Rapid protein separations in ultra-short microchannels: microchip sodium dodecyl sulfate–polyacrylamide gel electrophoresis and isoelectric focusing

We have developed novel protein gel electrophoresis techniques, sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) and isoelectric focusing (IEF) in short microchannels (∼millimeters) that take less than a minute. A photopatterning technique was used to cast in situ crosslinked polyacrylamide gel in a microchannel to perform SDS–PAGE. A fluorescent protein marker sample (Mr range of 20 000–200 000) was separated in less than 30 s in less than 2 mm of channel length. Crosslinked polyacrylamide gel, patterned in channels using UV light, provides higher sieving power and sample stacking effect, therefore yielding faster and higher-resolution separation in a chip. IEF of proteins was also achieved in a microchannel, and several proteins were focussed within tens of seconds in mm-length channels. As resolution in IEF is independent of separation distance, focusing in ultra-short channels results in not only faster separation but also more concentrated bands potentially allowing detection of low-concentration species.