CeO₂@Mn Nanozymes for Colorimetric and Fluorescence Detection of Iodide Ions in Urine and Blood

The abnormal levels of small molecules, such as iodide ions (I–), in biological systems can be key indicators of certain diseases and may pose risks to human health, playing a significant role in various physiological processes. Herein, we developed a solvothermal method for the synthesis of CeO2-based nanozymes (CeO2 NPs, CeO2@Mn NPs, and CeO2@Se NPs), which serve as recognition probes for the quantitative detection of I– in urine and blood using both colorimetric and fluorescence dual methods. The CeO2@Mn NPs showed the excellent catalytic activity with the aid of O-phenylenediamine (OPD) as the chromogenic substrate; the oxidation of OPD in the presence of H2O2 to produce yellow OPDOX was catalyzed by the CeO2@Mn NPs, acting as the peroxidase enzyme, in a neutral environment (pH = 6) and in the presence of I–. The OPDOX displayed distinct absorption peaks at 275 nm and 450 nm, along with a maximum fluorescence emission peak at 575 nm under 380 nm excitation. Based on these observations, a dual method for I– recognition, utilizing both colorimetric and fluorescence detection, was developed. The limits of detection for I– were found to be 20 μg/L (3σ/S) in colorimetric mode and 0.085 μg/L (3σ/S) in fluorescence mode. Furthermore, we achieved precise detection of I– in human urine and blood, offering significant advantages for use in resource-limited settings and on-site testing. This enhances its potential for broader application in public health surveillance and early disease screening.