| The study of molecular interactions in biological fluids is important (i) as a research tool to elucidate molecular and biological function, (ii) for discovering or designing molecules that have a desirable function, and (iii) for measuring or detecting analytes for clinical diagnostic purposes. Microfluidics is an emerging technology that has proven useful for studying and controlling molecular interactions with the potential advantages of reduced sample and reagent volumes, short reaction times, greater reaction control and efficiency, portable instrumentation, and high throughput.; For this work, novel methods of studying molecular binding interactions were developed by observing changes in the diffusive transport of indicator molecules due to specific binding to other molecules that were much larger in size. At microscale dimensions, diffusive transport of many biologically relevant molecules can cover large fractions of a fluid channel in a short time (seconds to minutes) making microfluidic devices well-suited for such analysis. The utility of the T-sensor, a microfluidic device element, was expanded by taking advantage of altered diffusive transport of molecules to infer levels of binding. With pressure driven flow, 1-D approximations of diffusive transport in the T-Sensor are not always accurate. A non-dimensional number is proposed that should prove useful for determining conditions under which 1-D approximations are justified.; Acrylamide "hydrogel wells" were also designed and fabricated within microchannels as an alternative means of generating diffusion potentials. Using a mechanically stable hydrogel simplified fluid handling, increased differentials in diffusive transport due to molecular binding, and better accommodated complex samples compared to the T-Sensor. Analysis of complex samples proved possible with both types of devices making diffusion-based analysis a robust diagnostic tool for working with biological samples. |
