Permittivity-based classification by the integration of impedance cytometry and microwave sensing

The direct determination of the permittivity of individual micro-objects has proven challenging due to the convoluting effect of their geometric size on capacitive signals (i.e., on the electric size of a particle). To overcome this challenge, we have developed a sensing platform to independently obtain both the geometric and electric size of organic and inorganic particles, by combining impedance cytometry and microwave resonant sensing in a microfluidic chip. This way the microwave signal is normalized to yield an intrinsic parameter that depends only on permittivity. The permittivity can then be used for material classification or single-cell interrogation.