Ionic Liquid-Based Thermally Responsive Electroactive Gel for Switchable Electroanalysis

A thermally responsive poly(N-isopropyl acrylamide-co-ViEtIm[ferrocenecarboxylate anion])/Au gel (abbreviated as poly(NIPAm-co-ViEtIm[FcCOO])/Au gel) with an electroactive function was designed and synthesized. The gel integrated copolymer poly(NIPAm-co-ViEtImBr), ferrocenecarboxylate anion (FcCOO–), and Au nanoparticles (Au NPs) to achieve thermally responsive electroactivity and electrocatalytic activity. The poly(N-isopropyl acrylamide) (PNIPAm)-based poly(NIPAm-co-ViEtImBr) gel was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization with the ionic liquid monomer and the NIPAm monomer under the action of the initiator to initiate the cross-linking agent. The immobilization of the FcCOO– was realized via the anion-exchange reaction of the ionic liquid fragment. Au NPs were further loaded by electrostatic attraction and in situ reduction of precursor AuCl4–, thus obtaining a thermosensitive poly(NIPAm-co-ViEtIm[FcCOO])/Au gel. The PNIPAm segment provides thermal responsiveness, which can reveal or seal the electroactive FcCOO–. This indicates that the conformational change of the PNIPAm segment at different temperatures can lead to controllable switching of the electrocatalytic performance of the poly(NIPAm-co-ViEtIm[FcCOO])/Au gel/GCE. Consequently, the modified electrode also exhibited a reversible "ON–OFF" effect on the electrocatalysis of ascorbic acid (AA). The poly(NIPAm-co-ViEtIm[FcCOO])/Au gel/GCE exhibited excellent electroactivity with a linear range of 0.100–25.8 mM, detection limit of 0.0929 mM, and sensitivity of 1.87 μA·cm–2·mM–1 in the "ON" state. This kind of switchable electrocatalytic performance of the electrode is expected to be widely used in the field of intelligent electrochemical sensors and devices.