Microwave resonator sensors are attractive for their contactless and label-free capability of monitoring bacterial growth in liquid media. This paper outlines a new label-free microwave biosensor based on a pair of planar split ring resonators for non-invasive monitoring of bacterial growth on a solid agar media. The sensor is comprised of two split ring resonators with slightly different resonant frequencies for differential operation. The transmission coefficient (S21) of the sensor is considered as the sensor's response with a designed and measured quality factor above 200 to ensure a high-resolution operation of the biosensor. Two resonant frequencies of 1.95 and 2.11 GHz represent the sensing signal and the reference signal, respectively. The developed sensor demonstrates high performance in monitoring the growth dynamics of Escherichia coli (E. coli) on Luria-Bertani (LB) agar with 4 mm thickness. The sensor's resonant amplitude response demonstrated 0.5 dB variation corresponding to the bacterial growth over 48 hours when bacteria were spread on LB agar starting with initial OD600 = 1.5. Moreover, 0.6 dB change in the sensor's response was observed over 96 hours of bacterial growth starting with an initial OD600 = 1.17 spotted on LB agar. The measured results fit well to the curves created using Richards’ bacterial growth model, showing the strength of the sensor as a potential candidate for use in predictive food microbiology systems.

中文翻译：

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使用微波生物传感器对固体培养基上的细菌生长进行无标签，非侵入性的快速监测

微波谐振器传感器具有监测液体介质中细菌生长的非接触式和无标签能力，因此颇具吸引力。本文概述了一种新的无标记微波生物传感器，该传感器基于一对平面裂环谐振器，用于无创监测固态琼脂培养基上的细菌生长。该传感器由两个裂环谐振器组成，谐振频率略有不同，用于差分操作。传感器的传输系数（S21）被认为是传感器的响应，其设计和测量的品质因数大于200，以确保生物传感器的高分辨率操作。1.95 GHz和2.11 GHz的两个谐振频率分别代表传感信号和参考信号。这款开发的传感器在监测大肠杆菌（E. coli）在4 mm厚的Luria-Bertani（LB）琼脂上的生长动力学方面表现出很高的性能。传感器的共振幅度响应表明，当细菌从初始OD600 = 1.5开始分布在LB琼脂上时，细菌在48小时内的生长对应于0.5 dB的变化。此外，从LB琼脂上观察到的初始OD600 = 1.17开始，在细菌生长的96小时内，传感器的响应发生了0.6 dB的变化。测量结果与使用理查兹细菌生长模型创建的曲线非常吻合，显示出传感器的强度，可作为预测性食品微生物系统的潜在候选者。当细菌在LB琼脂上扩散时，从初始OD600 = 1.5开始，对应于48小时内细菌生长的5 dB变化。此外，在细菌生长的96小时内观察到传感器响应的变化为0.6 dB，起始于LB琼脂上的初始OD600 = 1.17。测量结果与使用理查兹细菌生长模型创建的曲线非常吻合，显示出传感器的强度，可作为预测性食品微生物系统的潜在候选者。当细菌在LB琼脂上扩散时，从初始OD600 = 1.5开始，对应于48小时内细菌生长的5 dB变化。此外，在细菌生长的96小时内观察到传感器响应的变化为0.6 dB，起始于LB琼脂上的初始OD600 = 1.17。测量结果与使用理查兹细菌生长模型创建的曲线非常吻合，显示出传感器的强度，可作为预测性食品微生物系统的潜在候选者。