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 (Cu2O/CTS NPs) with Cr(VI)-specific oxidoreductaselike 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 Cu2O/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 mu M), 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 Cu2O/ 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.