Disclosed are methods, systems, and apparatuses for the free solution measurement of molecular interactions by backscattering interferometry (BSI). Molecular interaction can be detected between analytes in free-solution wherein at least one of the analytes is label-free and detection is performed by back-scattering interferometry. Further, molecular interaction can be detected between analytes in free-solution, wherein at least one of the analytes is label-free, wherein one of the analytes is present in a concentration of less than about 5.0×10−7M. Also disclosed are label-free, free-solution, and/or real-time measurements of characteristic properties and/or chemical events using the disclosed techniques. The disclosed methods can have very low detection limits and/or very low sample volume requirements. Also disclosed are various biosensor applications of the disclosed techniques. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.