Label-Free Detection of Bacteria Using Surface-Enhanced Raman Scattering and Principal Component Analysis

Recently, the possibility of creating surface-enhanced Raman scattering (SERS)-based biosensors for rapid detection of bacteria has been widely explored. For this purpose, we used ultrasensitive SERS spectroscopy to detect and identify common bacteria's spectral profiles in different experimental conditions: using in situ-synthesized silver colloids (Bacteria@AgNPs) and incubation of the biomass in silver colloids. Moreover, a label-free SERS-based detection protocol was optimized and the influences of taxonomic affiliation and time-dependent effects of incubation in silver colloid were monitored. Label-free detection and identification at single-cell level of common pathogens (Escherichia coli, Aeromonas hydrophila, and Bacillus cereus) were assessed using SERS mapping under the optimized experimental conditions. High-accuracy principal component analysis (PCA) was used for discrimination at strain level of the tested bacterial species. The reduced volume of sample required (3 mu L), rapid spectral acquisition (within minutes), and the use of SERS mapping at single-cell level provide an ideal candidate for developing SERS-based biosensors for food safety, water research, and health care real-life applications.