Near-infrared surface-enhanced-Raman-scattering-mediated detection of single optically trapped bacterial spores

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.