Universal control of proton concentration using an electrochemically generated acid compatible with miniaturization

Abstract

Controlling locally produced acidity in miniaturized spaces is of high importance to manage simultaneous chemical reactions. Here, we present a platform that hosts miniaturized micro-reactors each one enabling electrochemical control of the acidity in ∼nL volumes. We demonstrated the local control of chemical reactions with the deprotection of strong acid labile groups in a region of 150 μm of diameter of upstanding glass using high proton concentrations (∼10⁻¹ M) and the acidity contrasts between the cell region and the outside. We demonstrated accurate control of the proton concentration in aqueous and organic solvents and the control of chemical reactions in organic electrolytes achieved with a sulfonated tetrafluoroethylene-based membrane, which isolates the acid generating electrodes from the reagents in the solution. The quantitative control of the acidity by faradaic currents was demonstrated by the calibration of carboxyfluorescein adjusted with external titrations and with a tautomer transition occurring at pH 4.2. To the best of our knowledge, this platform shows the best control of acidity in the smallest volume reported so far.