Rapid concentration detection and differentiation of bacteria in skimmed milk using surface enhanced Raman scattering mapping on 4-mercaptophenylboronic acid functionalized silver dendrites

A novel method was developed to rapidly concentrate, detect, and differentiate bacteria in skimmed milk using surface enhanced Raman scattering (SERS) mapping on 4-mercaptophenylboronic acid (4-MPBA) functionalized silver (Ag) dendrites. The 4-MPBA functionalized Ag dendritic SERS substrate was used to capture the bacterial cells and enhance the bacterial signal. Salmonella, a significantly important food pathogen, was used as the representative strain to optimize and evaluate the developed method. The capture efficiency for Salmonella enterica subsp enterica BAA1045 (SE1045) was 84.92 ± 3.25% at 10⁶ CFU/mL and as high as 99.65 ± 3.58% at 10³ CFU/mL. Four different strains, two gram-negative and two gram-positive, can be clearly distinguished by their SERS spectra using principle component analysis. A mapping technique was utilized to automatically collect 400 spectra over an area of 60 μm × 60 μm to construct a visual image for a sensitive and statistically reliable detection within 30 min. Using this method, we were able to detect as low as 10³ CFU/mL bacterial cells in 50 mM NH₄HCO₃ solution and 10² CFU/mL cells in both 1% casein and skimmed milk. Our results demonstrate the feasibility of using SERS mapping method coupled with 4-MPBA functionalized Ag dendrites for rapid and sensitive bacteria detection in complex liquid samples. Graphical Abstract A novel SERS mapping method based on 4-mercaptophenylboronic acid functionalized silver (Ag) dendrites was developed to rapidly concentrate, detect, and differentiate bacteria.