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Co3O4 hollow nanocages (Co3O4 HNCs) were prepared by simple calcination with ZIF-67 as the precursor. Compared with ordinary nano-sized Co3O4, skeletal Co3O4 HNCs have a larger specific surface area and porosity, lead to better dispersion, which can expose more catalytic active sites, and obtain higher catalytic activity. Experiments indicate that Co3O4 HNCs are used as a catalyst to make H2O2 generate O2. At the same time, Co3O4 HNCs act as bridge to accelerate the electrons transfer from the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to the dissolved oxygen and efficiently obtain blue oxidized TMB (oxTMB) at low concentration of H2O2. Steady-state kinetic analysis shows a lower Km and a higher Vmax value than other materials, indicating its excellent affinity and high catalytic efficiency. Based on the inhibitory effect of dopamine (DA) on TMB oxidation in the system, a sensitive, visual colorimetric biosensing method is developed. The calibration curve of DA has a good linear response at both high and low concentrations. Compared with other system, it has the unique advantage of very low detection limit, while retaining a wide detection range, and realizes the accurate detection of actual samples with different concentrations.

In this work, a gold nanocluster with lysine (Lys) as a ligand was fabricated, and a novel nanocomposite probe (AuNCs@Lys-MnO2) was prepared based on fluorescence resonance energy transfer (FRET). AuNCs@Lys-MnO2 was manufactured for sensitive and rapid sensing of glutathione (GSH) in human serum. Gold nanoclusters (AuNCs@Lys) and manganese dioxide nanosheets (MnO2 nanosheets) are combined by electrostatic interaction. MnO2 nanosheets can quickly quench the fluorescence of AuNCs@Lys through FRET. GSH has strong reducing ability, which can reduce MnO2 and degrade AuNCs@Lys-MnO2 FRET system. The presence of GSH subsequently releases AuNCs@Lys, which causes partial recovery of fluorescent signal. The nanocomposite probe is successfully applied to detect GSH in human serum. Detection range is near the normal value in human serum, and there is no need to dilute the serum during the detection process. This is a fast, simple, and cost-effective strategy. The method can detect GSH in the concentration range of 0.5 to 1000 μM, and has a very high sensitivity, the detection limit is as low as 5 nM.