Surface‐enhanced Raman spectroscopy of bacteria: the effect of excitation wavelength and chemical modification of the colloidal milieu

Abstract

Surface-enhanced Raman spectroscopy (SERS) of bacteria infused with silver or gold colloids reflects the different biochemicals in the immediate, nano-vicinity of the particles. In particular we demonstrate high sensitivity to flavins, important coenzymes usually associated with the cell wall. Varying the type of colloid, the laser excitation wavelength and the chemical protocols enables us to observe spectral signatures from different biochemical components of the microorganism. Specifically, we can switch between normal Raman, resonance Raman, and SERS, altering the relative spectral contributions of the various cell constituents.

SERS of plant material

“…The similarity must therefore indicate contributions from biochemicals common to these biological systems, despite the fact that the composition of bacteria is quite different from that of plants. For silver-coated Escherichia coli 39 at a 514-nm excitation, most of the peaks were assigned to flavins. For 633 nm excitation, new peaks related to adenine derivatives at 730 cm 1 , 1330 and 1030 cm 1 were observed, similar to those found in plants.…”

“…SERS spectra for complex systems such as a bacteria, present only specific components and are different from Raman spectra the which shows all components of the systems. 39 It should be remembered, however, that the preparation of the colloids was different for the two types of material: for alfalfa and the other plants, the biological material itself was responsible for the reduction of the metal salt to colloidal metal, while for E. coli the colloidal metal was prepared in the culture medium by the addition of NaBH 4 as the reducing agent, followed by AgNO 3 or HAuCl 4 as the metal source. 39 Thus, the resemblance between the SERS spectra of our plant material and those of E. coli -both measured in the presence of metal colloids -probably indicates the presence of common features that are enhanced by the metal colloids.…”

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

“…However, the several issues inherent to the nature of the technique, mainly reproducibility, still persist and lower the applicability to its wide spread use in biological applications. The detection and identification of several biological molecules such as proteins [106][107][108][109][110], DNA [111][112][113][114], and RNA [115,116] and molecular organizations such as bacteria [117][118][119][120][121][122][123][124][125][126], yeast [127][128][129], and viruses [130,131] using SERS were reported. The detection scheme could be based on either using the intrinsic fingerprint information of the molecules or molecular structures or the use of an external label.…”

“…Whole microorganism detection and identification using SERS is another research area where the fingerprint spectra obtained from whole microorganisms can be used. There are a number of studies demonstrating the feasibility of technique for whole bacterial detection and identification [117][118][119][120][121][122][123][124][125][126]. The identification and classification of bacteria causing urinary tract infections were demonstrated by Goodacre group using citrate reduced AgNPs [123].…”

Surface‐enhanced Raman spectroscopy: advancements and applications

“…The SERS spectra obtained are compared with the normal and resonance Raman results. 44 Surface-enhanced Raman spectroscopy also provides an advantage in the detailed structural characterization of various materials such as carbon nanotubes, polymers and self-assembled layers. Lefrant et al report their systematic SERS study on single-walled carbon nanotubes, with emphasis on chemically transformed carbon nanotube thin films.…”