Identifying different types of microorganisms with terahertz spectroscopy

Abstract

Most microbial detection techniques require pretreatment, such as fluorescent labeling and cultivation processes. Here, we propose novel tools for classifying and identifying microorganisms such as molds, yeasts, and bacteria based on their intrinsic dielectric constants in the THz frequency range. We first measured the dielectric constant of films that consisted of a wide range of microbial species, and extracted the values for the individual microbes using the effective medium theory. The dielectric constant of the molds was 1.24-1.85, which was lower than that of bacteria ranging from 2.75-4.11. The yeasts exhibited particularly high dielectric constants reaching 5.63-5.97, which were even higher than that of water. These values were consistent with the results of low-density measurements in an aqueous environment using microfluidic metamaterials. In particular, a blue shift in the metamaterial resonance occurred for molds and bacteria, whereas the molds have higher contrast relative to bacteria in the aqueous environment. By contrast, the deposition of the yeasts induced a red shift because their dielectric constant was higher than that of water. Finally, we measured the dielectric constants of peptidoglycan and polysaccharides such as chitin, α-glucan, and β-glucans (with short and long branches), and confirmed that cell wall composition was the main cause of the observed differences in dielectric constants for different types of microorganisms.

Quantification of irrigated lesion morphology using near-infrared spectroscopy

“…NIRS can be used to characterize important physiological properties from spectral signatures. In prior work, several groups, including ours, have shown the ability of NIRS for tracking non-irrigated lesion depth in ex vivo myocardial slabs 29 – 32 . Though hopeful demonstrations, little to no work has been shown for directly monitoring of irrigated lesions, which constitute the vast majority of lesions delivered clinically today 33 – 35 .…”

Terahertz Spectroscopy Applied to Diagnostics in Public Health: A Review

“…Majority of techniques for microbial detection has required pre-treatment such as fluorescence and culture processes. Thus, new tools for microorganism classification and identification, such as mold, yeast, and bacteria, with basis in their THz frequencies, have been developed and established [34].…”

Synthesis and Characterization of Tin Oxide Nanopowder and Its Application to Sensing Different Pathogens

“…This behavior can be attributed to the lower dielectric constant of bacteria than that of yeasts/fungi. (43) The analyzed pathogens have different intrinsic structures and characteristics: C. albicans is a pathogenic yeast, whereas P. aeruginosa is a bacteria. The dielectric properties of yeasts/fungi and bacteria should be different because they have different cellular structures.…”

“…Yeasts consist of various types of polysaccharides, which produce relatively thick cell walls. (43) However, bacterial cell walls are relatively thin (mostly consisting of peptidoglycan). Moreover, yeasts are mainly composed of β-glucan (with long branches and a large molecular weight), while bacteria primarily consist of water.…”