Microfluidics-Integrated Microwave Sensors for Single Cells Size Discrimination

The size of a cell is one of the most fundamental biophysical parameters it possesses. Traditionally size measurements are done by using optical microscopy and quantitative phase imaging. However, a sensor with higher resolution, high throughput and lower cost is still needed. Here, a novel microfluidics-integratedmicrowave sensor is demonstrated to characterize single cells in real-time without labelling. Coplanar waveguide resonator is designed with a bowtie-shaped sensing electrodes separated by $50 \ \mu \mathrm{m}$. Cells are transported to sensing region by microfluidic channels and their sizes are measured simultaneously by the microwave sensors and optical microscopy. To enhance the microwave resolution, the microwave resonator is equipped with external heterodyne measurement circuitry detecting each and every cell passing through the sensing region. By comparing quantitative microscopic image analysis with frequency shifts, we show that microwave sensors can effectively measure cellular size. Our results indicate that microfluidics-integrated microwave sensors (MIMS) can be used for detecting.