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 CeO 2 -based nanozymes (CeO 2 NPs, CeO 2 @Mn NPs, and CeO 2 @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 CeO 2 @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 H 2 O 2 to produce yellow OPD OX was catalyzed by the CeO 2 @Mn NPs, acting as the peroxidase enzyme, in a neutral environment (pH = 6) and in the presence of I – . The OPD OX 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.