Copper ferrite nanoparticles loaded on reduced graphene oxide nanozymes for the ultrasensitive colorimetric assay of chromium ionsElectronic supplementary information (ESI) available. See https://doi.org/10.1039/d2ay01045c

Nowadays, due to the increasing threat of heavy metal ion pollution faced by the environment and living systems, the development of rapid and highly selective methods for the detection of chromium ions (Cr3+) has aroused increasing interest. In this study, copper ferrite nanoparticles (CuFe2O4) immobilized on reduced graphene oxide (CuFe2O4/rGO) were successfully fabricated by a simple co-precipitation method. The catalyst exhibits high peroxidase-like activity with 3,3′,5,5′-tetramethylbenzidine (TMB) as a chromogenic matrix due to its large specific surface area, adsorption performance and abundant catalytic active sites. Based on the excellent peroxidase-like activity of CuFe2O4/rGO and its Cr3+-mediated inhibition controllability, a novel colorimetric assay for the heavy metal Cr3+was created for the first time. Under optimal experimental conditions, CuFe2O4/rGO can be used as a peroxidase-like nanozyme to achieve the excellent detection of Cr3+in the range of 0.1–25 μM, and the detection limit is 35 nM. The peroxidase-like CuFe2O4/rGO can provide a general catalytic platform for the application of biomimetic enzymatic catalytic systems and colorimetry, and a new approach has been established for the specific determination of the heavy metal Cr3+.