Applying pure water plugs for electroosmotic flow monitoring in microchip electrophoresis

Electroosmotic flow (EOF) is essential for separation in conventional and microchip electrophoresis as well as liquid manipulation in microfluidic systems. Herein we explored the possibility of applying pure water for EOF measuring in microchip electrophoresis. The principle is that a water plug could greatly decrease the total conductivity of the solution in the microchannel because of its very high electric resistance. In this case, the separation current would be decreased. After the water plug move out of the separation channel, the separation current would be recovered. Thus EOF might be monitored based on the analysis of the current curve. Our experimental results revealed that this approach could reliably and repeatedly monitor EOF in native PDMS microchannel under various conditions. Moreover, EOF in native and gold nanoparticle modified PDMS microchannels could be differentiated. Because the introduction of pure water does not create any contamination or change the channel conditions, this approach could potentially become a routine step for EOF monitoring in microfluidic systems.