Microparticle classification based on permittivity by the concurrent use of resistive pulse sensing and microwave resonators

Official URL: https://risc01.sabanciuniv.edu/record=b3157893_(Table of contents)

Automated material classification of microparticles inside a liquid can provide critical functionality for biological and environmental problems, such as the monitoring of bacterial and microplastic pollution in water resources. In this regard applications using resistive pulse sensing (Coulter Counter Principle) and RF frequency impedance cytometry have been widely adopted. Although these technologies are well established in research laboratories, they provide information mainly about the geometrical size of the analyte. This limitation originates from the frequency regime employed (i.e., several kHz to tens of MHz). As a result, these techniques fail to differentiate between two analytes with different material composition but same size. To overcome this shortcoming, labelling techniques are employed with optical microscopes which decreases the throughput, and increases the cost and complexity. Instead of using labeling and optical techniques (such as Raman spectroscopy), an all-electronic detection/differentiation method is introduced. In the technique we developed, resistive pulse sensing and microwave resonator sensing methods are simultaneously exploited. Low-frequency (~1 MHz) resistive pulse sensing is used to extract volume information of particle/cell, whereas a high frequency microwave resonator is used to extract electrical volume information of the particle/cell. Electrical volume of a particle is a function of both permittivity and geometric volume of the particle. Therefore, by simultaneously measuring the geometrical and electrical volume of a particle its permittivity can be obtained and used for label-free material classification. In the scope of this thesis, narrowband phase sensitive detection circuits are implemented for microwave and low frequency measurements. Polystyrene and Soda-lime glass are used as microparticle materials. MDA-231 (breast cancer cells) are used to verify the technique in biological domain.