Nanoarchitectural Control of Nickel-Stabilized Prussian Blue Analogues Improves Hydrogen Peroxide Sensing at Microdisc Electrode Arrays

Hydrogen peroxide (H2O2) is a central analyte in enzymatic processing, environmental monitoring, and physiological redox signaling, yet its electrochemical quantification remains constrained by limited sensitivity and mediator instability. Here, we demonstrate that purposeful interfacial nanoengineering of a microfabricated microdisc electrode array (MDEA) yields substantial and mechanistically resolvable gains in H2O2 sensing performance. A Cell-on-a-Chip MDEA (37 Pt microdiscs, 25 μm radius) was modified with nickel-stabilized Prussian blue analogue (FeNiHCF) films deposited using two distinct strategies: (i) potentiostatic, layer-by-layer deposition (FeNiHCFPS) and (ii) potentiodynamic codeposition (FeNiHCFPD). Although both architectures enhanced charge-transfer kinetics relative to unmodified Pt, their electroanalytical performance diverged markedly. The FeNiHCFPS multilayer conferred 3.6-fold and 2.6-fold increases in H2O2 sensitivity over the FeNiHCFPD film in the 1–10 μM and 10–100 μM ranges, respectively, and produced up to a 200-fold increase in steady-state current compared with the single-layer architecture. Multiple-scan-rate cyclic voltammetry and electrochemical impedance spectroscopy revealed that these differences arise not from interfacial kinetics alone, but from fundamentally distinct intrafilm charge-transport regimes: FeNiHCFPS films are redox-dense yet transport-limited, whereas FeNiHCFPD films support faster but less extensive charge propagation. When integrated with the radial diffusion advantages of the MDEA geometry, the layered Fe|Ni hexacyanoferrate architecture achieves near-ideal steady-state amperometric behavior at physiologically relevant overpotentials. Characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS), these findings establish film architecture─not simply composition─as the dominant determinant of mediator performance and provide a generalizable design principle for high-sensitivity, low-overpotential electrochemical peroxide sensing.