Magnetic microspheres with polydopamine encapsulated ultra-small noble metal nanocrystals as mimetic enzymes for the colorimetric detection of H2O2 and glucose

Abstract

The exploitation of multifunctional nanocomposites as artificial mimetic enzymes has received significant attention. This study reports a novel sandwich-structural magnetic microsphere (Fe₃O₄@resorcinol/formaldehyde resin–metal@polydopamine), in which ultra-small noble metal nanocrystals can be sandwiched between the resorcinol/formaldehyde resin (RF) and polydopamine (PDA) layers. By changing the metal precursor, various microspheres decorated with mono- or bi-metallic nanocrystals (Pt, Pd, Au, PtAu, etc.) can be obtained. The dual-shelled magnetic microsphere not only provides abundant active sites for noble metal nanocrystals but also effectively restrains aggregation and leaching. The as-prepared Fe₃O₄@RF–Pt@PDA can efficiently catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H₂O₂, which confirms that the as-prepared nanocatalyst shows good peroxidase-like activity. The catalytic activity of Fe₃O₄@RF–Pt@PDA is dependent on pH and temperature, and the relevant catalytic kinetics follow the Michaelis–Menten behaviors. Moreover, this kind of magnetic microsphere can be further applied for H₂O₂ and glucose detections and the limit of detection (LOD) is found to be as low as 3.1 μM and 1.36 μM, respectively. Benefiting from a facile preparation process, superior structure, and outstanding catalytic activity, these multifunctional microspheres possess high potential as artificial enzymes in clinical diagnosis, analytical chemistry and environmental fields.