Surface-enhanced Raman scattering for the rapid discrimination of bacteria

Abstract

Raman spectroscopy is attracting interest for the rapid identification of bacteria and fungi and is now becoming accepted as a potentially powerful whole-organism fingerprinting technique. However, the Raman effect is so weak that collection times are lengthy, and this insensitivity means that bacteria must be cultured to gain enough biomass, which therefore limits its usefulness in clinical laboratories where high-throughput analyses are needed. The Raman effect can fortunately be greatly enhanced (by some 10(3)-10(6)-fold) if the molecules are attached to, or microscopically close to, a suitably roughened surface; a technique known as surface-enhanced Raman scattering (SERS). In this study we investigated SERS, employing an aggregated silver colloid substrate, for the analysis of a closely related group of bacteria belonging to the genus Bacillus. Each spectrum took only 20 s to collect and highly reproducible data were generated. The multivariate statistical technique of principal components-discriminant function analysis (PC-DFA) was used to group these bacteria based on their SERS fingerprints. The resultant ordination plots showed that the SERS spectra were highly discriminatory and gave accurate identification at the strain level. In addition, Bacillus species also undergo sporulation, and we demonstrate that SERS peaks that could be attributed to the dipicolinic acid biomarker, could be readily generated from Bacillus spores.

The Intricate Nature of SERS: Real‐Life Applications and Challenges

“…In the last decades, SERS was used to identify: DNA bases [58], a wide range of explosives and trace materials [59], food additives [60], therapeutic agents [61], different species of pathogenic and nonpathogenic bacteria [62][63][64], protozoa [65], fungi [66,67], and their spores [68], respectively. Furthermore, as previously described, vibrational spectroscopy can be used to study the uniqueness of microorganisms.…”

Detection of the Quorum Sensing Signal Molecule N-Dodecanoyl-DLHomoserine Lactone Below 1 Nanomolar Concentrations using Surface Enhanced Raman Spectroscopy

“…SERRS uses both the chromophore of RR and the plasmon resonance of SERS to achieve high enhancements, also here single molecules have been detected [13]. Like Raman, SERS has been applied with even greater success to bacteria samples in order to detect, identify and classify bacteria [15,16,17,18]. Pearman et al have investigated seven different types of signal molecules (differing by acyl chain lengths and varying from 4 to 12 carbons) using SERS with silver colloids, but not in the relevant concentration range, and not under physiological conditions [19].…”

Rapid bioparticle concentration and detection by combining a discharge driven vortex with surface enhanced Raman scattering

“…16,19 A scanning time of only 20 s has been reported for the rapid detection of bacteria using SERS, however, the concentration of bacteria used was directly from a growth plate ͑ϳ10 9 CFU/ ml͒. 20 Another difficulty in detecting bacteria with spectroscopy is that the bacteria needs to be immobilized, either in the suspension or on a substrate. This process can be accomplished using optical tweezers to eliminate Brownian motion away from the beam during scanning.…”