Sensitivity studies and optimization of an impedance-based biosensor for point-of-care applications

In this study, we examined the relationship between the sensitivity of interdigitated electrode (IDE) impedimetric biosensors and the gap between the IDEs. Our aim is to find an optimal design to maximize sensitivity. A three-dimensional COMSOL model was constructed for determining the effects of electrode gap, width, and height on impedance sensitivity, revealing a singular linear correlation with the inner gap. Considering both the simulation results and fabrication processes, we have developed three IDE prototype chips with electrode gaps of 3 μm, 4 μm, and 5 μm, respectively. For empirical validation, human anti-SARS-CoV-2 monoclonal antibody (mAb) was utilized, with immobilization of the SARS-CoV-2 spike protein on the chip's surface for mAb capture. This interaction, further amplified by Protein G conjugation, induced shifts in the impedance spectrum. The sensitivity of each prototype chip was evaluated across mAb concentrations ranging from 50 ng/mL to 500 ng/mL. The 3 μm configuration emerged as the most sensitive, demonstrating the ability to detect mAb concentrations as low as 50 ng/mL, a threshold unattainable by the other designs. This outcome underscores the critical influence of reduced inter-electrode gap on enhancing biosensor detection limits. The findings from this investigation offer a foundational approach for advancing biosensor sensitivity via electrode geometric optimization, with broad potential applications extending beyond COVID-19 diagnostics to a wide spectrum of clinical and research contexts.