Yoon S A, Cha S H, Jun S W, Park S J, Park J-Y, Lee S, Kim H S, Ahn Y H
Department of Physics and Department of Energy Systems Research, Ajou University, Suwon 16499, South Korea.
Co-first authors with equal contribution.
Biomed Opt Express. 2019 Dec 23;11(1):406-416. doi: 10.1364/BOE.376584. eCollection 2020 Jan 1.
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, -glucan, and -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.
大多数微生物检测技术都需要预处理，如荧光标记和培养过程。在此，我们提出了基于太赫兹频率范围内微生物固有介电常数对霉菌、酵母和细菌等微生物进行分类和鉴定的新工具。我们首先测量了由多种微生物组成的薄膜的介电常数，并使用有效介质理论提取了各个微生物的值。霉菌的介电常数为1.24 - 1.85，低于细菌的介电常数（2.75 - 4.11）。酵母表现出特别高的介电常数，达到5.63 - 5.97，甚至高于水的介电常数。这些值与使用微流控超材料在水环境中进行的低密度测量结果一致。特别是，超材料共振对霉菌和细菌发生蓝移，而在水环境中霉菌相对于细菌具有更高的对比度。相比之下，酵母的沉积导致红移，因为它们的介电常数高于水。最后，我们测量了肽聚糖和多糖（如几丁质、β - 葡聚糖和具有短支链和长支链的β - 葡聚糖）的介电常数，并证实细胞壁组成是不同类型微生物介电常数差异的主要原因。
