RF-microwave sensor development for cell and human in vitro and ex vivo monitoring

Abstract: In this research new RF/microwave-based sensor solutions were developed for the monitoring of biological cells and human beings to obtain a better understanding of their activity or state in a quick, cheap, easy and continuous way. The effect of different substances on cell behaviour can be monitored by measuring the electrical environment where changes are observed as cells react to a stimulus. The starting point of the study was a microchip with a capacitance measurement system integrated into the culturing chamber, enabling the monitoring of cell proliferation or death. The main challenge of the study was the correct interpretation of the received signals and the combination of “dry” electronics and “wet” biology, which is a difficult issue in terms of reliability and durability of the system. For this purpose, a low temperature co-fired ceramic package was developed which could withstand cell culture conditions and which did not interfere with the cell activity. A 1.1 MHz shift in resonance frequency of the system could clearly be measured, where the shift depended on the number of cells. Another topic of the research concentrated on a microwave sensor that can be utilized in the examination and analysis of fluid samples collected from the body which provide information about a person’s health status. A microwave sensor was developed, which was tested with liquid samples. Microfluidics were also integrated into the system which allowed the use of very small sample volumes and improved the usability of the device. The challenge of the work was to build the system so that the parts were integrated seamlessly without interfering with each other. The sensor concept was tested successfully using typical concentrations of NaCl found in human blood plasma i.e. 125 to 155 mmol/mol of water. The third topic of the thesis was aiming for a microwave sensor that enables real-time measurement of body fluid balance directly from the skin. The operation of the developed microwave sensor was based on a resonator whose resonance frequency reacted to the electrical properties of materials in its proximity, in this case the water content of the skin and its changes. The function of the sensor was tested with artificial skin, made in the laboratory, which corresponded to the properties of real skin. The observed changes in resonance frequency was +370 MHz and -220 MHz for dehydrated and hydrated skin compared to normal skin, thus providing a wide frequency range for detection of the status of the skin.