Electroosmotic Effects on Sample Concentration at the Interface of a Micro/Nanochannel.

Electroosmotic effect on electropreconcentration of analytes was investigated at the micro/nanochannel interface for a series of 1-D glass nanochannels with depths of 72, 54, 29, and 9 nm. The electric double layer approaches overlap conditions as the nanochannel depth decreases, suppressing the electroosmotic flow. The nanochannels' electroosmotic flows (μeonano) were determined and compared to the analyte's (fluorescein) electrophoretic mobility (μep). For the instances where μeonano > μep, the analytes were concentrated on the anodic side of the nanochannel (72, 54, and 29 nm deep channels), whereas when μeonano < μep, the analyte was concentrated on the cathodic side of the nanochannel (9 nm deep channel). In order to maintain a stable concentrated sample plug, a "drain" channel was incorporated for increasing the nanochannel electroosmotic flow while decreasing the sample channel electroosmotic flow. A sample preconcentration rate of over 20-fold per second was achieved. Finally, fundamental limits of the nanochannel-based preconcentration are discussed and experimentally demonstrated.