Fabrication of a bioconjugated dual-functional SERS probe for facile compound screening and detection

Surface-enhanced Raman spectroscopy (SERS) is an ultrasensitive technique for both detection and structural characterizations. To further exploit these advantages, we designed and fabricated a dual-functional SERS probe for specific capture and fast detection of small molecule ligands binding to target protein from a mixture of compounds such as extracts of natural products. As a proof of concept, we synthesized SiO2@Ag nanoclusters that are coated with 6-chlorohexanoic acid for covalent immobilization of serotonin transporter (5-HTT) fused with a Halo-tag through enzyme-substrate recognition. As such, we fabricated a bioconjugated SERS probe, and the synthesis, coating, protein immobilization, and affinity-based ligand binding have been characterized and verified by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and elemental mapping. By applying this probe to analyze Gardenia jasminoides extract, we have successfully identified crocin I as a compound binding to 5-HTT, which was further proved by using mass spectrometry (MS) and nuclear magnetic resonance (NMR). Taken together, we have developed a novel SERS probe by integrating the inherent strength of SERS in molecular analysis with an extended functionality of affinity-guided molecular capture, which has demonstrated the potential in drug screening of challenging systems.