester, for example. Supports made from highly crosslinked divinylbenzene can be surface derivatized by chloromethylation and subsequent functional group manipulation. Additionally, functionalized substrates can be made from etched, reduced polytetrafluoroethylene. When the support is constructed of a siliceous material such as glass, the surface can be derivatized by reacting the surface Si-OH, SiO-H, and/or Si-Si groups with a functionalizing reagent. In a preferred embodiment, wherein the substrates are made from glass, the covalent bonding of the reactive group to the glass surface is achieved by conversion of groups on the substrate's surface by a silicon-modifying reagent such as: (R a O) 3 — Si— R b — X a (2) where R a is an alkyl group, such as methyl or ethyl, R b is a linking group between silicon and X a , and X a is a reactive group or a protected reactive group. Silane derivatives having halogens or other leaving groups beside the displayed alkoxy groups are also useful in the present invention. In another prefeπed embodiment, the reagent used to functionalize the solid support provides for more than one reactive group per each reagent molecule. Using reagents, such as the compound below, each reactive site on the substrate surface is, in essence, "amplified" to two or more functional groups: (R a O)τ— Si— R b — (X a ) n (3) where R a is an alkyl group (e.g. , methyl, ethyl), R b is a linking group between silicon and X a , X a is a reactive group or a protected reactive group and n is an integer between 2 and 50, and more preferably between 2 and 20. The amplification of a SL by its attachment to a silicon-containing substrate is intended to be exemplary of the general concept of SL amplification. This amplification strategy is equally applicable to other aspects of the invention in which a SL analogue is attached to another molecule or solid support. A number of siloxane functionalizing reagents can be used, for example: 1. Hydroxyalkyl siloxanes (Silylate surface, functionalize with diborane, and H 2 O ; to oxidize to the alcohol) a. allyl trichlorosilane -» — » 3-hydroxypropyl b. 7-oct-l-enyl trichlorchlorosilane - → 8-hydroxyoctyl 2. Diol (dihydroxyalkyl) siloxanes (silylate surface and hydrolyze to diol) a. (glycidyl trimethoxysilane → → (2,3-dihydroxypropyloxy)propyl 3. Aminoalkyl siloxanes (amines requiring no intermediate functionalizing step) a. 3-aminopropyl trimethoxysilane -» aminopropyl 4. Dimeric secondary aminoalkyl siloxanes a. bis (3-trimethoxysilylpropyl) amine - bis(silyloxylpropyl)amine. It will be apparent to those of skill in the art that an array of similarly useful functionalizing chemistries is available when support components other than siloxanes are used. Thus, for example alkyl thiols, functionalized as discussed above in the context of siloxane-modifying reagents, can be attached to metal films and subsequently reacted with a SL to produce the immobilized compound of the invention. R groups of use for R b in the above described embodiments of the present invention include, but are not limited to, alkyl, substituted alkyl, aryl, arylalkyl, substituted aryl, substituted arylalkyl, acyl, halogen, hydroxy, amino, alkylamino, acylamino, alkoxy, acyloxy, aryloxy, aryloxyalkyl, mercapto, saturated cyclic hydrocarbon, unsaturated cyclic hydrocarbon, heteroaryl, heteroarylalkyl, substituted heteroaryl, substituted heteroarylalkyl, heterocyclic, substituted heterocyclic and heterocyclicalkyl groups and combinations thereof. Nucleic acid Capture Probes In one embodiment, an immobilized nucleic acid comprising a SL is used as a capture probe. The nucleic acid probe can be attached directly to a solid support, for example by attachment of the 3'- or 5'-terminal nucleotide of the probe to the solid support. More preferably, however, the probe is attached to the solid support by a linker (i.e., spacer arm, supra). The linker serves to distance the probe from the solid support. The linker is most preferably from about 5 to about 30 atoms in length, more preferably from about 10 to about 50 atoms in length. In yet another prefeπed embodiment, the solid support is also used as the synthesis support in preparing the probe. The length and chemical stability of the linker between the solid support and the first 3'-unit of nucleic acid play an important role in efficient synthesis and hybridization of support bound nucleic acids. The linker arm should be sufficiently long so that a high yield (> 97%) can be achieved during automated synthesis. The required length of the linker will depend on the particular solid support used. For example, a six atom linker is generally sufficient to achieve a > 97% yield during automated synthesis of nucleic acids when high cross-linked polystyrene is used as the solid support. The linker arm is preferably at least 20 atoms long in order to attain a high yield ( > 97%) during automated synthesis when CPG is used as the solid support. Hybridization of a probe immobilized on a solid support generally requires that the probe be separated from the solid support by at least 30 atoms, more preferably at least 50 atoms. In order to achieve this separation, the linker generally includes a spacer positioned between the linker and the 3 '-terminus. For nucleic acid synthesis, the linker arm is usually attached to the 3'-OH of the 3 '-terminus by an ester linkage which can be cleaved with basic reagents to free the nucleic acid from the solid support. A wide variety of linkers are known in the art, which may be used to attach the nucleic acid probe to the solid support. The linker may be formed of any compound, which does not significantly interfere with the hybridization of the target sequence to the probe attached to the solid support. The linker may be formed of, for example, a homopolymeric nucleic acid, which can be readily added on to the linker by automated synthesis. Alternatively, polymers such as functionalized polyethylene glycol can be used as the linker. Such polymers are presently prefeπed over homopolymeric nucleic acids because they do not significantly interfere with the hybridization of probe to the target nucleic acid. Polyethylene glycol is particularly prefeπed because it is commercially available, soluble in both organic and aqueous media, easy to functionalize, and completely stable under nucleic acid synthesis and post-synthesis conditions. The linkages between the solid support, the linker and the probe are preferably not cleaved during synthesis or removal of base protecting groups under basic conditions at high temperature. These linkages can, however, be selected from groups that are cleav able under a v anetv of conditions Examples of presentlv prefeπed linkages include carbamate, ester and amide linkages Acn lamide-Immobi zed Pi obes In another prefeπed embodiment, a species is within a matπx, such as an acrylamide matπx and the species bears a SL or the presence of the immobilized species is ascertained using a probe beaπng a SL In a prefeπed embodiment, the immobilization is accomplished in conjunction with the "acrydite" process inv ented and commercialized by Mosaic Technologies (Cambπdge, MA, see, Rehman et al , Nucleic Acids Research ,27 649-655 (1999)) The acrydite method allows immobilization of alkene labeled capture probes within a polymeπzed polyacrylamide network When target mixes are run past the immobilized probe band under electrophoresis conditions, the target nucleic acid is captured substantially quantitatively However, detection of this event cuπentlv requires a second probe In one embodiment, probes beaπng a SL, and/or a fluoφhore are immobilized in an acrylamide matπx and subsequently contacted with the target mix By using fluorescent probes as capture probes, signals from target mixes can be directlv detected in real time Microarravs The mvention also provides microaπays including immobilized SLs and compounds functionalized with SLs Moreover, the invention provides methods of inteπogating microarrays using probes that are functionalized with SLs The immobilized species and the probes are selected from substantially any type of molecule including, but not limited to, small molecules, peptides, enzymes nucleic acids and the like Nucleic acid microarrays consisting of a multitude of immobilized nucleic acids are revolutionary tools for the generation of genomic information, see, Debouck et al , in supplement to Nature Genetics, 21 48-50 (1999) The discussion that follow s focuses on the use of SLs in conjunction with nucleic acid microaπays This focus is intended to be illustrative and does not limit the scope of mateπals with which this aspect of the present invention can be practiced Thus, in another prefeπed embodiment, the compounds of the present invention are utilized m a microaπay format The SLs, or species beaπng SLs can themselves be components of a microaπay or, alternatively they can be utilized as a tool to screen components of a microaπay. Thus, in a prefeπed embodiment, the present invention provides a method of screening a microaπay. The method includes contacting the members of the microaπay with a SL-bearing probe and inteπogating the microaπay for regions of fluorescence. The fluorescent regions are indicative of the presence of an interaction between the SL-bearing probe and a microaπay component. In another version of this method, the microaπay is inteπogated for regions in which fluorescence is quenched, again indicating the presence of an interaction between the SL-bearing probe and a component of the microaπay. In another prefeπed embodiment, the aπay comprises immobilized SL- bearing FET probes as the inteπogating species. In this embodiment, the probe "turns on" when hybridized to its target. Such arrays are easily prepared and read, and can be designed to give quantitative data. Arrays comprising SL-bearing probes are valuable tools for expression analysis and clinical genomic screening. In another prefeπed embodiment, the immobilized SL-bearing probe is not a FET probe. A microarray based on such as format can be used to probe for the presence of interactions between an analyte and the immobilized probe by, for example, observing the quenching of analyte fluorescence upon interaction between the probe and analyte. In a further prefeπed embodiment, the microarrays comprise /; probes that comprise identical or different nucleic acid sequences. Alternatively, the microaπay can comprise a mixture of/, probes comprising groups of identical and different nucleic acid sequences identical nucleic acid sequences). In a prefeπed embodiment, n is a number from 2 to 100, more preferably, from 10 to 1,000, and more preferably from 100 to 10,000. In a still further prefeπed embodiment, the n probes are patterned on a substrate as n distinct locations in a manner that allows the identity of each of the /. locations to be ascertained. In yet another prefeπed embodiment, the invention also provides a method for preparing a microaπay of n SL-bearing probes. The method includes attaching SL- bearing probes to selected regions of a substrate. A variety of methods are cuπently available for making arrays of biological macromolecules, such as arrays nucleic acid molecules. The following discussion focuses on the assembly of a microarray of SL- bearing probes, this focus is for reasons of brevity and is intended to be illustrative and not limiting. One method for making ordered arrays of SL-bearing probes on a substrate is a "dot blot" approach. In this method, a vacuum manifold transfers a plurality, e.g., 96. aqueous samples of probes from 3 millimeter diameter ells to a substrate. The probe is immobilized on the porous membrane by baking the membrane or exposing it to UV radiation. A common variant of this procedure is a "slot-blot" method in which the wells have highly-elongated oval shapes. Another technique employed for making ordered aπays of probes uses an aπay of pins dipped into the wells, e.g., the 96 wells of a microtiter plate, for transferring an aπay of samples to a substrate, such as a porous membrane. One aπay includes pins that are designed to spot a membrane in a staggered fashion, for creating an aπay of 9216 spots in a 22 x 22 cm area. See, Lehrach, et al, HYBRIDIZATION FINGERPRINTING IN GENOME MAPPING AND SEQUENCING, GENOME ANALYSIS, Vol. 1, Davies et al, Eds., Cold Springs Harbor Press, pp. 39-81 (1990). An alternate method of creating ordered aπays of probes is analogous to that described by Pirrung et al. (U.S. Patent No. 5,143,854, issued 1992), and also by Fodor et al, (Science, 251: 767-773 (1991)). This method involves synthesizing different probes at different discrete regions of a particle or other substrate. This method is preferably used with relatively short probe molecules, e.g., less than 20 bases. A related method has been described by Southern et al. (Genomics, 13: 1008-1017 (1992)). Khrapko, et al, DNA Sequence, 1 : 375-388 (1991) describes a method of making an nucleic acid matrix by spotting DNA onto a thin layer of polyacrylamide. The spotting is done manually with a micropipette. The substrate can also be patterned using techniques such as photolithography (Kleinfield et al, J. Neurosci. 8:4098-120 (1998)), photoetching, chemical etching and microcontact printing (Kumar et al, Langmuir 10: 1498-511 (1994)). Other techniques for forming patterns on a substrate will be readily apparent to those of skill in the art. The size and complexity of the pattern on the substrate is limited only by the resolution of the technique utilized and the puφose for which the pattern is intended. For example, using microcontact printing, features as small as 200 nm are layered onto a substrate. See, Xia, Y., J. Am. Chem. Soc. 117:3274-75 (1995). Similarly, using photolithography, patterns with features as small as 1 μm are produced. See, Hickman et al, J. Vac. Sci. Techno! . 12:607-16 (1994). Patterns which are useful in the present invention include those which include features such as wells, enclosures, partitions, recesses, inlets, outlets, channels, troughs, diffraction gratings and the like. In a presently prefeπed embodiment, the patterning is used to produce a substrate having a plurality of adjacent wells, indentations or holes to contain the probes. In general, each of these substrate features is isolated from the other wells by a raised wall or partition and the wells do not fluidically communicate. Thus, a particle, or other substance, placed in a particular well remains substantially confined to that well. In another prefeπed embodiment, the patterning allows the creation of channels through the device whereby an analyte or other substance can enter and/or exit the device. In another embodiment, the probes are immobilized by "printing" them directly onto a substrate or, alternatively, a "lift off technique can be utilized. In the lift off technique, a patterned resist is laid onto the substrate, an organic layer is laid down in those areas not covered by the resist and the resist is subsequently removed. Resists appropriate for use with the substrates of the present invention are known to those of skill in the art. See, for example, Kleinfield et al, J. Neurosci. 8:4098-120 (1998). Following removal of the photoresist, a second CAP, having a structure different from the first probe can be bonded to the substrate on those areas initially covered by the resist. Using this technique, substrates with patterns of probes having different characteristics can be produced. Similar substrate configurations are accessible through microprinting a layer with the desired characteristics directly onto the substrate. See, Mrkish et al. Ann. Rev. Biophys. Biomol Struct. 25:55-78 (1996). Spacer Groups As used herein, the term "spacer group," refers to constituents of SL- bearing probes. The spacer group links donor and/or acceptor moieties and other groups to the nucleic acid, peptide or other polymeric component of the probe. The spacer groups can be hydrophilic (e.g., tetraethylene glycol, hexaethylene glycol, polyethylene glycol) or they can be hydrophobic (e.g., hexane, decane, etc.). In a prefeπed embodiment, the immobilized construct includes a spacer between the solid support reactive group and the SL analogue. The linker is preferably selected from C 6 -C o alkyl groups, C 6 -C 3 o substituted alkyl groups, polyols, polyethers (e.g., poly(ethyleneglycol)), polyamines, polyamino acids, polysaccharides and combinations thereof. In certain embodiments, it is advantageous to have a moiety of the probe attached to the polymeric component by a group that provides flexibility and distance from the polymeric component. Using such spacer groups, the properties of the moiety adjacent to the polymeric component is modulated. Properties that are usefully controlled include, for example, hydrophobicity, hydrophilicity, surface-activity, the distance of the donor and/or SL moiety from the nucleic acid and the distance of the donor from the SL. In an exemplary embodiment, the spacer serves to distance the SL from a nucleic acid. Spacers with this characteristic have several uses. For example, a SL held too closely to the nucleic acid may not interact with the donor group, or it may interact with too low of an affinity. When a SL is itself sterically demanding, the interaction leading to quenching can be undesirably weakened, or it may not occur at all, due to a sterically-induced hindering of the approach of the two components. When the construct comprising the SL is immobilized by attachment to. for example, a solid support, the construct can also include a spacer moiety between the reactive group of the solid support and the SL analogue, or other probe component bound to the solid support. In yet a further embodiment, a spacer group used in the probes of the invention is provided with a group that can be cleaved to release a bound moiety, such as a SL, fluorophore, minor groove binder, intercalating moiety, and the like from the polymeric component. Many cleaveable groups are known in the art . See, for example. Jung et al, Biochem. Biophys. Ada, 761 : 152-162 (1983); Joshi et al, J. Biol. Chem., 265: 14518-14525 (1990); Zarling et al, J. Immunol, 124: 913-920 (1980); Bouizar et al, Eur. J. Biochem., 155: 141-147 (1986); Park et α/., J Biol. Chem., 261 : 205-210 (1986); Browning et al, J. Immunol, 143: 1859-1867 (1989). Moreover a broad range of cleavable, bifunctional (both homo- and hetero-bifunctional) spacer arms are commercially available from suppliers such as Pierce. An exemplary embodiment utilizing spacer groups is set forth in Formulae VII and VIII, above. In these formulae, R b is either stable or it can be cleaved by chemical or photochemical reactions. For example, R groups comprising ester or disulfide bonds can be cleaved by hydrolysis and reduction, respectively. Also within the scope of the present invention is the use of R b groups which are cleaved by light such as. for example, mtrobenzyl derivatives, phenacyl groups, benzoin esters, eic. Other such cleaveable groups are well-known to those of skill in the art. Kits In another aspect, the present invention provides kits containing one or more of the SLs or SL-bearing compositions of the invention. In one embodiment, a kit will include a reactive SL derivative and directions for attaching this derivative to another molecule. In another embodiment, the kit include a SL-labeled nucleic acid that optionally is also labeled with a second fluorophore or quencher and directions for using this nucleic acid in one or more assay formats. Other formats for kits w ill be apparent to those of skill in the art and are within the scope of the present invention. The invention provides kits for practicing the methods noted above. The kits can include any of the compositions noted above, and optionally further include additional components such as instructions to practice the methods, one or more containers or compartments (e.g., to hold the assay components, nucleic acids, antibodies, inhibitors or the like), a robotic armature for mixing kit components or the like. The invention also provides integrated systems for performing the methods disclosed herein. For example, in the performing assays, in one embodiment, the delivery of individual compounds or compound components is accomplished by means of a robotic armature which transfers fluid from a source to a destination, a controller which controls the robotic armature, a label detector, a data storage unit which records label detection, and an assay component such as a microtiter dish comprising a well. When a labeled compound is used, it is detected by means of the label detector. A number of robotic fluid transfer systems are available, or can easily be made from existing components. For example, a Zymate XP (Zymark Coφoration; Hopkinton, MA) automated robot using a Microlab 2200 (Hamilton; Reno, NV) pipetting station can be used to transfer parallel samples to 96 well microtiter plates to set up several parallel simultaneous ligation reactions. Optical Amplification Optical signals are important for transmitting information. However, when an optical signal is transmitted through an optical fiber, attenuation will always occur to a certain extent, such that it is necessary to amplify the signal after a certain distance (typically in the order of about 50-100 km). Conventionally, for that puφose an electronic amplifier is used. At the amplifier station, the optical signal must then be converted into an electrical signal, which is amplified in an electronic amplifer, after which the amplified electrical signal is converted back into an optical signal. This involves not only the disadvantage that an amplifier station has a rather complicated structure with rather a large number of parts, among which optical/electrical converters and electrical/optical converters, but this also implies that the bandwidth and bit-rate of the overall system is limited by the electronic components. Therefore, optical fiber amplifiers have recently been developed, i.e. amplifiers which amplify the optical signal directly and do not need a conversion into an electrical signal. Such devices are disclosed in, for example, Yan et al, U.S. Patent No. 5,982,973, issued November 9, 1999; Kleinerman, U.S. Patent No. 5,928,222, issued July 27, 1999; Desurvire, Physics Today, January 1994, 20-27; Sloof et al, J. Appl Phys. 83: 497 (1998). Thus, in another embodiment, the present invention provides a substrate for the transmission and amplification of light, said substrate comprising a compound of the invention. The compound of the invention can be incoφorated into the substrate in any manner known in the art, including, but not limited to, covalent attachment, coating, doping, and the like. This substrate is also useful for converting UV light into visible light. The substrate can include any material useful for a particular application, including, but not limited to, glass, organic polymers, inorganic polymers and combinations thereof. Also provided is a method for amplifying light transmitted by the substrate derivatized with a compound of the invention, as described above. The method comprises transmitting light through such a substrate, thereby amplifying the light. The substrates and methods of the invention can be used in fiber optic devices, sensors (see, for example, Kopelman et al, U.S. Patent No. 5,627,922; and Pinkel et al, U.S. patent No. 5,690,894), fiber optic "refrigerators" and the like. Medical Applications The compounds of the invention can also be used to treat malignant tumors via photodynamic therapy (PDT). Additionally, the complexes of the invention be used in vivo and in vitro as chelating agents for: (1) certain paramagnetic metal ions to achieve higher contrast in magnetic resonance imaging (MRI); and (2) radioactive metal ions for tumor imaging in single-photon-emission tomography (SPECT) or position emission tomography (PET) and/or in radioisotope-mediated radiation therapy. Thus, appropriately radiolabeled salicylamidyl chelates can be imaged noninvasively in nuclear medicine employing SPECT or PET. See, for example, Margerum et al, U.S. patent No. 6,010,681 ; and Woodbum et al, U.S. Patent No. 6,022,526. Separations In another prefeπed embodiment, the specificity of the compounds of the invention for particular ions in solution is exploited to separate those ions from other solutes, including ions for which a compound of the invention has a lower affinity or specificity. Many examples of ion selective or ion specific chelating agents are known in the art. See, for example, Izatt, et al. SYNTHESIS OF MACROCYCLES, Wiley-ϊnterscience, New York, 1987; and Martell et al, DETERMINATION AND USE OF STABILITY CONSTANTS, 2 nd Ed., VCH Publishers, New York, 1992. The materials, methods and devices of the present invention are further illustrated by the examples which follow. These examples are offered to illustrate, but not to limit the claimed invention. EXAMPLES Example 1 sets forth the synthesis and the metallation of the ligand TRENSAM. Example 2 sets forth the spectrophotometric titration of TRENSAM. Example 3 sets forth the x-ray structure determination of Tb TRENSAM. Example 4 sets forth the synthesis of a versatile starting material for the ligands of the invention. Example 5 sets forth the synthesis of several ligands of the invention having backbones of variable length. EXAMPLE 1 This example details the synthesis and the metallation of the ligand TRENSAM. This synthesis is outlined in Fig. 1. 1.1 Materials and Methods Unless otherwise noted, starting materials were obtained from commercial suppliers and used without further purification. Flash column chromatography was performed using Merck silica gel 40-70 mesh. Microanalyses were performed by the Microanalytical Services Laboratory, College of Chemistry. University of California, Berkeley. Mass spectra were recorded at the Mass Spectrometry Laboratory, College of Chemistry, University of California, Berkeley. Η and l j C NMR spectra were recorded on an AMX 300 or AMX 400 Bruker superconducting Fourier transform spectrometer or on a DRX 500 Brucker superconducting digital spectrometer. Infrared spectra were measured using a Nicolet Magna IR 550 Fourier transform spectrometer. 1.2 Synthesis of Tris[(2-hvdrox\>benzoyl)-2-aminoethyll amine (TRENSAM). 1 Methyl salicylate (78 mmol) was mixed with distilled TREN (17 mmol). The mixture was sealed and heated to 100° C overnight. The thick resulting oil was purified on a silica column eluted with 0-4% MeOH in CH 2 C1 2 , resulting in a white powder after removal of solvent. Overnight drying in vacuo gave a colorless glass. Yield: 47%. IR (KBr) 1543, 1590, 1636 cm " '. Η NMR (300 MHz, CD 3 OD, 25 C) 2.78 (t, 3 J = 6.2 Hz, 6H, CH 2 ), 3.49 (t, 3 J= 6.2 Ηz, 6Η, CH 2 ), 6.68 (t, 3 J= 7.2 Ηz, 3Η. ArH), 6.80 (d. 3 J= 7.4 Ηz, 3Η, ArH), 7.23 (t, 3 J = 5.8 Ηz, 3Η, ArH), 7.63 (d, 3 J= 6.4 Ηz, 3Η, ArH), 8.44 (t br, 3Η, NH). 13 C NMR (400 MHz, CD 3 OD, 25 C) 39.0 (CH 2 ), 54.6 (CH 2 ), 117.1 (Ar), 118.4 (Ar), 120.2 (Ar), 129.0 (Ar), 134.7 (Ar), 160.9 (ArCO), 170.9 (CO). Anal. Calcd (Found) for C 27 H 30 N 4 O 6 : C, 64.02 (63.94); H, 5.97 (5.97); N, 1 1.06 (11.01). 1.3 Synthesis ofTb(TRENSAM) TRENSAM (0.12 mmol) was dissolved in 5 mL of MeOH to which the lanthanide (0.06 mmol, TbCl ) salt was added followed by an excess of pyridine (0.3 mL). The addition of the Tb 3+ gave a strongly green solution when irradiated by UV light (254 and 365 nm). After stirring for 15 hours the solution was diluted with Et 2 O (50 mL) to precipitate a white solid (42 mg) which was collected by filtration. Synthesis of the metal complexes was performed by suspending the ligand in methanol followed by addition of the appropriate lanthanide salt. After mixing, an excess of base is added (pyridine) and the reaction is stiπed for several more hours. The formation of the metal complexes can be monitored by iπadiation of the aqueous reaction mixtures with a UV lamp (254 and 365 nm). When illuminated, the reaction mixture of the Tb + complex emits bright green light. The color is readily visible with the naked ev e. The luminescence of the Tb ~ ~ complex remains very bright after isolation and drying of the compound. 1.4 Solution Behavior The complexes formed with the ligand TRENSAM have a lower water solubility compared to those formed with bicapped TRENSAM. For this reason, the stability and the nature of the complexes formed have been measured in methanol for practical reasons. The complexes are nevertheless soluble in water, as revealed by the very strong green luminescence of the complex in water which can be observed with the naked eye. This observation was made as part of the spectrometric titration described in Example 2. EXAMPLE 2 This example details the spectrophotometric titration of TRENSAM. 2.1 Materials and Methods Batch titration samples were prepared in MeOH (analytical grade). The samples were incubated at 37 °C for 15 hours before measurement to ensure fhermodynamic equilibrium had been reached. The ligand concentration was 2.18- 10° M for all samples and the TbCU was titrated from 0 to 2.3 equivalents. The spectra were recorded on a double-beam Perkin-Elmer Lambda 9 LTV-Visible spectrophotometer in 1.0 cm quartz Suprasil cell. The samples were kept at a constant temperature of 25.0 ± 0.2 °C using a Neslab RTE-1 1 1 water bath. The treatment of the data was performed with the using the software package SPECFIT 2.10 (Gampp et al. Talanta 33 : 943 (1986). 2.2 Results The experiment was performed as a batch titration. The factor analysis of the obtained spectra is particularly clear and indicates without any ambiguity the presence of only two absorbing species, indicating that only one type of complex is formed in solution with this ligand. The fitting of the data according to the model of Equation (1 ) confirms the existence of only one type of complex in solution and allows the identification as ML species. The stability of this complex is low. Tb 3+ + IL <-> [Eu(L)] logG0 ) = 4.8(2) (1) EXAMPLE 3 This example details the x-ray structure determination of TbTRENSAM. 3.1 Materials and Methods All X-ray structure data sets were collected on a Siemens SMART Area Detector diffractometer (SMART, Area-Detector Software Package; Siemens Industrial Automation, Inc.: Madison, 1994). Crystals were mounted on quartz capillaries in Paratone oil and were cooled in a nitrogen stream on the diffractometer. Peak integrations were performed using Siemens SAINT software package (SAINT, SAXArea- Detector Integration Program v. 4.024; Siemens Industrial Automation. Inc.: Madison, 1994). Space group determinations were done by the software XPREP. The structures were solved by direct methods and refined using the SHELXTL software package (PC version, SHELXTL, Ciystal Structure Analysis Determination Package; Siemens Industrial Automation, Inc.: Madison, 1994). All hydrogen atoms were fixed at calculated positions and their thermal parameters refined isotropically; all non-hydrogen atoms were refined anisotropically. 3.2 Results During crystallization attempts, the complex Tb[TRENSAM] + was obtained by co-precipitation with Tb(NO ) Suφrisingly, the solved structure revealed a ML 2 complex with many similarities to the structure of [Eu(bicappedTRENSAM) ] T . The Tb "^ metal center is octadentate and coordinated in a more distorted square-antiprism geometry. The non- chelated salicylate arms are pointing away from the cation and do not protect it anymore against solvent coordination. As in the case of [Eu(bicappedTRENSAM) 2 ] + , the two ligands do not arrange themselves in an orthogonal way. There are 4 possibilities to aπange the two ligands around the metal ion in order to have a coordination number of 8: 2 orthogonal aπangements, 1 possibility where the two backbones are supeφosed by an inversion center located on the Tb 3+ atom and 1 possibility where the two backbones are the closest together. An example of the last described possibility was found with the complex of [Tb(TRENSAM) 2 ] + where the proximity of the two tripodal backbones of each maximizes the steric interactions between the two non-chelating arms. The explanation can be found in the representation of the crystal structure which includes the two co- precipitated Tb(NO ) 3 . Each Tb 3+ atom of this nitrate presents two interactions with the phenolic coordinating oxygen of one coordinated ligand of the ML 2 complex. These particular interactions are probably mainly responsible for the orientation of one ligand compared to the other one. The X-ray structure does not correspond to the main species present in solution, but to the most insoluble complex has been isolated under particular experimental conditions. EXAMPLE 4 Example 4 sets forth the synthesis of a versatile starting material for ligands of the present invention. To a mixture of 3-methyl-salicylic acid ( 1 .32 mol)and anhydrous potassium carbonate (3.6 mol)dissolved in 3.5 L of dry acetone in a 5L round bottle flask, dimethylsulfate (2.2 mol) was added in several times. The mixture was refluxed overnight, and the reaction was monitored by TLC After filtration of the reaction mixture, the solvents of the filtrate were evaporated and 215 g of a pale yellow thick oil was obtained as the raw product. Yield 91 %. Η NMR (500 MHz, CDCh, 25 °C) δ: 2.263 (s, 3H, CH 3 ), 3.782 (s, 3H, OCH 3 ), 3.854 (s, 3H, OCH ), 6.984 (t. J = 7.5, IH, ArH), 7.276 (d, J = 7.5, IH, ArH), 7.582 (d, J = 7.5, I H, ArH); 13 C NMR (500 MHz, CDC1 3 , 25 °C) δ: 15.72, 51.81 , 61.17, 123.26, 124.36, 128.86, 132.46, 134.88, 158.16, 166.61. 4.1 2-Methoxy-3-methylbenzoic Acid. 3 To a solution of 2 (1.19 mol) in a mixture of methanol (2 L) and water (0.5 L), potassium hydroxide pellets (100 gram, 1.5 mol) were added under cooling. The mixture was refluxed overnight and evaporated to dryness. The residue was dissolved in water (0.5 L) and acidified with HCI 6N. The product precipitated and 189 g of product was collected as white crystals. Yield 95%. Η NMR (500 MHz, CDCI3, 25 °C) δ: 2.234 (s, 3H, CH 3 ), 3.717 (s, 3H, OCH 3 ), 7.062 (t, J = 7.5, IH, ArH), 7.365 (d. J = 7.5, IH, ArH), 7.496 (d, J = 7.5, IH, ArH). 4.3 2-Methoχy-isophthalic Acid. 4 3 (0.45 mol) was suspended in 4 L of water in a 5 liter flask equipped with a mechanic stiπer and a heating mantle. Under addition of sodium hydroxide (0.5 mol) the reaction mixture turned to be a clear solution. The solution was then heated to 75° C and potassium permanganate (1 mol) was added in small batch over a period of 6 hrs. The resulted brown slurry was stiπed overnight and the temperature of the reaction mixture was kept in the range of 80-85° C. The advancement of the reaction was monitored by proton NMR (in D 2 O-NaOD). The slurry was then filtered to remove Mn0 2 and the filtrate was acidified with cone. HCI. crystalline product started to precipitate slowly. 75 g of pure product was collected by filtration as snow-white crystal. Yield 85%. Η NMR (500 MHz, DMSO-d 6 , 25 °C) δ: 3.79 (s, 3H, CH ). 7.243 (t, J = 7.5. IH, ArH), 7.794 (d, J = 7.5, 2H. ArH). 4.4 DιmethvI-2-methoxyιsophthalate, 5 4 (0.75 mol) and anhydrous potassium carbonate (3.0 mol) were placed in 3.5 L of dry acetone in a 5 L round bottle flask. Dimethyl sulfate (2.5 mol) was added in several times. The mixture was refluxed overnight, and the reaction monitored by TLC The reaction mixture was filtered and the solvents of the filtrate were evaporated. 153 g of a pale yellow thick oil was obtained as the raw product. Yield 91 %. Η NMR(500 MHz, CDC1 3 , 25 °C) δ: 3.922 (s, 6H, OCH 3 ), 3.926 (s, 3H, OCH 3 ), 7.197 (t, J = 7.5, IH, ArH), 7.913 (d, J = 7.5, IH, ArH); 1 C NMR (500 MHz, CDCI 3 , 25 °C), δ: 52.17. 63.45, 123.25, 126.38, 159.41 , 165.85. 4.5 Monomethyl-2-methoxyisophthalic acid. 6 An aqueous solution of sodium hydroxide (5M, 100 mL) was added under cooling to a solution of 5 (0.5 mol) in methanol (1.5 L). The mixture was stirred for 3 days at room temperature. The solvents were removed under reduced pressure and the residue dissolved in hot acetone (2 L). A thick paste precipitated from the acetone solution overnight (room temperature). TLC reveals that the upper acetone solution mainly contained the starting diester and the mono-sodium salt of the acid and that the lower paste was a mixture of the mono- and disodium salt of the acid. Acetone was removed from both fractions and the chromatographic separation on a gradient flash silica gel column (0-3% methanol in CH 2 C1 2 ) of both fractions gave 40 g the desired product. Yield 63%. Η NMR (500 MHz, CDC1 3 , 25 °C), δ: 3.913 (s, 3H, OCH 3 ), 3.982 (s, 3H, OCH 3 ), 7.252 (t, J = 7.75, IH, ArH), 7.991 (d, J = 7.5, IH, ArH), 8.166 (d, J = 7.5, IH, ArH). 13 C NMR (500 MHz, CDC1 3 , 25 °C), δ: 52.48, 64.09, 124.10, 125.67, 136.38, 136.49, 159.76, 165.46, 167.69. 4.6 Methyl 2-methoxy-l-(2-mercaptothiazolιde)ιsophthalanude. 8 To the slurry of 6 (10.5 g, 0.05 mol) in toluene (100 mL). oxalvi chloride (9.1 g, 0.08 mol) and a drop of DMF were added with stirring. The mixture turned to a clear solution which was kept under stirring for 6 h. The volatiles were removed under reduced pressure and the raw methyl 2-methoxy-l-(2-mercaptothiazolide)isophthalic monoacid chloride obtained as a pale yellow oil, it was used without further purification. To a solution of this monoacid chloride in dry THF (100 mL), 2- mercaptothiozaline (7.2 g, 0.6 mol) and 20 mL of triethylamine in 100 mL dry THF were added dropwise under stirring and cooling. The resulting yellow slurry was evaporated to dryness and dissolved in methylene chloride. It was extracted with IN HCL and IN KOH successively. 14 g of pure monothiazolide were obtained after a flash silica purification. Yield:, 89%. Η NMR (500 MHz, CDC1 , 25 °C), δ: 3.377 (t, J = 7.5, 2H, CH 2 ), 3.850 (s, 3H, OCH 3 ), 3.869 (s, 3H, OCH 3 ), 4.604 (t, J = 7.5, 2H, CH 2 ), 7.137 (t, J = 7.5, IH, ArH), 7.421 (d, J = 7.5, IH, ArH), 7.862 (d, J = 7.5, IH, ArH). 13 C NMR (500 MHz, CDCI 3 , 25 °C), δ: 29.97, 52.21, 55.40, 63.16, 123.41, 124.14, 130.55, 132.66, 133.84, 156.98, 165.63, 167.17, 201.12. Anal. Calcd (Found) for Ci3H 13 NO 4 SrH 2 O (Mr. 329.396): C, 47.40 (47.02); H, 3.98 (3.78): N, 4.25 (4.11). EXAMPLE 5 Example 5 illustrates the synthesis of several ligands of the invention in which the backbones of the ligands are of variable length and the formation of lanthanide complexes of these ligands. 5.7 Me»H22IAMC 9 8 (4.8 mmol) was added to a solution of H(2,2)-amine (1 mmol) in CH 2 C1 2 (50 mL). The mixture was stiπed and the advancement of the reaction was monitored by TLC. The reaction mixture was applied onto a gradient flash silica gel column (2-7% CH 3 OH in CH C1 2 ) and the appropriate fractions were evaporated to dryness. 0.81 g of product was collected as white foam. Yield 79%. MS (FAB+, m/e) 1001.6. Η NMR (500 MHz, CDC1 3 , 25 °C), δ 2.699(s, 4H, CH 2 ), 2.718 (t, 8H, J= 6.4, CH 2 ), 3.479(q, J= 6.4, 8H, CH 2 ), 3.771 (s, 12H, CH 3 ), 3.798 (s, 12H, CH 3 ), 7.109 (t, 3H, J= 7.5, ArH), 7.770 (d, 4H, J= 7.5, ArH), 7.900 (d, 4H, J= 5.4, Amide H), 7.985 (d, 4H, J= 7.5, ArH). 13 C NMR (500 MHz. CDCh, 25 °C) δ: 37.59, 51.74. 52.12. 53.25. 63.21, 123.94, 124.80, 128.24, 134.1 1 , 135.10. 157.73, 164.74, 165.53 5.2 Me 5 H32IAMC. 10 This compound was prepared by the same procedure as compound 9 with the exception of H(2,2)-amine being used instead of H(3,2)-amine. Yield 79%. Η NMR (500 MHz, CDCh, 25 °C), δ 1.789 (quint, j = 6.5, 4H, CH 2 ), 2.675 (t, 4H, j = 7.5, CH 2 ), 2.801 (t, 8H, j = 6.5, CH 2 ), 3.583 (q, j = 6.5, 8H, CH 2 ), 3.823 (s, 9H, CH 3 ), 3.854 (s, 9H, CH 3 ), 3.896 (s, 3H, CH 3 ), 3.922 (s, 3H, CH 3 ), 7.154 (t, 3H, J = 7.5, ArH), 7.178 (t, IH, j = 7.5, ArH), 7.824 (d, 3H, j = 7.5. ArH), 7.906 (d, IH, j = 7.5, ArH), 7.9-8.1 (m, 8H, ArH + AmideH). 13 C NMR (500 MHz, CDC13, 25 °C), δ: 37.35, 51.91, 52.29, 52.39, 52.78, 63.39, 63.86, 123.99, 124.1 1, 125.03, 125.22, 128.45, 134.29, 135.13, 135.26, 135.78, 157.95, 165.11, 165.72. 5.3 Me 1 . H42IAMC 11 This compound was prepared by the same procedure as compound 10 with the exception of H(4,2)-amine being used instead of H(3,2)-amine. Yield 82%. Η NMR (500 MHz, CDC1 3 , 25 °C), δ 1.483 (s, br, 4H, CH 2 ), 2.597 (s,br, 4H, CH 2 ), 2.753 (t, 8H, J = 6.5, CH 2 ), 3.549 (q, j = 6.5, 8H, CH 2 ), 3.832 (s, 9H, CH 3 ), 3.866 (s, 9H, CH 3 ), 3.909 (s, 3H, CH 3 ), 3.943 (s, 3H, CH 3 ), 7.172 (t, 4H, j = 7.5, ArH), 7.837 (d, 4H, j = 7.5, ArH), 7.959 (t, 4H, J = 5.5, AmideH), 8.067 (d, J = 7.5, 4H, ArH). , 3 C NMR (500 MHz, CDCI 3 , 25 °C), δ: 24.15, 37.67, 52.30, 52.41, 52.84, 53.37, 53.84, 63.39, 63.91, 124.07, 124.14, 125.18, 128.36, 134.35, 135.37, 135.87, 157.97, 158.89, 164.97, 165.66, 165.71. 5.3 H22IAMC. 12 Me 8 H(2,2)IAMC (1.0 g, 1 mmol) was dissolved in dry degassed CH C1 2 (40 mL). The solution was cooled in an ice bath and BBn (2 mL, 23 mmol) was added via syringe under nitrogen. The resulted pale yellow slurry was stiπed for 96 hrs, after which the volatile was removed under vacuum and the residue quenched with methanol (30 mL). The methanol solution was diluted with water 40 mL) and boiled until a transparent solution was obtained. The solution was filtered, and a white precipitate deposited upon cooling, which was collected by filtration and vacuum dried. Yield: 50%. Η NMR (500 MHz, D 2 O-NaOD, 25 °C), δ: 2.757 (t, 12H, J = 7.2, NCH 2 ), 3.269 (t, 8H, j = 7.2, NCH ), 6.220 (t. J = " .5. 4H. .ArH), 7.045 (d. J=7.5, 4H. ArH). -.508 (d. J=7.5, 4H,ArH). 5.4 H32IAMC 13 This compound was prepared by the same BBn deprotection procedure as compound 12 with the exception of Me 8 H32IAMC being used instead of Me 8 H22IAMC. yield 65%. MS (FAB+, m/e) 903. Η NMR (500 MHz, D 2 0-NaOD, 25 °C), δ: 1.575 (s,br, 2H, CH 2 ), 2.453 (t, J = 7.2, 4H, CH 2 ), 2.636 (t, 8H, J = 7.2, NCH : ). 3.358 (t, 8H. J = 7.2, NCH 2 ), 6.324 (t, J = 7.5, 4H, ArH), 7.148 (d, J=7.5, 4H, ArH), 7.611 (d, J=7.5, 4H,ArH). 13 C NMR (500 MHz, D 2 0-NaOD, 25 °C), δ: 24.35, 36.19. 52.12. 52.32, 111.71, 1 18.86, 129.92, 131.52, 133.14, 166.59, 170.81, 178.98 5.5 H42IAMC 14 This compound was prepared by the BBr3 deprotection procedure as compound 12 with the exception of Me 8 H42IAMC being used instead of Me 8 H22IAMC, yield 61%. Η NMR (500 MHz, D 2 O-NaOD, 25 °C), δ: 1.349 (s,br, 4H, CH 2 ), 2.439 (s,br, 4H, CH 2 ), 2.651 (t, 8H, J = 7.2, NCH 2 ), 3.428 (t, 8H, J = 7.2, NCH 2 ), 6.442 (t, J = 7.5, 4H, ArH), 7.250 (d, J=7.5, 4H, ArH), 7.732 (d, J=7.5, 4H, ArH). 5.6 Tb[H42IAMCJ 12 was suspended in 17 mL of a solution of MeOH containing Tb(NO ) 3 .6H 2 O (0.047 mmol, 99.999 %). The suspension was heated until reflux. 45 drops of pyridine were added to the suspension and precipitate appeared, increasing the amount of solid of the reaction mixture. A strong green emission of the solution was observed upon UV iπadiation. After 6 hours of reflux, the solvent was removed. 18 mL of H 2 O and 10 drops of pyridine were added to the solid and the resulting suspension was st red under reflux for 15 hours. The product was filtered and washed with Et 2 0. After cooling, filtration and drying of the solid (vacuum oven), 42 mg of product was collected. Yield: 72 %. Calcd. (Found) for TbC 44 H 45 N 6 Oι 6 (HBr).3CH 3 OH: C, 45.17 (45.20); H, 4.68 (4.99); N, 6.72 (6.88). It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reading the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications are incoφorated herein by reference.

Claims: WHAT IS CLAIMED IS: 1. A luminescent lanthanide metal chelate comprising a metal ion of the lanthanide series and a complexing agent comprising at least one salicylamidyl moiety. 2. The chelate according to claim 1, having a quantum yield of at least about 0.1. 3. The chelate according to claim 2, wherein said lanthanide metal ion is an ion a member selected from europium, terbium and combinations thereof. 4. The compound according to claim 1 , further comprising at least one phthalamidyl moiety. 5. A compound having a structure according to Formula I: wherein R , 1 a „_ndJ r R > 2 are members independently selected from the group consisting of alkyl, substituted alkyl, halogen and — OR 6 , wherein R 6 is a member selected from the group consisting of H, alkyl, substituted alkyl groups and a single negative charge; R 4 , R 5 , R 7 , R 10 and R 20 are members independently selected from the group consisting of H, alkyl and substituted alkyl groups; R 3 , R 8 and R 9 are members independently selected from the group consisting of alkyl and substituted alkyl groups; R 1 1 , R 12 , R 13 , R 2 ! , R 22 and R 23 are members independently selected from alkyl, substituted alkyl, H, — NR 14 R 15 , — NO 2 , —OR 16 , :OOR 17 , wherein, R 1 . R'\ R 16 and R 1 ' are members independently selected from the group consisting of H, alkyl and substituted alkyl. wherein R !~ can optionally form a ring with R 1 ', R 13 or both, and R 22 can optionally form a ring with R 21 , R 23 or both, said rings being members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocyclyl and saturated heterocyclyl ring systems; and Q' is — OR 18 ; Q 2 is — OR 19 , wherein R 18 and R 19 are members independently selected from H, an enzymatically labile group, a hydrolytically labile group and a single negative charge; and a and z are independently selected from the group consisting of 0 and 1 , with the proviso that when a is 0, N 1 is covalently attached directly to carbonyl 1 ', and when z is 0, N is covalently attached directly to carbonyl group 2'. 6. The compound according to claim 5, wherein, R 1 , R 2 , R 3 , R 4 , R , R 6 , R 8 , R 9 , R 10 and R 20 are members independently selected from the group consisting of Ci to Cio alkyl and C to Cio substituted alkyl. 7. The compound according to claim 6 wherein, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 8 , R 9 , R 10 and R 20 are members independently selected from the group consisting of C 2 to C 6 alkyl and C to C 6 substituted alkyl. 8. The compound according to claim 5, wherein R 1 , R 2 , R 3 , R 4 , R , R 6 , R 8 , R 9 , R 10 and R 20 are members independently selected from the group consisting of alkyl substituted with aryl, alkyl substituted with substituted aryl and combinations thereof. 9. The compound according to claim 5, wherein R 1 , R 2 , R 3 , R 4 , R D , R 6 , R 8 , R 9 , R 10 and R 20 are members independently selected from the group consisting of alkyl substituted with a polycyclic aryl group. 10. The compound according to claim 5. wherem a member selected from the group consisting of R 1 , R 2 , R\ R 4 , R\ R 6 , R s , R 9 . R 10 and R 20 and combinations thereof is a pπmary alkyl amine 11. The compound according to claim 10, wherem said pπmary alky 1 amme as a to Co alkyl chain beaπng an amine moiety at the ω-position 12. The compound according to claim 11 , wherein said pπmary alky 1 amme as a C 2 to C & alkyl chain beaπng an amine moiety at the ω -position 13. The compound according to claim 5, wherein a member selected from the group consisting of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 8 , R 9 , R 10 and R 20 and combinations thereof is a polyether 14. The compound according to claim 13, wherein said polyether is a member selected from ethylene glycol, ethylene glycol ohgomers and combinations thereof, wherein said polyether has a molecular weight of from about 60 daltons to about 10,000 daltons 15. The compound according to claim 14, wherein said polyether has a molecular weight of from about 100 daltons to about 1,000 daltons 16. The compound according to claim 5, wherein R . R , R , R , R R 6 , R 8 , R 9 , R 10 and R 20 and combinations thereof are members selected from ω-carboxv 1 alkyl groups, ω-carboxyl substituted alkyl groups and combinations thereof 17. The compound according to claim 16, wherem said co-carboxyl substituted alkyl group has a structure according to Formula II wherem, X is a member selected from O, S and NR S0 , wherem R is a member selected from FI, alkyl and substituted alkyl, Y is a member selected from H and a single negative charge, and j and k are members independently selected from the group consisting of integers from 1 to 18. 18. The compound according to claim 17, wherein said c -carboxyl substituted alkyl group has a structure according to Formula III: 19. The compound according to claim 5, wherein both a and z are 0. 20. The compound according to claim 5, wherein R is a linear -C hydrocarbon. 21. The compound according to claim 5, wherein z is 0. 22. The compound according to claim 21 , wherein R 8 is (CH 2 ) P ; R 4 is an alkyl group substituted with a moiety having a structure according to Formula IV: wherein, R 29 is a member selected from the group consisting of alkyl, substituted alkyl, halogen and — OR 7 , wherein R 7 is a member selected from the group consisting of H, alkyl, substituted alkyl groups and a single negative charge; R 46 is a member selected from alkyl and substituted alkyl. R 31 , R 32 and R 33 are members independently selected from alkyl, substituted alkyl, H, — NR 24 R 25 , — NO 2 , —OR 26 , — COOR 27 , wherein, R , R , R" and R are members independently selected from the group consisting of H, alkyl and substituted alkyl, wherein R 32 can optionally form a ring with R " '. R " ' or both, said rings being members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl. aryl, substituted aryl, heteroaryl, substituted heteroaryl. heterocyclyl and saturated heterocyclyl ring systems; R 3 is (CH 2 ) X ; Q " — OR ~ \ wherein R" is a member selected from H. an enzymatically labile group, a hydrolytically labile group and a single negative charge; P and X are members independently selected from the group consisting of the integers from 1 to 5, inclusive. 23. A compound according to claim 22, having a structure according to Formula V: 24. The compound according to claim 22 wherein, R 29 and R 46 are members independently selected from the group consisting of C to Co alkyl and to Cio substituted alkyl . 25. The compound according to claim 24 wherein, R 29 and R are members independently selected from the group consisting of C 2 to C 6 alkyl and C 2 to C 6 substituted alkyl. 26. The compound according to claim 22, wherein R 29 and R are members independently selected from the group consisting of alkyl substituted with aryl, alkyl substituted with substituted aryl and combinations thereof. 27. The compound according to claim 22, wherein R 29 and R are members independently selected from the group consisting of alkyl substituted with a polycyclic aryl group. 28. The compound according to claim 22. wherein a member selected from the group consisting of R" 9 and R 46 and combinations thereof is a primary alkyl amine. 29. The compound according to claim 28. wherein said primary alkyl amine as a to Co alkyl chain bearing an amine moiety at the ω-position. 30. The compound according to claim 29, wherein said primary alkyl amine as a C 2 to C 6 alkyl chain bearing an amine moiety at the ω-position. 31. The compound according to claim 22, wherein a member selected from the group consisting of R 29 and R 46 and combinations thereof is a polyether. 32. The compound according to claim 31, wherein said polyether is a member selected from ethylene glycol, ethylene glycol ohgomers and combinations thereof, wherein said polyether has a molecular weight of from about 60 daltons to about 10,000 daltons. 33. The compound according to claim 32, wherein said polyether has a molecular weight of from about 100 daltons to about 1,000 daltons. 34. The compound according to claim 22, wherein R 29 and R and combinations thereof are members selected from ω-carboxyl alkyl groups, ω-carboxyl substituted alkyl groups and combinations thereof. 35. The compound according to claim 34, wherein said ω-carboxyl substituted alkyl group has a structure according to Formula II: wherein, X is a member selected from O, S and NR 50 , wherein R 50 is a member selected from H, alkyl and substituted alkyl; Y is a member selected from H and a single negative charge; and j and k are members independently selected from the group consisting of integers from 1 to 18. 36. The compound according to claim 35. wherein said ω-carboxyl substituted alkyl group has a structure according to Formula III: 37. The compound according to claim 5, wherein R is an alkyl group substituted with a group having a structure according to Formula IV; R 5 is an alkyl group substituted with a moiety having a structure according to Formula VI: wherein, R 39 is a member selected from the group consisting of alkyl, substituted alkyl, halogen and — OR 7 , wherein R 7 is a member selected from the group consisting of H, alkyl, substituted alkyl groups and a single negative charge; R 45 is a member selected from alkyl and substituted alkyl. R 41 , R 42 and R 43 are members independently selected from alkyl, substituted alkyl, H, — NR 34 R 35 , — NO 2 , —OR 36 , — COOR 37 , wherein, R 34 , R 35 , R 36 and R 37 are members independently selected from the group consisting of H, alkyl and substituted alkyl, wherein R " can optionally form a ring with R 41 , R 43 or both, said rings being members independently selected from the group of ring systems consisting of cyclic alkyl, substituted cyclic alkyl, aryl, substituted aryl, heteroaryl. substituted heteroaryl, heterocyclyl and saturated heterocyclyl ring systems. 38. A compound according to claim 37. having a structure according to Formula VII: wherein, M, N, P and Z are members independently selected from the group consisting of the integers between 1 and 5, inclusive. 39. The compound according to claim 37, wherein, R 39 and R 45 are members independently selected from the group consisting of C to Cio alkyl and C to do substituted alkyl. 40. The compound according to claim 39 wherein, R 39 and R 45 are members independently selected from the group consisting of C_ to C 6 alkyl and C? to C O substituted alkyl. 41. The compound according to claim 37, wherein R 39 and R 45 are members independently selected from the group consisting of alkyl substituted with aryl, alkyl substituted with substituted aryl and combinations thereof. 42. The compound according to claim 37, wherein R 39 and R 45 are members independently selected from the group consisting of alkyl substituted with a polycyclic aryl group. 43. The compound according to claim 37, wherein a member selected from the group consisting of R 39 and R 45 and combinations thereof is a primary alkyl amine. 44. The compound according to claim 37, wherein said primary alkyl amine as a C to do alkyl chain bearing an amine moiety at the ω-position. 45. The compound according to claim 44, wherein said primary alkyl amine as a C to C 6 alkyl chain bearing an amine moiety at the ω-position. 46. The compound according to claim 37, wherein a member selected from the group consisting of R 39 and R 45 and combinations thereof is a polyether. 47. The compound according to claim 46, wherein said polyether is a member selected from ethylene glycol, ethylene glycol ohgomers and combinations thereof, wherein said polyether has a molecular weight of from about 60 daltons to about 10,000 daltons. 48. The compound according to claim 46, wherein said polyether has a molecular weight of from about 100 daltons to about 1,000 daltons. 49. The compound according to claim 37, wherein R 39 and R 45 and combinations thereof are members selected from ω-carboxyl alkyl groups, ω-carboxyl substituted alkyl groups and combinations thereof. 50. The compound according to claim 49, wherein said ω-carboxyl substituted alkyl group has a structure according to Formula II: wherein, X is a member selected from O, S and NR 50 , wherein R 50 is a member selected from H, alkyl and substituted alkyl; Y is a member selected from H and a single negative charge; and j an k are members independently selected from the group consisting of integers from 1 to 18. 51. The compound according to claim 50, wherein said ω-carboxyl substituted alkyl group has a structure according to Formula III: 52. A compound according to claim 37, having a-structure according to Formula VIII: 53. The compound according to claim 5, in which R comprises a component of a dendrimer. 54. The compound according to claim 53, having a structure according to Formula IX: wherein, D is a dendrimer; and w is a member selected from the group consisting of the integers from 4 to 100, inclusive. 55. The compound according to claim 54, wherein said dendrimer is a poly(propyleneimine) dendrimer. 56. The compound according to claim 58. wherein said dendπmer is of a generation selected from the group consisting of generation 2 to generation 10. inclusive 57. The compound according to claim 54. wherem w is a member selected from the group consisting of the integers between 8 and 50. inclusive 58 . The compound according to claim 5, wherein said compound is covalently attached to a earner molecule 59. The compound according to claim 58, wherem said earner molecule is a member selected from the group consisting of synthetic polymers and biomolecules 60. The compound according to claim 59, wherem said biomolecule is a member selected from the group consisting of antibodies, antigens, peptides, nucleic acids, enzymes, haptens, carbohydrates and pharmacologically active agents 61. A complex formed between a metal ion and the compound according to claim 5 62. The complex according to claim 61, wherein said complex emits luminescence 63. The complex according to claim 62, wherem said luminescence is circularly polaπzed luminescence 64. The complex according to claim 61, wherem said luminescence is produced by electrochemical excitation of said complex 65. The complex according to claim 61, wherein said metal ion is an ion of the lanthanide seπes 66. The complex according to claim 65, wherein said lanthanide ion is a member selected from the group consisting of terbium, samaπum, europium, dysprosium and neodymium 67. The complex according to claim 61. wherein said compound is covalently attached to a carrier molecule. 68. The compound according to claim 67, wherein said carrier molecule is a member selected from the group consisting of synthetic polymers and biomolecules. 69. The compound according to claim 68, wherein said biomolecule is a member selected from the group consisting of antibodies, antigens, peptides, nucleic acids, enzymes, haptens, carbohydrates and pharmacologically active agents. 70. A method for determining whether a sample contains an enzyme, said method comprising: (a) contacting said sample with a peptide construct comprising i) a complex according to claim 61; ii) a quencher of light energy having an absorbance band overlapping an emission band of said complex; and iii) a cleavage recognition site for said enzyme, wherein said peptide is in a conformation allowing fluorescence energy transfer between said complex and said quencher when said complex is excited; (b) exciting said complex; and (c) determining a fluorescence property of said sample, wherein the presence of said enzyme in said sample results in a change in said fluorescence property. 71. A method for determining whether a compound alters an activity of an enzyme, said method comprising: (a) contacting a sample comprising said enzyme and said compound with a peptide construct comprising i) a complex according to claim 61; ii) a quencher of light energy having an absorbance band overlapping an emission band of said complex; and iii) a cleavage recognition site for said enzyme, wherein said peptide is in a conformation allowing fluorescence energy transfer between said complex and said quencher when said complex is excited; (b) exciting said complex; and (c) determining a fluorescence property of said sample, wherein said activity of said enzyme in said sample results in a change in said fluorescence property. 72. A method for detecting a nucleic acid target sequence, said method comprising: (a) contacting said target sequence with a detector oligonucleotide comprising a single-stranded target binding sequence, said detector oligonucleotide having linked thereto, i) a complex according to claim 61; ii) a quencher of light energy having an absorbance band overlapping an emission band of said complex, wherein said detector nucleic acid is in a conformation allowing fluorescence energy transfer between said complex and said quencher when said complex is excited; (b) hybridizing said target binding sequence to said target sequence, thereby altering said conformation of said detector oligonucleotide, causing a change in a fluorescence parameter; and (c) detecting said change in said fluorescence parameter, thereby detecting said nucleic acid target sequence. 73. The method according to claim 72, wherein said detector oligonucleotide has a format selected from molecular beacons, scoφion probes, sunrise probes, light up probes and TaqMan™ probes. 74. A method for detecting the presence of a nucleic acid target sequence, said method comprising: (a) hybridizing to said target sequence a detector oligonucleotide comprising a single-stranded target binding sequence and an intramolecularly associated secondary structure 5 ' to said target binding sequence, wherein at least a portion of the target sequence forms a single stranded tail which is available for hybridization to said target sequence, said detector oligonucleotide having linked thereto, i) a complex according to claim 61; ii) a quencher of light energy having an absorbance band overlapping an emission band of said complex, wherein said detector nucleic acid is in a conformation allowing fluorescence energy transfer between said complex and said quencher when said complex is excited; (b) in a primer extension reaction, synthesizing a complementary strand using said intramolecularly associated secondary structure as a template, thereby dissociating said intramolecularly associated secondary structure and producing a change in a fluorescence parameter; (c) detecting said change in said fluorescence parameter, thereby detecting said nucleic acid target sequence. 75. The method according to claim 74, wherein said intramolecularly associated secondary structure is a member selected from haiφins, stem-loop structures, pseudoknots, triple helices and conformationally assisted structures. 76. The method according to claim 74, wherein said complementary strand is synthesized in a target amplification reaction. 77. The method according to claim 74, wherein said complementary strand is synthesized by extension of the target sequence using said detector oligonucleotide as a template. 78. The method according to claim 74, wherein the intramolecularly associated secondary structure comprises a totally or partially single-stranded endonuclease recognition site. 79. The method according to claim 74, wherein said change in fluorescence is detected as an indication of the presence of said target sequence. 80. The method according to claim 74, wherein said fluorescence parameter is detected in-real time. 81. The method according to claim 74. wherein said intramolecularly base-paired secondary structure comprises a portion of said target binding sequence. 82. A method for detecting amplification of a target sequence comprising, in an amplification reaction: (a) hybridizing to said target sequence a detector oligonucleotide comprising a single-stranded target binding sequence and an intramolecularly associated secondary structure 5' to said target binding sequence, wherein at least a portion of said target sequence forms a single stranded tail which is available for hybridization to said target sequence, said detector oligonucleotide having linked thereto, i) a complex according to claim 61; ii) a quencher of light energy having an absorbance band overlapping an emission band of said complex, wherein said detector nucleic acid is in a conformation allowing fluorescence energy transfer between said complex and said quencher when said complex is excited; (b) extending said hybridized detector oligonucleotide on said target sequence with a polymerase to produce a detector oligonucleotide extension product and separating said detector oligonucleotide extension product from said target sequence; (c) hybridizing a primer to said detector oligonucleotide extension product and extending the primer with said polymerase, thereby linearizing said intramolecularly associated secondary structure and producing a change in a fluorescence parameter; and (d) detecting said change in said fluorescence parameter, thereby detecting said target sequence. 83. The method according to claim 82, wherein said target sequence is amplified by a method selected from Strand Displacement Amplification, Polymerase Chain Reaction 3SR, TMA and NASBA. 84. The method according to claim 82. wherein said secondary structure further comprises a partially or entirely single-stranded restriction endonuclease site. 85. The method according to claim 82. wherein a change in fluorescence intensity is detected. 86. The method according to claim 85, wherein said change in fluorescence intensity is detected in real-time. 87. The method according to claim 82, wherein said intramolecularly base-paired secondary structure comprises a portion of said target binding sequence. 88. A method of ascertaining whether a first nucleic acid and a second nucleic acid hybridize, said first nucleic acid comprising a complex according to claim 61, said method comprising: (a) contacting said first nucleic acid with said second nucleic acid; (b) detecting an alteration in a fluorescent property of a member selected from said first nucleic acid, said second nucleic acid and a combination thereof, thereby ascertaining whether said hybridization occurs. 89. The method according to claim 88, wherein said second nucleic acid comprises a quencher of light energy covalently attached thereto. 90. A microaπay comprising a complex according to claim 61, said quencher being conjugated directly to a solid support or to a carrier molecule attached to said solid support. 91. The microaπay according to claim 90, wherein said carrier molecule is a member selected from a nucleic acid, a peptide, a peptide nucleic acid and combinations thereof. 92. The microaπay according to claim 90, wherein said solid support is divided into a first region and a second region, said first region having attached thereto a first said complex attached to a first carrier molecule and said second region having attached thereto a second said complex attached to a second carrier molecule. 93. The microaπay according to claim 92. wherein said first and second carrier molecules are members independently selected from nucleic acids, peptides and peptide nucleic acids. 94. The microarray according to claim 92, wherein said first said quencher of light energy and said second complex have different structures. 95. A method of probing a microaπay for the presence of a compound, said method comprising: (a) contacting said microarray with a probe interacting with said compound, said probe comprising a complex according to claim 61; (b) detecting a difference in a fluorescence property of a member selected from said probe, said compound and combinations thereof, thereby ascertaining the presence of said compound. 96 . The method according to claim 95, wherein said compound is a member selected from nucleic acids, peptide, peptide nucleic acids and combinations thereof. 97. A method of providing radiation therapy to a subject harboring a growth requiring such therapy, said method comprising: administering to said subject a complex according to claim 61, said complex having radiosensitization properties; and administering ionizing radiation to the host in proximity to the growth, thereby providing radiation therapy to said subject. 98. A method for photodynamic therapy of a lesion or of a lesion obscured by melanodermic tissue of a subject, said method comprising: (a) administering a photosensitive complex according to claim 61 to the subject; and (b) photoiπadiating the lesion. 99. The method according to claim 98, wherein said photoiπadiating is with light having a wavelength range of about 700 to about 900 nanometers. 100. The method of claim 99 wherein the photoiπadiating is with light having a wavelength range of about 730 to about 770 nanometers. 101. The complex according to claim 61, wherein said compound comprises a component of an ink or a dye. 102. The complex according to claim 61, wherein said compound comprises a component of a substrate for the transmission and amplification of light. 103. The complex according to claim 102, wherein said substrate comprises a member selected from glass, organic polymers, inorganic polymers and combinations thereof. 104. A method for amplifying light transmitted by a substrate, said method comprising transmitting light through a substrate according to claim 102, thereby amplifying said light. 105. A method of performing a fluorescence assay of an analyte, said method comprising: (a) displacing with said analyte a binding partner from a binding partner- recognition moiety complex, thereby forming an analyte-recognition moiety complex and a free binding partner, said binding partner and said free binding partner comprising a compound according to claim 1 ; (b) forming a fluorescent complex between a lanthanide ion and a member selected from the group consisting of said binding partner, said free binding partner and combinations thereof; and (c) detecting said fluorescent complex. 106. The method according to claim 105, wherein said recognition moiety, said binding partner and said analyte are members independently selected from the group consisting of bioactive materials, biomolecules and combinations thereof. 107. The material according to claim 106, wherein said biomolecule is a member selected from the group consisting of haptens, antibodies, antigens, carbohydrates, nucleic acids, peptides, enzymes and receptors. 108. The method according to claim 105, wherein one or more members selected from the group consisting of said recognition moiety, said binding partner and said analyte are attached to a surface. 109. The method according to claim 105, wherein said fluorescent complex is formed prior to displacing said binding partner from said binding partner- recognition moiety complex. 110. The method according to claim 105, wherein said fluorescent complex is formed after displacing said binding partner from said binding partner- recognition moiety complex. 111. The method according to claim 105, further comprising, separating said free binding partner from a member of the group consisting of said recognition- binding partner pair, said analyte-recognition moiety pair and combinations thereof. 112. The method according to claim 111, wherein said fluorescent complex is formed following said separation.

Inventors: COHEN SETH, PETOUD STEPHANE, RAYMOND KENNETH N, XU JIDE, COHEN, SETH, PETOUD, STEPHANE, RAYMOND, KENNETH, N., XU, JIDE
Applicants: COHEN SETH, PETOUD STEPHANE, RAYMOND KENNETH N, UNIV CALIFORNIA, XU JIDE, COHEN, SETH, PETOUD, STEPHANE, RAYMOND, KENNETH, N., THE REGENTS OF THE UNIVERSITY OF CALIFORNIA, XU, JIDE
Application year: 2000
Main classification: C07C235
IPC codes: C07C15, C07C233, C07C235, C07C403, C07F5, C09K11, C12M1, C12N15, C12Q1, G01N21, G01N33