For electronic control and on-chip monitoring of pH we used the pH-dependent fluorescent dual emission dye, carboxy-SNARF-4F (Molecular Probes, Invitrogen) for visualization of the pH change.
Experiments within the microfluidic environment of the Chemical Microprocessor ChµP (right image) were done with SNARF-4F (10 µM) in a universal buffer solution (pH 8) to see a pH step triggered by changing the voltage at the microelectrodes using a very low flow rate of 1 µl/h. We observed that the fluorescence intensity at 640 nm increases at positively charged electrodes and decreases to zero at negatively charged electrodes.