Near-Infrared Surface-Enhanced-Raman-Scattering-Mediated Detection of Single Optically Trapped Bacterial Spores

Abstract

A novel methodology has been developed for the investigation of bacterial spores. Specifically, this method has been used to probe the spore coat composition of two different Bacillus stearothermophilus variants. This technique may be useful in many applications; most notably, development of novel detection schemes toward potentially harmful bacteria. This method would also be useful as an ancillary environmental monitoring system where sterility is of importance (i.e., food preparation areas as well as invasive and minimally invasive medical applications). This unique detection scheme is based on the near-infrared (NIR) surface-enhanced Raman scattering (SERS) from single, optically trapped, bacterial spores. The SERS spectra of bacterial spores in aqueous media have been measured using SERS substrates based on approximately 60-nm-diameter gold colloids bound to 3-aminopropyltriethoxysilane derivatized glass. The light from a 787-nm laser diode was used to trap and manipulate as well as simultaneously excite the SERS of an individual bacterial spore. The collected SERS spectra were examined for uniqueness and the applicability of this technique for the strain discrimination of Bacillus stearothermophilus spores. Comparison of normal Raman and SERS spectra reveals not only an enhancement of the normal Raman spectral features but also the appearance of spectral features absent in the normal Raman spectrum.

Understanding SERS of bacteria

“…Alexander et al [26] studied a spore trapped by optical tweezers nominally a few tens of a nanometers away from a SERS-active surface made by binding of gold colloids to silanized glass. Using 787 nm excitation they observed a spectrum which is very different from their direct NR of similar samples.…”

Detecting single Bacillus spores by surface enhanced Raman spectroscopy

“…These problems can be solved by using a much more sensitive vibrational spectroscopic method, surface enhanced Raman spectroscopy (SERS), which could reach the limit of detection (LOD) to a single spore or cell [9][10][11], molecules down to the parts per billion (ppb) level or possibly a single molecule [12]. Raman signals can be enhanced by more than a million times when the probed molecules are attached to metallic nanostructures (typically, Au, Ag, Cu, Pt or Pd), which allow the enhanced Raman scattering takes place in high local optical fields of these structures due to ''electromagnetic field enhancement'' and ''chemical enhancement'' of signals [12,13].…”

Characterization of multilayer-enhanced surface-enhanced raman scattering (SERS) substrates and their potential for SERS nanoimaging

“…Surface enhanced Raman scattering (SERS) has been demonstrated to be a powerful technique for analytical analyses in the last several decades [1,2], with applications ranging from homeland defense and security [3][4][5] to biological and biomedical analyses [6][7][8][9]. This wide range of applications is a result of the qualitative nature of SERS and the high degree of sensitivity that can be obtained for chemical and biochemical species in contact with a SERS active metal surface.…”