Diffusion coefficient measurements in microfluidic devices

Four methods for measuring diffusion coefficients were compared on a microfabricated fluidic device using rhodamine 6G as the analyte. The measurements were made using a static imaging method and three dynamic methods -stopped flow, varying the applied potential (E-field method), and varying the detection length (length method). Under conditions where analyte wall interactions (adsorption) are minimized, e.g. in a 50/50 (v/v) methanol/aqueous buffer, the stopped How (2.71 +/- 0.09 x 10(-6) cm(2) s-(1)), E-field (2.684 +/- 0.005 x 10(-6) cm(2) s(-1)) and the static imaging (2.69 +/- 0.02 x 10(-6) cm(2) s(-1)) measurements were all within experimental error of one another and previously reported values. Under 100% aqueous conditions, however, the diffusion coefficient measured dynamically was 11% larger than that measured statically. Diffusion coefficients for rhodamine B, fluorescein, 2',7'dichloro-fluorescein (DCF), rhodamine 6G, tetramethylrhodamine labeled glutamic acid and isoleucine, and fluorescein conjugated bovine serum albumin and ovalbumin were also measured using the static imaging method. (C) 2002 Elsevier Science B.V. All rights reserved.