Bow tie shaped coplanar waveguide microwave resonators for single cell detection, flow rate measurements, and nanopore sensing of viruses

Abstract

Measurement sensitivity of different biosensing applications can be enhanced by using the microwave resonators. In the first application, microwave sensors based on bow tie shaped coplanar waveguide (CPW) resonator was designed to detect single cells in real-time. While the resonator was kept at its resonance frequency, cells/particles were made a pass through the sensing electrodes and their frequency shift statistics were obtained. For each cell, the geometrical size that is obtained from the optical microscope was correlated to the electrical volume of the cell which was measured by the microwave signals. A linear relationship was observed between the electrical and geometrical volume of a cell. Dispersion caused by the device geometry was elucidated using the standard sized polystyrene microparticles. To observe the single-cell dynamic, a target cell was trapped around the sensing region, and its microwave response was continuously recorded. Then cells were treated with dimethyl sulfoxide (DMSO), a chemical accelerating dehydration, and a decline in the resonance shifts by time was observed as the cell lost total content. Secondly, the same microwave design was patterned on a low-stress thin film membrane and used for flow rate measurements. When the flow is on, there were certain shapes continuously formed on the membrane and after a critical point pulsation of the membrane cause a shift in the resonance frequency. When the flow rate was increased, it was observed that these shapes formed faster so does frequency shifts in the resonance. Therefore, the effective flow rate could be correlated to the pulsation frequency of the membrane. Then, devices with different membrane size and different channel geometry were fabricated to span different flow rate values. As a secondary sensing mechanism, the flow was given from the reset condition where there was no flow. In this case, the amount of frequency shift was related to the flow rate and a monotonically increasing relation was obtained. As a next step, instead of liquid, the air was pressurized to measure the flow rate. Airflow measurements have become important during the COVID19 pandemic as the flow rate sensors are the most essential component of the ventilation machines. Using the secondary mechanism, frequency shifts induced by airflow were recorded and a linear relation was observed between the applied air pressure and frequency modulations. In the last application, the sensing electrodes were patterned down to hundreds of nanometer apart to detect nanoparticles and biological samples such as polystyrene nanoparticles or viruses. A nanopore having a diameter around 400 nm was drilled on the membrane using focused ion beam (FIB) and analytes were translocated using electrokinetic motion. Since the events would be quick in electrokinetic motion, data were collected with CompactRIO (cRIO), however, when the PLL was running, there were spikes in cRIO for this reason after the resonator was locked to zero degrees, LabVIEW was stopped. Yet, since the resonator has low quality factor (≈100), the phase of the resonator dwells around zero degrees and still sensitive to translocations through the pore. In the control run, there were no precipitous jumps, however, when the particles were added sudden jumps induced by the particles were recorded. Therefore, can be optimized and proposed as a biophysical sensor to characterize single viruses.