4.5.4 Contactless wide-band nearfield microwave sensing techniques in microfluidic applications

There is a widespread need for highly-sensitive robust sensors for process measurements in microfluidics that have no direct contact to the fluid. This contribution describes how the measurement of the variation of the dielectric properties (conductivity and permittivity) offers an innovative approach to investigating biological and chemical matter and processes in microsystems, for example, cell growth, cell metabolite changes, and the concentration of large aqueous-based molecules. This presentation describes an innovative high frequency sensor that integrates RF/microwave detection in a microfluidic network for quick and precise biological and chemical analysis. It consists of a microstripline waveguide with resonant properties placed adjacent to a microfluidic channel. Contactless conductivity detection is of high interest for many applications in microfluidics and it is particularly attractive for measuring the concentration of inorganic and organic ions and matter that are not directly accessible by optical means.