A device for measuring biological small volume liquid samples in real time is appealing. One way to achieve this is by using a microwave sensor based on reflection measurement. A prototype sensor was manufactured from low cost printed circuit board (PCB) combined with a microfluidic channel made of polymethylsiloxane (PDMS). Such a sensor was simulated, manufactured, and tested including a vacuum powered sample delivery system with robust fluidic ports. The sensor had a broad frequency band from 150 kHz to 6 GHz with three resonance frequencies applied in sensing. As a proof of concept, the sensor was able to detect a NaCl content of 125 to 155 mmol in water, which is the typical concentration in healthy human blood plasma.

Fluid balance is important for a healthy human being. In this paper, a method to measure hydration status was developed and tested towards non-invasive measurement from human skin. Measurement of hydration status was performed by a microwave sensor utilizing a complementary split ring resonator (CSRR). The sensor was modeled, manufactured and then characterized by measuring tailor made skin phantoms based on the realistic electrical properties of skin with different degrees of hydration status. Qualitative longer term (>24 h) evaluation of the sensor was also performed by measuring polyester tissue that was drying over the time. Hydration status, represented by dehydrated, normal and hydrated skin phantoms, based on polyurethane with carbon and ceramic additives, was measured successfully by monitoring the changes in resonance frequency around 5.52 GHz. All results were compared to the dielectric reference measurements done by a commercial laboratory instrument.

A complementary metal-oxide-semiconductor (CMOS) chip biosensor was developed for cell viability monitoring based on an array of capacitance sensors utilizing a ring oscillator. The chip was packaged in a low temperature co-fired ceramic (LTCC) module with a flip chip bonding technique. A microcontroller operates the chip, while the whole measurement system was controlled by PC. The developed biosensor was applied for measurement of the proliferation stage of adherent cells where the sensor response depends on the ratio between healthy, viable and multiplying cells, which adhere onto the chip surface, and necrotic or apoptotic cells, which detach from the chip surface. This change in cellular adhesion caused a change in the effective permittivity in the vicinity of the sensor element, which was sensed as a change in oscillation frequency of the ring oscillator. The sensor was tested with human lung epithelial cells (BEAS-2B) during cell addition, proliferation and migration, and finally detachment induced by trypsin protease treatment. The difference in sensor response with and without cells was measured as a frequency shift in the scale of 1.1 MHz from the base frequency of 57.2 MHz. Moreover, the number of cells in the sensor vicinity was directly proportional to the frequency shift.