The biochemical origins of the surface-enhanced Raman spectra of bacteria: a metabolomics profiling by SERS

Abstract

The dominant molecular species contributing to the 785 nm excited SERS spectra of bacteria are the metabolites of purine degradation: adenine, hypoxanthine, xanthine, guanine, uric acid and AMP. These molecules result from the starvation response of the bacterial cells in pure water washes following enrichment from nutrient rich environments. Vibrational shifts due to isotopic labeling, bacterial SERS spectral fitting, SERS and mass spectrometry analysis of bacterial supernatant, SERS spectra of defined bacterial mutants, and the enzymatic substrate dependence of SERS spectra are used to identify these molecular components. The absence or presence of different degradation/salvage enzymes in the known purine metabolism pathways of these organisms plays a central role in determining the bacterial specificity of these purine-base SERS signatures. These results provide the biochemical basis for the development of SERS as a rapid bacterial diagnostic and illustrate how SERS can be applied more generally for metabolic profiling as a probe of cellular activity.

Strain-level typing and identification of bacteria – a novel approach for SERS active plasmonic nanostructures

“…The last two molecules are important in the process of cellular respiration taking place in the bacterial cell membrane and demonstrate a close interaction between SERS-active platform and cell wall/ membrane of bacteria. It should likewise be noticed that metabolites of purine degradation may also contribute to the intensity of the band at 730 cm -1 [42]. However, according to Premasiri et al the band at 1352 cm -1 (not observed in our spectra) represents a metabolic by-product like pyocyanin, a pigment that bacteria produce during their growth.…”

“…Previously, it was shown that the dominant molecular species giving their contribution to the SERS spectra of bacteria excited at 785 nm are the metabolites of purine degradation [42]. However, slight changes of the dominant SERS bands may be caused by the presence of the additional proteins/enzymes produced by bacterial cells, which can be concluded from the SERS experiments performed with E. coli strains.…”

Rapid Detection of Bacteria from Blood with Surface-Enhanced Raman Spectroscopy

“…Sodium diphosphate buffer was found to generate the SERS signal faster for certain species than washing with water. 61 The samples were spun down and the rinsing process was repeated 3×. Upon completion of the third centrifugation step, the supernatant was removed to leave approximately 10 μ L of sample for SERS analysis.…”

Bioanalytical applications of surface-enhanced Raman spectroscopy: de novo molecular identification

“…Analysis of SERS spectra together with isotopic labeling and MS resulted in dominating features of purine degradation products: adenine, hypoxanthine, xanthine, guanine, uric acid, and AMP as the bacterial cell went through the starvation process. 177 The results provided a fundamental point for the development of SERS as rapid bacterial detection as well as a mean to monitor cellular activity and the kinetic of metabolic pathway.…”

“…177 The SERS capacity for bacterial identification as well as the biochemical origins of the vibrational fingerprints on SERS spectra was fully exploit. In general, SERS spectra of bacteria were obtained with Ag-coated SiO 2 SERS chip substrate at 785 nm, which can eliminate strong SERS signals contributed from bacterial cell wall (lipids, polysaccharides, peptidoglycan, and proteins).…”