Controlling electroosmotic flow in poly(dimethylsiloxane) separation channels by means of prepolymer additives

The electroosmotic flow (EOF) in a poly(dimethylsiloxane) (PDMS) separation channel can be altered and controlled by adding a carboxylic acid to the prepolymer prior to curing. When the prepolymer is doped with 0.5 wt % undecylenic acid (UDA), the electroosmotic mobility in a modified PDMS channel rises to (7.6 +/- 0.2) x 10(-4) cm(2) V(-1) s(-1) (in HEPES buffer at pH 8.5), which is nearly twice that in the native PDMS channel. Because this modification does not significantly change the hydrophobicity of the PDMS surface, it is possible to combine the modified PDMS with a dynamic coating of n-dodecyl beta-d-maltoside (DDM), which prevents protein sticking (see Huang, B.; Wu, H. K.; Kim, S.; Zare, R. N. Lab Chip 2005, 5, 1005-1007). The modified PDMS channel with a dynamic coating of DDM generates an electroosmotic mobility of (5.01 +/- 0.09) x 10(-4) cm(2) V(-1) s(-1), which shows excellent reproducibility both in successive runs and during storage in water. Combining this surface modification and the dynamic coating of DDM is an effective means for both providing stable EOF in the PDMS channels and preventing protein adsorption on the channel walls. To demonstrate these effects, we show that the electrophoretic separation of immunocomplexes in free solution can be readily accomplished in a microfluidic chip made of UDA-doped (0.5 wt %) PDMS with a dynamic coating of DDM.