Synthesis of pH-switchable Pt/Co3O4 nanoflowers: Catalytic mechanism, four-enzyme activity and smartphone biosensing applications

Pt/Co3O4 were synthesized by precipitation and reduction methods, exhibited unparalleled four enzyme activities: oxidase-like, peroxidase-like, catalase-like and superoxide dismutase activities by adjusting pH. The mechanism of enzyme activity was deeply explored, it was found that its oxidase activity originated from the oxygen vacancies of the material and O2−, 1O2, the peroxidase activity was attributed to the 1O2 and OH formed by nanomaterials catalyzing H2O2. Density functional theory calculations showed that Pt-Co with strong metal-oxide interaction interface was the active center, which needed a lower energy than others in the key step of catalyzing O2 to produce O2−. Based on its excellent oxidase activity, a muti-functional colorimetric detection platform for thiram, Cu2+ and ziram had been constructed successfully. The linear ranges of thiram was 0.6–250 µM and the limit of detection was 0.065 µM. The linear ranges of Cu2+ and ziram were 10–200 µM and 5–50 µM, the limit of detection were 4.066 µM and 3.36 µM. It should be noted that the portable smart phone platforms for thiram, Cu2+ and ziram had also been established with instant and quick detection. It was worth noting that in-depth exploration of the detection mechanism combined with in situ diffuse reflectance infrared fourier transform spectroscopy revealed that hydrogen bonds can be formed between thiram and oxidation substrate. And Cu2+ would inhibit the combination. Furthermore, it also showed excellent applications in detecting pesticide and Cu2+ in environmental soil and water samples. This study presented herein may provide an intelligent detection method to monitor environment.