A label-free plasmonic nanosensor driven by horseradish peroxidase-assisted tetramethylbenzidine redox catalysis for colorimetric sensing H2O2 and cholesterol

Label-free gold nanoparticles (AuNPs) plasmonic sensors are limited in the biological assay for weak expansibility. Here, a novel H2O2-sensing AuNPs plasmonic sensor was proposed using 3, 3′, 5, 5′-tetramethylbenzidine (TMB) redox catalysis of H2O2-indcued cysteine oxidation for AuNPs coloration (TreHOAuC), and the application of TreHOAuC was examined by combining H2O2-generating oxidase. In the TreHOAuC platform, TMB is transformed into oxidized TMB (oxTMB) by horseradish peroxidase in the presence of H2O2, and oxTMB is restored into TMB after oxidizing cysteine into cystine. The redox cycling of TMB boosts H2O2-induced cysteine oxidation, and the cysteine oxidation is visualized by AuNPs. Critical parameters of the TreHOAuC platform were optimized such as concentration, time, pH, and buffer. Using the TreHOAuC system, H2O2 can be specifically sensed by naked eyes within 2 min, and the detection limit was less than 0.5 μM. As a proof-in-conception, a cholesterol oxidase-paired TreHOAuC system was used to detect cholesterol in serum samples, indicating a linear range of 2–40 μM and great preciseness. In summary, our proposed TreHOAuC method provided a novel and more comprehensive application for biological sensing.