Surface plasmon resonance imaging system and method

#This invention generally relates to optical imaging and, more particularly, to an optical imaging system suitable for surface plasmon resonance imaging.

#In surface plasmon resonance (SPR) imaging, an optical imaging system is used to observe biomolecular binding events which have spatial structure. Generally, such a system includes a light source to illuminate a sample surface under conditions which produce SPR and a detector to image the light reflected from the sample surface.

#FIG. 1A illustrates the SPR imaging principle. Light traveling through a high refractive index (RI) substrate 48 (e.g., BK7, n=1.51) reflects from a substrate surface, which is coated with a thin layer 51 of gold (50 nm). An aqueous sample (n=1.33), typically contained in a flowcell, contacts the opposite side of the gold. For certain wavelengths and angles of incident light, part of the incident energy will couple into a surface plasma wave traveling between the sample and the gold layer. The loss of this energy is observed as a decrease in reflectivity. Because the coupling conditions vary strongly with the refractive index of the sample, observations of reflectivity may be used as a sensitive measure of sample refractive index. Because the surface plasma wave is bound to the surface, the SPR phenomenon is only sensitive to the sample refractive index within the evanescent decay length, typically a few hundreds of nanometers. This surface sensitivity, combined with the fact that biomolecules such as proteins typically have refractive index much larger than water (n=1.6 typ.), allows the binding of biomolecules to the gold sensing surface to be detected as an increase in surface RI. To make an SPR imaging system for detection of specific substances, the gold surface is chemically functionalized (for instance by attaching antibodies to the surface) such that substances of interest will bind to the surface while other material will tend not to bind. Referring to FIG. 1A, a foundation layer 30 of biomolecules to which antibodies or other receptors (the “Y” molecules) are attached is illustrated adjacent to the gold layer 51.

#The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

#FIG. 1A is a diagram illustrating the SPR imaging principle;

#FIG. 1B is a gray-scale plot illustrating reflectivity as dependent upon the wavelength, angle of incidence, and the refractive index of the analyte close to the sensing surface;

#This invention generally relates to an optical imaging system particularly suitable for surface plasmon resonance (SPR) imaging that duplicates the effects of angular motion using a simplified mechanical design while also optimizing the system's attributes to enhance imaging results.

#FIG. 4 illustrates a schematic diagram of an SPR imaging system 40 in accordance with an embodiment of the invention. The system 40 includes a light source 42, at least one input optical element, a substrate surface 50, at least one output optical element and a detector 60. The at least one input optical element includes a collimating lens 44, which is disposed between the light source 40 and the substrate surface 50. The at least one output optical element includes a lens 52, which is disposed between the substrate surface 50 and the detector 60. The substrate surface 50 is preferably a surface of a prism 48.

#In SPR imaging, light at a selected wavelength is directed through a high refractive index (RI) substrate to a sample under analysis, such as a low RI aqueous analyte, positioned adjacent to the substrate. A resonance film, preferably a gold film, is disposed between the substrate and the sample. This film interface, also referred to as a sensing surface in SPR imaging, reflects the incident light, but electrons of some of the atoms at the medium interface resonate between conduction bands. In addition, because the resonance film is extremely thin (e.g., on the order of 500 .ANG.), an electromagnetic field component of incident light penetrates a very short distance into the surface of the lower refractive index material (i.e., the sample) in the form of an exponentially attenuating evanescent wave. For incident light that is monochromatic and TM polarized, there is a specific angle of incidence at which light is absorbed rather than reflected due to resonance energy transfer between the evanescent wave and the surface plasmons. This angle, at which reflected light intensity is at a minimum, is influenced by the properties of the sample adjacent to the thin gold film.