A compact microwave frequency reflectometer with attoFarad sensitivity: A path towards an integrated dielectrophoresis cytometer

Abstract

A microwave frequency reflectometer with atto-farad capacitance sensitivity has been designed and tested for detection of particles and cells in a microfluidic channel. The design is implemented on a printed circuit board. Capacitance sensitivity up to 1.25aF is achieved in a 50Hz bandwidth. The sensor was used for detection of 5.7μm polystyrene spheres and Chinese Hamster Ovary (CHO) cells flowing over co-planar electrodes in a microfluidic chip. The reflectometer was used in a dielectrophoresis cytometer. A statistical analysis of particle defection demonstrated that the microwave sensing voltages are below the limit required to prevent actuating beads and cells by dielectrophoresis. The use of a reflected signal rather than one transmitted through a resonator has eliminated the bulky resonator and allowed for a much more integrated design. The sensor nulling is accomplished by changing the RF generator frequency and the need for stable and bulky mechanical phase shifters required for resonator designs is eliminated. The open line design is less sensitive to media conductivity compared to resonator based cytometer and the sensitivity changes by less than 34% for media conductivities from 0.1 to 3S/m.