Sub-THz Vibrational Spectroscopy of Bacterial Cells and Molecular Components

In this work, sub-terahertz (THz) spectroscopy is applied to characterize lyophilized and in vitro cultured bacterial cells of non-pathogenic species of Escherichia coli (E. coli) and Bacillus subtilis (BG), spores of BG and DNA from E. coli. One of the goals of this research is to demonstrate that Fourier Transform (FT) spectroscopy in the frequency region of 10–25 cm-1 is sensitive enough to reveal characteristic spectral features from bio-cells and spores in different environment, to verify the differences between species, and to show the response of spores to vacuum and response of cultured cells to heat. The experimental technique was significantly improved for sensitivity and reliability. Observed spectra taken with a spectral resolution of 0.25 cm-1 using FT spectrometer with a detector operating at 1.7 K are rich in well resolved features having spectral widths of ~0.5–1 cm-1. The reproducibility of experimental results was verified and confirmed. Measured spectra from E. coli DNA and from the entire cell have many similarities, thus demonstrating that the cellular components might contribute to the vibrational spectrum of the cell. The results of this work confirm that observed spectroscopic features are caused by fundamental physical mechanism of interaction between THz radiation and biological macro-molecules. Particularly, the analysis of results indicates that the spectroscopic signatures of microorganisms originate from the combination of low frequency vibrational modes or group of modes at close frequencies (vibrational bands) within molecular components of bacterial cells/spores, with the significant contribution from the DNA. The significance of this study is justified by necessity for a fast and effective, label free and reagent free optical technology to protect against environmental and other biological threats, as well as for general medical research. The obtained results show that THz vibrational spectroscopy promises to add quantitative genetic information to the characteristic signatures of biological objects, increasing the detection accuracy and selectivity when appropriate spectral resolution is used.