Capillary-based analysis schemes, biochemical analysis, basic research in the biological sciences such as localized pH determinations in tissues and studies in protein folding, detection and study of microorganisms, and the miniaturization of instrumentation down to the size of a chip all require small volume detection. With the advent of lasers, light sources possessing unique properties including high spatial coherence, monochromaticity and high photon flux, unparalleled sensitivity and selectivity in chemical analysis has become possible; these technologies, however, can be both expensive and difficult to implement. In contrast, refractive index (RI) detection has been successfully applied to several small volume analytical separation schemes. For various reasons, RI detection represents an attractive alternative to fluorescence and absorbance: it is relatively simple, it can be used with a wide range of buffer systems, and it is universal, theoretically allowing detection of any solute, making it particularly applicable to solutes with poor absorption or fluorescence properties.
Conventional methods of probing intermolecular interactions typically require the use of one or more surface immobilized analytes in the interaction as well as the use of chemical labels on one or both analytes. Surface immobilized methods are cumbersome due to the extraordinary effort required to optimize immobilization protocols as well as their inherently high false positive and false negative binding detection rates, due to unwanted forces contributed by the supporting substrate. Moreover, these conventional methods typically fail to achieve detection at low detection limits or with low sample volume requirements.
However, there remains a need in the art for systems and methods for free-solution, label-free detection of intermolecular interactions between analytes, preferably with low detection limits and/or low sample volume requirements.