A convenient colorimetric assay for Cr(vi) detection based on the nanozyme Cu-4PDA-NH2 with oxidoreductase-like activity†

Abstract

Hexavalent chromium (Cr(VI)) poses a significant environmental hazard and is recognized as a carcinogen. Conventional instrumental assays do not allow rapid, on-site detection, making the development of an efficient and straightforward method to detect Cr(VI) imperative. Inspired by the structure of an oxidoreductase-like active center, a Cu-4PDA-NH₂ nanozyme, formed by mimicking oxidoreductase-like activity with 3-amino-4-pyridazinecarboxylic acid (4PDA-NH₂) as a ligand, can effectively exert the catalytic activity of an oxidoreductase-like enzyme. Cu-4PDA-NH₂ can be used independently of H₂O₂ to catalyze the reaction of Cr(VI) with the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to form oxTMB, resulting in a distinct blue color. Based on this, a convenient Cr(VI) colorimetric method was developed. The detection threshold for Cr(VI) using the sensor was 14.6 nM (3σ/s), with a linear response range from 0.05–20 μM. In addition, a detection cartridge for on-site detection was prepared by using the proposed method, and it was successfully utilized for detecting Cr(VI) in water samples from diverse environments, achieving satisfactory recovery rates. The developed technique offers a straightforward, efficient, sensitive, and inexpensive approach for Cr(VI) analysis, with no demand for complex conditions and extra separation processes, and it has strong potential for application in environmental assessments.