Surface-Enhanced Raman Scattering from Intracellular and Extracellular Bacterial Locations

Abstract

While surface-enhanced Raman scattering (SERS) can increase the Raman cross-section by 4-6 orders of magnitude, for SERS to be effective it is necessary for the analyte to be either chemically bonded or within close proximity to the metal surface used. Therefore most studies investigating the biochemical constituents of microorganisms have introduced an external supply of gold or silver nanoparticles. As a consequence, the study of bacteria by SERS has to date been focused almost exclusively on the extracellular analysis of the Gram-negative outer cell membrane. Bacterial cells typically measure as little as 0.5 by 1 mum, and it is difficult to introduce a nanometer sized colloidal metal particle into this tiny environment. However, dissimilatory metal-reducing bacteria, including Shewanella and Geobacter species, can reduce a wide range of high valence metal ions, often within the cell, and for Ag(I) and Au(III) this can result in the formation of colloidal zero-valent particles. Here we report, for the first time, SERS of the bacterium Geobacter sulfurreducens facilitated by colloidal gold particles precipitated within the cell. In addition, we show SERS from the same organism following reduction of ionic silver, which results in colloidal silver depositions on the cell surface.

Comprehensive Detection and Discrimination of Campylobacter Species by Use of Confocal Micro-Raman Spectroscopy and Multilocus Sequence Typing

“…This subsequently resulted in poor spectral reproducibility that could be compensated for, in part, by coadding individual spectra. Similar spectral reproducibility issues were also observed when using surface-enhanced Raman scattering spectros- copy for bacterial analysis (31,32). This is the major reason that we used traditional confocal micro-Raman spectroscopy for this study.…”

“…PCA and HCA are unsupervised classification methods that illustrate similarity relationships between Raman spectra without a priori knowledge about the bacteria investigated (28). DFA is a supervised classification method that constructs a dendrogram structure to segregate bacteria according to their known bacterial characterization (i.e., type) (31,32).…”

“…The use of pattern recognition can unmask relationships and cluster constituents on the basis of their perceived closeness. Among the spectroscopy-based pattern recognition methods, unsupervised principal-component (PC) analysis (PCA), hierarchical cluster analysis (HCA), and supervised discriminant function analysis (DFA) are three major types, providing either cluster plots or dendrogram structures for segregation and discrimination (31,32). Recently, soft independent modeling of class analog (SIMCA) has been extensively employed to study bacterial identification to the species level (42).…”

Laser-targeted photofabrication of gold nanoparticles inside cells

“…However, there are several limitations with these methods; bare nanoparticles do not readily penetrate cellular membranes, and even once inside the cell, they cannot move freely. A promising alternative has been to grow gold nanoparticles within bacteria [8][9][10][11] or human cells by infusion of a low-density chloroaurate solution 12,13 , albeit without the means to control location.…”

Surface-Enhanced Raman Scattering as an Emerging Characterization and Detection Technique

“…However, because any species in contact with the metal surface could potentially provide a signal, a significant background problem with such studies was found to exist. Furthermore, the strong interaction of some biological molecules with metal surfaces often resulted in biological fouling, as biomolecules randomly adsorbed onto the metal surfaces [73,75,77].…”