Surface-enhanced Raman scattering detection of bacteria on microarrays at single cell levels using silver nanoparticles

AbstractWe describe a method for the synthesis of SERS-active silver nanoparticles (AgNPs) directly on the surface of bacteria (bacteria@AgNPs), specifically of E. coli cells. This straightforward strategy allows for the sensitive determination of bacteria on a microarray platform. Antibodies were used as selective receptors on the microarray surface. The Raman signal of bacteria@AgNPs is about 10 times higher than that obtained previously with microarrays based on mixing bacteria and AgNPs (bacteria+AgNPs). The optimum SERS enhancement of bacteria@AgNPs is obtained under 633-nm laser excitation, and this most likely is due to the plasmonic interaction of aggregated AgNPs. The method allows for an identification and quantification even of single E. coli bacteria. In our perception, this straightforward approach represents a most valuable tool for the detection of E. coli and, conceivably, of other bacteria, and thus has a large potential in environmental monitoring, medical diagnosis, and in food safety and quality control. Graphical AbstractSynthesizing AgNPs directly on the surface of bacteria is demonstrated to be a highly efficient approach for a label-free readout of bacteria microarrays by surface-enhanced Raman scattering (SERS), resulting in signals about 10 times higher than previously reported results.