Facile preparation of Fe3O4 nanospheres/reduced graphene oxide nanocomposites with high peroxidase-like activity for sensitive and selective colorimetric detection of acetylcholine

Fe3O4 nanospheres/reduced graphene oxide (Fe3O4 NSs/rGO) nanocomposites (NCs) with well-dispersed and dense coverage of Fe3O4 NSs have been synthesized by a simple one-step solvothermal method. Significantly, the resulting Fe3O4 NSs/rGO revealed the highest peroxidase-like activity toward typical peroxidase substrate 3,3′,5,5′-tetramethylbenzidine oxidation, in comparison with Fe3O4 microspheres/rGO and Fe3O4 nano-polyhedrons/rGO. This indicated that the selective fabrication of Fe3O4/graphene composites with desired structures is very important to employ their peroxidase-like catalytic activities. On the basis of the high activity, the Fe3O4 NSs/rGO NCs were used to construct an economical colorimetric platform for the sensitive and selective detection of acetylcholine (ACh) by taking advantage of the specific catalytic reaction of acetylcholine esterase and choline oxidase. After the removal of Fe3O4 NSs/rGO under an external magnetic field, the color variation of the solution associated with ACh content was so obvious by visual observation, while its absorbance intensity was proportional to the logarithm of concentrations of ACh over a wide range from 100 nM to 10 mM with a detection limit as low as 39 nM (S/N = 3). The stability, ease of production, separation and storage, and high peroxidase-like catalytic activity of Fe3O4 NSs/rGO NCs make them a powerful tool to structure a rapid, simple, and sensitive colorimetric platform in pharmaceutical, clinical, and food inspection field.