Laccase-mimicking Ag/MnO₂-polydopamine-borate as electrochemical platform for sensitive detection of caffeic acid.

Caffeic acid (CA) is an important phenolic compound whose electrochemical oxidation is often limited by sluggish electron-transfer kinetics and electrode fouling, necessitating the development of efficient catalytic interfaces. Here, the electrocatalytic oxidation of CA at a laccase-mimicking Ag/MnO₂@polydopamine-borate (Ag/MnO₂@PDA-B)-modified electrode was investigated to evaluate its catalytic and sensing performance. The hybrid architecture, integrating conductive Ag-containing domains, redox-active MnO₂ centers, and a polydopamine-borate layer, promotes efficient oxidation of phenolic substrates. Cyclic voltammetry revealed a pronounced cathodic shift in the oxidation peak potential (210 mV) compared to that of a laccase-based biosensor, indicating reduced overpotential. The pH-dependent shift in peak potential is consistent with the involvement of proton-coupled electron transfer during CA oxidation. The nanozyme-modified electrode exhibited improved electrochemical stability and sustained catalytic activity. The sensor showed a linear response over 0.1-100 μM, with a detection limit of 22 nM and high sensitivity (37,900 A·M-1·m-2 in DPV and 23,580 A·M-1·m-2 in chronoamperometry). Overall, these results demonstrate the potential of Ag/MnO₂@PDA-B nanozymes as bioinspired electrocatalytic platforms for the sensitive detection of caffeic acid and related phenolic compounds.