Understanding SERS of bacteria

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been suggested as a powerful tool to identify bacteria, drawing from its high fingerprint (vibrational) information content, its extreme sensitivity (down to the single molecule level) and its obliviousness to the aqueous environment intrinsic to biological systems. We review here in a comparative manner the various studies that attempted to utilize SERS for this important goal in light of the work carried out by our own group over the past 10 years or so. We show that SERS has an additional major advantage, namely, it introduces a new dimension of selectivity, which, on the one hand, makes it even more suitable as an analytical tool, but on the other hand, it requires gaining control of the precise manner in which the SERS-active metal centers are produced and brought into contact with the micro-organism. Our emphasis in this review is on understanding the spectra in terms of the nature of the SERS-active centers and their placement within the bacterium. On the interpretation and assignment of the spectra, we constantly keep in mind the final goal of bacteria identification.

Functionalized arrays of Raman-enhancing nanoparticles for capture and culture-free analysis of bacteria in human blood

“…Recently, a type of SERS-active substrate with uniformly large and highly reproducible Raman-enhancing power has been developed by growing Ag nanoparticles on arrays of anodic aluminum oxide (AAO) nanochannels to take advantage of the sub-10-nm inter-particle gaps, which act as 'hot junctions' for creating the electromagnetic enhancement 4 . The high sensitivity and reproducibility of such a substrate-hereafter referred to as Ag/AAO-SERS substrate-facilitated the use of SERS for chemical/biological sensing applications [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] . SERS of various types of bacteria including Gram-positive, Gram-negative and mycobacteria have been acquired and the response of bacteria to antibiotics has been examined 21 .…”

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

“…The NPs can be either coated on the outside of the bacterial cell wall or directed to the interior of the bacterial cells. Whereas the first preparation results in spectral information mainly derived from cell wall components, the second one contains additional cytoplasmic information [18,19]. Figure 1 shows the SERS signal acquisition process from a microbiologic sample, when the silver coverage of the bacteria (in blue) is successful.…”

“…Efrima and Zeiri also proposed a novel approach, to use colloid produced in the presence of the biomass [18,19]. The authors used the 633 nm laser line as an excitation wavelength, therefore they were able to report the ring breathing mode band observed at 1004 cm −1 and assigned to the phenylalanine residue [10].…”

Surface-enhanced Raman scattering microfluidic sensor

“…138,139 These advantages showed tremendous potential for bio/chemical molecular analysis at the trace and even single molecule level.…”