Highly Resolved Sub-Terahertz Vibrational Spectroscopy of Biological Macromolecules and Cells

Sub-terahertz (sub-THz) vibrational spectroscopy for biosensing is based on specific resonance features, vibrational modes or group of modes at close frequencies, in the absorption (transmission) spectra of large biological molecules and entire bacterial cells/spores. Further improvements in sensitivity, especially in the discriminative capability of sub-THz vibrational spectroscopy for detection, characterization, and identification of bacterial organisms, require spectral resolution adequate to the width of spectral features. Evidences exist for long-lasting relaxation processes for atomic dynamics (displacements) resulting in narrow spectral lines and justifying the development and application of highly resolved vibrational spectroscopy. Here we describe a new continuous-wave frequency-domain spectroscopic sensor with imaging capability operating at room temperature in the sub-THz spectral region between 315 and 480 GHz. We present experimental spectra from biological macromolecules and species obtained using this spectrometer and compare some spectra with simulation results using molecular dynamics. Observed multiple intense and specific resonances in transmission/absorption spectra from nano-gram samples with spectral line widths as small as 0.1
${\rm cm}^{-1}$
provide conditions for reliable discriminative capability, potentially to the level of the strains of the same bacteria, and for monitoring interactions between biomaterials and reagents in near real-time.