LAUSR

An innovative ratiometric surface-enhanced Raman scattering (SERS) sensor using a 4-mercaptoboric acid (4-MPBA)-modified silver nanoparticles-decorated silicon wafer (Si@Ag NPs chip) was proposed for the ultra-sensitive determination of F‒ ions in aqueous solutions. The principle of sensing strategy is based on the fluoride-induced structural symmetry breaking and charge redistribution of phenylboronic acid, leading to a band shift of C-C stretching mode of 4-MPBA from 1589 to 1576 cm-1. Accordingly, a ratiometric signal of the area ratio (A1576/A1589) between the fluoride-bond MPBA molecules and unoccupied MPBA molecules can be used for the quantitative response of F‒ ions. In comparison with other SERS-based sensing methods, this ratiometric method can avoid a large error resulting from the inhomogeneity of substrates. Under the optimized analytical conditions, the proposed SERS sensor possesses a quick response to F‒ ions within two minutes and exhibits high selectivity for F‒ ions with the determination limit of 10-8 M, which is over three orders of magnitude lower than the World Health Organization (WHO) guideline value for F‒ ions in drinking water. Of particular significance, the present sensor features favorable recyclability, which preserves suitable reproducibility during 6-time cyclic determination of F‒ ions. The practical utility of this sensing system for the determination of F‒ ions was tested with real water and toothpaste samples, and the results demonstrate that this sensor shows high recoveries (90-110%). Given its simple principle and easy operation, the present silicon-based SERS sensor could serve as a promising sensor for various practical applications.