Biosensor Using a One-Port Interdigital Capacitor: A Resonance-Based Investigation of the Permittivity Sensitivity for Microfluidic Broadband Bioelectronics Applications

Abstract

Electronics is a field of study ubiquitous in our daily lives, since this discipline is undoubtedly the driving force behind developments in many other disciplines, such as telecommunications, automation, and computer science. Nowadays, electronics is becoming more and more widely applied in life science, thus leading to an increasing interest in bioelectronics that is a major segment of bioengineering. A bioelectronics application that has gained much attention in recent years is the use of sensors for biological samples, with emphasis given to biosensors performing broadband sensing of small-volume liquid samples. Within this context, this work aims at investigating a microfluidic sensor based on a broadband one-port coplanar interdigital capacitor (IDC). The microwave performance of the sensor loaded with lossless materials under test (MUTs) is achieved by using finite-element method (FEM) simulations carried out with Ansoft's high frequency structure simulator (HFSS). The microfluidic channel for the MUT has a volume capacity of 0.054 µL. The FEM simulations show a resonance in the admittance that is reproduced with a five-lumped-element equivalent-circuit model. By changing the real part of the relative permittivity of the MUT up to 70, the corresponding variations in both the resonant frequency of the FEM simulations and the capacitance of the equivalent-circuit model are analyzed, thereby enabling assessment of the permittivity sensitivity of the studied IDC. Furthermore, it is shown that, although the proposed local equivalent-circuit model is able to mimic faithfully the FEM simulations locally around the resonance in the admittance, a higher number of circuit elements can achieve a better agreement between FEM and equivalent-circuit simulation over the entire broad frequency going range from 0.3 MHz to 35 GHz.

Microfluidic Modules Integrated with Microwave Components—Overview of Applications from the Perspective of Different Manufacturing Technologies

“…The accuracy for a presented solution was ±0.24 °C over a range of 20–55 °C. In [ 10 ], the authors indicated the possibility of using the IDC for sensing biological materials. Similarly, the substrate of the mentioned sensor was quartz and the components were made using microfabrication methods.…”

“…The use of microfluidic devices with integrated microwave components is notable mainly in biochemical and chemical applications, such as detecting the biological material [ 9 , 10 , 11 , 12 ]. Furthermore, due to the possibility of noncontact sensing and delivering the microwaves to the systems (using the antenna-based circuits), the possibilities are still increasing [ 13 , 14 , 15 ].…”

Simultaneous measurement of thickness and permittivity using microwave resonator‐based planar sensor

“…A higher width and gap between the sensing element fingers increases the sensing field lines through the MUT, which means a strong collaboration intervenes between MUT and resonator. 22 Sensitivity of the sensor can be improved via the optimization of different sensing elements, such as F w , F g , F L , and N E . The proposed design normalizes sensitivity can be estimated from the following Equation (4): 3…”

On the Wireless Microwave Sensing of Bacterial Membrane Potential in Microfluidic-Actuated Platforms

“…Electro-magnetic (EM) wave biosensors are attracting a lot of attention due to multiple benefits, such as being minimally invasive and cost effective [19][20][21]. Recent advances in microwave sensing [22][23], together with other applications of microwaves in the frequencies [24][25][26], enable to explore new narrow band windows for membrane interactions research. Studies of the effects of a weak (non-thermal) microwave radiation on the cellular structures have clearly shown that the reaction of cells to weak microwave radiation is highly selective in frequency.…”