Date of Award
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
Microwave dielectric sensing has become a popular technique in biological cell sensing for its potential in online, label-free, and real-time sensing. At microwave frequencies probing signals are sensitive to intracellular properties since they are able to penetrate cell membranes, making microwave flow cytometry a promising technology for label-free biosensing. In this dissertation a microwave flow cytometer is designed and used to measure single biological cells and micro particles. A radio frequency (RF)/microwave interferometer serves as the measurement system for its high sensitivity and tunability and we show that a two-stage interferometer can achieve up to 20 times higher sensitivity than a single interferometer. A microstrip sensor with an etched microfluidic channel is used as the sensing structure for measuring single cells and particles in flow.
The microwave flow cytometer was used to measure changes in complex permittivity, , of viable and nonviable Saccharomyces cerevisiae and Saccharomyces pastorianus yeast cells and changes in complex permittivity and impedance of two lifecycle stages of Trypanosoma brucei, a unicellular eukaryotic parasite found in sub-Saharan Africa, at multiple frequencies from 265 MHz to 7.65 GHz.
Yeast cell measurements showed that there are frequency dependent permittivity differences between yeast species as well as viability states. Quadratic discriminate analysis (QDA) and k-nearest neighbors (KNN) were employed to validate the ability to classify yeast species and viability, with minimum cross-validation error of with cross validation errors of 19% and 15% at 2.38 GHz and 265 MHz, respectively.
Measurements of changes in permittivity and impedance of single procyclic form (PCF) and bloodstream form (BSF) T. brucei parasites also showed frequency dependence. The two cell forms had a strong dependence on the imaginary part of permittivity at 2.38 GHz and below and a strong dependence on the real part of permittivity at 5.55 GHz and above. Three PCF cell lines were tested to verify that the differences between the two cell forms were independent of cell strain. QDA gave maximum cross-validation errors of 15.4% and 10% when using one and three PCF strains, respectively. Impedance measurements were used to improve cell classification in cases where the permittivity of a cell cannot be detected.
Lastly, a microwave resistance temperature detector (RTD) is designed, and a model is developed to extract the temperature and complex permittivity of liquids in a microfluidic channel. The microwave RTD is capable of measuring temperature to within 0.1°C. The design can easily be modified to increase sensitivity be lengthening the sensing electrode or modified for smaller volumes of solute by shortening the electrode.
Osterberg, Jeffrey A., "Design and Operation of a Microwave Flow Cytometer for Single Cell Detection and Identification" (2022). All Dissertations. 3096.
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