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 (μ_eo^nano) were determined and compared to the analyte's (fluorescein) electrophoretic mobility (μ_ep). For the instances where μ_eo^nano > μ_ep, the analytes were concentrated on the anodic side of the nanochannel (72, 54, and 29 nm deep channels), whereas when μ_eo^nano < μ_ep, 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.