Quantitative analysis of molecular interaction in a microfluidic channel: The T-sensor

The T-sensor is a recently developed microfluidic chemical measurement devi ce that exploits the low Reynolds number flow conditions in microfabricated channels. The interdiffusion and resulting chemical interaction of compone nts from two or more input fluid streams can be monitored optically, allowi ng measurement of analyte concentrations on a continuous basis. In a simple form of T-sensor, the concentration of a target analyte is determined by m easuring fluorescence intensity in a region where the analyte and a fluores cent indicator have interdiffused. An analytical model has been developed t hat predicts device behavior from the diffusion coefficients of the analyte , indicator, and analyte-indicator complex and from the kinetics of the com plex formation. Diffusion coefficients depend on the local viscosity which, in turn, depends on local concentrations of all analytes, These relationsh ips, as well as reaction equilibria, are often unknown. A rapid method for determining these unknown parameters by interpreting T-sensor experiments t hrough the model is presented.