THz Resonance Spectra of Bacillus Subtilis Cells and Spores in PE Pellets and Dilute Water Solutions

摘要

This paper reports on the THz frequency characterization of highly diluted mixtures of Bacillus Subtilis (BG) cells and spores pressed into pellets with high densities of polyethylene (PE) micro-powders and compares the results with the THz signatures of BG cells and spores in dilute water solutions. The technique of forming matrices of sparsely distributed biological (bio) materials by mixing them into larger concentrations of PE is one that has been previously applied to study spectral signature phenomenology. In particular, previously results have suggested that isolating the microscopic bio-particles leads to an enhancement of the THz signatures - i.e., yielding sharper and stronger absorption resonances. However, it is important to minimize the influence of etalon effects because they can introduce sharp artificial fringes in the transmission spectra that obscure the underlying THz signatures. This paper will present results from optimally prepared PE matrices and very diluted solutions containing reduced concentrations of BG cells and spores. Here, the BG-PE matrices consist of thicknesses of approximately 30 micrometers and contain BG concentrations from 0.1 to 0.3%. Very good reproducibility of resonance frequencies is demonstrated for dilute solutions with the concentrations from 0.1 to 3 mg/m1. As will be shown, these thinner layers allow for the more accurate characterization of smaller amounts of bio samples and reveal new information on the THz signatures of BG cells and spores. In particular, these results show very close correlations between the spectra of BG cells and spores and suggest both contain common genetic components. These studies provide new information that will be useful in the future development of THz-based sensors.