Microwave biosensors for single-cell dielectric characterization: a review

The dielectric property of biological cells exhibits a rich frequency-dependent behavior that is related to the cellular structure, function and molecular makeup. Assessing the dielectric properties of single cells offers a label-free and non-invasive method for disease diagnosis, cell identification, and monitoring of cellular structure and function. This article reviews the fundamentals and applications of microwave biosensors for single-cell analysis, with a focus on how electromagnetic interactions across the α-, β- and γ-dispersion regimes can be leveraged to extract cellular parameters such as membrane capacitance, cytoplasmic conductivity, and intracellular hydration. We begin by discussing the physical principles of dielectric dispersion and the equivalent circuit models in biological cells that underpin microwave-based sensing. We then examine major classes of sensing platforms, including transmission line sensors, capacitive electrode arrays, and resonant structures, highlighting their design strategies, strength and weakness, and applications in single-cell sensing. The role of dielectrophoresis (DEP) as both a manipulation tool and a sensing mechanism is also discussed, particularly in the context of hybrid systems that combine low-frequency trapping with high-frequency dielectric readout. Together, these technologies represent a convergence of microwave engineering, biophysics, and microsystem design to enable high-resolution, real-time interrogation of single cells. After describing the theoretical foundations with recent experimental advances, we provide a perspective on the design of next-generation dielectric biosensors tailored to the demands of single-cell diagnostics, drug screening, and functional phenotyping.