A multifunctional biosensor for selective identification, sensitive detection and efficient photothermal sterilization of Salmonella typhimurium and Staphylococcus aureus

Background: The foodborne pathogens, e.g., Salmonella typhimurium (S. typ) and Staphylococcus aureus (S. aureus), pose a serious threat to human health. Accurate identification, rapid detection and efficient inactivation are crucial in the early diagnosis and treatment of S. typ and S. aureus. To date, however, the majority of studies have only concentrated on the construction of single-function biological platform for detection or inactivation of S. typ and S. aureus. Therefore, it is imperative to develop a multifunctional surface-enhanced Raman scattering (SERS) biosensor that can effectively sterilize S. typ and S. aureus while simultaneously achieving sensitive detection and selective identification.

Results: Herein, we designed and constructed a multifunctional SERS biosensor based on sandwich structure of "capture probe/bacteria/signal probe" in order to simultaneously identify, detect and kill S. typ and S. aureus. Aptamer-modified ZnO/Ag was used as a capture probe to accurately identify and capture the target bacteria in complex environments. Au@Ag-4-MPBA-Aptamer was employed as signal probe to provide the corresponding bacterial SERS "fingerprint" information. The SERS enhancement mechanism of the sandwich-structure ZnO/Ag-Au@Ag SERS substrate was discussed. The sandwich-type SERS biosensor exhibited the strong localized surface plasmon resonance (LSPR) effect and the detection limit for S. typ and S. aureus was as low as 10 cfu/mL. Furthermore, the sandwich-type SERS biosensor offered excellent photothermal conversion efficiency (54.32 %), enabling photothermal killing of target bacteria when exposed to laser irradiation.

Significance and novelty: A dual enhancement strategy based on a sandwich structure was proposed to maximize the sensitivity of SERS signals using synergistic action of electromagnetic enhancement and chemical enhancement. SERS enhancement factor (EF) was as high as 4.67 × 10⁵. In addition, the sandwich-type SERS biosensor not only exhibited negligible cytotoxicity, but also was proved to be a promising tool for photothermally inactivate of S. typ and S. aureus in food samples.