Electrochemical Control of pH in Nanoliter Volumes.

The electrochemical management of the proton concentration in miniaturized dimensions opens the way to control and parallelize multistep chemical reactions, but still it faces many challenges linked to the efficient proton generation and control of their diffusion. Here we present a device operated electrochemically that demonstrates the control of the pH in a cell of ∼140 nL. The device comprises a microfluidic reactor integrated with a pneumatic mechanism that allows the exchange of reagents and the isolation of protons to decrease the effect of their diffusion. We monitored the pH with a fluorescence marker and calculated the final value from the redox currents. We demonstrate a large pH amplitude control from neutral pH values beyond the fluorescence marker range at pH 5. On the basis of the calculations from the Faradaic currents, the minimum pH reached should undergo pH ∼ 0.9. The pH contrast between neutral and acid pH cells can be maintained during periods longer than 15 min with an appropriate design of a diffusion barrier.