Highly Specific Colorimetric Probe for Fluoride by Triggering the Intrinsic Catalytic Activity of a AgPt–Fe3O4 Hybrid Nanozyme Encapsulated in SiO2 Shells

Current colorimetric probes for fluoride (F–) primarily rely on organic chromophores that often suffer from unsatisfactory selectivity, complex organic synthesis, and low aqueous compatibility. Herein, we proposed a highly specific colorimetric method for F– with 100% aqueous compatibility by triggering the intrinsic peroxidase-like activity of a AgPt–Fe3O4 nanozyme encapsulated in SiO2 shells. The excellent catalytic performance of the AgPt–Fe3O4 nanozyme serves as an ideal platform for sensitive colorimetric sensing. After being encapsulated in SiO2, the enzyme-like activity of AgPt–Fe3O4 is inhibited and only F– can exclusively etch the SiO2 shell to expose the active site of the nanozyme, thereby inducing color changes via oxidation of the chromogenic substrate. The limit of detection of the proposed method can reach as low as 13.73 μM in aqueous solution, which is lower than the maximum allowable concentration (79 μM) stipulated in the World Health Organization drinking water regulation. More importantly, this method is highly specific toward F– over other types of anions commonly found in environmental water, making it capable of analyzing sewage samples with very complex matrices. Finally, the nanoprobe is embedded into a test strip by electrostatic spinning to enable the rapid, visual, and on-site detection of F–.