Isoelectric Focusing in a Poly(dimethylsiloxane) Microfluidic Chip

Abstract

This paper reports the application of ampholyte-based isoelectric focusing in poly(dimethylsiloxane) (PDMS) using methylcellulose (MC) to reduce electroosmosis and peak drift. Although the characteristics of PDMS make it possible to fabricate microfluidic chips using soft lithography, unstable electroosmotic flow (EOF) and cathodic drift are significant problems when this medium is used. This paper demonstrates that EOF is greatly reduced in PDMS by applying a dynamic coat of MC to the channel walls and that higher concentrations of MC can be used to increase the viscosity of the electrode solutions in order to suppress pH gradient drift and reduce "compression"of the pH gradient. To illustrate the effect of MC on performance, several fluorescent proteins were focused in microchip channels 5 microm deep by 300 microm wide by 2 cm long in 3-10 min using broad-range ampholytes at electric field strengths ranging from 25 to 100 V/cm.

Effect of Joule heating on isoelectric focusing of proteins in a microchannel

“…This finding is in line with the experimental observation in microchip IEF. 3 Identification of the final focus point of the proteins is very important for optimum protocol design in microchip IEF. Numerical results also show that the Joule heating effect worsens at a higher electric field.…”

“…For that reason, the IEF channel is typically coated with chemicals to suppress undesired electroosmotic flow. 1, 3 The effects of electroosmosis are studied extensively for capillary zone electrophoresis 17,26,27 and isoelectric focusing. 28 In this study, we assume that our channels are perfectly coated to knock down the electroosmosis so that the detrimental effects of Joule heating can be studied precisely.…”

Capillary electrophoresis of proteins 2003–2005

“…However, a growing number of research groups perform CIEF on chips [81,146,147]. Recently, whole-column detection was introduced to CIEF [21,94,97,148,149], which allows monitoring dynamics of CIEF.…”

“…Microchip format is also advantageous for CE methods that require specific design, such as electric field gradient focusing [147,179] or column coupling for online combination of ITP and CZE [16].…”

Microfluidic free-flow electrophoresis for proteomics-on-a-chip

“…Transversal electroosmotic flow was efficiently minimized by including HPMC in the solution as dynamic coating substance. The successful suppression of EOF in microfluidic channels with HPMC has recently been reported [83]. Fig.…”