Sources of variability in SERS spectra of bacteria: comprehensive analysis of interactions between selected bacteria and plasmonic nanostructures (original) (raw)
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Analytical and bioanalytical chemistry, 2018
One of the potential applications of surface-enhanced Raman spectroscopy (SERS) is the detection of biological compounds and microorganisms. Here we demonstrate that SERS coupled with principal component analysis (PCA) serves as a perfect method for determining the taxonomic affiliation of bacteria at the strain level. We demonstrate for the first time that it is possible to distinguish different genoserogroups within a single species, Listeria monocytogenes, which is one of the most virulent foodborne pathogens and in some cases contact with which may be fatal. We also postulate that it is possible to detect additional proteins in the L. monocytogenes cell envelope, which provide resistance to benzalkonium chloride and cadmium. A better understanding of this infectious agent could help in selecting the appropriate pharmaceutical product for enhanced treatment. Graphical abstract ᅟ.
Applied Spectroscopy, 2011
The characterization, detection, and identification of bacteria using surface-enhanced Raman scattering (SERS) spectroscopy is drawing considerable attention due to its ability to provide rich intrinsic molecular information about molecules and molecular structures in close proximity to noble metal surfaces. However, sample preparation methods and experimental conditions must be carefully evaluated in order to obtain healthy, interpretable, and comparable results. In this study, several bacterial species including E. coli, B. megaterium, S. aureus, and S. cohnii were systematically evaluated to demonstrate the source of the spectral features of bacterial SERS spectra. It was found that the features observed in bacterial SERS spectra originate mostly from the bacteria surface with some contributions from metabolic activity or molecular species detached from the bacteria surface during sample preparation.
The Analyst, 2012
The on time diagnostics of bacterial diseases is one of the essential steps in the foregoing treatment of such pathogens. Here we sought to present an easy to use and robust method for the discrimination between Gram-positive (Enterococcus faecalis and Streptococcus pyogenes) and Gram-negative (Acinetobacter baumannii and Klebsiella pneumoniae) bacterial genera based on surface enhanced Raman scattering (SERS) spectroscopy. The robustness of our approach lies in the novel method for the production of the SER substrate based on silver nanoparticles and their subsequent recrystallization in solutions containing high concentrations of chloride ions. The method presented here could be an interesting alternative both to commonly used histochemical approaches and commercial SERS substrates.
Surface-Enhanced Raman Scattering of Bacterial Cell Culture Growth Media
Applied Spectroscopy, 2010
The application of surface-enhanced Raman spectroscopy (SERS) to characterizing bacteria is an active area of investigation. Micro-and nano-structured SERS substrates have enabled detection of pathogens present in biofluids. Several publications have focused on determining the spectral bands characteristic of bacteria from different species and cell lines. In this report, the spectra of fifteen commonly used bacterial growth media are presented. In many instances, these spectra are similar to published spectra purportedly characteristic of specific bacterial species. The findings presented herein suggest that bacterial fingerprinting by SERS requires further examination.
Detection of bacteria by surface-enhanced Raman spectroscopy
Analytical and Bioanalytical Chemistry, 2006
In recent years there has been a strong interest in the development of rapid detection techniques of biological species, especially pathogens that are involved in food poisoning, water contamination, and airborne diseases. Conventional detection methods are time consuming and usually involve overnight culture of bacteria in a suitable growth medium. In this study we used surface-enhanced Raman scattering (SERS) to develop a rapid method of identifying bacteria. Molecules in close contact to the nanometallic surfaces show a huge enhancement in their Raman signature. The enhancement can be as great as 10 8-10 14. We also explored the application of dry nanostructured surfaces to characterize biomolecules by softly landing them on plasma-etched silver surfaces. By such landings, biomolecular gas phase ions were allowed to chemically bind to the surface so that the Raman effect was significantly enhanced and fluorescence was suppressed.
Differentiation of bacterial strains by means of surface enhanced FT-Raman spectroscopy
Lithuanian Journal of Physics, 2012
The silver nanoparticle colloid was used to obtain surface enhanced Raman spectra of Listeria monocytogenes, Salmonela enterica, and Esherichia coli bacteria. The SERS spectra were captured using for excitation the near-infrared (1064 nm) laser radiation with reduced intensity, which ensured the prevention of the fluorescence background as well as photo-and thermal decomposition of the samples. It was found that the optimal size of silver nanoparticles for the enhancement of the Raman signal in the near-infrared spectral region is ca. 50 nm. The spectral data obtained in this study indicate that relative intensities of SERS spectral bands of bacteria can be used for spectral differentiation of bacteria. In case of Listeria, Salmonela, and Esherichia cells, the intensity ratio of spectral bands of adenine and cysteine can be used as a spectral marker for differentiation of the bacteria.
Applied Spectroscopy, 2004
Treatment of bacteria with silver yields intense and highly speci c surface-enhanced Raman spectroscopy (SERS) spectra from various cellular chemical components located in the vicinity of the silver colloids. In particular, we demonstrate an extreme sensitivity to avin components associated with the cell envelope and to their state of oxidation. Different spectra, possibly associated with DNA, carboxylates, and perhaps phosphates, are obtained from the soluble interior fraction of the cell.
Characterization of Thermophilic Bacteria Using Surface-Enhanced Raman Scattering
Applied Spectroscopy, 2008
Surface-enhanced Raman scattering (SERS) can provide molecular-level information about the molecules and molecular structures in the vicinity of nanostructured noble metal surfaces such as gold and silver. The three thermophilic bacteria Bacillus licheniformis, Geobacillus stearothermophilus, and Geobacillus pallidus, a Gram-negative bacterium E. coli, and a Gram-positive bacterium B. megaterium are comparatively characterized using SERS. The SERS spectra of thermophilic bacteria are similar, while they show significant differences compared to E. coli and B. megaterium.
Applied Spectroscopy, 2011
It has been recently suggested [N. E. Marotta and L. A. Bottomley, Appl. Spectrosc. 64, 2010, 601-06] that previously reported SERS spectra of vegetative bacterial cells are due to residual cell growth media that were not properly removed from samples of the lab cultured microorganism suspensions. SERS spectra of several commonly used cell growth media are similar to those of bacterial cells as shown here and reported elsewhere. However, a multivariate data analysis approach shows that SERS spectra of different bacterial species grown in the same growth media exhibit different characteristic vibrational spectra, SERS spectra of the same organism grown in different media display the same SERS spectrum, and SERS spectra of growth media do not cluster near the SERS spectra of washed bacteria. Furthermore, a bacterial SERS spectrum grown in a minimal medium, which uses inorganics for a nitrogen source and displays virtually no SERS features, exhibits a characteristic bacterial SERS spectrum. We use multivariate analysis to show how successive water washing and centrifugation cycles remove cell growth media and result in a robust bacterial SERS spectrum in contrast to the previous study attributing bacterial SERS signals to growth media.
Analytica Chimica Acta, 2011
The development of ultrasensitive and rapid methods for the detection of dipicolinic acid (DPA), a biomarker for bacterial spores including Bacillus anthracis, is increasingly important. This paper reports the results of an investigation of surface enhanced Raman spectroscopy (SERS) based ultrasensitive detection of DPA using a gold nanoparticle/polyvinylpyrrolidone/gold substrate (AuNPs/ PVP/Au). The strong SERS effect of this substrate exploits the particle-particle and particle-substrate plasmonic coupling, which is optimized by manipulating the diameter of the nanoparticles (50-70 nm). The correlation between the SERS intensity of the diagnostic band and the DPA concentration (0.1 ppb to 100 ppm) was shown to exhibit two linear regions, i.e., the low-(<0.01 ppm) and highconcentration (>1 ppm) regions, with an intermediate region in between. The presence of a linear relationship in the low-concentration region was observed for the first time in SERS detection of DPA. A detection limit of 0.1 ppb was obtained from the substrates with 60 nm sized Au NPs, which is, to our knowledge, the lowest detection limit reported for DPA using this type of SERS substrate. This finding was also supported by the estimated enhancement factor (∼10 6) and a large adsorption equilibrium constant for the low-concentration region (1.7 × 10 7 M-1). The adsorption characteristics of DPA on the SERS substrates were analyzed in terms of monolayer and multilayer adsorption isotherms to gain insights into the correlation between the SERS intensity and the DPA concentration. The observed transition from the low-to high-concentration linear regions was found to correspond to the transition from a monolayer to multilayer adsorption isotherm, which was in agreement with the estimated minimum DPA concentration for a monolayer coverage (∼0.01 ppm).