Electrochemical pH modulator coupled with Ni-based electrode for glucose sensing

The non-enzymatic electrochemical detection of glucose by direct oxidation using electrodes modified with suitable electrocatalysts is now well-established. However, it most often requires highly alkaline media, limiting dramatically the use of such electrodes at neutral pH. This is notably the case of Ni-based electrodes. Here, we propose a new concept to overcome this limitation. It implies the use of an additional stainless-steel grid electrode positioned parallel and close (0.6 mm) to the working Ni-based electrode. In such configuration, applying a suitable cathodic potential (-1.2 V) to the grid enables the solvent reduction, generating OH^- species that contribute to increasing the pH in the vicinity of the Ni-based electrode, thereby enabling effective electrochemical detection of glucose without the need for any alkaline additives in the medium. The present manuscript presents a proof-of-concept for the proposed approach based on a 3D-printed prototype. Under optimized conditions for both preparation of the nickel electrode (electrodeposition from 0.4 M NiCl₂ for 120 s at a current density of -354 mA cm^-2) and for the operation of the electrochemical pH modulator (at -1.2 V for 400 s), the amperometric detection of glucose at an applied potential of +0.55 V exhibited linearly over the concentration range from 0.1 to 1 mM, with a limit of detection estimated to 73 μM. The method offers promising perspectives for enzyme-less, non-invasive electrochemical detection of glucose in real media.