Experiments on and with backscattering interferometry

Abstract

This research project was directed at improving the performance and expanding the application of backscattering interferometry (BSI). It will be shown that several steps, including the implementation of sample and reference channels and isolation of BSI from environmental noise, have resulted in an order of magnitude improvement in the detection limits of BSI. Implementation of a new approach for measuring fringe shift greatly simplifies alignment and improves position sensing resolution. A software program has also been developed that facilitates turn-key operation and full external control of BSI. The combined efforts have resulted in a user friendly instrument that can by used by an unskilled investigator in a populated, fully illuminated laboratory. This new BSI embodiment was then used to rapidly determine the solubility of three substances ranging from hundreds of mM to hundreds of ƒÝM. Solubility values determined with BSI compare well with literature values and were obtained with an injection volume of just 1 £gL of solution in a format inherently compatible with high-throughput screening. As part of the development efforts, a method for creating circular channels in acrylic chips was demonstrated. Finally, for the first time an on-chip polarimeter was also constructed and optical activity measurements were performed at high sensitivity within a probe volume of just 1.8 nL.