Colorimetric determination of ascorbic acid using a polyallylamine-stabilized IrO2/graphene oxide nanozyme as a peroxidase mimic

The authors describe a peroxidase-mimicking nanozyme composed of IrO 2 and graphene oxide (GO). It was synthesized from monodisperse IrO 2 nanoparticles with an average diameter of 1.7 ± 0.3 nm that were prepared by pulsed laser ablation in ethanol. The nanoparticles were then placed on polyallylamine-modified GO nanosheets through electrostatic interaction. The peroxidase-like activity of the resulting nanocomposites was evaluated by catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of H 2 O 2 . Kinetic results demonstrated that the catalytic behavior of the nanocomposites follows Michaelis-Menten kinetics. Experiments performed with terephthalic acid and cytochrome C confirmed that the peroxidase-like activity originated from the electron transfer mechanism rather than from generation of hydroxy radicals. The peroxidase-like activity is inhibited in the presence of ascorbic acid (AA). Based on this property, a colorimetric assay was developed for the determination of AA by exploiting the peroxidase-like activity of IrO 2 /GO nanocomposites. The linear relationship between absorbance at 652 nm and the concentration of AA was acquired. The limit of detection for AA is 324 nM. Further applications of the method for AA detection in real samples were also successfully demonstrated. Schematic of the preparation of polyallylamine (PAH)-stabilized IrO 2 /GO nanocomposites and the colorimetric detection of AA based on the peroxidase-like activity of IrO 2 /GO nanocomposites.