Combining vancomycin-modified gold nanorod arrays and colloidal nanoparticles as a sandwich model for the discrimination of Gram-positive bacteria and their detection via surface-enhanced Raman spectroscopy (SERS)

This study reports the development of a highly sensitive antibiotic-based discrimination and sensor platform for the detection of Gram-positive bacteria through surface-enhanced Raman spectroscopy (SERS). Herein, a combination of gold nanorod arrays (GNAs) and colloidal gold nanoparticles (AuNPs) was used as a SERS platform. To specifically capture Gram-positive bacteria, both GNAs and AuNPs were functionalized with thiol-modified vancomycin (HS-Van) molecules. Three different strains of bacteria (Bacillus subtilis and Staphylococcus aureus as Gram-positive, and Escherichia coli as Gram-negative) were employed to test the proposed system. HS-Van functionalized GNAs (GNA@Van) captured Gram-positive bacteria with high specificity. Also, the bacteria captured by GNA@Van (GNA@Van@Bct) systems showed high signal-to-noise SERS signals with high reproducibility. Addition of AuNP@Van to GNA@Van@Bct resulted in the emergence of a sandwich system (GNA@Van@Bct@Van@AuNP). This system led to a further enhanced SERS signal. The chemometric analysis of GNA@Van@Bct@Van@AuNP enabled the obvious discrimination and detection of Gram-positive bacteria. For comparison, we also tested a smooth gold surface with the same procedure and a similar trend was observed with lower SERS activity.