Ultrasensitive ppt-Level Detection of Perfluorooctanoic Acid (PFOA) via a Hybrid Nanozyme, Fe3O4@MWCNTs, with Enhanced Peroxidase-Like Activity

Increasing concerns over perfluorooctanoic acid (PFOA), a representative per- and polyfluoroalkyl substance (PFAS) often referred to as "forever chemicals", underscore the urgent need for simple, rapid, and sensitive detection strategies for water monitoring. Herein, we report an ultrasensitive colorimetric sensing platform for monitoring trace levels of PFOA in environmental water using a highly efficient hybrid nanozyme, Fe3O4@MWCNTs. UV-vis absorbance analysis confirmed that the nanozyme composite effectively catalyzes the oxidation of chromogenic substrates, such as 3,3',5,5'-tetramethylbenzidine (TMB), exhibiting a characteristic blue color in the presence of hydrogen peroxide (H2O2). Upon exposure to PFOA, the active sites on the nanozyme interface were blocked by PFOA, suppressing TMB oxidation and resulting in a clear "Turn-off" optical response. This sensing platform enabled quantitative detection of ultralow concentrations of PFOA, ranging from 10 to 1,000 ng/L, with a limit of detection (LOD) of 3.12 ng/L. This work provides a cost-effective, rapid, and practical approach for monitoring environmentally relevant PFOA concentrations in water.