A method may include steps of binding an analyte to a ligand, exposing the analyte to light of differing wavelengths, and observing a difference in spectral response of the analyte at the differing wavelengths. Further steps may include comparing the observed difference with a known difference in spectral response of a reference substance at the differing wavelengths, and determining whether the observed difference meets a predetermined threshold of identity with the known difference. The method may be performed with reference to a surface having a reflective area with a known size a non-reflective area adjacent to the reflective area. The method may thus include the steps of providing a ligand in alignment with the non-reflective area of the surface, and binding an analyte to the ligand in a position reaching across the reflective area. Further steps may include forming an image of the analyte and the reflective area, observing the size of analyte relative to the reflective area in the image, and comparing the observed size of the analyte with a known size of a reference subject to determine a degree of identity between the analyte and the reference subject.