(240a) Visualizing the Formation of Natural pH Gradients within Microchannels Using Fluorescent Dyes

Hydrolysis reactions at electrode surfaces generate H+ ions at the anode and OH- ions at the cathode. In micro- and nano-scale systems, these ions can cause significant pH shifts in the vicinity of the electrodes, and their transport through the system can cause the formation of so-called ?natural pH gradients.? Natural pH gradients have been exploited for a number of applications, such as capillary isoelectric focusing. Natural pH gradients may also affect microfluidic systems by altering the surface charge of microchannel walls thus impacting electroosmotic flow, or by causing changes in zwitterionic analytes, affecting their electrokinetic mobility. The effects of electric field strength, microchannel length and diameter on the formation of natural pH gradients in fused silica circular microchannels were studied. The pH sensitive fluorescent dye dextran conjugated 5-(and-6)-carboxy SNARF-1 (C.SNARF-1) was used for the ratiometric measurement of the pH both radially and axiometrically within the microchannels.