Frequency bandwidth limitation of external pulse electric field in microchannels - Applications to analyte velocity modulation detections

摘要

Pulse field driven electro-separations have been used for different analytical advantages, such as signal quality improvement and separation performance improvement. We have studied the temporal electro-osmosis in microchannels due to viscous diffusivity under the external pulse electric fields. Theoretical studies derived from Navier-Stokes equations conclude the dependence of the time to steady state electro-osmosis on the channel sizes. Pulse field frequency should be limited by the electro-osmosis setting-in time. We also observed the unstable electro-osmosis as the external field frequency increases. As channel geometry characterization results are employed in the mathematical models, the threshold frequencies obtained in experimental data are consistent with the computational predictions. In previous studies, effective signal quality improvement of electro-separations has been demonstrated, when external pulse fields modulate analyte velocities with synchronous lock-in detection. The results indicate signal-to-noise ratio improvement would be more significant at the high frequency regime where flicker noise is not dominant. Since bandwidth limitation due to fluid viscosity constrains the pulse frequency, optimum analyte velocity modulation is in need of further investigation. Under the bandwidth constrains, we have investigated the theoretical optimum modulation frequencies. (C) 2004 Elsevier B.V. All rights reserved.