Abstract:
A method of sensing at least one target on a receptor having a substrate and a translucent coating includes minimizing interference fringe patterns in an image of the target. The method also includes passing the image of the target through an imaging system intermediate the receptor and a detector.

Description:
PRIORITY INFORMATION 
   The present application claims the benefit of U.S. Provisional Application No. 60/844,842, filed Sep. 15, 2006. The present application expressly incorporates by reference, U.S. Publication No. 2003/0112446, published Jun. 19, 2003 (U.S. application Ser. No. 10/282,274, filed Oct. 28, 2002). 

   FIELD OF THE INVENTION 
   The present invention generally relates to biomolecular detection and a system thereof and, more particularly, to locating an imaging system optically intermediate an illuminated receptor and a detector, wherein the receptor is illuminated with coherent light. 
   BACKGROUND OF THE INVENTION 
   Technologies capable of biological sensing can offer substantial advances in the medical diagnostics field by introducing the capacity to detect molecular targets in a label-free and rapid format. Current methods used for biological sensing utilize fluorescence, calorimetric, or surface plasmon resonant techniques as indicators of a successful molecular recognition event and are thus not amenable for use by non-technical operators. 
   While these methods are main-stream in their respective adoption for the molecular diagnostics arena, they are not without functional limitation. For fluorescence monitoring and Enzyme Linked Immunosorbent Assay [ELISA], superfluous tags must be conjugated to the desired target through the mechanism of additional labeled antibodies, thus adding necessary complexity and cost. Colorimetric assays require the generation of a color change, often mediated via an enzymatic mechanism, and are thus non-ideal for generating high density arrays. 
   Miller et al. in PCT Application WO 03/036225 A1, filed May 1, 2003, sets forth a device that enables the label-free detection of biomolecules. The Miller sensing system is functionally bipartite and is comprised of: 1) a receptor for at least one target, the receptor including a substrate and a transparent coating on the substrate having front and back surfaces; and 2) a light source positioned to direct at least a portion of the light from the light source toward the coating on the receptor; and a detector positioned to capture the light reflected from the front and back surfaces of the coating, where the detector identifies the presence of at least one target based on the change in the interference pattern of the captured light. 
   However, the Miller system does not lend itself to quantitative detection of biomolecules in high density receptor arrays. Therefore, the need remains for the label-free detection of biomolecules, wherein a resulting image allows for quantitative analysis. 
   SUMMARY OF THE INVENTION 
   The present system generally includes the light-source and detection system, wherein the present system compensates for diffraction patterns intrinsic to the reflected signal from the receptor. Particularly, the present system removes fringe patterns from the image of the receptor. By minimizing higher order diffraction patterns and fringes, the present system enhances intensity determination and hence, allows for the quantitative detection of biomolecules at the receptor in a highly multiplexed format. 
   In an exemplary embodiment of the present disclosure, a method of sensing at least one target on a receptor having a substrate and a translucent coating includes minimizing interference fringe patterns in an image of the target. The method also includes passing the reflected signal of the target through an imaging lens or optical system intermediate the receptor and a detector. 
   In another exemplary embodiment of the present disclosure, a method of sensing at least one target on a receptor having a substrate and a translucent coating includes compensating for diffraction effects in an image of the target. The method also includes passing the image of the target through an imaging lens or optical system intermediate the receptor and a detector. 
   In a further exemplary embodiment of the present disclosure, an apparatus for imaging a receptor on a substrate having a translucent coating includes a coherent light source generating a coherent beam along a beam path, and a receptor disposed in the beam path to reflect the beam, the receptor forming a reflected beam along the beam path. The apparatus also includes a detector located in the beam path to image the reflected beam and an imaging lens or optical system in the beam path optically intermediate the receptor and the detector. 
   The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale, and sizes of various elements may be distorted for clarity. The drawings illustrate one or more embodiment(s) of the invention and, together with the description, serve to explain the principles and operation of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a biomolecular detection system in accordance with an exemplary embodiment of the present disclosure. 
       FIG. 1   a  is a block diagram of a biomolecular detection system in accordance with another exemplary embodiment of the present disclosure. 
       FIG. 2  demonstrates the present improvement of the array resolution and sensitivity. 
       FIG. 2   a  illustrates a high density array according to an exemplary embodiment of the present disclosure. 
       FIG. 3  reports a more detailed theoretical simulation of the expected sensitivity of the present device. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a biomolecular detection system  30  according to an exemplary embodiment of the present disclosure. The system  30  includes a laser source  33 , an aperture  35 , an optical cutoff or laser line (notch) filter  36 , a spatial filter comprised of an objective  37  and an optical pinhole  39 , a collimating lens  41 , a linear polarizer  43 , a receptor mount  45 , an imaging lens  47 , and an optical detector  49  with multiple sensing elements. 
   The present system provides an improvement to the system described within Miller et al. for detection of molecular adsorption based on simple reflectivity. While the present configuration is set forth in terms of the recited components, it is understood, certain permutations of these components could also lead to other configurations resulting in an operably equivalent devices. That is, the present description is merely exemplary of the present system  30 , and is intended to provide an overview or framework for understanding the nature and character of the invention. 
   Referring to  FIG. 1 , the laser source  33  may be any gas laser known in the art. The laser source  33  in the detection system  30  generates and transmits monochromatic light towards the surface of a receptor  44  supported by the receptor mount  45 . In this exemplary embodiment, the laser source  33  is a collimated monochromatic light source that is tunable or not tunable. That is, the wavelength of the generated beam can be varied by any of a number of mechanisms known in the art. Alternative light sources such as a laser diode, a DFB laser source, or a lamp with a narrow bandpass filter could also be used. The medium in which the light travels from the laser source  33  to the substrate holder  45  could be air, an optical fiber  32  ( FIG. 1   a ), an aqueous solution, or any other waveguide material known in the art. 
   The aperture  35  is configured to remove substantially all stray radiation generated by laser source  33 . It is understood that the light emitted by the laser source  33  can be highly collimated, thus, the resulting beam can be extremely thin with very little divergence. A cavity (not shown) of the laser source  33  can include substantially parallel anterior and posterior mirrors configured to constrain the emitted laser beam to a path which is substantially perpendicular to the mirrors. The anterior mirror can be approximately 100% reflective while the posterior mirror can be approximately 99% reflective, such that approximately 1% of the beam can be emitted by the laser source  33 . This emitted beam is represented by the laser line illustrated in  FIG. 1 . Thus, it is understood that the light can pass back and forth between the anterior and posterior mirrors of the laser source  33  to gain intensity by the stimulated emission of additional photons at the same wavelength. If the reflected light is even slightly off axis, it will be lost from the resulting emitted beam (the laser line). Thus, in the event that the beam emitted from the laser source  33  is not completely collimated, the aperture  35  can be configured to remove any divergent portions thereof. 
   Optical cutoff or laser line (notch) filter  36  can be configured to remove superfluous background radiation generated by laser source  33  at wavelengths other than that of the desired wavelength. The beam emitted by the laser source  33  can be produced by a single atomic transition and can, thus, have a single precise wavelength. Such a beam can have a single spectral color and can be almost purely monochromatic. The spectral emission line from which the emitted beam originates, however, may not have a finite width. This variance in width can be caused by a number of factors, including the Doppler effect of the moving atoms or molecules from which the beam originates. Since the wavelength of the emitted beam is relatively small compared to the overall size of the cavity of the laser source  33 , many resonant modes of the cavity can exist within the tiny spectral bandwidth of the emitted beam. The laser line filter  36  can be configured to effectively cutoff the variant spectral portions of the emitted beam. In an exemplary embodiment, the optical cutoff filter  36  can be used in conjunction with a laser source  33  such as, for example, a diode laser having a high bandwidth. In a further exemplary embodiment wherein a narrow bandwidth laser source  22  such as, for example, a DFB laser is used, the optical cutoff filter  36  can be omitted. 
   The objective  37  can be, for example, a spatial filter such as, but not limited to, a microscope objective. The optical pinhole  39  can be disposed at the focal point of objective  37  and can be configured to substantially remove nonuniformities in the intensity of the beam generated by the laser source  33 . It is understood that the intensity of a beam is the absolute measure of the light wave&#39;s power density. Accordingly, the optical pinhole  39  can be configured to assist in creating a uniform and expanded beam profile. It is also understood that the output of an optical fiber can itself be considered a point source (pinhole). The expanding beam that emerges from such a fiber can have a highly uniform profile. It is further understood that the objective  37  need not be self contained. The objective can be comprised of a single aspheric lens or a series of lenses configured to focus and/or expand a diameter of an incoming light beam to a desired pre-defined diameter. 
   The collimating lens  41  can be any lens, lens system, or other optical device configured to calibrate the pointing and focus of an optical imaging system. As used in the system  30  of the present disclosure, the collimating lens  41  can be configured to recollimate the beam emitted by the laser source  33  and exiting the optical pinhole  39 , to ensure parallel propagation of the beam radiation incident on receptor  44 . It is understood that forming a well collimated parallel propagating beam insures that substantially all optical rays are incident on the receptor  44  at the same angle. Variability of incident angles can be a source of error in the system  30 . Thus, in an exemplary embodiment, the system  30  can include all-reflective elements, such as, for example, mirrors configured to substantially eliminate the interference effects associated with multiple reflections from the surfaces of transparent refractive optical elements (i.e., lenses). 
   As illustrated in  FIG. 1 , the linear polarizer  43  can be disposed substantially within the path of the laser line and can be configured to polarize the beam emitted from the laser source  33  in a single direction. The polarizer  43  can be any optical component known in the art capable of assisting in converting an unpolarized or mixed-polarization beam of electromagnetic waves into a beam with a single polarization state. The polarizer  43  can be, for example, an absorptive polarizer or a beam-splitting polarizer. In an exemplary embodiment, the polarizer  43  can be configured to remove p-wave component and ensure pure s-wave polarization of the beam generated by the laser source  33  and incident to receptor  44 . In an exemplary embodiment, the effective elimination of the p-polarized light component can increase the sensitivity of the detection system  30 . 
   Although not shown in  FIG. 1 , in an exemplary embodiment, the system  30  can include a rotational driving device connected to the polarizer  43  and configured to rotate the polarizer  43  about an axis defined by the laser line. Rotating the polarizer  43  can enable the ratio of p-polarized to s-polarized light to be measured, thereby providing an internal reference that can be utilized to further improve the accuracy of the system  30 . In a further exemplary embodiment, a polarized light source or polarizing optical fiber can be used instead of the non-polarized laser source  33 . In such an embodiment, the polarizer  43  can be omitted. 
   The receptor  44  can be any substrate known in the art and the receptor  44  can be disposed or otherwise positioned in the path of the polarized light emitted by the polarizer  43 . In an exemplary embodiment, light can be emitted by the laser source  33  so as to intersect the receptor  44  at a desired angle. In an exemplary embodiment, components of the systems described herein such as, for example, the detector  49 , can be mounted, angled, tilted and/or otherwise disposed at an angle relative to the beam emitted by the laser source  33 . The receptor  44  can include a surface receptive to the adsorption of one or more targets. In an exemplary embodiment, the receptor  44  can comprise a substrate that is substantially covered with a coating or array of various coatings across the surface. The substrate can be made from any conventional substrate material known in the art such as, for example, glass, silicon, and other like materials. 
   The coating can be a single layer of material or, alternatively, can be a plurality of layers of material. Such materials can include, for example, silicon dioxide (glass), silicon nitride, any known polymer, and an evaporated molecular material. In an exemplary embodiment, the coating can be functionalized to include probe molecules specific for a desired target molecule. In such an exemplary embodiment, a layer of the coating can be silicon dioxide and the coating can be configured to include a further adsorbate that is receptive to adsorption of one or more targets of a biological sample applied thereto. In an exemplary embodiment, the coating can include antibodies and/or other proteins. In each of the above exemplary embodiments, the coating of the receptor  44  can be substantially non-reflective. 
   In an exemplary embodiment, the coating can comprise a front surface and a back surface. The front surface can be the surface presented to the beam emitted by the polarizer  43  and the back surface can be the surface of the coating in contact with the substrate. The front and back surfaces of the coating can be configured to reflect incidental light and, as will be described in greater detail below, the front and back surface reflections can result in a measurable amount of destructive interference. The adsorbing target biomolecules can effectively change the coating thickness to afford a change in the destructive interference pattern of the reflected light. 
   The receptor support  45  is configured to rigidly hold the receptor  44  in place with minimal movement for imaging on the detector  49 . The receptor support  45  can be disposed substantially behind the receptor  44  such that it can be occluded from the laser line by the receptor  44 . Disposing the receptor support  45  in this way serves to reduce and/or substantially prevent the creation of optical artifacts by the receptor support  45 . The receptor support  45  can comprise any support structures known in the art such as, for example, vacuum chucks, brackets, mounting plates, clips, beams, and the like. It is understood that the receptor support  45  can also include any conventional structures or means to facilitate a rigid, substantially permanent connection between the receptor support  45  and the receptor  44  such as, for example, vacuum, clamps, adhesives, bolts, screws, and other like structures. 
   As shown in  FIG. 1 , the imaging lens  47  can be disposed optically intermediate the illuminated receptor  44  and the detector  49 . The imaging lens  47  can be any optical lens, or optical system (refractive or reflective in nature) known in the art configured to desirably focus one or more beams of light. The imaging lens  47  can be any size and/or shape known in the art, and the imaging lens  47  can be configured to compensate for diffraction effects in the propagating (reflected) beam received from the receptor  44 . Without compensation from the imaging lens  47 , individual spots in the resulting image are washed out by interference patterns and cannot be quantitatively analyzed. This compensation effect can be achieved with a single imaging lens  47  or by a collection of imaging elements  47   a ,  47   b  (discussed in greater detail below with respect to  FIG. 1   a ), and the compensation effect facilitated by the imaging lens  47  can enhance image clarity as measured by the detector  49  disposed downstream thereof. For example, as illustrated in  FIG. 2 , even with a highly collimated illumination source, an imaging lens  47  may still be required to compensate for diffraction effects. The known practice of simply collecting the reflected light with an arrayed detector, on the other hand, can yield poor results that are often not useful. 
   The detector  49  illustrated in  FIG. 1  is disposed and/or otherwise configured to measure the reflected light from the receptor  44  downstream of the imaging lens  47 . The detector  49  can include any reflected beam measurement device known in the art such as, for example, a spectrometer. The detector  49  can be configured to measure the amplitude of the reflected light at a single polarization (i.e., the intensity pattern resulting from reflection of the beam off of the receptor  44 ), and the detector  49  can be configured to ignore phase. The detector  49  can include an array of optical detection elements to assist in measuring the intensity pattern of the reflected beam. In an exemplary embodiment of the present disclosure, the detector  49  can include a charge couple device (CCD) imaging device, a complementary metal oxide semi-conductor (CMOS) imaging device, or other detection devices, wherein the detection devices can include multiple sensing elements (1 or 2 dimensional). The interference between reflected light from the front and back coating surfaces of the receptor  44  can be sensed and/or otherwise measured by the detector  49 , and a change in the interference pattern afforded by a particular coating results from adsorption of a target molecule to the coating surface thereby increasing the effective thickness of the coating. 
   Although illustrated in block diagram format in  FIG. 1 , as discussed above, the detector  49  can be disposed at, for example, an oblique angle relative to a laser beam received by the detector  49 . Such a configuration is more clearly shown by the angle b in  FIG. 1   a . It is understood that in each of the exemplary embodiments of the present disclosure, a sensing element of the detector  49  can be disposed at an oblique angle relative to a laser beam received by the detector  49 . 
   It is understood that tilting the detector  49  to image the reflected beam obliquely can result in several advantages. For example, if the incident angle of the detector  49  matches that of the image formed by the system  30 , the entire receptor  44  can be sharply imaged. Such a process is known as diffraction limited imaging. The image formed may never be perfectly perpendicular to the beam because the beam strikes the receptor  44  at a non-normal incident angle. In addition, if the detector  49  is tilted to approximately its Brewster angle, and the polarization of the light is p-wave relative to the detector  49 , no additional antireflective coatings will need to be integrated into the detector  49 , as reflection will intrinsically be minimized. 
     FIG. 1   a  illustrates a biomolecular detection system  30   a  according to an additional exemplary embodiment of the present disclosure. Where possible, like reference numbers have been used to identify components of the system  30   a  that correspond to similar components of the system  30  illustrated in  FIG. 1 . The system of  FIG. 1   a  is contained substantially within a housing  34 . The housing can be made from any metal or alloy, plastic or composite known in the art and, in an exemplary embodiment, the housing  34  can be made from anodized aluminum. The housing  34  can be relatively light-weight but can be rigid enough to support and/or protect components of the system  30   a  bolted and/or otherwise connected thereto. 
   As shown in  FIG. 1   a , the system  30   a  can include, for example, a laser source  33  connected to a fiber collimator  42  by an optical fiber  32 . the system  30   a  can also include a polarizer  43  downstream of the collimator  42 , a receptor  44  mounted incident to and/or otherwise in the path of a laser line exiting the polarizer  43 , and a fold mirror  46  positioned to intercept the laser line reflected off of the receptor  44 . The system  30   a  can also include imaging optics  47   a ,  47   b  positioned to intercept the laser line reflected off of the fold mirror  46  and a detector downstream of the imaging optics  47   a ,  47   b.    
   In an exemplary embodiment, the laser source  33  of  FIG. 1   a  can be, for example, a He—Ne laser or a diode laser. In an exemplary embodiment, the laser source  33  can be a 635 nm, 658 nm, or 760 nm laser diode module. In such an embodiment, the laser source  33  can include fiber coupling optics and/or other components conventionally used to transmit laser energy emitted by a laser source through fiber optic hardware. As described above with respect to  FIG. 1 , the laser source  33   a  can be configured to generate and transmit monochromatic light towards the surface of the receptor  44 . 
   The optical fiber  32  can be any type of glass or plastic fiber configured to guide light along its length by confining the light in a propagating form. The optical fiber  32  can be, for example, a single-mode or a multi-mode optical fiber, and the fiber  32  can be a graded-index fiber, a step-index fiber, a birefringent polarization-maintaining fiber, or a photonic crystal fiber. 
   As shown in  FIG. 1   a , the optical fiber  32  can connect the light source  33  directly to the collimator  42 . In such an embodiment, the aperture  35 , the objective  37  and/or the optical pinhole  39  discussed above with respect to  FIG. 1 , can be eliminated. It is understood that the beam transmitted from the optical fiber  32  can have essentially the same configuration as the beam emitted by the optical pinhole  39  of  FIG. 1 . Accordingly, using the optical fiber  32  can simplify the system  30   a  by eliminating the need for two or more separate elements requiring alignment. 
   The collimator  42  can take the place of the collimating lens  41  discussed above with respect to  FIG. 1 . The collimator can be any device configured to filter a stream of light rays such that only those traveling parallel to a specified direction are allowed through. The collimator  42  can be any type of collimator known in the art such as, for example, those made from refractive (lenses) or reflective (mirrors) optical elements. 
   The polarizer  43  is configured to intercept the collimated beam exiting the collimator  42 . The polarizer  43  can be structurally similar to the polarizer  43  discussed above with respect to  FIG. 1  and the polarizer  43  can be disposed substantially perpendicular to the laser line exiting the collimator  42 . In an additional exemplary embodiment, the polarizer  43  can be disposed between the fiber  32  and the collimator  42 . Disposing the polarizer  43  between, for example, the fiber  32  and the collimator  42  can reduce the potential for interference patterns in the resulting beam. It is understood that the polarizer  43  can also be angled slightly from a perpendicular orientation to further reduce interference patterns. 
   The polarizer  43  is configured to direct a collimated polarized beam incident the receptor  44 . The receptor  44  can be structurally similar to the receptor  44  discussed above with respect to  FIG. 1 . In the embodiments of  FIGS. 1 and 1   a , the receptor  44  can be configured to hold a micro-array of antibodies disposed on the coating of the substrate. The antibodies can be disposed in any array configuration known in the art and, in an exemplary embodiment, each antibody can be separated by approximately 100 microns on the coating of the substrate. The antibodies disposed on the coating of the receptor  44  can be selected for their ability to desirably attract and/or bond with bio-molecules that are put into contact therewith. In such an embodiment, potentially thousands of antibodies and/or other detection elements can be disposed on the receptor  44 , and multiple disparate detection elements can be disposed on the same receptor  44 . A sample of blood, urine, or other bio-molecular material can then be introduced to the micro-array of antibodies in a health care facility or laboratory. In such an embodiment, the system  30 ,  30   a  of the present disclosure can be configured to image the entire array of antibodies simultaneously.  FIG. 2   a  is an image of an exemplary high-density array captured by the system  30 ,  30   a  of the present disclosure. Accordingly, a healthcare professional examining the array can be able to view thousands of data points from a single bio-molecular sample and can be able to diagnose multiple aspects of the bio-molecular sample in a single imaging application. Since multiple detection sites can be used on the receptor  44 , redundant antibodies can be disposed thereon to reduce the risk of false positive readings. The imaging capabilities of the systems  30 ,  30   a  disclosed herein enable thousands of detection sites to be imaged simultaneously, and thus enable this redundancy. In particular, the high-density enabled by the systems  30 ,  30   a  greatly increases the information that can be obtained by the user. Known systems, on the other hand, are not capable of reading such small spots, and are typically limited to reading 5-10 detection total, making the cost of redundancy much higher. In addition, such known systems do not enable users to see the actual image, instead, the user merely sees a list of values corresponding to the parameter of interest for each target (such as, for example, concentration). 
   As shown in  FIG. 1   a , the laser line can reflect off of the receptor  44  and can intercept the fold mirror  46 . The fold mirror can be any type of flat or substantially flat reflective surface known in the art. The fold mirror  46  can be configured to assist in folding the reflected image of the micro-array from the receptor  44  to the imaging optics  47   a ,  47   b . It is also understood that illuminating the receptor  44  with the laser beam at the angle a may cause the resulting reflected image received by the fold mirror  46  to be compressed and/or otherwise deformed. For example, a 10 mm long receptor  44  can create a reflected beam 2-4 mm wide when incident at a highly oblique angle. Thus, tilting components of the system  30 ,  30   a  such as, for example, the detector  49  may compensate for the deformation of the resulting image. It is understood that folding the reflected image can allow greater design freedom, and can result in a system  30 ,  30   a  that is compact and easily handled relative to known systems. 
   The imaging optics  47   a ,  47   b  can be disposed downstream of the fold mirror  46  and can be mounted and/or otherwise configured such that a portion of the imaging optics  47   a ,  47   b  is substantially perpendicular to the laser line reflected from the fold mirror  46 . The imaging optics  47   a ,  47   b  can be, for example, an Offner relay design comprising two nearly concentric spherical mirrors. The imaging optics  47   a ,  47   b  can be configured to relay images at approximately 1:1 magnification with very high resolution and low distortion. In an exemplary embodiment, the system  30 ,  30   a  can have a resolution of approximately 10 microns and can have substantially no measurable distortion. It is understood that, in an additional exemplary embodiment, the imaging optics  47   a ,  47   b  can comprise a much more complex system than what is depicted in  FIG. 1   a  and in such an exemplary embodiment, the imaging optics  47   a ,  47   b  may comprise a complex configuration of mirrors and/or lenses configured to relay a high resolution image at low distortion. 
   The mirrors of the imaging optics  47   a ,  47   b  can be precisely aligned with respect to each other and with respect to, for example, the reflected multi-array such that the images presented to the detector  49  are limited only by diffraction. Imaging a collimated coherent source at an oblique incident angle with all reflective optics  47   a ,  47   b  can eliminate the potential for multiple reflections from within refractive lens elements. Accordingly, the systems  30 ,  30   a  disclosed herein may be significantly less expensive to manufacture as compared to known lens-based systems requiring highly specialized antireflective coatings. 
   It is understood that in coherent imaging systems, any dust/particles resident on optical surfaces can create fringe patterns. This may be especially true for reflective optics including mirrors where the scatter from the particle can be enhanced by a strong reflection from the underlying mirror. Accordingly, the systems  30 ,  30   a  disclosed herein can be assembled and/or sealed in a substantially dust-free environment so as to substantially eliminate contamination on the reflective optics and/or within surface coatings. 
   The detector  49  can be, for example, a CCD camera. In such an exemplary embodiment, the CCD camera can be board-mounted and a portion of the protective films and/or other devices causing interference with the imaging capabilities of the system  30   a  can be removed. As shown in  FIG. 1   a , the laser line is incident to the receptor  44  at an angle a, and the reflected object passes through multiple imaging planes. This configuration requires a relatively large depth of field in order for the image of the entire receptor  44  to remain in focus. It is understood that the depth of field can be defined as the distance along the optical axis (along the laser line) over which the desired object will be in sharp focus. The Offner relay defined by the imaging optics  47   a ,  47   b  is configured to tolerate this condition and the depth of field is extended by tilting the detector  49  at the angle b relative to the beam received from the imaging optics  47   a ,  47   b.    
   It is understood that if the detector  49  was disposed perpendicular to the beam received from the imaging optics  47   a ,  47   b , only the center of the receptor  44  would be in focus, and the image would blur toward the close and far edges of the receptor  44 . By tilting the detector  49  such that the detector  49  is aligned with the series of images carried by the received beam, each of the images can be brought into sharp focus. In addition, by illuminating the detector  49  at an angle, the system  30   a  is configured to take advantage of the Brewster angle of the image. It is understood that, at a single particular angle of incidence (Brewster&#39;s angle), light with a particular polarization cannot be reflected, and at angles near the Brewster angle, reflectance is quite low. The polarization that cannot be reflected at this angle is the polarization (p-wave or p-polarization) for which the electric field of the light waves lies in the same plane as the incident ray and the surface normal (i.e., the plane of incidence). In short, although tilting the detector  49  enables the entire receptor  44  to be in focus, such a configuration results in considerable reflective interference and poor optical coupling efficiency. To compensate for this, the system  30   a  can include, for example, a polarization rotator, a waveplate, and/or other like structure (not shown) to rotate the polarization of the imaged light by 90 degrees. Through such rotation, the imaging angle would be sufficiently close to the Brewster angle such that highly efficient coupling and enhanced sensitivity could be obtained. 
   The image display system  30 ,  30   a  of the present disclosure can be used in a variety of different environments to assist in diagnosis of different medical conditions. For example, diagnostic chips can be examined using the system  30 ,  30   a  and the chips can be analyzed for, among other things, a given disease state, a function or dysfunction of a specific organ system, and a triage diagnostic in a first responder setting. The chips can also be used in a deployed environment with a portable system  30 ,  30   a.    
   In additional embodiments of the present disclosure, the diagnostic chips can be used in, for example, immunodiagnostic assays, proteomics applications, and nucleic acid detection. For example, in immunodiagnostic testing, antibodies can be used as selectivity elements. In such testing, target molecules can include cytokines, chemokines, coagulation factors, plasma proteins, membrane and integral proteins, cytoplasmic and nuclear proteins, non-human proteins, peptides, plasma factors, small molecules, carbohydrates, and lipids. The aforementioned molecules are commonly found in bodily fluids, exudates, secretions, tissue samples, and serum. Commercial antibodies are available for the preceding targets and can be readily incorporated into the diagnostic chips of the present disclosure. 
   In further exemplary embodiments of the present disclosure, recombinant or native proteins or protein fragments can be used as selectivity elements. In such proteomic applications, target molecules can include: cytokines, chemokines, coagulation factors, plasma proteins, membrane and integral proteins, cytoplasmic and nuclear proteins, non-human proteins, peptides, plasma factors, small molecules, carbohydrates, and lipids. The aforementioned molecules are commonly found in bodily fluids, exudates, secretions, tissue samples, and serum. 
   In still another exemplary embodiment of the present disclosure, complementary cDNA, DNA, RNA, and rRNA molecules can be used as selectivity elements. In such nucleic acid detection applications, the target molecules can include genomic, ribosomal, messenger, transcript, and ribozymal nucleic acid sequences. The label-free nature of this technique allows all these measurements to be performed in a highly multiplexed format, rapidly, and with minimal cost. 
   For example,  FIGS. 2   a  and  2   c  illustrate images acquired for a known standard sample receptor array. As seen in  FIGS. 2   a  and  2   c , it is not possible to acquire non diffraction-contaminated images using known image display systems, such as the systems described in Miller et al.  FIGS. 2   a  and  2   c  illustrate images obtained using a known system having a sample array simulating receptor comprised of a silicon wafer with varying thicknesses of the antireflective layer simulating arrayed probe functionalization. 
     FIGS. 2   b  and  2   d , on the other hand, illustrate images of the same standard sample acquired using the system  30 ,  30   a  of the present disclosure. As illustrated in  FIGS. 2   b  and  2   d , the system  30 ,  30   a  allows for precise intensity determination of array elements disposed on receptor  44 . In particular, the system  30 ,  30   a  effectively removes spurious interference fringes intrinsic within the images obtained by known systems. The removal of the higher order interference fringes allows for detection of subtle reflectance changes within the array elements contained within receptor  44  that are directly related to the ultimate sensitivity of the technique implemented by the present system  30 ,  30   a . Thus, quantitative detection of biomolecules is possible in the present system  30 ,  30   a , wherein such detection was not possible with existing systems. In addition to allowing accurate quantitative data to be collected, the present system  30 ,  30   a  allows smaller spots to be imaged at a relatively high image density, such as, for example, imaging an array of spots 100 micron in diameter that are separated by approximately 100 microns. As discussed above, an image of such an exemplary high-density array is shown in  FIG. 2   a . It is understood that the spot size is only limited by the wavelength of light. Thus, imaging spots that are approximately 1 micron or slightly less in diameter is possible with the system  30 ,  30   a  even though arraying spots of this size may be difficult. This enables commercial arraying tools to be used to apply the detection spots. Few commercial technologies currently print the large spots that are required by known systems. 
     FIG. 3  illustrates a more detailed theoretical simulation of the expected sensitivity of the present system  30 ,  30   a . The reflected signal increases nearly 1000 fold with the addition of a single angstrom of material. This level of sensitivity is not achievable in known devices. 
   Other embodiments of the disclosed image display system  30 ,  30   a  will be apparent to those skilled in the art from consideration of this specification. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being indicated by the following claims.