CMOS lab on a chip device for dielectric characterization of cell suspensions based on a 6 GHz oscillator

In this paper we present a dielectric sensor approach to detect concentration of a cell species in a biological cell suspension based on an oscillator. Center frequency of the oscillator (sensor) is chosen to be 6 GHz, to avoid cell parameter dependent variation of dielectric permittivity of the cell suspension at lower frequencies. A theoretical basis of microwave dielectric permittivity of biological cell suspensions has been derived in this work. Interdigitated capacitor is used as the sensor and is coupled with inductors in a cross coupled oscillator topology for read out. Sensitivity (frequency shift) of 15 MHz per unit permittivity at the center frequency of 6 GHz has been observed from the measurements, which is very close to the simulated value of 20 MHz - 22 MHz per unit permittivity change. The proof of concept is established using solutions or materials of known permittivity which are close to the calculated permittivity of cell suspensions with given cell concentrations. A further characterization of the sensor is done using standard supersaturated sugar solution.