Aptamer- and nucleic acid enzyme-based systems for simultaneous detection of multiple analytes

The present invention provides aptamer- and nucleic acid enzyme-based systems for simultaneously determining the presence and optionally the concentration of multiple analytes in a sample. Methods of utilizing the system and kits that include the sensor components are also provided. The system includes a first reactive polynucleotide that reacts to a first analyte; a second reactive polynucleotide that reacts to a second analyte; a third polynucleotide; a fourth polynucleotide; a first particle, coupled to the third polynucleotide; a second particle, coupled to the fourth polynucleotide; and at least one quencher, for quenching emissions of the first and second quantum dots, coupled to the first and second reactive polynucleotides. The first particle includes a quantum dot having a first emission wavelength. The second particle includes a second quantum dot having a second emission wavelength different from the first emission wavelength. The third polynucleotide and the fourth polynucleotide are different.

BACKGROUND

The ability to determine the presence of an analyte in a sample is of significant benefit. For example, analytes composed of certain ions and metals, such as those toxic elements belonging to the RCRA-8 metal group (lead (Pb), mercury (Hg), arsenic (As), chromium (Cr), cadmium (Cd), barium (Ba), silver (Ag), and selenium (Se)), pose significant health risks when present in water supplies. It is common to perform sample analysis on drinking water, ground water, and waste water to monitor and safeguard water quality used for human consumption and agricultural purposes, as well as to preserve the environment.

Sample analysis is equally important for medical reasons and for homeland security. Biological fluids, such as blood and those originating from body tissues, also may be tested for a variety of analytes to determine if the body has been exposed to harmful agents or if a disease state exists. In a similar vein, the detection of harmful agents, such as bioterrorist materials (for example, poisons like anthrax), minute quantities of highly explosive materials (for example, C4 plastic explosive and Trinitrotoluene (TNT)), and illegal drug substances and related contraband (for example, cocaine) is important for the safety of both individuals and society at large.

Colorimetric methods are commonly used for the detection of analytes in soil, water, or waste-stream samples, biological samples, body fluids, and the like. In relation to instrument-based methods of analysis, such as atomic absorption spectroscopy, calorimetric methods tend to be rapid and require little in the way of equipment or user sophistication. While conventional calorimetric tests are extremely useful, they only exist for a limited set of analytes, and often cannot detect very small or trace amounts of the analyte.

Recently, colorimetric sensors based upon aptamers have been developed. Aptamers are nucleic acids (such as DNA or RNA) that recognize target effector molecules with high affinity and specificity (Ellington and Szostak 1990, Jayasena 1999). Aptamers have several unique properties that make them an ideal platform for designing highly sensitive and selective analyte sensors. First, in vitro selection methods can be used to obtain aptamers for a wide range of target effector molecules with exceptionally high affinity, having dissociation constants in the picomolar range (Brody and Gold 2000, Jayasena 1999, Wilson and Szostak 1999). Second, aptamers are easier to obtain and less expensive to produce than antibodies, because aptamers can be generated in vitro in short time periods (for example, within days) and at economical cost. Third, aptamers display remarkable structural durability and can be denatured and renatured many times without losing their ability to recognize their targets.

One particularly advantageous calorimetric sensor is an aptamer design that directs assembly or disassembly of metallic particle aggregates in response to an analyte. Metallic particles are exquisitely sensitive calorimetric reagents, having extinction coefficients three orders of magnitude higher than those of organic dyes (Link et al. 1999). Aptamer systems may be designed to bind two or more oligonucleotides that are coupled to particles (oligo-particles), thereby resulting in formation of an aggregate of particles (particle aggregate). Upon exposure to a sample containing the effector molecule (analyte), the aptamer binds to the effector molecule by undergoing a conformational change that precludes or weakens binding of the oligo-particles to each other, and the particle aggregate dissociates. Because particle aggregates display spectral attributes dependent upon the distance between the particles, the aggregation status of the oligo-particles is reflected by the appearance of distinct calorimetric properties. Since aptamers are designed to recognize a specific analyte, the presence of the specific analyte in a sample is reported calorimetrically as the particle aggregates dissociate. An example of this technology is described in U.S. Patent Application Publication No. 20070037171 A1, entitled APTAMER-BASEDCOLORIMETRICSENSORSYSTEMSto Y. Lu et al., published Feb. 15, 2007.

Other types of sensors based upon nucleic acid enzymes (for example, aptazymes, DNAzymes, and RNAzymes) have been described. Nucleic acid enzymes are well known in the art, and have been used in sensor applications designed to detect single analyte species (see, for examples, U.S. Patent Application Publication No. 20030215810 A1, entitled SIMPLECATALYTICDNA BIOSENSORSFORIONSBASEDONCOLORCHANGESto Y. Lu et al., published Nov. 20, 2003; U.S. Patent Application Publication No. 20040175693 A1, entitled NUCLEICACIDBIOSENSORSto Y. Lu et al., published Sep. 9, 2004).

Because aptamers and nucleic acid enzymes are selected for their ability to bind to specific target effector molecules, colorimetric sensors based on these conventional designs are limited to detecting a single analyte species in a sample. However, there is often a need to detect more than one type of analyte species in a given sample. For example, for a complete environmental analysis of mercury contaminants in a given sample, it is important to analyze the sample for the presence of both organic and inorganic mercury species. Even if aptamer and nucleic acid enzyme-based sensor system designs were available that recognize two or more analyte species, calorimetric sensor designs have not been implemented to permit selective detection of the different analyte species. Thus, sensors capable of simultaneously detecting multiple analytes present in a sample have not been described.

SUMMARY

In a first aspect, the invention is a system for simultaneously detecting multiple analytes in a sample that includes a first reactive polynucleotide that reacts to a first analyte; a second reactive polynucleotide that reacts to a second analyte; a third polynucleotide; a fourth polynucleotide; a first particle, coupled to the third polynucleotide; a second particle, coupled to the fourth polynucleotide; and at least one quencher, for quenching emissions of the first and second quantum dots, coupled to the first and second reactive polynucleotides. The first particle includes a quantum dot having a first emission wavelength. The second particle includes a second quantum dot having a second emission wavelength different from the first emission wavelength. The third polynucleotide and the fourth polynucleotide are different.

In a second aspect, the invention is a method for simultaneously detecting multiple analytes in a sample that includes combining at least one aggregate with a sample; and detecting a first and second emission responsive to the first and second analytes, respectively. The at least one aggregate includes a first reactive polynucleotide that reacts to a first analyte; a second reactive polynucleotide that reacts to a second analyte; a third polynucleotide; a fourth polynucleotide; a first particle, coupled to the third polynucleotide; a second particle, coupled to the fourth polynucleotide; and at least one quencher, for quenching emissions of the first and second quantum dots, coupled to the first and second reactive polynucleotides. The first particle includes a quantum dot having a first emission wavelength. The second particle includes a second quantum dot having a second emission wavelength different from the first emission wavelength. The third polynucleotide and the fourth polynucleotide are different.

In a third aspect, the invention is a kit for the simultaneous detection of multiple analytes in a sample that includes an aggregate forming system and a first container. The aggregate forming system includes a first reactive polynucleotide that reacts to a first analyte; a second reactive polynucleotide that reacts to a second analyte; a third polynucleotide; a fourth polynucleotide; a first particle, coupled to the third polynucleotide; a second particle, coupled to the fourth polynucleotide; and at least one quencher, for quenching emissions of the first and second quantum dots, coupled to the first and second reactive polynucleotides. The first particle includes a quantum dot having a first emission wavelength. The second particle includes a second quantum dot having a second emission wavelength different from the first emission wavelength. The third polynucleotide and the fourth polynucleotide are different. The first container contains the aggregate forming system, where a sample may be added to a container selected from the group including the first container and a second container.

In a fourth aspect, the invention is an indicator for a system for simultaneously detecting multiple analytes in a sample that includes a third polynucleotide; a fourth polynucleotide; a first particle, coupled to the third polynucleotide; and a second particle, coupled to the fourth polynucleotide. The first particle comprises a quantum dot having a first emission wavelength. The second particle comprises a second quantum dot having a second emission wavelength different from the first emission wavelength. The third polynucleotide and the fourth polynucleotide are different.

DEFINITIONS

The term “sample” is defined as a composition that will be subjected to analysis that is suspected of containing the analyte of interest. Typically, a sample for analysis is in a liquid form, and preferably the sample is an aqueous mixture. A sample may be from any source, such as an industrial sample from a waste-stream or a biological sample, such as blood, urine, or saliva. A sample may be a derivative of an industrial or biological sample, such as an extract, a dilution, a filtrate, or a reconstituted precipitate.

The term “analyte” is defined as one or more substances potentially present in a sample. The analysis determines the presence, quantity, and/or concentration of the analyte present in a sample.

The term “sensitivity” refers to the smallest increase in an analyte concentration that is detectable by the sensor system (resolution) or to the lowest concentration limit at which a sensor system can differentiate a signal responsive to the analyte from a background signal (detection limit). Thus, the more sensitive a sensor system is to an analyte, the better the system is at detecting lower concentrations of the analyte.

The term “selectivity” refers to the ability of the sensor system to detect a desired analyte in the presence of other species.

The term “hybridization” refers to a first polynucleotide forming a complex with a second nucleotide through hydrogen bonding.

The term “complementary” refers to the ability to form base-pairing relationships between nucleobases, such as the ability to form a base-pairing between guanosine and cytosine or a base-pairing between adenine and thymine (or uridine). A polynucleotide may be partially or fully complementary with another polynucleotide. For example, a first polynucleotide having the sequence 5′-GATTCTAAGC-'3 (SEQ ID NO: 61) is partially complementary to a second polynucleotide having the sequence 5′-GAATCGCCCGAT-'3 (SEQ ID NO: 62) (the underlined sequences represent the possible base-pairing relationships between the two sequences). A first polynucleotide having the sequence 5′-GATTCTAAGC-'3 (SEQ ID NO: 61) is fully complementary to a second polynucleotide having the sequence 5′-GCTTAGAATC-3′ (SEQ ID NO: 63).

The term “coupled” refers to attachment by either a covalent bond or a non-covalent bond. An example of a non-covalent bond is a hydrogen bond.

The term “aptamer” refers to a nucleic acid that undergoes a conformational change in response to an analyte.

The term “nucleic acid enzyme” means an enzyme composed of a nucleic acid. Examples of nucleic acid enzyme include ribozymes (RNAzymes), deoxyribozymes (DNAzymes), and aptazymes.

The term “aptazyme”, also referred to as “allosteric nucleic acid enzyme” or “allosteric (deoxy)ribozyme,” is a nucleic acid enzyme in which the enzymatic activity is regulated by an effector. An aptazyme typically contains an aptamer domain, which recognizes an effector, and a catalytic domain. See, for example, Hesselberth et al. (2000); Soukup et al. (2000); and Tang et al. (1997).

The term “conformational change” refers to the process by which an aptamer adopts a tertiary structure from another state. For simplicity, the term “fold” may be substituted for conformational change.

The term “reactive polynucleotide” is a generic term that includes aptamers, aptazymes, and nucleic acid enzymes.

The term “react,” as related to the term “reactive polynucleotide,” refers to the reactive polynucleotide responding to the analyte by undergoing a conformational change or by causing or catalyzing a reaction (for example, a cleavage of a substrate).

The terms “oligo,” “oligonucleotide,” and “polynucleotide” are used interchangeably.

DETAILED DESCRIPTION

The present invention makes use of the discovery of sensor systems that include polynucleotides coupled to quantum dots (oligo-particles, where the particles are QDs) having at least two different types of QDs with distinct emissions to permit simultaneous detection of multiple analytes in a single sample. Because QD's display sharp emission peaks, it is possible to have over ten distinct emission wavelengths in the visible range. By using QDs of different emission wavelengths, the identity of the analytes can be distinguished. In this manner, sensors are provided that are capable of reporting the presence of different analytes in a given sample, thus providing an advantage over previous sensor systems. Furthermore, the sensor systems may include aptazymes, RNAzymes, and DNAzymes, thereby broadening the range of analyte which may be detected. Finally, the sensor systems display remarkable stability under conditions that would normally degrade nucleic acids. This unexpected property affords the advantage of using the sensor systems which can detect multiple analytes in a sample obtained from biological sources, such as blood serum.

FIG. 1Aillustrates one preferred embodiment of simultaneous detection of multiple analytes in a single sample102with the described sensor systems. Aggregate system154contains first and second polynucleotides142and144; first and second particles coupled to third and fourth polynucleotides (oligo-particles)146and148, respectively; and optionally, a third oligo-particle152that includes a fifth polynucleotide. The first and second polynucleotides142and144may include first and second reactive polynucleotides122and124, respectively. The first oligo-particle146includes a third polynucleotide that may be partially complementary to a portion of the first reactive polynucleotide122, while the second oligo-particle148includes a fourth polynucleotide that may be partially complementary to the second reactive polynucleotide124. Oligo-particles146and148each may contain a particle encoding a unique QD (QD1and QD2, respectively) having a distinct spectral property. A representative portion of the first and second oligo-particles146and148may also encode a quencher, Q, that may serve to quench the spectral property of the QD. When included, the third oligo-particle152includes a fifth polynucleotide that may be partially complementary to a portion of the first and second polynucleotides142and144. The oligo-particle152may also encode a quencher, Q, that quenches the spectral property of the QDs.

The aggregate system154may be combined with a sample102suspected of containing analytes112and/or114. In the presence of112, reactive polynucleotide122becomes reactive and causes partial disaggregation of aggregate154to release oligo-particles146from aggregate154. As an oligo-particle146floats away from aggregate154, the QD1of the oligo-particle146is no longer quenched, and spectral property of the QD1becomes evident at a distinct wavelength (for example, increased luminescence emission at 585 nm). Similarly, in the presence of114, reactive polynucleotide124becomes reactive and causes partial disaggregation of aggregate154to release oligo-particles148from aggregate154. As an oligo-particle148floats away from aggregate154, the QD2of the oligo-particle148is no longer quenched, and spectral property of the QD2becomes evident at a wavelength different from that of QD1.

FIG. 1Billustrates a second preferred embodiment for the simultaneous detection of multiple analytes in a single sample102with the described sensor systems. Aggregate system154represents a mixture of separate aggregates156and158. Aggregate156includes reactive polynucleotide122that specifically binds to analyte112, oligo-particle146, and optionally, oligo-particle152. Aggregate158includes reactive polynucleotide124that specifically binds to analyte114, oligo-particle148, and optionally, oligo-particle152. Oligo-particles146and148each may contain a particle encoding a unique QD (QD1and QD2, respectively) having a distinct spectral property. A representative portion of the first and second oligo-particles146and148may also encode a quencher, Q, that may serve to quench the spectral property of the QD. When included, the third oligo-particle152includes a fifth polynucleotide that may be partially complementary to a portion of the first and second polynucleotides142and144. The oligo-particle152may also encode a quencher, Q, that quenches the spectral property of the QDs.

The aggregate system154may be combined with a sample102suspected of containing analytes112and/or114. In the presence of112, reactive polynucleotide122becomes reactive and causes disaggregation of aggregate156to release oligo-particles146from aggregate156. As an oligo-particle146floats away from aggregate156, the QD1of the oligo-particle146is no longer quenched, and spectral property of the QD1becomes evident at a distinct wavelength (for example, increased luminescence emission at 585 nm). Similarly, in the presence of114, reactive polynucleotide124becomes reactive and causes disaggregation of aggregate158to release oligo-particles148from aggregate158. As an oligo-particle148floats away from aggregate158, the QD2of the oligo-particle148is no longer quenched, and spectral property of the QD2becomes evident at a wavelength different from that of QD1.

Examples of reactive polynucleotides include aptamers, aptazymes, RNAzymes, and DNAzymes. Aptamers become reactive upon binding an analyte by undergoing a conformational change. Aptazymes, RNAzymes, and DNAzymes become reactive upon binding an analyte by undergoing a chemical reaction (for example, cleaving a substrate). In each instance, the outcome of the reactive polynucleotide becoming reactive is to cause disaggregation of the aggregate and the release of at least one oligo-particle having a distinct spectral property.

FIG. 2represents in greater detail an analysis100for simultaneously determining the presence and optionally the concentration of two or more different analytes112and114in a sample102. Analysis100includes processes110,120,140,150,160, and170. Optionally, analysis100includes process130. Though aptamers have been selected as the exemplified reactive polynucleotides in100, one skilled in the art will appreciate that the same principles can be applied to make and use nucleic acid enzymes (for example, aptazymes, RNAzymes, and DNAzymes) as the reactive polynucleotides.

In110, the desired analytes112and114for which the method100will determine the presence/concentration of are selected. If additional analytes are to be detected, a plurality of110may be performed, where each110is specific for a particular analyte.

In one aspect, the analytes112and114may be any ions that cause aptamers122and124to fold. In another aspect, the analyte112and114may be any metal ions that cause aptamers122and124to fold. Preferable monovalent ions having a 1+ formal oxidation state (I) include NH4+, K(I), Li(I), Tl(I), and Ag(I). Preferable divalent metal ions having a 2+ formal oxidation state (II) include Mg(II), Ca(II), Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Cu(II), Pb(II), Hg(II), Pt(II), Ra(II), Sr(II), Ni(II), and Ba(II). Preferable trivalent and higher metal ions having 3+ (III), 4+ (IV), 5+ (V), or 6+ (VI) formal oxidation states include Co(III), Cr(III), Ce(IV), As(V), U(VI), Cr(VI), and lanthanide ions. More preferred analyte ions include monovalent metal ions and metal ions that are toxic to living organisms, including elements belonging to the RCRA-8 metal group (lead (Pb), mercury (Hg), arsenic (As), chromium (Cr), cadmium (Cd), barium (Ba), silver (Ag), and selenium (Se)).

Preferred ions also include those compounds that share a common metal element, but differ only in their formal oxidation state. For example, inorganic mercury species possess an oxidation state of 2+, whereas organic mercury species possess an oxidation state of 1+. Samples that contain both inorganic and organic mercury species would be amenable to simultaneous detection with the present invention by using two different aptamers that recognize selectively the different oxidation states of the mercury species.

Following section of multiple analytes in110, multiple aptamers, each specific for a given analyte, are selected in120. The aptamer selection120may be performed by in vitro selection, directed evolution, or other method known to those of ordinary skill in the art. The aptamer selection120may provide one or more aptamers that demonstrate enhanced folding in the presence of the selected analytes (thereby providing sensor sensitivity). The selection120also may exclude aptamers that fold in the presence of selected analytes, but that do not fold in the presence of non-selected analytes and/or other species present in the sample102(thereby providing sensor selectivity). Since aptamers are intended to permit detection of a specific analyte (for example, aptamer122being specific for analyte112and aptamer124being specific for analyte114), selection120should be performed with each aptamer to exclude binding to different analytes, which might be subject to simultaneous detection in a given sample.

For example, an aptamer may be selected that specifically binds Pb while not significantly binding Hg, As, Cr, Cd, Ba, Ag, Se, or other competing metal ions. In one aspect, this may be achieved by isolating aptamers that bind Pb, then removing any aptamers that bind Hg, As, Cr, Cd, Ba, Ag, or Se. In another aspect, aptamers that bind Hg, As, Cr, Cd, Ba, Ag, or Se are first discarded and then those that bind Pb are isolated. In this manner, the selectivity of a particular aptamer may be increased.

In a similar manner, a pair of different aptamers122and124may be selected, in which each aptamer specifically binds to individual analyte species112and114that share a common element, but which differ in their formal oxidation state. For example, an aptamer122may be selected that specifically binds to analyte112that is an organic mercury species having an oxidation state of 1+ while not binding to analyte114that is an inorganic mercury species having an oxidation state of 2+. In one aspect, this may be achieved by isolating aptamers that bind mercury species having an oxidation state of 1+, then removing any aptamers that bind mercury species having an oxidation state of 2+. In another aspect, aptamers that bind mercury species having an oxidation state of 2+ are first discarded and then those that bind mercury species having an oxidation state of 1+ are isolated. In this manner, the selectivity of a particular aptamer122for a given analyte112may be increased.

Aptamers122and124include a nucleic acid strand that folds in the presence of specific analytes112and114, respectively. In one aspect, the folding may be considered the conversion of a primary or duplex structure to a tertiary structure. The base sequence of the aptamer may be designed so that the aptamer may undergo at least partial hybridization with at least one polynucleotide coupled to a particle (oligo-particle). In this aspect, at least portions of the base sequence of the aptamer122and124may be complementary to at least one portion of another polynucleotide, such as oligo-particles146and148, respectively.

Aptamers122and124may be formed from deoxyribonucleotides, which may be natural, unnatural, or modified nucleic acids. Peptide nucleic acids (PNAs), which include a polyamide backbone and nucleoside bases (available from Biosearch, Inc., Bedford, Mass., for example), also may be useful.

Numerous examples of analytes and aptamers that bind with and fold in response to that analyte are well known in the art. Examples of each are described in U.S. patent application Ser. No. 11/202,380, entitled APTAMER-BASEDCOLORIMETRICSENSORSYSTEMSto Y. Lu et al., filed Aug. 11, 2005 and in Lee et al. (2004). Some of these examples are shown in Table I.

Referring again toFIG. 2, analysis100for the simultaneous detection of multiple analytes in a sample is performed with the following system components. A first aptamer122that contains a binding region for a first analyte112may be adapted for use in a first polynucleotide142. For example, the non-analyte binding region of an aptamer specific for adenosine may be modified to provide the aptamer and the included polynucleotide142.

In a similar manner, a second aptamer124that contains a binding region for a second analyte114may be adapted for use in a second polynucleotide144. For example, the non-analyte binding region of aptamer specific for another analyte unrelated to adenosine (for example, cocaine) may be modified to provide the aptamer and the included polynucleotide148.

After selecting an appropriate aptamer or aptamers in120, the polynucleotides142and144are formed that includes the aptamers122and124, respectively. In one aspect (process140), the aptamers122and124may serve directly as the polynucleotides142and144, respectively. In another aspect (process130), the polynucleotides142and144may be formed by joining one or more extensions132and134with the aptamers122and124, respectively.

In130, extensions132and134may be any nucleic acid sequence that may be joined with aptamers122and124, that may undergo at least partial hybridization with at least one oligo-particle, and that is compatible with the analysis100. In this aspect, at least a portion of the base sequence of the extension132and134may be complementary to at least one portion of one or more oligo-particles. In one aspect, solid phase synthesis may be used to join aptamers122and124to extensions124and134to form polynucleotides142and144, respectively. In another aspect, after the aptamer122portion of the polynucleotide142is synthesized, the synthesis is continued to form the extension132. Similarly, the polynucleotide144containing aptamer124may be extended to include the extension134. In these latter aspects, any method commonly employed in the art may be used, such as chemical methods (for example, solid phase-based procedures) or enzymatic methods (for example, PCR-based procedures).

Preferably, extensions132and134include from 1 to 100 bases. In one aspect, preferably at least 25, 50, 70, or 90% of the bases present in extension132are capable of hybridizing with a complementary portion of an oligo-particle, such as the 5′-TCACAGATGAGT (SEQ ID NO. 56) portion of oligo-particle352inFIG. 3B, while at least 50, 35, 25, or 10% of the bases present in the extension332are capable of hybridizing with another polynucleotide coupled to a particle, such as particle346inFIG. 3B.

Referring to140ofFIG. 2, the polynucleotide142hybridizes with the oligo-particles146and includes the aptamer122and may include the extension132. For example, if the polynucleotide portions of the oligo-particles346and352have base sequences of 5′-CCCAGGTTCTCT-3′ (SEQ ID NO. 45) and 5′-TCACAGATGAGT(A)12-3′ (SEQ ID NO. 44), respectively, an appropriate sequence for the polynucleotide342that includes the aptamer322that folds in the presence of an adenosine analyte and the extension332may be

For the adenosine analyte, the extension332portion of the polynucleotide342is the 5′-ACTCATCTGTGAAGAGA-3′ (SEQ ID NO. 57) portion of the sequence, which allows the extension332to hybridize with five bases of oligo-particle346and twelve bases of oligo-particle352(FIG. 3B) Similarly, the aptamer322portion of the polynucleotide342is the 5′-ACCTGGGGGAGTATTGCGGAGAAGGT-3′ (SEQ ID NO. 58) portion of the sequence, which allows the 5′-ACCTGGG-3′ (SEQ ID NO. 59) portion of the aptamer322to hybridize with the 5′-CCCAGGT-3′ (SEQ ID NO. 60) portion of the oligo-particle346(FIG. 3B).

Referring toFIGS. 1 and 2, the extensions132and134need not be the identical sequence for the polynucleotides142and144. Preferably, oligo-particles146and148include a plurality of sequences that are complementary to a portion of extensions132and134, respectively. Thus, a plurality of polynucleotides142and144can hybridize to oligo-particles146and148(FIGS. 1 and 2). The formation of unique complexes142:146and144:148are possible where the sequence complementarities differ in the hybridized portions of the complexes.

The oligo-particle152includes a sequence complementary to an identical portion of extensions132and134such that oligo-particle152can hybridize to both polynucleotides142and144. Preferably, the oligo-particle152contains a plurality of such sequence complementarities, thereby permitting a plurality of polynucleotides142or144to bind to the single oligo-particle152, to form an aggregate system154containing both polynucleotides142and144(FIG. 1A; corresponding toFIG. 2, process150). Preferably, the aggregate system154includes the polynucleotides142and144, as well as oligo-particles146,148and152. Considering the physical size of its components, the aggregate system154may be quite large.

Aggregate system154also may be composed of separate aggregates156and158, which are prepared by separately mixing oligo-particles152with mixtures of polynucleotides142and oligo-particles146and mixtures of polynucleotides144and oligo-particles148, respectively (FIG. 1B; corresponding toFIG. 2, process150). The resultant aggregates156and158are responsive to separate analytes112and114, respectively. Thus, aggregate system154may include a mixture of separate aggregates156and158for the simultaneous detection of analytes112and114in sample102.

Because the oligo-particles146and148demonstrate distance-dependent optical properties, the particles are quenched when closely held in the aggregate system154and undergo an increase in emission (for example, increased fluorescence) as the distance between the particles increases. For example, when the oligo-particles146and148include quantum dots, the aggregate system154displays a distinct emission spectrum characteristic of each quantum dot as disaggregation proceeds (FIG. 1).

Referring toFIG. 2, process for simultaneous detection of analytes112and114in sample102is performed in process100in the following manner. In160, aggregate system154is combined with sample102. In170, one of several fates may be possible for aggregate system154. If neither analyte112and114is present in sample102, then aggregate system154may not undergo any disaggregation. Under these circumstances, there may not be any discernible change in the spectral properties of aggregate system154.

Disaggregation of aggregate system154may occur under one of three scenarios. In the presence of analyte112, disaggregation may occur when the aptamer122portion of the polynucleotide142binds with and folds in response to the analyte112. When the aptamer122folds, a portion of the hybridization with the oligo-particles146is lost. This hybridization loss may allow the oligo-particles146to separate from the aggregate system154. Thus, as the oligo-particles146diffuse away from the aggregate system154, the solution luminescence at a specific wavelength may increase.

In the presence of analyte114, disaggregation also may occur when the aptamer124portion of the polynucleotide144binds with and folds in response to the analyte114. When the aptamer124folds, a portion of the hybridization with the oligo-particles148may be lost. This hybridization loss may allow the oligo-particles148to separate from the aggregate system154. Thus, as the oligo-particles148diffuse away from the aggregate system154, the solution luminescence at a wavelength different from that associated with oligo-particles346may increase.

In the presence of both analytes112and114, the aptamer122and124portions of the polynucleotides142and144bind with and fold in response to the analytes112and114, respectively. When these aptamers fold, portions of the hybridization with the oligo-particles146and148may be lost, which permits their separation from the aggregate system154. Thus, as both particles146and148diffuse away from the aggregate system154, the solution luminescence emission at two different wavelengths may increase.

In process170ofFIG. 2, the sample102may monitored for distinct emissions, such as an increase in a specific luminescence emission. Thus, the analysis100may provide a discriminatory sensor system because distinct emissions occur in the presence of the analytes112and114.

The oligo-particles146,148, and152may be composed of any particle species that demonstrate distance-dependent optical properties and are compatible with the operation of the sensor system. Quantum dots are preferred particles, because each type of quantum dot displays a unique emission wavelength. Preferred quantum dot particles include quantum dot semiconductors, such as CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, Pln, and PbSe. Additional preferred quantum dots may include ternary quantum dots, such as CdxZn1-xSe or CdSxSe1-x. Additional preferred quantum dots may include core-shell quantum dots, such as those having a CdSe core and ZnS shell. The quantum dots can also have different morphologies, including dots, rods, tetrapods, and the like. In a preferred aspect, the particles are quantum dot semiconductors having average diameter from 2 to 50 nanometers.

Other particles may be used in conjunction with quantum dots that may quench the spectral properties (for example, emission) of the quantum dots in aggregate system154. Preferred quenchers include those selected from the family of noble metal elements (Au, Ag, Pt, and Pd) and their alloys. Other preferred quenchers include organic quenchers, such as Dabycl, Black hole quenchers, Iowa black quenchers. These quenchers may be attached to other nanoparticles such as polystyrene or silica nanoparticles for use in oligo-particles146,148, and152. An especially preferred quencher is a gold nanoparticle.

Because energy transfer occurs to the quenching particles instead of the quantum dots, an increase in luminescence emission may realized by the inclusion of quenching oligo-particles in the aggregate mixture154(for example, a 200% increase), thereby improving the sensitivity of the sensor system. A portion of oligo-particles146and148may represent quenching particles, such as Au particles, while the remaining portion of the oligo-particles146and148may represent specific types of quantum dots. In a preferred aspect, the ratio of Au particles to quantum dots in oligo-particles146and148, ranges from 1:10 to 3:1, including 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, and 2:1. An especially preferred aspect, the ratio of Au particles to quantum dots in oligo-particles146and148is 1:1.

The rate at which a substantially complete spectral change occurs in response to analytes112and114may be considered the response time of the sensor system. In one aspect, the emission may be considered substantially complete when the extinction coefficient at 522 nm over 700 nm increases by 200% for quantum dots. Preferable response times for the sensor system are from 1 second to 60 minutes or from 2 seconds to 10 minutes. More preferable response times for the sensor system are from 5 seconds to 2 minutes or from 8 to 12 seconds. Preferable temperature ranges for operation of the sensor system are from 0° to 60° or from 15° to 40° C. More preferable ranges for operation of the sensor system are from 23° to 37° or from 25° to 30° C. In another aspect, when the analysis100is conducted from 23° to 37° C., a preferable response time may be less than 2 minutes or from 1 to 12 seconds.FIGS. 5A, B, and C provide the spectral characteristics of aggregate456, a kinetic time course, and the dependence of emission of a QD as a function of the concentration of an adenosine analyte.FIGS. 5D, E, and F provide the spectral characteristics of aggregate458, a kinetic time course, and the dependence of emission of a QD as a function of the concentration of a cocaine analyte.

The degree the spectral change in response to the analytes112and114may be quantified in170by quantification methods known to those skilled in the art. Various fluorimeters may be adapted for use with the present invention. Standards containing known amounts of the selected analyte may be analyzed in addition to the sample to increase the accuracy of the comparison. If higher precision is desired, various types of fluorimeters may be used to plot a calibration curve in the desired concentration range. The emission of the sample may then be compared with the curve and the concentration of the analyte present in the sample determined.

FIG. 3Adepicts an aggregate356that contains a polynucleotide342, oligo-particles346and352. The polynucleotide342includes an aptamer322and optionally an extension332. The oligo-particle346includes a polynucleotide that is complementary to a portion of the extension and a particle that may be either a quantum dot (Q1) or a quenching agent (2). The oligo-particle352includes a polynucleotide that is complementary to a portion of the extension and a particle that may be a quenching agent (1). The quantum dots of oligo-particles346are quenched by quenching particles (1and2) when present in aggregate356. As the oligo-particles346are released, the aggregate356, which has low luminescence, begins to disaggregate. This partial disaggregation displays enhanced luminescence as the oligo-particles346that contain a specific quantum dot diffuse away from the aggregate356. If enough of the adenosine analyte312is present in the sample, the reaction will continue until all of the oligo-particles346are released from aggregate356. Complete disaggregation of oligo-particles346from aggregate356results in high luminescence intensity of the spectral emission wavelength characteristic of the quantum dot of particle346due to the greater distance between the particles346(that is, those particles containing a quantum dot Q1) and352that contain a quencher (or other particles, such as oligo-particles346, that include a quencher)).

FIG. 3Bprovides greater detail of the structure of the aggregate356and its disaggregation in the presence of adenosine analyte312. The aggregate356is formed from multiple aggregate subunits. Some of the aggregate units may be formed from a first polynucleotide342, which is hybridized to polynucleotide-coupled particles (oligo-particles)346and352. The polynucleotide342includes an aptamer portion322and an extension portion332. The polynucleotide portion of oligo-particle352(3′-A12AdeAu) (A12disclosed as SEQ ID NO: 72) hybridizes with the extension332, while the polynucleotide portion of particle346(5′-AdeQ1) hybridizes with the extension332and the aptamer322to from the aggregate unit. In the presence of the analyte312(adenosine), the aptamer322undergoes a conformation change to form folded conformation355to release of oligo-particles346.

FIG. 3Cdepicts the detailed structure of aggregate358that undergoes disaggregation in the presence of a cocaine analyte314. Similar to that described above for the adenosine sensor, the aggregate358is formed from multiple aggregate subunits. Some of the aggregate units may be formed from a first polynucleotide344, which is hybridized to a portion of the polynucleotides of oligo-particles348and352. The polynucleotide344includes an aptamer portion324and an extension portion334. The 3′-A12AdeAuparticle352hybridizes with the extension334, while the 5′-AdeQ1particle348hybridizes with the extension334and the aptamer324to from the aggregate unit. In the presence of the analyte314(cocaine), the aptamer324undergoes a conformation change to form a folded conformation (not shown) to release oligo-particles348from the particle aggregate358, and an increase in the emission of the QD's (labeled as Q2inFIG. 3B) associated with oligo-particles348results as the oligo-particles348float away from the aggregate358.

TABLE IAPolynucleotides and corresponding SEQ ID Nos.SEQSequenceID NO.GTCTCCCGAGAT64ACTCATCTGTGAATCTCGGGAGACAAGGATAAATCCTTCAAT65GAAGTGGGTCTCCCTCTCTTGGACCCAAAAAAAAAAAA66GGAAGAGATGAGTGTCTACTCA67GGGTCCAAGAGAACTCACTATA68CACGTCCATCTCTGCAGTCGGGTAGTTAAACCGACCTTCAG69ACATAGTGAGTGGAAGAGATGGACGTGAGTGTCTACTCA70GGGTCCAAGAGAACTCACTATAGGAAGAGATGGACGTGAGT71GTCTACTCA

The oligo-particles346,348, and352are designed with the particle moiety coupled to either the 5′- or 3′-terminus of the respective polynucleotides. Other particle attachment locations are possible within the polynucleotide, including site-specific attachment locations internal to the polynucleotide. Furthermore, different types of coupling linkers are possible for attaching different types of particles to oligonucleotides. For example, the oligo-particle352may contain a sulfur linker between a gold particle and the 3′ terminus of the polynucleotide, whereas, the oligo-particle346may include a biotin linker between the quantum dot particle and the 5′ terminus of the polynucleotide (FIGS. 3Band C). The structure of the quantum dot of oligo-particle346that is shown inFIG. 3D, which includes an internal core, an outer shell, a polymer coating attached to the outer shell, and streptavidin attached to the polymeric coating, would be amenable for coupling to a polynucleotide containing a biotin moiety. The particles may include nanoparticles, such as particles having an average outer diameter of 10-100 nm, including 15, 20, 25, 50, and 75 nm. The preparation of these and other polynucleotide-coupled particles is described in U.S. Provisional Patent Application Ser. No. 60/865,744, entitled ALIGNMENT OFNANOMATERIALS ANDMICROMATERIALSto Lu et al., filed Nov. 14, 2006.

Referring toFIGS. 3Band C, preferred oligo-particles346(and348) and352may include quantum dots and gold particles, respectively. Optionally, a proportion of the oligo-particles346(and348) may be substituted with quenching particles. Preferred proportions of particles346and348that may be substituted with quenching particles include 0 to 90% of the total population of particles346and348, including 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, and 90%. Even more preferably, the quenching particles may be present at 30-70% of the total population of particles346and348. Most preferably the quenching particles may be present at 40-60%, such as 50%, of the total population of particles346and348. By substituting some of the quantum dot particles of particles346and348with quenching particles, such as gold particles, the basal luminescence of the quantum dot may be reduced further, thereby improving the signal to noise ratio of the sensor system upon exposure to bona fide analytes.

While one base sequence for the polynucleotide342(and344) and the particles346(and348) and352are shown inFIGS. 3 and 4, the bases may be changed on the opposing strands to maintain the complementary relationships (that is, base-pairings). For example, any cytosine in portions of the extension332(and334) may be changed to thymine, as long as the corresponding base pairing partner of the oligo-particle is changed from guanine to adenine.

The oligo-particles346and348may be composed of quantum dots having different spectral emission properties. This feature is especially advantageous to enable simultaneous detection of multiple analytes in a sample. For example, if an aggregate subunit disaggregates in response to a first analyte, such as adenosine, then only the spectral emission property of the quantum dot particle associated only with the aptamer specific for adenosine will be affected. If an aggregate unit disaggregates in response to a second analyte, such as cocaine, then only the spectral emission property of the quantum dot particle associated only with the aptamer specific for cocaine will be affected. If both types of analytes are present in a sample, then it will be possible to simultaneously detect the luminescence associated with the unique spectral emission properties of both types of quantum dot particles.

Aggregate system154may include other types of nucleic acid-based sensors, such as nucleic acid enzymes (aptazymes, DNAzymes, and RNAzymes). Aggregate system154may include two or more aptamers, aptazymes, DNAzymes, RNAzymes, or mixtures thereof. Rather than promoting disaggregation through a conformational change in their structure, however, nucleic acid enzymes may promote disaggregation of aggregate system154by cleaving a substrate in a polynucleotide that forms a linking part of the aggregate system154. Rather than selecting for aptamers in process120ofFIG. 2, nucleic acid enzymes are instead selected (see for example, Lu et al. 2003 and 2004).

InFIG. 1, polynucleotides142and144include the reactive polynucleotides122and124, respectively, and optionally, extensions132and134, respectively. Thus, in one preferred embodiment, polynucleotides142and144represent a single nucleic acid, wherein the reactive polynucleotide is covalently connected to the extension. In another preferred embodiment, however, the reactive polypeptide may be separated from the extension to provide a polynucleotide142that includes two separate nucleic acids. According to this embodiment, oligo-particles146,148, and152may be available to hybridize to the polynucleotide containing the extension. Preferably, the polynucleotide containing the extension may also include a substrate for the reactive polynucleotide. Preferably, this substrate may be located in a region of the polynucleotide142that lies between the hybridization sites for different oligo-particles (for example oligo-particles146and152). Thus, the reactive polynucleotide will not be available to simultaneously hybridize to two different oligo-particles. Upon binding the desired analyte, the reactive polynucleotide becomes reactive, hybridizes to the substrate portion of the polynucleotide142, and catalyzes cleavage of the substrate. The result of substrate cleavage is the release of specific oligo-particles from the particle aggregate.

Examples of this preferred embodiment are illustrated inFIG. 4. An aggregate456may be designed to disaggregate in response to an analyte acting as an effector for an aptazyme or as a cofactor for a DNAzyme. Referring toFIG. 4A, aggregate456includes a polynucleotide442that contains a substrate for a nucleic acid enzyme443and oligo-particles446and452. Portions of the polynucleotides present in oligo-particles446and452are complementary to portions of polynucleotide442. The oligo-particles446and452preferably contain quantum dots and quenching particles (for example, gold particles), respectively. The nucleic acid enzyme443may be selected to react as an endonuclease to cleave the substrate of polynucleotide442in the presence of a cofactor, such as a metal ion (for example, Pb(II)). Upon exposure to the Pb(II) analyte412, the nucleic acid enzyme443becomes active and cleaves the substrate of polynucleotide442. Once cleaved, the oligo-particles containing the QD are released from the aggregate456, resulting in an increase of luminescence emission.FIG. 4Bdepicts an analogous system (that is, aggregate458, which includes a polynucleotide444that contains a substrate for a nucleic acid enzyme445and oligo-particles448and452) that uses a nucleic acid enzyme that is reactive to a different analyte (UO2(II)).

The aggregates display remarkable stability in human blood serum (FIG. 8). This result suggests that the aggregate structure, itself, may afford some protection from nucleolytic degradation caused by serum-borne nucleases. This feature is an unexpected, surprising result, because most nucleic acids exposed to serum would be degraded quickly under normal circumstances. The robustness of the aggregates to withstand nucleolytic degradation suggests their advantageous use in sample analysis from body fluids, such as blood, and from other samples that may contain nucleases.

The methodology ofFIG. 2may be applied to other analytes (for example, analytes such as those listed in Table 1), besides those described for adenosine, cocaine, Pb(II), and UO2(II). Table II gives the base sequences of the linkers and particles for adenosine, K(I), UO2(II), Pb(II), and cocaine sensor systems. The aptamer portion of each linker is presented in uppercase, while the extension portion of each linker is presented in lowercase.

TABLE IIPolynucleotides and corresponding SEQ ID Nos.(A12disclosed as SEQ ID NO: 72).SEQIDNameSequenceNO.Adenosine5′-actcatctgtgaagagaACCTGGGGGAGTATTGCGGAGGAAGGT43Linker3′-A12AdeAu3′-AAAAAAAAAAAATGAGTAGACACT445′-AdeAu5′-CCCAGGTTCTCT45Potassium5′-actcatctgtgatctaaGGGTTAGGGTTAGGGTTAGGG46Linker3′-A12K(I)Au3′-AAAAAAAAAAAATGAGTAGACACT475′-K(I)Au5′-AACCCTTAGA48Cocaine5′-actcatctgtgaatctc49LinkerGGGAGACAAGGATAAATCCTTCAATGAAGTGGGTCTCCC3′-A12CocAu3′-AAAAAAAAAAAATGAGTAGACACT505′-CocAu5′-GTCTCCCGAGA51Pb(II)5′-gggtccaagagaACTCACTATArGGAAGAGATGagtgtctactca52substrateLinkerP(II)Enzyme5′-CATCTCTTCTCCGAGCGGTCGAAATAGTGAGT53UO2(II)5′-gggtccaagagaACTCACTATArGGAAGAGATGGACGTG54substrateagtgtctactcaLinkerUO2(II)5′-CACGTCCATCTCTGCAGTCGGGTAGTTAAACCGACCTTCA55EnzymeGACATAGTGAGT

The ionic strength of the sample may influence how tightly the moieties that form the aggregate bind together. Higher salt concentrations favor aggregation, thus slowing sensor response, while lower salt concentrations may lack the ionic strength necessary to maintain the aggregates. In one aspect, the sample may include or be modified with a reagent to include a monovalent metal ion concentration of 30 mM and greater. The ionic strength of the sample may be modified with Na+ions, for example. In a preferred aspect, the monovalent metal ion concentration of the sample, which contains the aggregate, is from 30 mM to 1 M. At present, especially preferred monovalent metal ion concentrations are about 300 mM for adenosine and potassium analytes and about 150 mM for cocaine as an analyte. pH also may influence the aggregate binding, possibly attributable to the protonation of the polynucleotide base pairs at lower pH. In one aspect, a pH from 5 to 9 is preferred, with an approximately neutral pH being more preferred. Chemical denaturants, such as urea and formamide, also may influence the aggregate binding, possibly attributable to the formation of hydrogen bonds of the polynucleotide base pairs with the chemical moieties of the chemical denaturants.

Thus, the performance of the sensor may be improved by adjusting the ionic strength and pH of the sample, or the inclusion of chemical denaturants in the sample, prior to combining it with the aggregate. Depending on the sample, it may be preferable to add the sample or analyte to a solution containing the aggregate (where the ionic strength, pH, or presence of chemical denaturant may be controlled).

The sensor system, including the aptamers, an extension, and oligo-particles may be provided in the form of a kit. In one aspect, the kit includes the aptamer and the extension joined to form polynucleotide. In yet another aspect, the kit includes the extension, but excludes the aptamer, which is then provided by the user or provided separately. In this aspect, the kit also may include the reagents required to link the supplied extension with an aptamer. In this aspect, the kit also may be used to determine the specificity and/or selectivity of various aptamers to a selected analyte. Thus, the kit may be used to select an appropriate aptamer in addition to detecting the analyte. In yet another aspect, the kit includes an exterior package that encloses a polynucleotide and oligo-particles.

One or more of these kit components may be separated into individual containers, or they may be provided in their aggregated state. If separated, the aggregate may be formed before introducing the sample. Additional buffers and/or pH modifiers may be provided in the kit to adjust the ionic strength and/or pH of the sample.

The containers may take the form of bottles, tubs, sachets, envelopes, tubes, ampoules, and the like, which may be formed in part or in whole from plastic, glass, paper, foil, MYLAR®, wax, and the like. The containers may be equipped with fully or partially detachable lids that may initially be part of the containers or may be affixed to the containers by mechanical, adhesive, or other means. The containers also may be equipped with stoppers, allowing access to the contents by syringe needle. In one aspect, the exterior package may be made of paper or plastic, while the containers are glass ampoules.

The exterior package may include instructions regarding the use of the components. Fluorimeters; standard analyte solutions, such as a 10 μm solution of the analyte; and visualization aids, such as thin layer chromatography (TLC) plates, test tubes, and cuvettes, also may be included. Containers having two or more compartments separated by a membrane that may be removed to allow mixing may be included. The exterior package also may include filters and dilution reagents that allow preparation of the sample for analysis.

EXAMPLES

All DNA samples were purchased from Integrated DNA Technologies, Inc. (Coralville, Iowa). The aptamer DNA molecules were purified by denaturing polyacrylamide gel electrophoresis. Thiol-modified and biotinylated DNA were purified by standard desalting. Quantum dots may be obtained from commercial sources. For example, streptavidin coated QDs were purchased from Invitrogen (Carlsbad, Calif.). Adenosine, cytidine, uridine, Tris(2-carboxyethyl)-phosphine hydrochloride (TCEP), and cocaine hydrochloride were purchased from Aldrich (St. Louis, Mo.). Gold nanoparticles (AuNPs) (13 nm diameter) were prepared by literature procedures, and the extinction of the nanoparticle at 522 nm peak was about 2.4.

Coupling Polynucleotides to Particles to Form Oligo-Particles

Thiol-modified DNA molecules (1 mM) were activated with two equivalents of TCEP at pH 5.5 for one hour at room temperature. After mixing TCEP activated thiol-modified DNA and AuNPs at room temperature for 16 hours or longer, the solution was brought to 100 mM NaCl and 5 mM Tris acetate, pH 8.2. The solution was allowed to sit at room temperature for another day. DNA-coupled AuNPs were purified by centrifugation at 13,200 rpm for 15 minutes followed by careful removal of the supernatant. Buffer (100 mM NaCl, 25 mM Tris acetate pH 8.2) was added to re-disperse the nanoparticles. The centrifugation process was repeated to completely remove free DNA. Streptavidin coated QDs (1 μM) were mixed with 5 equivalents of biotinylated DNA at 4° C. for at least 30 minutes and the mixture was directly used without further treatments.

Preparation of Aptamer-Coupled Nanoparticles

To prepare adenosine aptamer-coupled nanoparticles (seeFIG. 1A), 1 mL of particle1(12 nM) and 1 mL of particle2(12 nM) were purified by centrifugation as described above. The two kinds of nanoparticles were mixed in a buffer (300 mM NaCl, 25 mM Tris acetate, pH 8.2) with a final volume of 1.4 mL. 10 μL of biotinylated DNA-coupled QDs (1 μM, emission peak at 525 nm) and a final concentration of 100 nM of the adenosine aptamer DNA was added. The mixture was incubated at 4° C. overnight to form aggregates, which were harvested by centrifugation and removal of supernatant. Finally, the nanoparticles were suspended in 1 mL of 200 mM NaCl, 25 mM Tris acetate, pH 8.2. The supernatant was almost colorless, suggesting that all gold nanoparticles were aggregated. Comparing the luminescence intensity of the supernatant with that of the aggregates (after disassembly) suggested that only 40% of the QDs were aggregated (data not shown). As a result, the molar ratio of particles 1:2:Q1was estimated to be 3:3:1. To prepare cocaine-responsive aptamer-containing aggregates, the procedures were the same except that 5 μL of 1 μM QDs (emission peak at 585 nm) was added and therefore the ratio of 1:3:Q2was around 6:6:1.

Detection with Individual Sensors Based on Emission

The luminescence of QDs was monitored on a fluorometer (FluoroMax-P, Jobin Yvon Inc.). The excitation wavelength was set at 450 nm and emission at 525 nm and 585 nm was monitored for the adenosine and cocaine sensors, respectively. In a 0.5×0.5 cm quartz cuvette, 225 μL of 100 mM NaCl 25 mM Tris acetate, pH 8.2 buffer, 175 μL of 200 mM NaCl 25 mM Tris acetate buffer and 50 μL of the above nanoparticle aggregates so that final NaCl concentration was 150 mM and the final volume was 450 μL. The cuvette was vortexed before measurement to assure a homogenous suspension. After monitoring emission for 50 seconds, the cuvette was quickly taken out and a small volume of concentrated adenosine or cocaine solution was added. The cuvette was vortexed again and placed back into the fluorometer to continue the emission monitoring.FIG. 5summarizes the spectral emission characteristics of these systems; the kinetic time course for emission production; and the dependence of the emission yield upon the concentration of the analyte.

Detection with Individual Sensors Based on Color

In a 96 well plate (flat bottom), 80 μL of 100 mM NaCl solution was first added and then varying concentrations of adenosine or cocaine were added to each well. The reaction was initiated by addition of 80 μL of adenosine or cocaine sensor aggregates (dispersed in 200 mM NaCl). The plate was scanned at 5 min after addition of mixing.FIG. 6shows the colorimetric results for aggregates containing aptamers that bind to adenosine or cocaine analytes.

Detection with Mixed Sensors

The adenosine and cocaine sensors were mixed at a 2:1 ratio so that the emission intensities at the 525 and 585 peaks were roughly the same. The buffer condition was the same as in the individual sensors (150 mM NaCl, 25 mM Tris acetate, pH 8.2). The mixed sensors were added with varying analytes or combination of analytes. After 1 min the emission spectra were collected with excitation at 450 nm.FIG. 7illustrates the spectra of aggregate systems upon disaggregation in the presence of control analytes (cytidine or cytidine and uridine; seeFIG. 7A), adenosine alone (FIG. 7B), cocaine alone (FIG. 7C), or both adenosine and cocaine (FIG. 7D).

Stability and Performance of Aptamer-Coupled Aggregates in Serum

Human blood serum (10% vol/vol) was prepared by diluting 50 μL of serum (Sigma) into 450 μL of buffer (300 mM NaCl, 25 mM Tris acetate, pH 8.2). Aggregates made from AuNPs1and2inFIG. 3Bwere dispersed in the serum. Adenosine (2 mM) was added into one of the tubes and a photo was taken 20 seconds after adenosine addition (FIG. 8A). The absorption spectra of the nanoparticles were also recorded on a UV-vis spectrometer (Hewlett-Packard Model No. 8453) by using freshly prepared 10% serum as the blank (FIGS. 8Band C).

As any person of ordinary skill in the art will recognize from the provided description, figures, and examples, that modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of the invention defined by the following claims and their equivalents.

REFERENCES