Photoreduced Ag surrounding single poly(4-cyanostyrene) nanoparticles for undifferentiated SERS sensing and killing of bacteria.

Developing a rapid, low cost and sensitive sensing strategy for undifferentiated detection and fast killing of bacterial pathogens are critical to alleviating bacteria infections. Here, we propose a direct photoreduction method to synthesize the SERS tag by integrating poly(4-cyanostyrene) nanoparticles (NPs) and silver ions, which are applied as bio-sensing system for bacteria sensing and fast killing. Under a focused laser spot, silver ions on the surface of the poly(4-cyanostyrene) NPs could be photoreduced into Ag NPs, thereby causing the Raman signal amplification of poly(4-cyanostyrene) NPs up to 40 times, and there is a good linear correlation between the Raman intensity of poly(4-cyanostyrene) NPs and different concentrations of Ag. Moreover, 4-mercaptophenylboronic acid, performing the same recognition function for both the Gram-positive and Gram-negative bacteria, is used as bridge between the bacteria and Ag by the inherent chemical bonding. Based on further constructed bio-sensing system, we achieved the quick count and killing of both Gram-positive bacteria, e.g., Staphylococcus aureus (S. aureus), and Gram-negative bacteria, e.g., Escherichia coli (E. coli). Notably, the sensing strategy can detect at least ∼100 cells of E. coli, ∼10 cells of S. aureus and ∼10 cells of their mixture in less than 40 min. The detection accuracy for actual samples can also reach over 80% and the bacteria were entirely killed by Ag after the detection, avoiding bacterial contamination in the environment. This novel method is anticipated to perform as a simple yet effective tool for fast and sensitive bacteria counting and killing.