Towards microwave imaging of cells†
Integrated detection techniques that can characterize the morphological properties of cells are needed for the widespread use of lab-on-a-chip technology. Herein, we establish a theoretical and experimental framework to use resonant microwave sensors in their higher order modes so that the morphological properties of analytes inside a microfluidic channel can be obtained electronically. We built a phase-locked loop system that can track the first two modes of a microstrip line resonator to detect the size and location of microdroplets and cells passing through embedded microfluidic channels. The attained resolution, expressed in terms of Allan deviation at the response time, is as small as 2 × 10−8 for both modes. Additionally, simulations were performed to show that sensing with higher order modes can yield the geometrical volume, effective permittivity, two-dimensional extent, and the orientation of analytes. The framework presented here makes it possible to develop a novel type of microscope that operates at the microwave band, i.e., a radar for cells.