A Dual-Modal Sensing Platform for Ascorbic Acid Based on Pt-Doped Polymer Nanogels with Oxidase-Like Activity

Nanozymes have attracted extensive attention due to their tunable composition, low preparation cost and facile synthesis. In this study, oxidase -like Pt-doped poly (N-isopropylacrylamide) nanogels (Pt@PNIPAM NG) were prepared by in situ polymerization of N-isopropylacrylamide in the presence of Pt nanoparticles (Pt NPs). The catalytic mechanism was studied by selective scavengers for specific reactive oxygen species (ROS). Results revealed that Pt@PNIPAM NGs could catalyze molecular oxygen to produce singlet oxygen (1O2) and superoxide radicals (O2•-). Michaelis-Menten kinetics analysis revealed that Pt@PNIPAM NGs exhibit a significantly lower Km (0.121 mM) than pure PNIPAM NGs (7.617 mM). This enhanced substrate affinity indicates that incorporating Pt NPs into the nanogel matrix effectively boosts the overall oxidase-like catalytic performance. Pt@PNIPAM NG can catalyze the oxidation of colorless 3,3,5,5-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB). Moreover, ascorbic acid (AA) can reduce oxTMB back to TMB, resulting in a color change and a corresponding decrease in absorbance. Additionally, Pt@PNIPAM NG can also catalyze the oxidation of AA to dehydroascorbic acid (DHA) by reactive oxygen species; o-phenylenediamine (OPD) subsequently reacts with DHA to form fluorescent quinoxaline derivatives. Based on these reactions, a dual-mode colorimetric and fluorometric detection platform for AA was constructed. The platform enabled rapid detection of AA within 10 min. The platform enabled rapid AA detection within 10 min with linear ranges of 1–85 and 1–120 μM and LODs of 0.76 and 0.062 μM for colorimetric and fluorometric modes, respectively. Finally, the dual-mode detection platform was validated using serum mimetic samples, yielding satisfactory analytical results.