Enhanced peroxidase-like activity of palladium–iron bimetallic nanoparticles supported on N-doped mesoporous carbon for colorimetric detection of ascorbic acid and dopamine

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 of 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 K_m 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 application in biosensing, food analysis and clinical diagnostics.