Enhanced Peroxidase-like Activity of Palladium-Iron Bimetallic Nanoparticles Supported on N-doped Mesoporous Carbon for Colorimetric Detection of Ascorbic Acid and Dopamine

Abstract

Nanozymes, despite their promising stability and cost-effectiveness, often suffer from lower catalytic activity compared to natural enzymes, limiting their practical applications. Herein, we report the rational design, synthesis, and comprehensive characterization of novel bimetallic palladium-iron nanoparticles supported on nitrogen-doped mesoporous carbon (Fe-Pd@N-MC) as a highly efficient peroxidase-mimicking nanozyme. Structural and morphological analyses using XRD, HR-TEM, XPS, and N2 physisorption confirmed the successful formation of uniformly dispersed, superparamagnetic bimetallic nanoparticles composed Pd0 and Fe3O4. Benefiting from the synergistic effect between Pd and Fe species, Fe-Pd@N-MC exhibited markedly enhanced peroxidase-like activity compared to its monometallic counterparts (Fe@N-MC and Pd@N-MC) toward both 3,3′,5,5′-tetramethylbenzidine (TMB) and o-phenylenediamine (OPD). Kinetic studies revealed excellent catalytic efficiency and high substrate affinity, with Km values of 0.156 mM for TMB and 0.088 mM for OPD. Mechanistic investigations identified hydroxyl radicals (•OH) as the dominant reactive species driving the oxidation processes. Exploiting its robust and rapid catalytic performance, Fe-Pd@N-MC was further employed to construct a sensitive and selective colorimetric platform for the detection of dopamine and ascorbic acid, achieving limits of detection of 3.44 μM and 2.87 μM, respectively. The practical applicability of this nanozyme-based sensor was demonstrated through the accurate quantification of ascorbic acid in fresh fruit juice samples, highlighting its potential for applications in biosensing, food analysis and clinical diagnostics.