A high oxidase-like activity, bimetallic single-atom nanozyme FeCe/NC prepared by FeCe-ZIF-8 approach for sensing tannic acid in tea.

To improve the activity of single-atom nanozymes (SAzymes) for applications in food analysis, a new bimetal SAzyme FeCe/NC was developed. Its oxidase-like activity is 40% higher than that of single metal SAzyme Fe/NC. Based on a series of characterization investigations, the catalytic mechanism is that it directly catalyzed O2 to generate •OH, O2 •-and 1O2. It could directly catalyze oxidation 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxTMB, thereunder, a FeCe/NC SAzyme-TMB colorimetric method for the detection of tannic acid (TA) was constructed after the optimization of catalytic conditions. The method has a high R2 of 0.995, a low limit of detection (LOD) of 0.26 µmol/L, and high stability. The detection performance was validated by the real samples (tea). Therefore, the prepared bimetallic SAzyme FeCe/NC can be applied for TA detection without the addition of H2O2, and will have broad applications in the areas of food, feed, and life science.

A point-of-care aptasensor based on the upconversion nanoparticles/MoS2 FRET system for the detection of Pseudomonas aeruginosa infection.

The rapid detection of Pseudomonas aeruginosa (P. aeruginosa) is of great significance for the diagnosis of medical infection. In view of the above, a novel aptasensor based on fluorescence resonance energy transfer (FRET) was developed. It contained aptamer-coupled upconversion nanoparticles (UCNPs-apt) as a donor (excitation 980 nm) and molybdenum disulfide (MoS2) nanosheets as an acceptor. The upconversion fluorescence aptamer system was investigated to obtain the optimal parameters of MoS2 concentration, the incubation time of UCNPs-apt/MoS2 and P. aeruginosa, and pH. Based on the optimal parameters, a linear calibration equation (emission 654 nm) with a wide detection range 8.7 × 10 ~ 8.7 × 107 cfu/mL, a high coefficient of determination R2 0.9941, and a low limit of determination (LOD) 15.5 cfu/mL were established. The method was validated with P. aeruginosa infected foci of mouse wound. The advantage of this aptasensor is that analysis results can be obtained  within 1.5 h, which was much faster than that of the standard method (18-24 h). Furthermore, combined with a portable instrument, it can be used as a point-of-care testing for the early detection of P. aeruginosa infection, which is useful for selecting the correct antibiotics to achieve good therapeutic effects. Additionally, it also has a broad application prospect in food and environmental areas.