SERS-active Au@Ag core-shell nanorod (Au@AgNR) tags for ultrasensitive bacteria detection and antibiotic-susceptibility testing

There is a challenge to obtain an ultrasensitive and rapid approach to detect bacteria and identify resistance. As a powerful bioanalytical tool, surface-enhanced Raman scattering (SERS) in bacterial detection have attracted increasing attentions. Herein, we developed a SERS-active Au@Ag core-shell nanorod (Au@AgNR) tag platform for ultrasensitive bacteria detection and antibiotic-susceptibility testing (AST). The platform established that surface enhanced Raman scattered Rhodamine 6G (R6G) absorption at 1517 cm^-1 had a good linearity (RI = 3865 + 193logC; R² = 0.97) with logarithm of E. coli concentration over a range of 10⁷–10² CFU (colony forming unit)/mL with limit of detection as low 102 CFU/mL. When E. coli was exposed to ampicillin at minimum inhibitory concentration (MIC, 4 μg/mL), Raman spectroscopy showed the obvious variation between ampicillinsusceptible E. coli (Amp^--E. coli) and the ampicillin-resistant E. coli (Amp⁺-E. coli). Combined with principal component analysis (PCA) statistical analysis, the Raman intensity variation mentioned above allows to obtain rapid antibiotic resistance testing (<3.5 h). In addition, E.coli spiked into blood from C57BL/6 mice can be identified clearly, indicating the potential for point-of-care diagnostics.