Narrow terahertz attenuation signaturesin Bacillus thuringiensis

Abstract

Terahertz absorption signatures from culture-cultivated Bacillus thuringiensis were measured with a THz photomixing spectrometer operating from 400 to 1200 GHz. We observe two distinct signatures centered at ∼955 and 1015 GHz, and attribute them to the optically coupled particle vibrational resonance (surface phonon-polariton) of Bacillus spores. This demonstrates the potential of the THz attenuation signatures as "fingerprints" for label-free biomolecular detection.

Biomedical Applications of Terahertz Spectroscopy and Imaging

“…For instance, spores of Bacillus species [35], Escherichia coli, and Bacillus subtilis [36] have different absorption spectra. Additionally, the absorption differences between thermally treated and untreated cells of the same species can be used to assess the living state of bacteria [36].…”

Terahertz spectroscopy for bacterial detection: opportunities and challenges

“…Second, the hydration level of bacterial spores may play a role in the THz signatures. Fresh (normal hydration) B. thuringiensis spores have a distinct signature at 917 GHz, whereas the corresponding signature for less hydrated B. thuringiensis spores increases by 38 to 955 GHz (Zhang et al 2014). This difference between signatures can be reproducible in repeated measurements, and neither signature appears for completely dried samples, indicating that the source of THz absorption is likely from the polarized spore outer coat, which is sensitive to environmental changes and alters its hydration level accordingly.…”

“…This spectrometer has an instrumental resolution of 500 MHz defined by the frequency step, as well as a high dynamic range of typically 70-80 dB around 0.1 THz and 40-50 dB at 1 THz (Zhang et al 2014). Due to its excellent spectral resolution, distinct signatures can be directly observed in the transmission spectra without calculating the aforementioned spectral parameters.…”

“…1. Some distinct spectral signatures (absorption peaks) have been detected for spores of Bacillus species by Fourier transform spectroscopy (FTS) (Brown et al 2006), THz time-domain spectroscopy (THz-TDS) (Yu et al 2005), and photomixing spectrometer (Zhang et al 2014). In addition, vegetative cells of Bacillus subtilis and Escherichia coli exhibited different absorption spectra, although better spectral resolution is required for more obvious discrimination .…”

Terahertz vibrational signature of bacterial spores arising from nanostructure decorated endospore surface

“…Hence, for different vibrational spectroscopic methods, the probed vibrations correspond to the different vibrations in the bacterial spore outercoat based on the penetration depth of the source signal. From THz spectroscopy, Bacillus subtilis (Bs) spores have shown absorbance peaks at 210, 415 and 1035 GHz , Bacillus thurigiensis (Bt) has shown peaks at 917 and 974 GHz , and Bacillus cereus (Bc) has shown absorbance peaks at 811, 830 and 880 GHz . To the best of our knowledge, this is the very first theoretical effort to explore the THz range vibrational activity in the spores, which involves a very large number of atoms.…”