Layer-by-layer coating of bacteria with noble metal nanoparticles for surface-enhanced Raman scattering

Abstract

A simple layer-by-layer method to coat the bacterial cells with gold and silver nanoparticles (AuNPs and AgNPs) for the acquisition of surface-enhanced Raman scattering (SERS) spectra is reported. First, the bacteria cell wall is coated with poly (allylamine hydrochloride) (PAH), a positively charged polymer, and then with citrate reduced Au or AgNPs. In order to increase the stability of the coating, another layer of PAH is prepared on the surface. The SEM and AFM images indicate that the nanoparticles are in the form of both isolated and aggregated nanoparticles on the bacterial wall. The coating of bacterial cells with AgNPs or AuNPs not only serves for their preparation for SERS measurement but also helps to visualize the coated of bacterial cells under the ordinary white-light microscope objective due to efficient light-scattering properties of Au and AgNPs. A comparative study single versus aggregates of bacterial cells is also demonstrated for possible single bacterial detection with SERS. The two bacteria that differ in shape and cell wall biochemical structure, Escherichia coli and Staphylococcus cohnii, Gram-negative and -positive, respectively, are used as models. The preliminary results reveal that the approach could be used for single bacterial cell identification.

Raman and Surface-Enhanced Raman Scattering for Biofilm Characterization

“…The main goal of the study was to monitor changes in the SERS spectral pattern during biofilm formation. The deterministic peaks of Escherichia coli were observed at 659, 730, 1320, and 1445 cm −1 with pattern differences from the previous studies [55][56][57][58][59]. The differences were explained in that study by changes in the bacterial strain, growth conditions, instrumentation, and SERS substrates.…”

IR and Raman Spectroscopy for Pathogen Detection

“…By applying different SERS substrates, numerous groups have shown that SERS spectra of different bacterial species show different spectral features, which allows the qualitative differentiation of the species by their SERS spectra [113,117,120,124,126,[128][129][130][131][132][133][134][135][136][137][138][139][140]. The range of the investigated bacteria comprises Gram-positive as well as Gram-negative bacteria.…”

“…The range of the investigated bacteria comprises Gram-positive as well as Gram-negative bacteria. Often, both are represented in the same study [113,120,126,[130][131][132][133][134][135][136]139], but not necessarily so. It is worth noting, though, that sometimes different spectra are reported for the same species [120,127].…”

Application of surface‐enhanced Raman scattering in cell analysis

“…7). [73] SERS from the surface of cells can be used to monitor biological changes continuously. For example, the self-repair process of Proteus vulgaris var.…”