Sodium hydroxide treatment of PDMS based microfluidic devices.

We discuss the use of aqueous NaOH as a facile surface treatment method to control the electroosmotic flow in PDMS microchannels. Flushing of PDMS/PDMS and glass/PDMS microchannels with 1 M NaOH for 24 h leads to a doubling of the electroosmotic flow. This high flow rate is comparable to the flow rates achieved by treating PDMS microchannels with O2 plasma. Contact angle measurements and ATR-FTIR analysis show that the surface chemistry of the NaOH treated PDMS differs from O2 plasma treated PDMS. An important advantage of the NaOH treated surfaces is the enhanced stability, irrespective of whether the devices are stored in air or water.