LENS AND ASSOCIATABLE FLOW CELL

Abstract: Improvements in a biosensor of the type having reservoirs or wells for analyzing a biological liquid are disclosed. A biosensor (190) includes a waveguide (164) placed between a plurality of members such as plates (100, 186), at least one of the members (100) being formed to define the walls (132, 134, 136) of the reservoirs where the liquid is biologically analyzed. The walls of the reservoirs are made of an inert, opaque material such as a metal. Although the biosensor may include a gasket (162), the gasket is associated with the members and waveguide in such a way (e.g. by recessing the gasket into a channel formed into a metal plate) so that the gasket does not form any significant portion of the reservoir wall. Waveguides of varying composition (e.g. plastic, quartz or glass) may be associated with the members to form the biosensor. The metal plate of the biosensor has input and output ports for infusing, draining, or oscillating the liquid to be analyzed in the reaction reservoir. Also disclosed is a sled-shaped waveguide associated with a rear lens to couple light out of the waveguide to serve as a quality control measure thus insuring that the biosensor is properly placed and that the light is working.

Description: LENS AND ASSOCIATABLE FLOW CELL Technical Field: This invention relates generally to components of a diagnostic apparatus, and more particularly to an improved biosensor having a lens ("waveguide") and associated flow cell. Background Art: International AppUcation No. PCT/US94/05567 (International Publication No. 94/27137, published Nov. 24, 1994) to the University of Utah Research Foundation discloses an apparatus for multi-analyte homogeneous fluoroimmunoassays. In one embodiment, the apphcation discloses an apparatus which uses a biosensor having a planar waveguide sandwiched, with an associated gasket, between two plates (FIGs. 3A-3C of Internat'l Publ. No. 94/27137). The inner edges of the gaskets serve as walls for a reaction reservoir or well. Fluorescence-emitting tracer molecules are bound to the waveguide surface and are excited by an evanescent field penetrating into the adjacent solution from a Ught beam propagated within the waveguide, the beam being introduced at, for example, a front end of the waveguide. In the reaction reservoir, a Uquid (e.g. serum or blood) is introduced and is allowed to admix with capture molecules associated with the waveguide surface (e.g. by "coating chemistry" as disclosed on pages 32 to 33 of the international appUcation). The emitted fluorescence is then directly coUected from the zone of evanescent penetration. In one particular embodiment, the biosensor has transparent waUs which define the reservoirs. (E.g.. FIGs. 11A-C of Internatl. Publn. No. 94/27137). The appUcation also discloses integraUy foimed or molded biosensors. (E.g.. FIGs. 12A, 12B & 13 of Internatl. Publn. No. 94/27137). Unfortunately, the waveguide portion of integrally formed or molded biosensors may exhibit deformation upon fabrication, or warping during storage or temperature changes. Also, gaskets may not reliably seal or are not always sufficiently inert to reactants, and thus may interfere with the desired analysis. It would be desirable to have a biosensor having reservoirs with inert waUs, the waUs being readUy detachable from the waveguide so that one waveguide could be readily exchanged for another. Disclosure of Invention The invention includes a biosensor with a reservoir or reservoirs, the biosensor including a waveguide placed (e.g. "sandwiched") between a pluraUty of members such as plates, at least one of the members being formed to define the waUs of the reservoir or reservoirs where the reaction to be analyzed takes place. The reservoir waUs are preferably an inert, opaque material such as a passivated metal (e.g. , black anodized aluminum). Although the biosensor may include a gasket, the gasket is associated with the pluraUty of members and waveguide in such a way (e.g. by recessing the gasket into a channel formed into a metal plate) so that the gasket does not form any significant portion of the reservoir waU. Waveguides of varying composition (e.g. plastic, quartz, glass or siUconoxynitride) may be associated with the members to form the biosensor. A lens or lenses may be integrated with the waveguide. The metal plate of the biosensor has input and output ports for infusing, draining, or oscillating the Uquid to be analyzed in the reaction reservoir. Due to the sandwiching of the waveguide in between the members, the planar waveguide is generaUy less distorted than that of an integraUy formed biosensor. A reaction to be analyzed is not interfered with due to the use of opaque, inert metal to structuraUy define the reservoir. The biosensor design is advantageously configured to interact with a flat waveguide having a rear integrated lens design for reading Ught passing through the waveguide (not fluorescent/evanescent Ught, but reading the core laser beam Ught) to monitor coupling efficiency and beam quahty. The invention thus also includes a flat waveguide associated with a rear lens to couple Ught out of the waveguide (and a biosensor using such a lens) to serve as a quahty control measure, thus insuring that the biosensor is properly placed and that the Ught source is working. The invention also includes orienting the biosensor in a particular position relative to an optical reading device and laser which increases the performance of the biosensor to the point where, surprisingly, whole blood can be quickly analyzed. Brief Description of Drawings In the drawings, which depict presently preferred embodiments of the invention and in which like reference numerals refer to like parts in different views: FIG. 1 depicts an enlarged bottom view of the flow ceU top which may be used with the invention. FIG. 2 depicts an enlarged section view of the flow ceU top of the preceding figure along section line 2-2. FIG. 3 depicts an enlarged section view of the flow ceU top of FIG. 1 along section line 3-3. FIG. 4 depicts an enlarged, exploded, perspective view of a biosensor according to the invention. FIG. 5 depicts an enlarged, side view of a laminated gasket which interacts with the flow ceU top of FIG. 1. FIG. 6 depicts an enlarged view of a plastic, molded flat waveguide with integrated input and output coupling lenses. FIG. 7 is an enlarged side view of the waveguide of the preceding figure. FIG. 8 is a schematic diagram of a fluorescent assay apparatus useful for practicing the invention, showing the flow ceU assembly of FIG. 4 in a particularly useful orientation with respect to the earth. FIG. 9 is a stylized, enlarged side view of a portion of a waveguide and biochemical components of a competition immunofluorescent assay according to the invention. FIG. 10 depicts an enlarged, exploded, perspective view of the flow ceU portion of a biosensor according to the invention. FIG. 11 depicts an enlarged perspective view of a gasket for use with the invention. FIG. 12 depicts an enlarged top view of a second frame member ("flow ceU bottom") for association with the flow ceU top of FIGs. 1 through 3. FIG. 13 depicts an enlarged side view of the second frame member of the preceding figure. FIG. 14 depicts an enlarged perspective view of the registration plate forming part of the flow ceU assembly of FIG. 4. FIG. 15 depicts an enlarged top view of the stage member of the flow ceU assembly of FIG. 4. FIG. 16 depicts an enlarged side view of the stage member of the preceding figure. FIG. 17 depicts an enlarged view of the preceding two figures. FIG. 18 depicts an enlarged, exploded, perspective view of a biosensor according to the invention. FIG. 19 depicts an enlarged, stylized, side view of a portion of a plastic film waveguide having an optical diffraction grating coupler. FIG. 20 depicts an enlarged, stylized, side view of a poition of a plastic film waveguide to which a separate optical diffraction grating has been associated. FIG. 21 is a graph depicting the results of a correlational analysis comparing an evanescent assay (CK-MB) of the instant invention with a prior art device. FIG. 22 is a graph depicting the double logarithm plot of the data of the preceding figure showing the correlation. FIG. 23 is a graph depicting the effect of agitation (osciUation) on a CK-MB assay on whole blood ("WB"), 50% WB, and 50% plasma using a device according to the invention (dUution with outdated CPDA anticoagulant solution). FIG. 24 is an enlarged, stylized Ulustration of wavelength- and spatiaUy- resolved detection of fluorescence emitted from a planar waveguide sensor using different capture molecules and tracer molecules for detecting different analytes of interest in a sample solution. Best Mode for Carrying Out the Invention A. Flow CeU: The flow ceU top, generaUy 100, depicted in FIGs. 1 through 3 is preferably made of a Ught absorbing material (e.g. a metal such as aluminum having a passivated surface such as black anodized surface). The depicted flow cell top 100 is generaUy plate-like, and is formed to contain a pluraUty of weUs or reservoirs 102, 104, 106 (for example, two to ten reservoirs). A design with at least two individual reservoirs has significant advantages over a single reservoir embodiment for instances when it is desirable to measure the test sample fluorescence simultaneously with fluorescence from a "control" region on the same waveguide. For example, the level of non-specific binding to the waveguide (or non-specific fluorescence) can be subtracted from the test sample fluorescence. Also, measurement changes due to fluctuations in intensity of the exciting Ught can be corrected. In a displacement assay, the "control" region could be a pre-loaded waveguide with no analyte present in the sample, or with a known amount of analyte. With the depicted embodiment of three or more weUs, fluorescence can be measured for both a no-analyte control and at least one known caUbration analyte sample in addition to the "unknown" or test sample. Although, even with a single reservoir, the invention is able to analyze multiple analytes in a single sample (e.g. by use of a single waveguide in multiple experiments). In the depicted embodiment, the reservoirs 102-106 have respective inlet/outlet apertures 108, 110, 112, 114, 116, 118 extending through the flow ceU top 100 for injecting and withdrawing the Uquid to be analyzed into the reservoirs 102-106. In some cases, this Uquid may be osciUated into and out of the reservoir with a pump, which enhances the mixing of the analyte and reactant (see, e.g. , FIG. 23). With oscillation, the performance (e.g. speed) of the assay is increased. In the depicted embodiment, each port 108-118 is associated with its own depressed recess formed 120, 122, 124, 126, 128, 130 in the flow ceU top 100. Between the recesses associated with a particular reservoir, lateral or longitudinal channels may be formed in the flow ceU top to aid in mixing the Uquid contained within the reservoir (not shown). The outer periphery of the reservoirs 102-106 are each defined by respective waUs 132, 134, 136 which are preferably integraUy foimed with the rest of the flow ceU top 100, although they may be a separate component of the flow ceU top. The inner circumferences 138, 140, 142 of the waUs 132-136 are made of an inert, opaque material such as an inert, opaque plastic, or a metal such as passivated, black anodized aluminum, copper, stainless steel, or similar aUoy. In the depicted embodiment, the entire flow ceU top 100 is made of a metal, while in other embodiments (not shown), the flow ceU may be made of a non-metaUic material, and an opaque, dark material or metal sleeve placed within the reservoirs (not shown). Material in contact with the Uquid should exhibit low protein absoφtion properties. Accordingly, a metal, a hydrophiUc non-metaUic material or a hydrophobic non-metaUic material coated with a thin film of hydrophiUc material (e.g. PEG, PLURONICS or other hydrogels) may be used. In the depicted embodiment, the apertures 108-118 associated with the respective reservoirs 102-106 fluidicaUy communicate the recessed portions 120-130 of the reservoirs with a pair of respective receptacles 144, 146, 148, 150, 152, 154 (shown by construction Unes in FIG. 1) for receiving fluid inlet/ outlet ports 156, 158 which are associated with the flow ceU top 100 (FIG. 4). Although the fluid inlet/outlet ports 156, 158 wiU be described with regard only to one reservoir, it is to be understood that the description appUes likewise for the other reservoirs of the flow ceU (if any). As depicted in FIG. 4, the fluid inlet/outlet ports 156, 158 may be male threaded nipples which interact with corresponding threaded members (threads not shown) bored into the flow ceU top 100. The open ends of the nipples are in fluid communication (e.g. by tubing or other conduit - FIG. 8) with a, for example, syringe pump (not shown). Other fluid tight arrangements between the ports and the flow ceU top can be used, so long as the sample fluid communicates to the apertures 108-118. The Uquid to be analyzed (e.g. whole blood, plasma, dmients, or mixtures thereof) can thus be injected and withdrawn from the reservoirs 102-106 by use of an, for example, osciUating pump (not shown). As further depicted in FIGs. 1 and 4, the outer peripheries of the waUs 132- 136 also partiaUy define a recess 160 formed in the flow ceU top. This recess 160 is formed to accept a gasket 162 (FIGs. 4, 5 & 11) which is more thoroughly described hereinafter. This gasket 162 cushions placement of a waveguide onto the flow ceU top 100 and impedes sUppage of the waveguide when associated with the flow cell top. As is also more thoroughly described herein, the gasket, preferably, does not serve as any part of the waUs 132-136 to contain the Uquid within a reservoir 102-106. The flow ceU may be used with a quartz waveguide or, more preferably, with the hereinafter described plastic molded waveguide 164. B. The Waveguide: As depicted in FIGs. 4, 6 & 7, a preferred waveguide 164 is a plastic molded waveguide (e.g. molded of an optical plastic) having integrated input 166 and output 168 coupling lenses. Such a waveguide 164 is preferably sled-shaped, having a planar (optical substrate) portion 170 with first 172 and second 174 paraUel plane surfaces and an edge having a thickness 176 extending therebetween (FIG. 9). At least one of the waveguide surfaces 172 has a pluraUty of capture molecules 240 associated therewith (e.g. immobilized thereon as depicted in FIG. 9, although other methods of bringing the capture molecules into sufficiently close association with the surface may be used (e.g. by placing a strip immunoassay onto the waveguide surface, or using a fibrous "mat" with capture molecules attached to the fibers)). These surfaces 172, 174 should have the best optical smoothness possible. For example, surface waviness and roughness spacing should Ue outside a range of about 65 nm to 195 micrometers ("μm"), whUe spacings close to 650 nm should be avoided (when 632.8 nm laser Ught is used). Surface roughness ampUtude or "Ra" (theoretical surface plane to average peak or vaUey) should be less than 0.0065 μm (0.26 μin); however twice this amount is still functional. The thickness wul typicaUy be between 0.20 and one millimeter ("mm"), more preferably about 0.5 mm. The edge of the planar portion has a receiving region (e.g. lens 166) for receiving Ught to be internaUy propagated. In the embodiment depicted in FIGs. 6 & 7, an input or receiving lens 166 is integraUy adapted to the waveguide adjacent the receiving region at the "front" of the waveguide. Other methods of opticaUy associating the lens to the planar portion could also be used. Surface specifications for such a lens or lenses are simUar to the planar or "plate" portion of the waveguide. A maximum roughness ampUtude of 0.013 to 0.025 μm (0.5 to 1 μiή) is preferred. Preferably, machine lines should be paraUel (vertical when looking at lens) to the long axis of the waveguide. Surface specifications for the side of the part and lens ramp areas are less stringent than the top and bottom surfaces of the plate structure. In another embodiment (not shown), the lens (or lenses) is not integraUy associated with the waveguide, but is adapted to interact opticaUy with the waveguide, or multiple waveguides. Alternatively, rather than using a lens to couple Ught into the waveguide, a grating could be used. Various gratings as weU as methods for incoφorating them into a waveguide are known. See, e^, U.S. Patent 5,480,687 (Jan. 2, 1996) to Heming et al. at column 4, lines 1-10, and column 6, line 20 to column 7, line 55, U.S. Patent 5,081,012 (Jan. 14, 1992) to Flanagan et al., U.S. Patent 5,455,178 (Oct. 3, 1995) to Fattinger, U.S. Patent 5,442,169 (Aug. 15, 1995) to Kunz, and U.S. Patent 5,082,629 (Jan. 21 , 1992) to Burgess, Jr. et al. Gratings may be fabricated by a number of means including but not limited to: embossing, molding, photoUthography, direct etch electron beam Uthography, interference Uthography, and phase shift Uthography. Embossed gratings are mechanicaUy stamped or thermally imbued onto a surface and thereupon affixed to a substrate. PhotoUthographic gratings are formed from the chemical development and etching of photoresist and substrate after masked illumination by an appropriate source. Interference and phase shift lithography are simUar techniques which aUow finer resolution of etched structures than does conventional photolithography. Ion or particle beam methods fabricate precise gratings by directly etching or "writing" a grating substrate with a stream of ions or molecular particles. The grating itself can consist of an etched pattern of regular features in a metal film coated onto the planar poition of the waveguide or the front ramp. Standard diffraction gratings such as those used in spectrometers like "repUca" gratings (gratings comprised of a dried epoxy coated with metal) can be used. The use of such grating couplers helps to avoid fabrication complexities associated with the use of a receiving lens or plasma-etched gratings. The procedure for applying such couplers is presently used to emboss holograms onto plastic credit cards, and, using such a process, the coupler could be mass produced at a relatively low cost. In an alternative embodiment shown in FIG. 19, a corrugated waveguide with gratings 314 (> 5 nanometers ("nm") deep or thick) is associated with (e.g. molded on, adhered to, or hot stamped onto or embossed onto) the receiving region of a plastic thin film waveguide 316 (or a cast thin plastic planar waveguide) associated with (e.g. adhered to) a lower index substrate 318. Although in the depicted embodiment, the grating 314 is positioned between the thin film and the lower index substrate, other orientations such as applying the grating to the surface 172 of the thin film waveguide could also be used. Also, alternatively, the Ught could be directed into the waveguide from a different direction. In any event, the grating receives Ught 218 to be internaUy propagated. In such a case, the waveguide portion wiU typicaUy be made of a transparent optical plastic and have a thickness of from about 10 micrometers to about 200 micrometers, preferably about 125 micrometers. In the case of extremely thin waveguide films (e.g. about 10 to 25 μm), the resulting film may be attached to a preferably rigid, open support structure 317 (FIG. 20). Alternately, the resulting thin film may be affixed to a supporting substrate having a lower index of refraction than the film (FIG. 19). From efficiency measurements, it can be determined that for an integrated optic waveguide-fluoroimmunoassay, the most efficient etch depths are about 1.5 times that of the grating period. For diffraction to occur in a grating, the period d should be on the order of the wavelength of Ught (lambda). Given the pathlength difference, δ, between the light rays from two neighboring grating features (sUts, rigids, and the like), a constructive interference pattern is estabUshed by the Ught leaving the grating when δ is an integer multiple, m, of the wavelength. δ = d(n,sinθ, - n,sinθ,) = lambda(/w) wherein d is the grating period, θ t and θ, are the transmitted and incident angles at the grating interface (measured relative to the surface normal), and n, and n, are the refractive indices of the transmitting and incident mediums (i.e. the waveguide and the substrate). Using this formula, one determines that the incident angle for coupling 632.8 nm Ught is 38.03° when the grating period is 0.7 μm. The angle of incidence of Ught from air into the lowest order made of the waveguide and the groove density into waveguide films can be calculated by the use of the equation above, and was determined to be 4.6°, 27.4° and 57.2° for polystyrenes having densities of 2400 g/mm, 1800 g/mm, and 1200 g/mm, respectively, for incident Ught of 632.8 μm wavelength. In still other embodiments, laser Ught may be prism-coupled onto an integrated optic waveguide ("IOW") (not shown), end-fire coupled (i.e. direct focusing of Ught into the waveguide), or taper-coupled (e.g. by use of an adlayer film tapered in thickness or refractive index, preferably in conjunction with a grating coupler) into the waveguide (also not shown). In order to taper-couple Ught into the flow ceU, a gentle tapered section (e.g. either curved or linear) can be used to "funnel" Ught into the end of a thin planar waveguide. A weU-coUimated input beam (e.g. a laser) couples into a multi-mode waveguide (e.g. about 50 μm in thickness) due to the "Law of Brightness" constraint (i.e. the product of the beam extent and numerical aperture is a constant through the taper). The taper may be also coupled with a lens. The waveguide depicted in FIGs. 6 & 7 has a shelf or ridge 176. The ridge 176 abuts against an edge of the flow ceU top when the waveguide 164 is functionaUy associated with the flow ceU (FIG. 4). As shown (FIG. 1), the flow ceU top 100 has two apertures 178, 180 which interact with registration members ("registration pins") 182, 184 of a second frame member ("flow ceU bottom") 186 structured to interact with the flow ceU top 100 and waveguide 164 in order to hold ("sandwich") the waveguide in place (FIG. 4). Laser light preferably enters the receiving lens 166 at mean angle θ (FIG. 8). The mean angle θ wiU typicaUy vary dependent upon the type of material used to form the waveguide and the optical properties of the media opposite both faces of the waveguide. When the waveguide or waveguide layer is made of polystyrene (e.g. NOVOCOR), then the mean angle wUl generaUy be less than 32°, e.g. 15° to 25°. Typical beam widths vary from 0.5 to 2.0 mm. On the other side of the waveguide, an outcoupUng 188 interacts with the rear or output lens 168 to ensure that Ught is detected (FIG. 8). The outcoupUng 188 may be a single photodetector, multiple photodetectors, standard CCD (charge- coupled device) or like device. The Ught passing through the waveguide 164 and received by the outcoupUng 188 is analyzed for quaUty and/or intensity. Unlike the end coUection of Ught described in U.S. Patent 4,582,809 to Block et al. (April 15, 1986), in the present invention, the Ught may be detected at the end of the waveguide for two reasons. The first reason is as a quaUty control measure. The Ught passing through the waveguide may be measured so that the operator of the device knows that the biosensor has been properly placed in the apparatus and that the Ught source is still working. Alternatively, the device may be configured so that a predetermined strength of Ught must first be detected at the rear lens 168 before the apparatus will operate, again to ensure that the flow ceU assembly ("biosensor"), generaUy 190, has been properly placed. The second reason for end detection involves caUbration of the device to ensure that the amount of Ught traveUing through the waveguide is uniform and, if it is not uniform to accommodate any differences. The Ught outcoupled from the lens 168 associated with the rear of the waveguide is preferably measured over the width of the lens to ensure that sufficient Ught is passing through the lens to create detectable fluorescence. Preferably, a plastic waveguide such as that depicted in FIGs. 6 & 7 wiU be made (e.g. injection-molded) of an optical plastic such as polystyrene, polymethylmethacrylate ("PMMA"), polycarbonate or equivalent mateiial, and wiU have a refractive index greater than 1.33 (the index of water being 1.33). The size of the waveguide wiU depend on its desired use. Although the front lens ramp 192 and rear lens ramp 194 are shown in a "concave" or arced position relative to one another and the planar portion 170 (FIG. 7), the ramps need not angle towards a common center, and one of the lens ramps could be angled in the opposite direction from the plane of the planar portion, and the ramps would faU in roughly paraUel planes (not shown). In another embodiment (not shown), the waveguide includes a laminate of layers, one layer serving as a structural substrate, and the other (e.g. thin film SiON) serving to transmit the Ught, such as those disclosed in International AppUcation No. PCT/US96/02662 (International PubUcation No. WO 96/26432, pubUshed 29 August, 1996) to the University of Utah Research Foundation. In such an embodiment, the structural substrate can be made of a plastic such as polystyrene, PMMA, polyvinyl chloride ("PVC"), polyimide, polyester, polyurethane, organicaUy modified ceramics, polymers of diethylene glycol bisaUyl carbonate, aUyldiglycolcarbonate, polycarbonate, or equivalent material. The waveguide layer is preferably an optical plastic such as polystyrene, although it can be made of other suitable materials such as TiO 2 , a mixture of TiO 2 -SiO 2 , SiO 2 , ZnO, Nb 2 O 5 , Si 3 N 4 , Ta 2 O 5 , HfO 2) or ZrO 2 . Waveguide layers such as TiO 2 , SiO 2 , or Si 3 N 4 can be deposited by plasma chemical vapor deposition ("PVCD"), plasma impulse chemical vapor deposition ("PICVD") process, or the like. C. Gasket: A gasket 162 is preferably seated between waveguide 164 and flow ceU top 100 (FIGs. 4, 5 & 11). A preferred gasket 162 for use with the waveguide 164 with integrated lenses includes a clear TEFLON layer 196 adhered (e.g. with the use of a suitable glue or double-sided tape, e.g. MACTAC No. SB 1154 avaUable from Morgan Adhesives Co. of Stow, Ohio, USA) to a siUcon rubber gasket 198 shaped to fit the recess of the flow ceU top. Alternatively, synthetic resin polymers (i.e. TEFLON-like materials) may be used. The depicted gasket 162 is configured with three intemal openings (FIG. 11 and construction lines 200 of FIG. 5) which surround, but do not interact with, the reservoirs 102-106. Upon assembly of the biosensor, in the reservoirs 102-106, the first planar surface 172 of the waveguide 164 constitutes a floor or ceiling (FIG. 8) of the particular reservoir, whUe the flow ceU top 100 is formed to constitute the ceiling or floor and the waUs. The orientation depicted in FIG. 8, wherein the planar surface 172 serves as a ceiling and lays level with the earth has been found to be especiaUy useful, enhancing the ability of the device to detect the presence of target molecules in even whole blood over a shorter period of time (e.g. five to ten minutes), especiaUy with osciUation. However, it is, of course, understood that the flow ceU assembly 190 may be oriented in any position (e.g., vertical or any angle). Angling the flow ceU assembly 190 assists in removing bubbles or heavy materials away from the waveguide 164, if desired. Alternatively, a dye can be incoφorated into the sample solution for absorbing interfering signals. Although the reservoirs 102-106 are here shown to be generaUy rectangular in shape, other shapes could be used. The gasket 162 is preferably made of a semi-rigid material having an index of refraction less than that of the waveguide material in the wavelength range of the exciting Ught. For best results, it is beUeved that the index of refraction of the gasket material should be as low as possible compared to that of the waveguide. For a waveguide made of quartz or glass, the index of refraction would typicaUy be from about 1.46 to 1.52, higher for high-lead glass. A transparent (non-pigmented) siUcon rubber (siloxane polymer) with an index of refraction of 1.35-1.43 is a presently preferred material for gasket 162. TEFLON or TEFLON-type materials such as PTFE (polytetrafluoroethylene) or FEP (fluorinated ethylene propylene) have indices of refraction of around 1.34-1.35, and may also be suitable for use as layer 196. The other portion 198 of the gasket may be formed of an opaque (e.g. red or black) neoprene or siUcon rubber material which is preferably biologicaUy inert although due to the metal waUs, it need not be. D. The Flow CeU Assembly As depicted in FIG. 18, a preferred flow ceU assembly 190 according to the invention generaUy includes a flow ceU portion (generaUy 200, FIG. 10), gasket 162, and waveguide 164. As shown in FIG. 10, the flow ceU portion includes the flow ceU top 100, flow ceU bottom 186, and a flow ceU stage (or "flow ceU platform") 202. As shown in FIG. 8, and as more thoroughly described herein, these three components of the biosensor 190 are integrated with one another in such a manner that excitation Ught enters the front lens 166 of the waveguide 164, travels through the front lens ramp 192 and planar portion 170, and passes out of the rear lens ramp 194 and rear lens 168 to the outcoupUng 188. The flow ceU assembly can also include means for associating the flow ceU top 100 with the flow cell bottom 186 thus sandwiching the gasket 162 and waveguide 162 therebetween. The depicted means for doing so are threaded clamping bolts 204, 206 which interact with correspondingly threaded holes 208, 210 in the flow ceU bottom 186. Of course however, equivalent means such as screws, nuts and bolts, clamps, snap fits, and the like could alternatively be used. A waveguide registration plate 212 is shown associated with the flow ceU bottom 186 (FIG. 4). The waveguide is reproducibly positioned between the flow ceU top and bottom when aUgned with the registration plate. Also depicted is a 3- channel beam mask 214 having three apertures for receiving a Ught beam. E. The Apparatus: Once the flow ceU 200, gasket 162 and particular waveguide 164 have been associated with one another, the thus formed biosensor 190 may be used in an apparatus for performing immunoassays such as fluoroimmunoassays. As depicted in FIG. 8, such an apparatus includes a Ught source 216 which provides a Ught beam 218 which is directed by means of mirrors 220, 222, 224 to an optical biosensor 190. The Ught source 216 may be an argon laser or laser diode capable of emitting at center wavelengths of between 488 and 514.5 nm and 600 to about 900 nm (e.g. 633 nm), respectively. The embodiment of FIG. 8 further includes a 45° angle mirror 226 which is positioned for assisting in focussing the beam 218 onto the input lens 166 of a particular biosensor 190 if desired. The biosensor 190 has an optical substrate with one end 166 positioned to receive Ught from beam 218. In the case of a non- integrated quartz waveguide, a focussing lens 228 is preferably positioned between angle mirror 226 and the biosensor 190 for focussing Ught from beam 218 onto the end of the biosensor. Focussing lens 228 is removable, and is depicted mounted on an X-Y translation unit so that its position may be adjusted for best focussing. Furthermore, the translation unit can be moved to adjust the angle θ for waveguides of differing composition. A significant portion (in the case of the quartz waveguide, the entire portion) of the optical substrate 164 is of a generaUy planar shape having two planar surfaces spaced by a width 176 as shown in FIG. 9, which is more thoroughly described herein. Light detection means, generally 230, are positioned to detect fluorescent Ught emitted from the biosensor 190. As more thoroughly described herein with regard to FIG. 9, the emitted Ught is reflective of the concentration of a selected analyte in a sample. The Ught detection means 230 depicted in FIG. 8 includes a coUection lens 232 positioned to coUect the emitted fluorescence from a direction substantially orthagonal to the direction of propagation of Ught 218 through optical substrate 164. The distance 234 between collection lens 232 and optical substrate 164 is selected as known to those skilled to maximize the collection of Ught emitted from the region of evanescent Ught penetration whUe at the same time imaging this Ught onto the face of the photodetector. The Ught coUected by coUection lens 232 is then sent to detection means 230, which responds by outputting signals reflective of the level of coUected fluorescent Ught. Detection means 230 may be any type of photodetector useful to detect Ught in the wavelength region spanning the wavelength range of the emitted fluorescence, as known in the art. However, in a preferred embodiment for simultaneous multi- analyte assays, detection means 230 is an imaging-type detector providing direct imaging of each of the fluorescent signal(s) originating in the evanescent zone 236 (FIG. 9). In the apparatus of FIG. 8, detection means 230 is a CCD detector which produces a signal. Such imaging signal coUection provides simultaneous measurement of multiple samples in a much simpler way than a system in which a separate optical element is needed to read each weU or patch. The present imaging detection system also provides for coUection of emitted fluorescence directly from the evanescent zone 236, rather than via evanescent penetration of the fluorescence into the waveguide (FIG. 9). Alternatively, detection means 230 may be a photomultiplier, a semiconductor photodiode, or an array of such detectors. In embodiments other than a CCD, an array is generally preferable to a single detector for some puφoses. With an array of smaU detectors, the user can determine that the maximum fluorescence is being detected and is not inadvertently missed due to misaUgnment of the coUection and detection optics. OptionaUy, a grating spectrograph is coupled to the CCD or other detection means to provide spectral analysis of the detected Ught. In that case, means are also provided to integrate the signal function around each peak to determine the total coUected fluorescence from a sample. Alternatively, in an embodiment for use in a setting such as in a testing laboratory, and for which aU the parameters of the assay have been standardized, the spectrograph may be replaced by a filter which passes only wavelengths in the region of tracer fluorescence. As is better seen in FIG. 9, optical substrate 164 is embodied as a planar portion of a waveguide having at least one planar surface 172 spaced from a second surface 174 by a width 176. At least one surface 174 is disposed in contact with a sample solution 238. Capture molecules 240 are immobilized on the exposed surface 172 of the waveguide. In one embodiment, the sample solution 238 contains a pluraUty of analyte molecules 242 of a selected analyte which also includes tracer molecules 244. The tracer molecules can be incoφorated into the sample solution by, for example, admixing them with the sample solution before incoφoration into the assay or by "drying" the molecules onto the waveguide surface without actuaUy chemicaUy binding them to the surface 172 (or at least not binding them permanently as would be the case when the tracer molecules are associated with the surface by use of a water soluble component (e.g. a soluble sugar that does not interfere with the particular interaction between capture and tracer molecules)). The capture molecules are chosen or constructed to bind to a binding moiety present on each of the analyte molecules 242. The tracer molecule 244 is a molecule chosen to be complementary (in a binding sense) with the capture molecules and is constructed to emit fluorescent Ught in response to stimulation by Ught of the appropriate wavelength (e.g. by tagging the capture molecule with a fluorescent label). The level of fluorescence emitted by the tracer molecules 244 is a measure of the amount of analyte bound to the capture molecule and is thereby reflective of the concentration of analyte molecules 242 in the solution. When Ught is being propagated in the waveguide 164 and internaUy reflected at the surfaces 172, 174 an evanescent Ught field is produced having an intensity curve 230 which drops off with distance from the surface 172, as diagrammed relative to a distance axis 232 and a horizontal axis 234 (not to scale). Evanescent Ught intensity varies along axis 232, co-linear with distance. An excitation zone 236 is the only region of the solution in which the evanescent Ught intensity is sufficient to excite a significant or detectable fraction of tracer molecules 244 (not to scale). Tracer molecules 244 outside zone 236 wiU contribute Uttle or no induced fluorescence. Excitation zone 236 is typicaUy between about 1000 and 2000 A in depth. Capture molecules 240 are reactive with the analyte molecules 242, and may be whole antibodies, antibody fragments such as Fab' fragments, peptides, epitopes, membrane receptors, whole antigenic molecules (haptens) or antigenic fragments, oUgopeptides, oUgonucleotides, mimitopes, nucleic acids and/or mixtures thereof. Capture molecules 240 may also be a receptor molecule of the kind usuaUy found on a ceU or organeUe membrane and which has specificity for a desired analyte, or a portion thereof carrying the analyte-specific-binding property of the receptor. The capture molecules 240 may be immobilized on the surface 172 by any method known in the art. However, in the preferred embodiment, the capture molecules are immobilized in a site-specific manner. As used in this appUcation, the term "site-specific" means that specific sites on the capture molecules are involved in the coupling to the waveguide, rather than random sites as with typical prior art methods. Int'l Publ. No. 94/27137, which has been previously referenced, detaUs methods for site-specific immobilization of capture molecules to the surface of the optical substrate by means of a protein-resistant coating on the substrate. The waveguide can be designed so that multiple (e.g. four) different assays can be performed on the same sample. This is accompUshed by immobilizing different types of capture antibodies on different regions of the waveguide, a process referred to as patterning. Three different patterning methods appear suitable for immobilizing antibodies to the polystyrene sensors ~ gasketed multi- weU coating tray, Uquid jet printing and photoUthography. In the former, a machine similar to an ink jet printer is used to spray reagents onto a specific region of the waveguide; in the latter, ultraviolet Ught is used to photochemicaUy cross-link antibodies to selected regions. One immobilization chemistry is based on physical adsoφtion of antibodies to the waveguide. In one method, an antibody is briefly exposed to acidic conditions just prior to immobUization. It has been shown that this acid pre¬ treatment step improves the antigen-binding capacity (AgBC) of immobilized antibodies by up to 3-fold in some cases. This immobilization chemistry is relatively simple and compatible with gasketed multi-weU coating tray or Uquid jet printing technology, but in some cases it exhibits a higher degree of non-specific binding than other methods. The other two immobilization chemistries are based on a famUy of tri-block polymers of the form PEO-PPO-PEO, where PEO stands for poly (ethylene oxide) and PPO stands for poly (propylene oxide). These surfactants are sold under the trade name PLURONICS and come in a variety of chain lengths for both the PEO and PPO blocks. The PPO block is significantly more hydrophobic than the PEO blocks and adsorbs readUy to non-polar surfaces such as polystyrene, leaving the PEO blocks exposed to bulk solution. The free ends of the PEO chains exhibit high mobihty, UteraUy sweeping proteins away from the surface. In both the second and third immobilization chemistries, the surface of the waveguide is coated with pluronics before attachment of antibodies, but the two chemistries differ in how the antibodies are attached. In the second chemistry a photochemical cross-Unking agent is used to conjugate antigen-binding fragments (Fab') to the PEO blocks, making this method suitable for patterning by photoUthography. In the third chemistry, Fab' fragments are attached to pluronics using a chemical cross-linking agent, making this method compatible with gasketed multi-weU coating tray or Uquid jet patterning. The photochemical cross-Unking method was evaluated with two different PLURONICS (F108 & P105) and two different photochemical crossUnkers (BPM and BPIA). WhUe acceptable levels of total antigen binding can be obtained with aU four pairwise combinations, an unacceptable level of NSB may be obtained when antibodies are immobilized to F108 using the BPIA crosslinker. The other three pairwise combinations give very low levels of NSB (about 1.5 % of total binding). Furthermore, the P105/BPM pair is especiaUy good, giving an undetectable level of NSB. In FIG. 9, a competition assay scheme is depicted (also termed a displacement assay). However, as wiU be apparent to the skiUed person, alternate assay schemes such as sandwich assays may be performed with the present apparatus. See, e.g. U.S. Patents 4,376,110 and 4,486,530 to Hybritech, Inc. In the embodiment of FIG. 9, the competition immunoassay has tracer molecules 244 constructed such that the capture molecules 240 wiU bind tracer molecules 244 in place of analyte molecules 242. Higher concentrations of analyte molecules 242 wUl cause most of the tracer molecules 244 to be displaced into the surrounding solution from capture molecules 240, thus reducing the number of tracer molecules within excitation range 236 of the substrate 164. This reduced binding of tracer molecules in turn reduces the amount of fluorescence. In contrast, lower concentrations of analyte molecules 242 wiU aUow tracer molecules 244 to bind to capture molecules 240, and thus to be held within the excitation range 236. In tests conducted with the point-of-care cardiovascular marker CK-MB (associated with acute myocardial infarction) on both plasma and whole blood, the results were comparable (taking into consideration diffusion and viscosity differences). In the embodiment of the apparatus of FIG. 8, measurements of fluorescence are made by spectroscopy. Fluorescence detection was done with a monochromator (SPEX Industries, Inc., Model 1680C) and a CCD (Photometries Ltd. Series 200, or CH-250). Altematively, Ught source 216 can be any Ught source emitting at the wavelength desired for excitation of selected fluorescent dyes. Also, once an assay procedure has been vaUdated and standardized, it may not be necessary to measure the fluorescence spectrum or spatial distribution of fluorescence. The detection means may be simplified in accordance with the minimum requirements of the assay. In another altemate embodiment, Ught source 216 is a laser diode emitting in the red wavelength region of 600-700 nm which is commerciaUy avaUable. The laser diode may provide about 12 miUiwatts of power with a peak emission wavelength of about 635 nm. Laser diodes emitting at 633 nm are also available and can be used. For an embodiment using a wavelength in this region, it is necessary to use dyes such as cyanine dyes, whose fluorescence can be stimulated by excitation with wavelengths in the red spectral region. An example of such a dye is the fluorescent dye CY5, avaUable from Biological Detection Systems, Inc., Pittsburgh PA (catalog no. A25000). The CY5 dye can be conjugated to the desired tracer molecule by the manufacturer's instmctions and/or with a kit available from BDS. A second dye, CY7, may also be suitable. The dyes and methods for conjugating are also characterized in the paper by Southwick, P.L. , et al. , titled "Cyanine Dye Labelling Reagents - CarboxymethyUndocyanine Succinimidyl Esters", Cvtometrv 11:418-430 (1990). The use of laser diodes as a Ught source permits the biosensor and waveguide to be formed of plastic, which considerably reduces the expense of manufacture and facUitates the integral molding of the semi- cylindrical lens with the waveguide and reservoirs. Different labels can be used which emit Ught at different wavelengths if desired. In such a circumstance, different types of capture molecules (e.g. antibodies reactive with different antigens) can be immobilized to the surface so that the waveguide can be used to detect more than one molecule to be detected. In such a case, multiple wavelengths can be detected by multiplexing the signal from the waveguide. FIG. 24 styUsticaUy Ulustrates simultaneous wavelength- and spatiaUy- resolved detection of fluorescence emitted from a waveguide sensor using different capture molecules (Capture Ab,, Capture Ab 2 , Capture Ab 3 , . . . Capture AbJ, tracer molecules (Tracer Ab,, Tracer Ats^, Tracer Ab 3 , . . . Tracer AbJ, and labels (Fj, F 2 , F 3 , . . . FJ with the puφose of detecting different analytes of interest (Analyte,, Analytej, Analytej, . . . Analyte in a sample solution 238. In the depicted embodiment, the device works as otherwise herein described, but each tracer molecule (e.g. Tracer Ab,, Tracer Ab 2 , Tracer Ab 3 , . . . Tracer Ab.) is labeled with a different colored flourophore (F l5 F 2 , F 3 , . . . FJ. The waveguide is iUuminated by one or more different wavelengths of Ught 218 appropriate to excite aU the fluorophores located within the evanescent region of the waveguide. In one configuration, the emissions from the different fluorophores are distinguished using bandpass filters. Light rays 248, 249 and 250 are emitted from the respective labels on the tracer molecules. This Ught then passes through a lens 252 coUimates the emitted Ught onto a band pass filter 254 selective for the wavelength emitted by the particular tracer molecule label, in the depicted case, Tracer Ab,. A filter switching member, such as a wheel 256, houses, for example, three different band pass filters — each selective for a different fluorophore label. Thus, only the Ught rays 248 emitted by Tracer Ab, pass through the filter 254. If spatial resolution is desired in addition to wavelength selection, the Ught 248 passing through the filter 254 passes through a second lens 258 which images the Ught 248 onto a spatiaUy-resolved photodetector 260 such as a CCD or diode array. If only wavelength resolution is desired, the photodetector 260 may be a single spatiaUy-integrating device, and lens 258 may be optionaUy omitted Altematively, the wavelength selectivity may be accompUshed by one of several means instead of a filter wheel, such as employing a diffraction grating, a prism, or an acousto-optical modulator to angularly separate the different emitted wavelengths and thus direct them to separate individual photodetector elements whose outputs are representative of the signal strengths in each wavelength band. In another arrangement which avoids the use of the rotating filter wheel, stationary beam spUtters are employed to direct portions of the emitted Ught through stationary filters placed in front of individual photodetector elements. Altematively, if the excitation wavelengths of the different fluorophores are sufficiently separated without appreciable overlap, the Ught source may sequence in time through each excitation wavelength. The emitted Ught at any given time is related to the signal strength of the fluorophore set whose excitation wavelength is chosen at that particular time, and no further wavelength selective devices, such as filters, are needed. The invention is further explained by the foUowing illustrative examples. EXAMPLES EXAMPLE I A waveguide with integrated lenses, such as that depicted in FIGs. 6 & 7, was injection molded in a clean environment from a transparent, general purpose polystyrene. The waveguide had a length of 38 mm, and a width of 25 mm. The thickness 176 of the planar surface 170 was a consistent 0.5 mm. The ridge or "shelf had a height of 1.3 mm. The front lens and rear lens had bottom edges co- planar with their respective centers of curvature. The front lens horizontal angle 262 was about 15°. The rear lens horizontal angle 264 was about 19°. The radu of curvature of the front and rear lenses were about 3.2 mm and 1.6 mm respectively. The mean angle θ of the front lens was 21 °. The mean angle of the rear lens was about 24°. EXAMPLE π A flow ceU top, such as that depicted in FIGs. 1-3, and 8, was made of hard black anodized 6061-T6 aluminum. It contained three reservoirs each of which had a 0.25 mm (0.010 in.) thick wall surrounding it, a flat floor in middle, two half- capsule shaped recesses at either end 1.6 mm (1/16 in.) in width, and ports 1.6 mm (1/16 in.) in diameter running into the center of each recess. The ports opened into a #10-32 (standard thread, not NPT) connector which ran out to the opposite face of the flow ceU and was 5.1 mm (0.200 in.) deep. A 90° countersink 266 (FIG. 2) was given at the surface of the port connector (a plastic barbed tubing connector screwed into the port connector and sealed on the countersink). On both sides of the array of reservoirs were two raised platforms which were referred to as lands 268, 270. Each land had three holes mnning through the thickness of the part. The four #31 clamping holes 272, 274, 276, 278 were formed (i.e. driUed through). The two apertures 178, 180 were driUed and reamed to achieve a close sUding fit with 2.4 mm (3/32 in.) nominal four-sided pins 182, 184 press fit into the second frame member 186. EXAMPLE UI A gasket 162, such as that depicted in FIGs. 4, 5, and 11, was made as a composite stmcture laminated from 1.6 mm (1/16 in.) siUcone rubber sheeting and 0.076 mm (0.003 in.) self-adhesive FEP film (total thickness: 1.676 mm (0.066 in.) nominal). Its outer dimensions were about 25 mm (1 in.) by 25.40 mm (1.000 in.) and it had three intemal openings which corresponded to the flow ceU reservoirs. The gasket was produced using a waterjet cutter and was seated on the flow ceU such that the FEP layer faced away from the flow ceU surface. EXAMPLE IV A second member 186, such as that depicted in FIGs. 4, 10, 12, 13 and 18 was made from hard black anodized 6061-T6 aluminum. It contained three intemal openings 280, 282, 284 which corresponded to the three reservoirs 102, 104, 106 of the flow ceU 100 (but were sUghtly longer). The intemal openings were positioned in a shaUow depression (0.46 mm (0.018 in.) deep) 286 which seated the waveguide, and aUow evanescent Ught emitted from any reacting tracer molecules on the waveguide surface to be detected by the detection means 230. As with the flow ceU 102, two lands 288, 290 resided on either side of the intemal openings, each land having three holes. Four clamping holes (e.g. 208, 210) were driUed through and tapped to #4-40 to receive thumb screws. Two apertures were driUed through to receive a 3.2 mm (1/8 in.) nominal dowel which was press fit into the hole. The dowel was stainless steel and projected approximately 7 mm (0.280 in.) above the top surface and 6.6 mm (0.260 in.) below the bottom surface of the second member. The exposed dowel was machined down to 2.4 mm (3/32 in.) nominal diameter and was squared off to produce a low -friction locating pin 182, 184. The bottom aspect of the secondary member was miUed out to provide a single large window 292 for emitted fluorescence from the waveguide. The front surface of the secondary member contains two mounting holes 294, 296 #2-56 driUed and tapped to a depth of about 4 mm (0.15 in.) to fasten the flow ceU registration plate 212. The registration plate, depicted in FIGs. 14, is a simple U- shaped bracket which was produced from 1.6 mm (1/16 in.) nominal 6061-T6 aluminum plate. It contained two #42 holes which corresponded to the holes on the front of the second member. The puφose of the registration plate was to provide a lateral hard-stop for the waveguide during clamping into the flow ceU. The upright arms of the part contact the waveguide at the outer edges of the input coupling lens while aUowing unimpeded coupling with the incoming laser beam. EXAMPLE V A stage 202, best depicted in FIGs. 15-17, is a plate-like stmcture which was made from hard black anodized 6061 -T6 aluminum. The receiving site 298 of the part was down-stepped and contains a single rectangular intemal opening. Three #2-56 driUed and tapped holes 300, 302, 304 were positioned on the front of the part which were used to fasten a laser beam mask (not shown). Two #10-32 holes 306, 308 were driUed to a depth of 19 mm (0.750 in.) on the right side of the part to mount the stage to the test apparatus. The intemal opening had beveled front 310 and rear 312 sides. Located on either side of the window were two 2.4 mm (3/32 in.) apertures (analogous to those in the flow ceU) which aUowed the clamped flow ceU and second member to be mounted to the stage 202. EXAMPLE VI The waveguide and integrated lenses of EXAMPLE I, the flow ceU top of EXAMPLE π, the gasket of EXAMPLE HI, the second member and registration plate of EXAMPLE IV, and the stage of EXAMPLE V were associated as in FIG. 4. A hard, black anodized coating was added to the parts with a nominal buUd-up of 0.0025 mm (0.001 in.), however, the assembly 190 was checked as much as possible prior to anodization to maximize the probabiUty of proper fit. The gasket was cut to conespond to the outside dimensions of the three reservoirs 102-106 of the flow cell top 100. The siUcone rubber surface contacted the flow ceU and the FEP surface contacted the waveguide when the assembly was clamped. Any flash present on the gasket which interfered with seating or which came over the top of the waUs was carefuUy trimmed back with a razor knife (the top of the dam was exposed to the surface of the waveguide, but did not touch it; flash from the gasket can interfere with proper clamping). The waveguide 164 was seated in the shaUow depression in the second member 186. The waveguide fit into the depression with minimal lateral movement, but without compression or pinching. A smaU amount (e.g. less than about 0.1 mm (0.003 in.)) of lateral movement was acceptable. If pinching occurred, additional milling to the waUs of the depression was necessary to aUow proper seating. To insure that the waveguide 164 was reproducibly positioned directly beneath the flow ceU, it was butted up against the registration plate 214 after being seated in the secondary member 186. Contact with the registration plate 214 was only at the outermost comers of the front lens; no contact with the injection mold stub on the underside of the front lens occurred (injection mold may be designed to place resultant stub at an altemate location). The front of the second member may need to be miUed to ensure the waveguide sits directly beneath the flow ceU when in contact with the registration plate. After seating the gasket into the flow cell and positioning the waveguide on the second member, the flow ceU was mated with the second member by engaging the locating pins into the apertures in the flow ceU. When fuUy engaged, but without adding additional clamping force (i.e., the gasket was not compressed), there was a 0.15 mm (0.006 in.) gap between the lands of the flow ceU and the lands of the second member. When fuUy clamped with four thumb screws such that the lands are in contact, the gasket is compressed 0.15 mm (0.006 in.). The flow cell and second member readUy separated using manual force; no sticking occurred, but a thin coat of lubricant may be used on the pins if necessary. It may be desirable to shghtly countersink the press fit hole on the second member and/or the aperture on the flow ceU to avoid burrs or bulges which might impair mating of the two parts. The locating pins from the bottom of the second member readUy aUgned and fit into the apertures on the stage. No perceptible play existed between the parts when mated. As with the flow cell and second member fit, the second member and stage readUy separated using moderate manual force. EXAMPLE Vu As shown in FIG. 20, onto a polystyrene sheet waveguide 316 (Scenic Materials, 125 μm thick, n = 1.60) was adhered a piece of holographic diffraction grating 314 (Edmund Scientific #43226, 2400 g / mm, Al/NoF 2 coated) with an index-matching cement 320 consisting of 10% polystyrene chips dissolved in toluene. IncoupUng into the resulting waveguide was achieved with a heUum-neon laser at an approximately 5° angle. The resulting coupling stmcture was thinner than a molded lens input coupler. EXAMPLE VU! A. Waveguide Fabrication: Thin film channel waveguide layers of SiON were formed on grating etched quartz wafers in a manner such as that described in Walker et al. "Corning 7059, siUcon oxynitride, and siUcon dioxide thin-film integrated optical waveguides: In search of low-low, non-fluorescent reusable glass waveguides", Appl.Spectrosc. 46: 1437-1441 (1992). Briefly, the wafers were introduced into a plasma impulse chemical vapor deposition ("PECVD") chamber (Texas Instruments) operating at 300° C, 50 W, and 1.25 Torr. The gases used were SiH,, sUane, nitrogen, ammonia, and nitrous oxide. SiON films were produced at a deposition rate of approximately 590 A/minute for 25.42 min. , yielding a film thickness of 1.5 μ. As described in Plowman et al., "Femtomolar sensitivity using a channel-etched thin film waveguide fluoroimmunosensor", Biosensors & Bioelectronics. 11: 149-160 (1996), nine paraUel 1 mm X 65 mm channels are formed when etched into the SiON from an additional layer of photoresist. The resulting waveguide wafers were diced (Disco DAD-2H/6) into three rectangular pieces measuring about 2.5 cm X 7.8 cm each with three waveguiding channels (although in this EXAMPLE, grating waveguides without channels were employed). B. Grating Fabrication: Quartz wafer substrates (Hoya, Woodcliff Lake, NJ, QZ 4W55-325-UP) measuring 100 mm in flat length and 0.5 mm in thickness were cleaned at room temp, in a 6% solution of H 2 O 2 in H 2 SO 4 . The wafers then received a HMDS vacuum vapor prime, were spin-coated with photoresist (Shipley SNR 200, MA, USA) at a rate of 4200 φm for 1 min. to produce a film approximately 0.7 mm thick and then soft-baked at 100° C for 1 min. The negative resist was exposed to define 0.7 μ periodic groove patterns using ultraviolet Ught (248 nm KrF excimer laser, Laser Stepper GCA-ALS, Tukesbury, MA, USA) with a chrome-quartz mask (DuPont, Kokomo, IN, USA) at a dose of 20 mJ/cm 2 . The wafers received a post- exposure bake at 130° C for 90 sec. Photoresist was developed in a solution of Shipley MF 312 (MA, USA) at a normalization of 0.17, then spun dry. A 60 sec. 100° C post-development bake was then performed. The resulting photoresist pattern was reactive ion-etched (8110 Reactive Ion Etcher, AME, Santa Clara, CA, USA) with O 2 and CHF 3 gases at an etch rate of 450 A min. Etch times of 13.33, 17.77 and 22.22 min. were employed to produce grating etch depths of 0.6, 0.8, and 1.0 μ giving aspect ratios of 0.8, 1.0, and 1.4, respectively. Residual photoresist was removed by O 2 plasma. C. Testing: When used as Ught couplers for thin film IOWs, the gratings were roughly half as efficient as prisms in coupling laser Ught (the Ught source being a 2 mW He- Ne laser (632.8 nm, 10 mW maximum, MeUes-Groit, Uniphase, Manteca, CA, USA). Both approaches (i.e. prism and grating) detected samples with femtomolar concentration above background. EXAMPLE IX An evanescent wave assay apparatus of the instant invention was compared with a standard ABBOTT STAT CK-MB IMx system. A. Clinical Samples 63 clinical samples (submitted by physicians for hospital CK-MB testing) were obtained, and were assayed for CK-MB using the ABBOTT IMx system. The values thus obtained for each clinical sample was noted. Each sample was aUquoted into 0.550 ml sample size, assigned a lot number, and stored at -20° C. B. Instrumentation / Assay standardization: The samples were then assayed on a CK-MB system utilizing the biosensor 190 of the instant invention. CK-MB specificity was determined by spiking CK-MB stripped plasma (sohd-phase absoφtion) with 1000 ng/ml CK-MM and CK-BB. Cross-reactivity with CK-MM was less than 0.1 % . Standards were prepared by addition of a known mass quantity of recombinant CK-MB (Genzyme). C. Monoclonal antibodies Monoclonal antibodies were as described by J. Ladenson, Clinical Chemistry, vol. 32, pp. 657-63 (1986). The capture antibody was coated onto the waveguide's surface with 2 hour incubation at room temp., at a concentration of 0.1 micromolar (dUuted in PBS A buffer). After the incubation, each waveguide was washed once with PBS A, and then incubated with 1 ml of post-coating solution (0.5 % bovine serum albumin ("BSA")/0.1 % trehalose/PBSA) at room temp, for 1 hour. The post-coating solution was discarded and the waveguides dried in a vacuumed desiccator for an hour. E. Specific Performance The conelation of an apparatus according to the instant invention with the ABBOTT IMx assay for an CK-MB assay is graphicaUy depicted in FIGs. 21 & 22. The results showed the two sets of values to be comparable at a correlation coefficient of 0.98, and the sample population contained a higher proportion of samples below 50 ng/ml, the range in which the critical decision point for clinical evaluation has been estabhshed in the clinical laboratory environment. FIG. 21 plots the value obtained with the instant invention (y axis, in ng CK-MB/ml) against the ABBOTT IMx value on the x-axis (also ng CK-MB/ml). FIG. 22 depicts the double logarithm plot of the data from FIG. 21 (again, instant invention y-axis, ABBOTT IMx x-axis). EXAMPLE X The preceding example was continued to further estabUsh the utiUty of the system, and to incoφorate more extensive studies of known interfering substances (e.g. hemoglobin and bilirubin), known CK-MB concentrations were analyzed (20 ng/ml CK-MB into human plasma), with concentrations of hemoglobin (15 mg/ml) and bilirubin (1 mg/ml) known to interfere with immunofluourescence assays. The system was still able to detect 100% of the CK-MB. Characteristics of the described and Ulustrated embodiments are intended for illustrative puφoses, and are not to be considered limiting or restrictive. It is to be understood that various adaptations and modifications may be made by those skiUed in the art to the embodiments illustrated herein, without departing from the spirit and scope of the invention, as defined by the foUowing claims thereof.

Claims: Claims What is claimed is: 1. An improvement in a biosensor of the type for use in an apparatus for analyzing a biological liquid, the biosensor comprising: a waveguide having at least one planar surface, said waveguide associated, in liquid tight attachment, with a first member, said first member, in conjunction with the waveguide, defining walls of reservoirs for containing the biological liquid while, a planar surface of the waveguide defines a floor of said reservoirs, the floor being associated in part with capture molecules, the improvement comprising reservoir walls formed of an inert, opaque material. 2. The improvement of claim 1 wherein said inert, opaque material is metal. 3. The improvement of claim 1 wherein the entire first member is made of metal. 4. The improvement of claim 1 wherein said first member has ports for oscillating liquid into and out of a reservoir. 5. The improvement of claim 1, wherein the biosensor further comprises a gasket positioned to cushion the attachment of the first member to the waveguide. 6. The improvement of claim 5, wherein the gasket is a laminate of elastic material and a synthetic resin polymer material. 7. The improvement of claim 1 wherein the waveguide is made of an optical material selected from the group of optical materials consisting of plastic, quartz, and glass. 8. The improvement of claim 8 wherein the waveguide is flat, and is associated with a rear lens for reading Ught passing through the waveguide to monitor coupling efficiency and beam quality. 9. The improvement of claim 1 wherein the biosensor further includes a second member, the waveguide being sandwiched between said first member and said second member. 10. The improvement of claim 9 wherein the biosensor further includes a registration plate. 11. The improvement of claim 10 placed in an assay apparatus wherein the biosensor further includes a third member, the third member having a means for connecting the biosensor to the assay apparatus. 12. The improvement of claim 7 wherein the waveguide is flat, and is associated with a grating for coupling Ught into the waveguide. 13. A waveguide comprising: a front ramp with associated lens end for receiving Ught, a rear ramp with associated lens for transmitting Ught out of said waveguide, and a planar portion having first and second paraUel planar surfaces for transmitting light from the front ramp to the rear ramp so as to transmit Ught received at the lens associated with the front ramp through the lens associated with the rear ramp. 14. The waveguide of claim 13 wherein capture molecules are associated with the first planar surface of the planar portion. 15. The waveguide of claim 13 wherein the waveguide is made from an optical plastic, and the front ramp is angled away from the planar portion's plane at a mean angle of from about 15° to 32°. 16. A biosensor of the type for use in an apparatus for analyzing a biological Uquid, the biosensor comprising: a waveguide having at least one planar surface and being opticaUy associated with a rear lens oriented for reading light passing through the waveguide, to monitor coupUng efficiency and beam quaUty, said waveguide further associated in Uquid tight attachment with a first member, said first member, in conjunction with the waveguide, defining metal waUs of a pluraUty of reservoirs for containing the biological Uquid while a planar surface of the waveguide defines a non- metal floor of said pluraUty of reservoirs, the floor being associated in part with capture molecules, a gasket positioned to cushion the attachment of the first member to the waveguide, and a second member, the waveguide being sandwiched between the first and second members. 17. The biosensor of claim 16 wherein said first member has ports for infusing and draining Uquid into and out of a reservoir. 18. A biosensor of the type for use in an apparatus for analyzing a biological Uquid, the biosensor comprising: a waveguide having at least one planar surface and being opticaUy associated with a rear lens oriented for reading Ught passing through the waveguide, to monitor coupUng efficiency and beam quaUty, said waveguide further associated in Uquid tight attachment with a first member, said first member, in conjunction with the waveguide, defining at least one reservoir for containing the biological Uquid while a planar surface of the waveguide defines a floor or ceiling of said reservoir, the planar surface being associated in part with capture molecules, and an inlet and outlet in fluid communication with said reservoir for infusing and draining said biological Uquid into said reservoir so as to aUow the biological Uquid to contact said capture molecules. 19. An improvement in an apparatus for analyzing a biological Uquid, said apparatus being of the type having: a Ught source; a biosensor comprising: a waveguide having at least one planar surface, and being further associated in Uquid tight attachment with a first member, said first member, in conjunction with the waveguide, defining at least one reservoir for containing the biological Uquid, the planar surface being associated in part with capture molecules, and an inlet and outlet in fluid communication with said reservoir for infusing and draining said biological Uquid into and out of said reservoir so as to aUow the biological Uquid to contact said capture molecules; and a Ught detector for detecting Ught emitted through said planar surface; the improvement comprising orienting said biosensor in such a way that the planar surface is generaUy horizontal and level with a surface upon which the apparatus sits and so that the planar surface forms a ceiling to said reservoir.

Inventors: CHRISTENSEN DOUGLAS A, HERRON JAMES A, MCEACHERN RICHARD D, POLLAK VICTOR A, SIMON ERIC M, CHRISTENSEN, DOUGLAS, A., HERRON, JAMES, A., MCEACHERN, RICHARD, D., POLLAK, VICTOR, A., SIMON, ERIC, M.
Applicants: CHRISTENSEN DOUGLAS A, HERRON JAMES A, MCEACHERN RICHARD D, POLLAK VICTOR A, SIMON ERIC M, UNIV UTAH RES FOUND, CHRISTENSEN, DOUGLAS, A., HERRON, JAMES, A., MCEACHERN, RICHARD, D., POLLAK, VICTOR, A., SIMON, ERIC, M., UNIVERSITY OF UTAH RESEARCH FOUNDATION
Application year: 1997
Main classification: G01N21
IPC codes: G01N21, G01N33, G02B6