Elliptical Electrode Designs in Quartz Crystal Microbalances: Enhancing Sensitivity in Liquid Biosensing Applications

The demand for highly sensitive and versatile sensors is rapidly growing in biomedical applications, where specific, sensitive, and rapid detection are essential. Quartz crystal microbalance (QCM) is a popular analytical tool for such applications due to its high sensitivity and real-time monitoring capabilities. However, conventional QCM-based biosensing assays often suffer from poor sensitivity and high sample consumption, limiting their practicality. This study introduces a modified electrode design and a single droplet-based assay to enhance QCM-based bio-detection. Through extensive experiments, including contact angle analysis, damping, and viscosity measurements, we identified an optimal elliptical electrode design for single droplet-based liquid sensing. Using QCM crystals coated with molecularly imprinted polydopamine (MIPDA) sensing films containing recognition sites for detecting pepsin as a model protein, we demonstrate that QCM crystals with elliptical electrodes exhibit up to 10 times higher sensitivity than the industry-standard 1-inch circular QCM crystal. Additionally, the optimized QCM crystals showed linear sensitivity over a wider volume range, providing consistent detection at 250Hz/μl compared to the circular crystal's narrower range at 50Hz/μl. These findings establish a foundation for next-generation QCM platforms with superior sensitivity, reduced sample requirements, and broader adaptability, paving the way for advancements in biomedical diagnostics and environmental monitoring.