Gas recognition based on the physicochemical parameters determined by monitoring diffusion rates in microfluidic channels

Abstract

Monitoring the diffusion progress rates of different gases in a microfluidic channel affords their discrimination by the comparison of their temporal profiles in a high-dimensional feature space. Here, we demonstrate gas recognition by determination of their three important physicochemical parameters via a model-based examination of the experimentally determined diffusion rates in two different cross-section channels. The system utilized comprises two channels with respective cross-sectional diameters of 1000 μm and 50 μm. The open end of both channels are simultaneously exposed to the analyte, and the temporal profiles of the diffusion rates are recorded by continuous resistance measurements on the chemoresistive sensors spliced to the channels at their other ends. Fitting the solutions of the diffusion equation to the experimental profiles obtained from the large cross-section channel results in the diffusivity of the analyte. The results of small cross-section channel, however, fit the solutions of a modified diffusion equation which accounts for the adsorption of the analyte molecules to the channel walls, as well. The latter fitting process results in the adsorption parameter for the analyte-channel wall interactions and the population of the effective adsorption sites on the unit area of the walls. The allocation of these three meaningful parameters to an unknown gaseous analyte affords its recognition.