Development of an electrochemical enzymatic lactate sensor covered by a non-volatile poly(vinyl alcohol)-based water-in-eutectogel.

Biosensors coated with hydrogels exhibit high performance by providing structural and functional stability to the bioreceptors mounted on the sensing element. However, the volatility of the gel solvent (water) limits stable measurements. In this study, a non-volatile poly(vinyl alcohol) gel consisting of a biocompatible and non-volatile deep eutectic solvent and bound water (water-in-eutectogel) was prepared and used as the reaction medium for an enzyme sensor. To the best of our knowledge, this is the first proof-of-concept study worldwide. The water-in-eutectogel did not volatilize for more than a week at room temperature under atmospheric pressure and exhibited high ionic conductivity and mechanical strength. Moreover, a lactate oxidase-modified electrode coated with the water-in-eutectogel exhibited a lactate concentration-dependent current response with a sensitivity of 3.52 μA μM-1 cm-2 (linear range 0-1.31 μM, R2 = 0.996) and a limit of detection of 0.0673 μM. Overall, this work represents a first step toward the realization of electrochemical biosensors capable of operating in non-volatile water-in-eutectogels for biochemical analysis.