Silver-ceria nanozyme as a colorimetric probe for the rapid detection of lead ions based on oxidase mimic activity

Heavy metals are discharged into the environment from different industrial activities. Due to their high density and toxic effects on human organs, their detection is crucial. Strong methods of detection are required to ensure public health protection and environmental safety. Colorimetric detection, which depends on a visible color change to indicate the presence of a substance, is a simple yet effective method. The visible color change enables the detection of heavy metals with the naked eye. In this work, the Ag/CeO₂ is prepared as an efficient oxidase mimetic nanozyme to detect lead ions in an aqueous medium. The structural, optical, and morphological properties of Ag/CeO₂ are analyzed utilizing powder X-ray diffractometer, UV-Vis spectrophotometer, high-resolution transmission electron microscopy, Fourier transform infrared spectrophotometer, and field emission scanning electron microscope. Further, the oxidase-like property of Ag/CeO₂ is confirmed when Ag/CeO₂ catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue colored oxidized TMB (ox-TMB). The significant contribution of superoxide radicals in the catalytic process is confirmed by the reactive oxygen species (ROS) test. Selectivity analysis shows that Pb²⁺ ions inhibit the oxidase-like activity of Ag/CeO₂. Thus, Ag/CeO₂ shows high selectivity and sensitivity for Pb²⁺ ions with a lower limit of detection of 22 nM in the range from 0.4 μM to 3.8 μM, which is significantly lower than the permissible limits set by WHO and US-EPA. Further, the sensor is applied in the detection of Pb²⁺ ions in tap, well, and river water samples.