Colorimetric detection of chromium (VI) ion using poly(N-phenylglycine) nanoparticles acting as a peroxidase mimetic catalyst

This paper reports on enzyme-like catalytic properties of polyethylene glycol-functionalized poly(N-phenylglycine) (PNPG-PEG) nanoparticles, which have not been explored to date. The developed nanoparticles have the ability to display great inherent peroxidase-like activity at very low concentrations, and are able to catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) substrate in presence of hydrogen peroxide (H2O2). The oxidized product of TMB has a deep blue color with a maximum absorbance at ~655 nm. The PNPG-PEG nanoparticles exhibit Km values of 0.2828 for TMB and 0.0799 for H2O2, indicating that TMB oxidation takes place at lower concentration of H2O2 in comparison to other nanozymes. Based on the known mechanism of H2O2 oxidation by hexavalent chromium [Cr(VI)] ions to generate hydroxyl radicals (•OH), these nanoparticles were successfully applied for the colorimetric sensing of Cr(VI) ions. The sensor achieved good performance for Cr(VI) sensing with detection limits of 0.012 μM (0.01–0.1 μM linear range) and 0.52 μM (0.05–12.5 μM linear range). The detection scheme was highly selective, and successfully applied for the detection of Cr(VI) in real water samples.