A thermosensitive α-amino acid hydrogel layer deposited on an electrode surface: Actuator and sensor performance

The aim of this work was the development of a novel stimuli-responsive hydrogel layer containing an acryloyl derivative of an α-amino acid and its electroanalytical characterization. The electroactive, electrosensitive, and thermosensitive gel layer was obtained through a two-step process. First, a hydrogel (p(NIPA-ArOr)) based on N-isopropylacrylamide (NIPA) and an acryloyl derivative of ornithine (ArOr) were synthesized and electrodeposited using electrochemically induced free-radical polymerization. Cyclic voltammetry combined coupled with gravimetric analysis enabled simultaneous formation and real-time monitoring of the gel layer. In the second step, the layer was modified with copper ions (p(NIPA-ArOr-Cu²⁺)), which formed stable complexes with the α-amino acid groups, increasing the crosslinking density. The resulting material functions as an actuator, with its thickness modulated by applied electrical potential, and as an electrochemical sensor for hydrogen peroxide detection. The thickness changes, monitored using Quartz Crystal Microbalance with Dissipation (QCM-D), demonstrated temperature-dependent reversible behavior. The sensor exhibited practical applicability and stable performance over three weeks, maintaining approximately 91 % of its initial response. Additionally, the influence of various support electrolytes was examined, revealing that ion size significantly affects the electrochemical response. Overall, the p(NIPA-ArOr-Cu²⁺) modified electrode demonstrated high potential as a reliable and stable hydrogen peroxide sensor, with promising prospects for further development in smart sensing and actuation applications.