Ultrasensitive Stimulation Effect of Fluoride Ions on a Novel Nanozyme–SERS System

Recently, nanomaterial-based enzyme mimics (nanozymes) have captured extensive interest owing to their high stability and low cost compared with natural enzymes. The mechanism of the stimulation effect of external substances on the nanozymes and their sensing applications are significantly attractive. In this study, we have constructed an excellent nanozyme–SERS system based on reduced MnCo₂O₄/Au nanotubes (R-MnCo₂O₄/Au NTs) through a self-reduction process with the assistance of oxygen vacancies. In the R-MnCo₂O₄/Au NTs, R-MnCo₂O₄ possesses rich oxidation states of Mn²⁺/Mn³⁺ and Co²⁺/Co³⁺, giving them excellent peroxidase-like catalytic activity; on the other hand, Au NPs on the surface of R-MnCo₂O₄ NTs contribute to their favorable SERS activity. Meanwhile, the important contribution of •OH and O₂^•– radicals in the catalytic mechanism of nanozymes was proposed. Furthermore, the peroxidase-like activity of the R-MnCo₂O₄/Au NTs is reduced with the introduction of fluoride, which is related to the inhibition of the formation of •OH radicals. Owing to the inhibition effect, an ultrasensitive sensing platform for fluoride detection was developed. The work in this study provides a deep insight into the mechanism of the catalytic activity of nanozymes and opens up broad promising prospects in biosensing.