Dual-functional carboxymethyl chitosan-coated silver nanoparticles for bacterial detection integrated with spectral processing and sterilization.

The development of a dual-functional nanomaterial integrating microbial detection and sterilization capabilities are of great significance for advancing food safety applications. In this work, we synthesized carboxymethyl chitosan coated with spherical silver nanoparticles (CMCS@Ag NPs). CMCS@Ag NPs exhibited improved stability of surface-enhanced Raman scattering (SERS) signals compared to single silver nanoparticles in the detection of three strains including E. coli, S. aureus and S. putrefaciens. Through deuterium isotope labelling, metabolically active bacterial cells produced characteristic carbon-deuterium (C-D) vibrational signatures detectable by Raman spectroscopy. The spectral overlap between C-D and C-H stretching modes showed concentration-dependent linear responses, achieving a detection sensitivity of 0.64 CFU/mL for E. coli. Meanwhile, different combinations of algorithm were used to pretreatment with the raw Raman spectra, among that adaptive iterative reweighting punishment least square method and moving average smoothing (air-PLS + MAS) sensitively obtain better preprocessing accuracy of the three strains. Principal component analysis (PCA) was used to extract characteristic peaks from pretreatment spectra to successfully discriminate the three microorganisms. Furthermore, CMCS@Ag NPs incubated with phosphate-buffered saline (pH ∼ 5.8) exhibited potent antibacterial activity, achieving 99 % reduction in viability for E. coli, S. aureus and S. putrefaciens at a concentration of 5×107 CFU/mL within 45 min. This work presents a versatile nanomaterial-based strategy for simultaneous pathogen detection and inhibition.