The effect of dilution on the dispersion with respect to microfluidic channel geometries

In most microfluidic devices, single or multiple dilutions of reagents are required to perform reactions or measurements over a range of concentrations using a set of sample solutions to fill the inlets. In this paper, we discuss the results of a study to understand the effects of different dilution schemes on the Taylor dispersion of sample plugs in microchannels. Taylor dispersion arises due to axial spreading of the solute plug due to variations of fluid velocity in the transverse direction. Dilution ratios (DR), channel dimensions, and channel layouts are varied. The results show that the one-sided dilution scheme provides a wider plug of 1.9%, 1.2% and 0.7% when DR = 0.5, DR = 0.25 and DR = 0.1, than its two-side dilution counterpart, independent of dilution channel angle and shift. This deviation increases by increasing the Péclet number, where σ_1ch²-σ_2ch²∼Pe². Moreover, we discussed the effects of the compression ratio of the plug, the width ratio between plug and dilution channel, the angle of the dilution channel, the staggered dilution channel, and the 3-dimensional case having different width to height ratios. The compression and width ratios change the final length of the plug dramatically, whereas the channel geometry, i.e. channel angle and shift variation do not. For the 3-dimensional extension, the converged Taylor dispersion values increase with decreasing aspect ratios. These physical understandings and findings for fundamental fluid flow are important for the design of microfluidic devices.