SERS of whole cell bacteria and trace levels of biological molecules

Through its several orders of magnitude signal enhancement over normal Raman, surface-enhanced Raman spectroscopy (SERS) provides an opportunity to extend the benefits of vibrational spectroscopy to trace level detection. SERS in particular holds great potential for biological sensing due to the weak Raman bands of water and the reduction in fluorescence backgrounds from interactions of the analyte with the metal SERS substrate. This work examines the trace level detection (<100 ppm) of biological molecules and oligomers such as amino acids, peptides, and oligonucleotides as well as the detection of whole cell bacteria. The SERS substrates employed are electrochemically roughened gold. The biological molecules show well-resolved and intense bands that are an effective spectral signature; these bands also persist in corresponding oligomeric compounds. Spectra from;A,hole cell bacteria have been obtained for several species, including gram-positive and gram-negative strains. Viable and nonviable cells have also been examined and significant spectral differences are observed. The results show the potential for using SERS as an analytical tool for the identification of biological molecules and microorganisms with applications in biological agent detection, food and water monitoring, and the search for signs of extraterrestrial life.