Chitosan modified cuprous oxide nanoparticles with specific oxidoreductase-like activity for rapid and sensitive colorimetric detection of Cr(VI)

In this work, chitosan modified cuprous oxide nanoparticles (Cu 2 O/CTS NPs) with Cr(VI)-specific oxidoreductase-like activity were facilely synthesized via one-step reduction method. In the presence of Cr(VI), colorless 3,3′,5,5′-tetramethylbenzidine (TMB) was rapidly oxidized to blue colored oxTMB with the aid of Cu 2 O/CTS NPs. Systematic studies including steady-state kinetics analysis, X-ray photoelectron spectra (XPS) analysis, radical trapping experiments and photoluminescence spectroscopy were conducted to investigate the catalytic mechanism, which was verified to be electron transfer and active species-involved redox reaction. Based on promoted catalytic oxidation of TMB, a selective and sensitive colorimetric method for fast detection of Cr(VI) was proposed. Under the optimal conditions, this colorimetric method exhibited a wide linear range (0.01–35 μM), low limit of detection (0.5 nM) and short assay time (1 min). In addition, test strip for visual detection of Cr(VI) was constructed by processing the Cu 2 O/CTS NPs+TMB+Cr(VI) sensing system on paper. With the aid of smartphone, a detection limit of 312 nM was achieved within 5 min, showing great potential for on-site detection. Moreover, the method was applied to detect Cr(VI) in spiked tap and lake water samples, the good recoveries (96.10%−103.13%) and low relative standard deviations (1.03%−3.25%) demonstrated the feasibility of the assay.