Simultaneous separation and detection of cations and anions on a microfluidic device with suppressed electroosmotic flow and a single injection point

摘要

A rapid and simultaneous separation of cationic and anionic peptides and proteins in a glassnmicrofluidic device that has been covalently modified with a neutral poly(ethylene glycol) (PEG)ncoating to minimize protein adsorption is presented. The features of the device allow samples thatncontain both anions and cations to be introduced from a central flow stream and separated in differentnchannels with different outlets—all in the presence of low electroosmotic flow (EOF) imparted by thenPEG coating. The analytes are electrophoretically extracted from a central hydrodynamic stream andnelectrophoretically separated in two different channels, in which pressure driven flow has beennsuppressed through the use of hydrodynamic restrictors. Having different outlets for thenelectrophoretic separation channels that are spatially separated from the injection enables couplingnwith further downstream functionalities or off-chip detection, such as mass spectrometry. A plug ofncharged analyte is hydrodynamically pumped to the sampling intersection and anions from the plugnmigrate electrophoretically toward the anode in one channel while cations migrate toward the cathodenin the other channel due to suppressed EOF from the PEG coating. The separations presented herenrequired less than a minute to complete and produced average separation efficiencies of up to aboutn3,500 plates from a separation length of 2 cm. The extraction efficiency of both cations and anions fromnthe hydrodynamic stream is determined experimentally and compared with a previously reportednmodel that was used to determine anion extraction efficiency. The extraction efficiency is determined tonbe 87% and 98% for the two sample mixtures analyzed, and the values predicted by the model are withinn3.5% of the experimental data. It is anticipated that this basic approach for simultaneous separation ofnanions and cations with reduced EOF will be integrated into larger microfluidic systems because thendesign provides separate outlets that can feed downstream processes or linked to off-chip detection.