In this study, an innovative cerium dioxide-modified iron oxyhydroxide (CeO₂/FeOOH) nanozyme with peroxidase-like activity was synthesized by one-step hydrothermal method. The CeO₂/FeOOH nanozyme could catalyze the decomposition of hydrogen peroxide (H₂O₂) to produce hydroxyl and superoxide anion radicals, which in turn could oxidize 3,3’,5,5’-tetramethylbenzidine (TMB) to produce a blue substance (oxidized TMB, ox-TMB). Based on this, a CeO₂/FeOOH-based colorimetric sensor was constructed for the detection of H₂O₂. The results showed that the colorimetric sensor exhibited a highly sensitive response to H₂O₂ with a detection limit of 3.92 μmol/L and a linear range of 10 to 1000 μmol/L. The recoveries for spiked samples ranged from 90.59% to 93.42% with relative standard deviations (RSDs) not more than 4.25%. The developed method had the advantages of high sensitivity, high accuracy, speediness and simplicity.

In this study, cerium dioxide-modified cobalt oxyhydroxide (CeO₂/CoOOH) nanomaterial was synthesized by a liquid-phase precipitation method. CeO₂/CoOOH showed good oxidase-like activity toward 3,3’,5,5’-tetramethylbenzidine (TMB), and could directly oxidize TMB to ox-TMB, which presented a clear blue color. Reversely, ascorbic acid (AA) could reduce ox-TMB to TMB, leading to a decrease in the absorbance of ox-TMB at 652 nm and a fading of the blue color. Based on this phenomenon, a new colorimetric sensor for AA detection was developed. The sensor exhibited a highly sensitive response to AA with a limit of detection (LOD) of 2.73 μg/mL and a wide detection range of 5-100 μg/mL and could be successfully applied for rapid detection of AA in oranges and apples.

To explore a simple, rapid and sensitive method for the detection of doxycycline hydrochloride (DOX), metronidazole (MTZ) and sulfadimidine (SM₂) in pork and milk, a porphyrinic zirconium metal-organic framework (MOF) material, PCN-225, was synthesized as a fluorescence probe and used to construct a fluorescence sensor to determine the concentrations of DOX, MTZ and SM₂. First, the morphology, structure and properties of PCN-225 were characterized and optimized, and the sensing mechanism of PCN-225 was analyzed by fluorescence spectroscopy and ultraviolet-visible (UVVis) absorption spectroscopy. Second, the sensing performance of PCN-225 for detecting the three antibiotics was studied. The results showed that the developed method showed excellent selectivity and sensitivity for the detection of DOX, MTZ and SM₂, with detection limits of 4.70, 5.30 and 4.84 nmol/L, respectively. Finally, the sensor was used to detect DOX, MTZ and SM₂ in pork and milk. The recovery rates ranged from 94.7% to 110.8%, with relative standard deviations (RSDs) not higher than 1.1%. In conclusion, this method shows great potential for the detection of DOX, MTZ and SM₂ in a simple, efficient, sensitive and rapid manner.