Novel Au-anchored Fe–NC nanozyme-enabled rapid and sensitive colorimetric detection of Cr( <scp>vi</scp> )

Hexavalent chromium (Cr(VI)), as a highly biologically toxic heavy metal ion, poses great threats to environmental safety and human health. Herein, we report a facile and cost-effective colorimetric sensing platform for Cr(VI) detection based on Au nanoparticle-anchored Fe-NC nanozyme (AuNPs/Fe-NC) catalysis. The AuNPs/Fe-NC nanozyme shows comparable catalytic activity and kinetics to natural horseradish peroxidase (HRP), which can catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to its oxidized form, exhibiting a blue color. In the presence of 8-hydroxyquinoline (8-HQ), the catalytic activity of the prepared AuNPs/Fe-NC was inhibited, which weakened the AuNPs/Fe-NC-catalyzed oxidation of TMB. After Cr(VI) was introduced, the catalytic activity of AuNPs/Fe-NC nanozyme was recovered, resulting in an enhanced blue color. By monitoring the variation of UV-vis absorbance, Cr(VI) had been quantified analysis and shown excellent sensitivity with the detection limit as low as 0.25 μM, and the linear range was 1-165 μM. It also exhibited high selectivity toward a series of metal cations and was successfully applied to the detection of Cr(VI) in tap water.