Phenylboronic acid modification-based novel dumbbell-shaped Au–Ag nanorod SERS substrates for ultrasensitive detection of SO42

Based on the coordination principle of Lewis acids, a 4-mercaptophenylboronic acid (4-MPBA)-modified novel dumbbell-shaped Au–Ag nanorod (4-MPBA@DS Au–AgNR) substrate was developed, which could be combined with the surface-enhanced Raman scattering (SERS) technique to detect SO42− with high sensitivity and specificity. DS Au–AgNRs synthesized in this study with a dumbbell-shaped structure were verified by finite-difference time domain (FDTD) simulation to be capable of stimulating strong localized electromagnetic enhancement (EM) at nano-edge and gap, generating a large number of “hot spots” exhibiting excellent SERS performance. The 4-MPBA modified on its surface could specifically recognize SO42−, producing a change in the spectral peak at 1382 cm−1, thus realizing highly sensitive and specific sensing of SO42−. Under optimized conditions, this SERS sensor responded rapidly to SO42− within 2 minutes and demonstrated outstanding specificity. Calculation of the ratio of the characteristic peaks at 1382 and 1070 cm−1 (I1382/I1070) enabled the quantitative detection of SO42− in the range of 1 × 10−8–1 × 10−3 M, and the detection threshold was as low as 1 nM, which was superior to those of similar detection methods. Importantly, the utility and reliability of this SERS substrate for the determination of SO42− in actual samples were evaluated using ion chromatography as the gold standard, and there was no significant difference between the two protocols (P > 0.05), and the RSD was less than 6% with a satisfactory recovery rate (97.6–102.3%). Therefore, the present protocol has the advantages of simplicity and rapidity, high sensitivity, specificity, stability, and practicability in the determination of SO42− in aqueous solution, providing a reliable solution for tracing SO42− in the fields of food safety and environmental testing.