Abstract:
Light-sensing systems and methods thereof are described. A light source illuminates target areas arrayed on a surface. Light guides receive light reflected from the target areas. The amount of light reflected from a target area corresponds at least in part to the composition of a substance associated with that target area. Detectors receive reflected light carried by the light guides.

Description:
TECHNICAL FIELD  
       [0001]     Embodiments in accordance with the invention pertain to light sensors.  
       BACKGROUND ART  
       [0002]     In surface plasmon resonance (SPR) spectroscopy, light from a light source is directed onto a metal film and the intensity of the light reflected from the metal film is measured. The intensity of light reflected from the metal film depends on the angle of incidence or the wavelength of light from the light source, and also depends on the refractive index of a substance on the side of the metal film that is opposite the side facing the light source.  
         [0003]     SPR can be used to perform highly sensitive measurements of chemical and biological substances. For example, SPR can be used to measure interactions between proteins. A first protein (e.g., a ligand) is attached to the metal film on the side of the film not facing the light source, and a second protein (e.g., an analyte) is placed in solution and flowed over the first protein. If the first and second proteins bind to some degree, a composition of the first and second proteins is formed on the surface of the metal film away from the light source. The refractive index of the composition depends on the relative amounts of the first and second proteins, and will vary with time if the relative amounts of the first and second proteins change with time. The metal film is illuminated with light at different wavelengths or different angles of incidence. By measuring the intensity of the reflected light at those different angles of incidence or wavelengths, the amount of binding can be derived. The measurements can be repeated so that the amount of binding as a function of time can be plotted. Association and dissociation rates for the two proteins can be determined in this manner. These rates are of key interest in the field of drug discovery, for example.  
         [0004]     Multiple experiments can be conducted at the same time by arraying a number of samples on the surface of the metal film. For example, different types of ligands can be tested at the same time to measure binding affinity with a particular analyte. Light reflected from the samples can be imaged using a camera. In essence, the camera takes pictures of the array of samples at a frequency that corresponds to the frame rate of the camera. The images are then processed to measure the intensity of light reflected from each sample versus time.  
         [0005]     A camera used for SPR may use an imager consisting of a 320×256 array of pixels. For each image frame, the digital values of the pixels (e.g., 81,920 pixel values for a 320×256 array of pixels) are transferred to a computer system for processing. For each sample tested, the pixel values that correspond to that sample are extracted from the other values. The pixel values extracted for a sample are then averaged to provide a data point for that sample.  
         [0006]     It is desirable to increase the number of samples that can be tested at a time, so that testing can be completed more efficiently. It is also desirable to increase the rate at which data is collected, allowing information about the interaction between substances (e.g., proteins) to be captured in more detail. The data collection rate can be increased by increasing the rate at which the samples are imaged. This can be achieved using a camera capable of operating at higher frame rates.  
         [0007]     However, increasing the number of samples and the frame rate increases the amount of data that needs to be transferred and processed. Tests may be conducted over a period of days, so a tremendous amount of data can be collected, placing a heavy burden on the resources used to transfer and process the data. Additional computational resources can be used to alleviate data handling and processing loads, but that can increase the cost of testing.  
         [0008]     Also, cameras that operate at higher frame rates are quite expensive. For example, a camera that operates at 60 frames per second (fps) may cost around $20,000, while a camera that operates at 400 fps may cost around $50,000. Cameras can have other shortcomings as well. For example, cameras have a limited full well capacity (that is, they can only store a limited number of electrons per pixel before becoming saturated). Also, cameras have a relatively low quantum efficiency (the rate at which photons are converted to electrons) of less than 20 percent.  
       SUMMARY  
       [0009]     Accordingly, a system and/or method that can be used with a sufficiently large number of samples and that can permit higher data collection rates, without substantially increasing either cost or data handling and processing loads, would be valuable.  
         [0010]     Embodiments in accordance with the invention pertain to light-sensing systems and methods thereof. In one embodiment, a light source illuminates target areas arrayed on a surface. Light guides receive light reflected from the target areas. The amount of light reflected from a target area corresponds at least in part to the composition of a substance associated with that target area. Detectors receive reflected light carried by the light guides.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. The drawings referred to in this description should not be understood as being drawn to scale except if specifically noted.  
         [0012]      FIG. 1  illustrates one embodiment of a light-sensing system in accordance with the invention.  
         [0013]      FIG. 2  illustrates sample areas arrayed on a surface in one embodiment in accordance with the invention.  
         [0014]      FIG. 3  illustrates a second embodiment of a light-sensing system in accordance with the invention.  
         [0015]      FIG. 4  illustrates a third embodiment of a light-sensing system in accordance with the invention.  
         [0016]      FIG. 5  illustrates a fourth embodiment of a light-sensing system in accordance with the invention.  
         [0017]      FIG. 6  illustrates a fifth embodiment of a light-sensing system in accordance with the invention.  
         [0018]      FIG. 7  illustrates a sixth embodiment of a light-sensing system in accordance with the invention.  
         [0019]      FIG. 8  illustrates a seventh embodiment of a light-sensing system in accordance with the invention.  
         [0020]      FIG. 9  is a flowchart of one embodiment of a method of sensing reflected light in accordance with the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Reference will now be made in detail to various embodiments in accordance with the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the invention.  
         [0022]      FIG. 1  illustrates a light-sensing system  10  in one embodiment in accordance with the invention. In one embodiment, system  10  is used for surface plasmon resonance (SPR) spectroscopy. In the present embodiment, system  10  includes light source  11 , optically transmissive elements  13  and  14 , metal film  15 , detector array  18 , exemplary detector  19 , and light guides (exemplified by light guide  20 ) between metal film  15  and detector array  18 .  
         [0023]     Optically transmissive element (e.g., prism)  13  is made up of a transparent material. In the example of  FIG. 1 , and in other examples herein, optically transmissive element  13  is illustrated as being roughly triangular-shaped (in cross-section); however, the present invention is not so limited. In general, optically transmissive element  13  has a higher index of refraction than air, and as such it functions to increase the momentum of incident light  12  to match the momentum of the light to the momentum of a plasmon wave created in the metal film  15 .  
         [0024]     In one embodiment, optically transmissive element  14  is a transparent plate or slide that supports the metal film  15 . Metal film  15  may be embodied as a coating that is applied to optically transmissive element  14 . In one embodiment, metal film  15  is a thin film of gold; silver can also be used.  
         [0025]     Coupled to the surface of the metal film  15 , on the side of the film facing away from light source  11 , are sample areas exemplified by sample area  16 . In the present embodiment, sample area  16  and the other sample areas identify the positions at which ligands can be placed. Different ligands may be used in different sample areas. One or more types of analytes can be presented to the ligands in buffer chamber  17 . In one embodiment, an analyte is placed in solution and flowed through buffer chamber  17  over the sample areas.  
         [0026]     Light source  11  can be an ordinary light source with suitable filters and collimators. Alternatively, light source  11  can be a laser or a superluminescent light emitting diode (SLD). Other types of light sources may be used.  
         [0027]     Also, multiple light sources may be used, with each light source placing a beam of light on each area of the surface of metal film  15  that corresponds to a respective sample area (e.g., there may be one light source per sample area). Alternatively, a diffractive plate can be placed between light source  11  and the sample areas, so that the light from the light source is split into multiple beams of light, each beam of light illuminating an area on the surface of metal film  15  that corresponds to a respective sample area.  
         [0028]     In one embodiment, the wavelength of light emitted by light source  11  can be varied. In another embodiment, light source  11  can be moved so that the angle of incidence θ (the angle formed by incident light  12  and a vector that is normal to the plane of metal film  15 ) can be varied.  
         [0029]     Light source  11  transmits light  12  onto and through optically transmissive elements  13  and  14  to metal film  15 . In the embodiment of  FIG. 1 , light reflected from metal film  15  is carried by a number of light guides (exemplified by light guide  20 ) to detector array  18 , which includes a number of detectors exemplified by detector  19 .  
         [0030]     In one embodiment, detector array  18  is a linear array. In one embodiment, a V-groove assembly with a pitch that corresponds to the pitch of the detectors in detector array  18  is used to align the light guides with the detectors. In one embodiment, the detectors (e.g., detector  19 ) are photodiodes. In one embodiment, the light guides (e.g., light guide  20 ) are optical fibers. The use of a system such as system  10  instead of a system that uses a camera, for example, can result in significant cost savings because the cost of a detector array may be orders of magnitude less than the cost of a suitable camera. As will be discussed further below, embodiments in accordance with the invention provide other advantages as well.  
         [0031]     The number of light guides generally corresponds to the number of sample areas, and the number of detectors generally corresponds to the number of light guides; however, the invention is not so limited. In one embodiment, each light guide is associated with a single sample area, and each detector in detector array  18  is associated with a single light guide (and hence with a single sample area). In such an embodiment, the light reflected from the area of metal film  15  that corresponds to sample area  16  will be captured by light guide  20 , and carried by light guide  20  to detector  19 , for example. Light reflected from other areas on metal film  15 , corresponding to other sample areas, will be similarly captured by a corresponding light guide and carried to a respective detector.  
         [0032]     The light guides can be placed sufficiently close to metal film  15  so that the light reflected from an area on metal film  15  can be coupled into a respective light guide without significant crosstalk with light reflected from other areas. For example, the light guides can be pressed against or nearly against optically transmissive element  13 .  
         [0033]     In one embodiment, the cross-sectional area of a light guide (e.g., light guide  20 ) is not more than the size of a sample area (e.g., sample area  16 ). More precisely, the cross-sectional area of a light guide is less than the size of the area on metal film  15  from which light associated with a particular sample area is reflected. In general, a light guide is sized and positioned so that it does not capture light reflected from outside a defined area on metal film  15 . For example, light guide  20  is sized and positioned so that it does not capture light reflected from metal film  15  outside of the area on metal film  15  associated with sample area  16 .  
         [0034]     System  10  is now described in operation for SPR spectroscopy. Ligands are coupled to metal film  15  (e.g., at sample area  16 ). An analyte solution is flowed past sample area  16  in buffer channel  17 . Light from light source  11  is incident on metal film  15 , having passed through optically transmissive elements  13  and  14 . Light reflected from the area on metal film  15  that corresponds to sample area  16  is coupled into light guide  20 . Light carried by light guide  20  is received at detector  19 . This process continues over time until the test is completed.  
         [0035]     The amount of light reflected from metal film  15  is a function of the refractive index of the substance at sample area  16  and the wavelength or angle of incidence of the incident light  12 . The refractive index of the substance at sample area  16  is in turn a function of the degree to which the ligand and the analyte interact (e.g., the degree to which the analyte and the ligand bind). The angle of incidence θ or the wavelength of the incident light  12  can be varied to produce a condition that resonates the free electrons at the reflecting surface of metal film  15 . At the SPR condition, the intensity or amount of light reflected by metal film  15  is decreased. The amount of reflected light received at detector  19 , along with the angle of incidence or the wavelength of the incident light  12 , can be used to determine the amount of interaction between the ligand and the analyte at sample area  16 . System  10  functions in a similar manner with regard to the other sample areas, light guides and detectors.  
         [0036]      FIG. 2  illustrates a number of sample areas, including sample area  16 , arrayed on a chip or substrate  25  in one embodiment in accordance with the invention. Different numbers of sample areas, perhaps arranged differently than shown in  FIG. 2 , can be used. In one embodiment, with reference also to  FIG. 1 , chip  25  is mounted to the surface of metal film  15  that faces away from light source  11 . In one embodiment, a light guide and a detector are associated with each of the sample areas in chip  25 . Thus, for example, a 4-by-4 array of samples can be coupled to a 16-element detector array (e.g., a linear array of 16 detectors). Additional detector arrays can be used if the number of samples is greater than the number of detectors in a single array.  
         [0037]      FIG. 3  illustrates a light-sensing system  30  in one embodiment in accordance with the invention. In one embodiment, system  30  is used for SPR spectroscopy.  
         [0038]     In the present embodiment, system  30  includes light source  11 , optically transmissive element (e.g., slide or plate)  14 , metal film  15 , detector array  18 , exemplary detector  19 , and light guides (exemplified by light guide  20 ) between metal film  15  and detector array  18 , previously described herein.  
         [0039]     System  30  also incorporates a group  31  of light guides (exemplified by light guide  32 ) that carry light from light source  11  to the sample areas. In one embodiment, the light guides are optical fibers. The light guides in the group  31  can be pressed against or nearly against the areas on metal film  15  that correspond to the sample areas. In an SPR application, a collimator can be placed between the light guides and the metal film  15 .  
         [0040]     The light guides that receive reflected light (e.g., light guide  20 ) can also be pressed against or nearly against areas of metal film  15  corresponding to the sample areas. In one embodiment, a block  33  (e.g., a plastic block) can be used to hold the light guides that deliver light to metal film  15  and the light guides that receive light reflected from metal film  15  in place relative to the areas on metal film  15  that correspond to the sample areas. The group  31  of light guides can be moved within block  33  so that the angle of incidence of the incident light can be varied.  
         [0041]     The number of light guides in the group  31  of light guides generally corresponds to the number of sample areas; however, the invention is not so limited. In one embodiment, each of the light guides in the group  31  of light guides is associated with a single sample area. For example, light guide  32  is associated with sample area  16 .  
         [0042]     In another embodiment, in place of block  33 , an optically transmissive element  13  ( FIG. 1 ) can be interposed between the group  31  of light guides and the metal film  15 , and as such also between the metal film  15  and the light guides that receive reflected light (exemplified by light guide  20 ). In such an embodiment, the incident light guides (e.g., light guide  32 ) and the light guides that receive reflected light (e.g., light guide  20 ) can be pressed against or nearly against the optically transmissive element  13 .  
         [0043]      FIG. 4  illustrates a light-sensing system  40  in one embodiment in accordance with the invention. In one embodiment, system  40  is used for SPR spectroscopy.  
         [0044]     In the present embodiment, system  40  includes light source  11 , optically transmissive element (e.g., slide or plate)  14 , metal film  15 , detector array  18 , exemplary detector  19 , and light guides (exemplified by light guide  20 ) between metal film  15  and detector array  18 , previously described herein. System  40  also includes a group  41  of optically transmissive elements (exemplified by prism  43 ) composed of a transparent material. In general, the number of elements in the group  41  corresponds to the number of sample areas; however, the invention is not so limited. In one embodiment, each of the optically transmissive elements in the group  41  is associated with a single sample area. For example, prism  43  may be associated only with sample area  16 .  
         [0045]     The optically transmissive elements (e.g., prism  43 ) in the group  41  are smaller than optically transmissive element  13  of  FIG. 1 , and so the light guides (exemplified by light guide  20 ) can be placed closer to metal film  15 . For example, light guide  20  can be pressed against or nearly against prism  43 .  
         [0046]     In one embodiment, each light guide is associated with a single optically transmissive element in the group  41  of optically transmissive elements. For example, light guide  20  may be associated only with prism  43 .  
         [0047]      FIG. 5  illustrates a light-sensing system  50  in one embodiment in accordance with the invention. In one embodiment, system  50  is used for SPR spectroscopy.  
         [0048]     In the present embodiment, system  50  includes light source  11 , optically transmissive element (e.g., slide or plate)  14 , metal film  15 , detector array  18 , exemplary detector  19 , and light guides (exemplified by light guide  20 ) between metal film  15  and detector array  18 , previously described herein.  
         [0049]     System  50  also includes a group  51  of optically transmissive elements (exemplified by prisms  53  and  55 ) composed of a transparent material. In general, the number of these elements corresponds to the number of sample areas; however, the invention is not so limited. In one embodiment, each of the optically transmissive elements in the group  51  is associated with a single sample area. For example, prism  53  may be associated only with sample area  54 , and prism  55  may be associated only with sample area  16 .  
         [0050]     System  50  also includes a group  56  of light guides (exemplified by light guide  52 ) that carry light from light source  11  to the optically transmissive elements (exemplified by prism  53 ). In one embodiment, these light guides are optical fibers. The light guides in the group  56  can be pressed against or nearly against the optically transmissive elements in the group  51 . For example, light guide  52  can be pressed against or nearly against prism  53 . In one embodiment, each of the light guides in the group  56  is associated with a single optically transmissive element in the group  51 . That is, for example, light guide  52  may be associated only with prism  53 . In an SPR application, a collimator can be placed between the light guides and the group  51  of optically transmissive elements.  
         [0051]     The light guides (exemplified by light guide  20 ) that carry light reflected from metal film  15  can also be placed closer to metal film  15 . For example, light guide  20  can be pressed against or nearly against prism  55 .  
         [0052]      FIG. 6  illustrates a light-sensing system  60  in one embodiment in accordance with the invention. In one embodiment, system  60  is used for SPR spectroscopy.  
         [0053]     In the present embodiment, system  60  includes light source  11 , optically transmissive element (e.g., prism)  13 , optically transmissive element (e.g., slide or plate)  14 , metal film  15 , detector array  18 , and detector  19 , previously described herein.  
         [0054]     System  60  also includes a number of light guides (exemplified by light guide  62 ) coupled to the detector array  18 . The number of lights guides generally corresponds to the number of sample areas, and the number of detectors generally corresponds to the number of light guides; however, the invention is not so limited. In one embodiment, each light guide is associated with a single sample area, and each detector in detector array  18  is associated with a single light guide (and hence with a single sample area), as previously described herein.  
         [0055]     In contrast to the embodiment of  FIG. 1 , for example, the light guides (e.g., light guide  62 ) do not extend up against or nearly up against the optically transmissive element  13 . Instead, in one embodiment, an imaging lens  61  is interposed between the light guides (e.g., light guide  62 ) and the metal film  15 , so that the ends of the light guides fall in the image plane (indicated as plane  65 ) of the imaging lens  61 . In another embodiment, a diffractive optical element can be used in place of imaging lens  61 .  
         [0056]     In the embodiment of  FIG. 6 , light reflected from the metal film  15  passes through imaging lens  61 . Imaging lens  61  in essence maps a position in the sensor plane into a position in the imaging plane  65 . For example, light reflected from the area of metal film  15  that corresponds to sample area  16  is reflected to lens  61 , which maps that light to a position  66  in the image plane  65 . Light guide  62  is positioned at the image plane  65  at the point  66  to receive light reflected from the area of metal film  15  that corresponds to sample area  16 . The light carried by light guide  62  is received at detector  19 .  
         [0057]      FIG. 7  illustrates a light-sensing system  70  in one embodiment in accordance with the invention. In one embodiment, system  70  is used for SPR spectroscopy.  
         [0058]     In the present embodiment, system  70  includes light source  11 , optically transmissive element (e.g., prism)  13 , optically transmissive element (e.g., slide or plate)  14 , metal film  15 , detector array  18 , and detector  19 , previously described herein.  
         [0059]     System  70  also includes a group  76  of light guides (exemplified by light guide  72 ) coupled to the detector array  18 . The number of lights guides generally corresponds to the number of sample areas, and the number of detectors generally corresponds to the number of light guides; however, the invention is not so limited. In one embodiment, each light guide is associated with a single sample area, and each detector in detector array  18  is associated with a single light guide (and hence with a single sample area), as previously described herein.  
         [0060]     Similar to the embodiment of  FIG. 6 , for example, the group  76  of light guides (e.g., light guide  72 ) do not extend up against or nearly up against the optically transmissive element  13 . In contrast to the embodiment of  FIG. 6 , a lens  71  is coupled to the end of each of the light guides. For example, lens  71  is coupled to the end of light guide  72 .  
         [0061]     In one embodiment, an imaging lens  61  is positioned so that light reflected from metal film  15  passes through lens  61  before reaching the group  76  of light guides. In such an embodiment, the group  76  of light guides are situated within the image plane of lens  61 .  
         [0062]     In the embodiment of  FIG. 7 , light reflected from the metal film  15  passes through imaging lens  61 . Imaging lens  61  in essence maps a position in the sensor plane into a position in the image plane of lens  61 . For example, light reflected from the area of metal film  15  that corresponds to sample area  16  is reflected to lens  61 , which maps that light to a position in the image plane  65  that corresponds to the position of lens  71 , which couples that reflected light to light guide  72 . The light carried by light guide  72  is received at detector  19 .  
         [0063]     In another embodiment, diffractive optical elements can be used instead of lenses such as lens  71 . An array of micro-lenses can be formed on a sheet of plastic, for example, and positioned up against or nearly up against the group  76  of light guides, such that each light guide is aligned with a respective micro-lens.  
         [0064]      FIG. 8  illustrates a light-sensing system  80  in one embodiment in accordance with the invention. In one embodiment, system  80  is used for SPR spectroscopy.  
         [0065]     In the present embodiment, system  80  includes light source  11 , metal film  15 , detector array  18 , and detector  19 , previously described herein. System  80  also includes a grating  84  to match the momentum of the light to the momentum of a plasmon wave created in the metal film  15 . In one embodiment, grating  84  provides support for metal film  15 . In such an embodiment, metal film  15  follows the contours of grating  84 . Light passes through the film  15  to the grating  84 .  
         [0066]     The features of system  80  can be combined with the other features described above. That is,  FIGS. 1 and 3 - 7  describe various features for delivering light from a light source to a surface and various features for capturing light reflected from the surface. Those light-delivery and light-capture features can also be used with the embodiments described in conjunction with  FIG. 8 . In particular, use of a grating such as grating  84 , for example, allows light guides used for delivering light to the surface, or for capturing light reflected from the surface, to be placed against or nearly against the areas of the surface that correspond to the sample areas (e.g., sample area  16 ).  
         [0067]     Also, for example, the features described in conjunction with  FIGS. 1 and 3  can be combined, or the features described in conjunction with  FIG. 6  or  7  can be combined with the features described in conjunction with  FIG. 3, 4  or  5 . In general, the features of each of the various embodiments described above can be used alone or appropriately combined with the features from one or more other embodiments.  
         [0068]     In addition to the cost savings mentioned above, embodiments in accordance with the invention provide a number of other advantages. For one, samples can be collected at a faster rate; that is, the sample rate is not limited by frame rate. Sample rates as high as five mega-samples per second are achievable. Thus, more time-wise continuous plots of test results can be generated.  
         [0069]     Also, a single data point (e.g., the detector output) is collected for each sample area, eliminating the transfer of large amounts of data for processing. This also eliminates the extraction and averaging of pixel values for each of the samples tested, simplifying processing.  
         [0070]     Furthermore, detectors (e.g., photodiodes) are more precise than cameras, measured in terms of the number of output bits. Also, cameras have limited full well capacity and may saturate if too much light is placed on the sample areas. Detectors are not subject to these limitations, in particular for the levels of light used in applications such as SPR.  
         [0071]     In addition, the quantum efficiency of detectors (e.g., photodiodes) is on the order of 75 percent, which is greater than the quantum efficiency of cameras. Thus, for a given amount of light, a detector will output a better signal than a camera.  
         [0072]      FIG. 9  is a flowchart  90  of a method of sensing light reflected from a surface in one embodiment in accordance with the invention. In step  91 , a plurality of areas on the surface (e.g., metal film  15  of  FIG. 1 ) are illuminated by a light source. The areas on the surface correspond to an arrangement of sample areas (e.g., sample area  16 ). In one embodiment, the sample areas are present on the side of the surface not facing the light source (e.g., as in  FIGS. 1 and 3 - 7 ); in another embodiment, the sample areas are on the side of the surface facing the light source (e.g., as in  FIG. 8 ).  
         [0073]     In one embodiment, light is transmitted to an area on the surface through an element (e.g., optically transmissive element  13  of  FIG. 1 ) that increases the momentum of the light. In another embodiment, there is a plurality of such elements (exemplified by prism  43  of  FIG. 4 ), where each of the elements is associated with a single area on the surface. In yet another embodiment, there is a grating (e.g., grating  84  of  FIG. 8 ) that matches the momentum of light to the momentum of a plasmon wave.  
         [0074]     In yet another embodiment, the light is transmitted to the surface via a plurality of light guides (e.g., light guide  32  of  FIG. 3 ).  
         [0075]     In step  92  of  FIG. 9 , the light reflected from areas on the surface is received into a plurality of light guides (e.g., light guide  20  of  FIG. 1 ). In one embodiment, the reflected light passes through a lens (e.g., lens  61  of  FIG. 6 ) before reaching a light guide. In one such embodiment, a lens is coupled to each of the light guides (e.g., lens  71  is coupled to light guide  72  of  FIG. 7 ). In another embodiment, a diffractive optical element or an array of diffractive optical elements can be used instead of the lens or lenses.  
         [0076]     In step  93  of  FIG. 9 , light carried by the light guides is received at a plurality of detectors (e.g., detector array  18  of  FIG. 1 ). In an SPR embodiment, the amount of reflected light received at the detectors is used to determine an amount of interaction between a ligand and an analyte that are presented to each other below the reflecting surface.  
         [0077]     The invention is thus described in various embodiments. While the invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the following claims.