Molecular control of electrochemically deposited cobalt-polymer composite interfaces for non-enzymatic lactate...

Metal-polymer composite films are widely used in electrocatalysis and electroanalysis, yet achieving the controlled co-deposition of redox-active metals with electropolymerized matrices remains challenging. Herein, we report a single-step, additive-free electrochemical co-deposition of cobalt-polymer hybrid interfaces for lactate electrooxidation. By evaluating nine aromatic monomers across three donor sets (diamines, -NH₂/-NH₂; aminophenols, -NH₂/-OH; diols, -OH/-OH) and three substitution patterns (1,2-, 1,3-, 1,4-), we demonstrate that monomer structure directly dictates the co-deposition pathway. Time-resolved UV-vis spectroscopy reveals that monomer isomerism controls pre-deposition cobalt coordination, which governs the subsequent growth kinetics and voltammetric signatures. Consequently, monomer selection acts as a handle to tune film morphology, surface cobalt speciation (confirmed via SEM and XPS), and interfacial charge-transfer resistance (EIS). These structural variations directly define the catalytic sensitivity and detection limits for lactate analysis via cobalt redox cycling. Compared to conventional stepwise multi-step fabrication, this single-step strategy yields superior stability and low-concentration performance. The optimal Co _x O _y @1,2-NH₂-NH₂ electrode achieves limits of detection (3S _B/m) of 0.145 mM (oxidation) and 0.086 mM (reduction), alongside a high cathodic sensitivity of 0.70 µA mM^-1. This robust cathodic response enables a highly selective dual-channel readout, establishing monomer design as a predictive tool for controlling metal-polymer assembly and electrocatalytic performance.