Advanced Immunoassay Detection Using Microwave Whispering Gallery Mode Resonators

This study introduces a novel immunoassay technique that utilizes a microwave Whispering Gallery Mode (WGM) silicon resonator, illuminated by near-infrared (NIR) light, for highly sensitive detection of antigen-antibody interactions. The WGM resonator, integrated with a microstrip transmission line, acts as the primary sensing element for detecting specific binding events within the NIR spectrum. Antigen-antibody complexes are immobilized at the bottom of a transparent plexiglas container, allowing NIR light from a light-emitting diode (LED) to illuminate the resonator. This interaction modifies the resonator’s conductivity and alters the transmission coefficient (S21) at the resonant frequency, with changes in S21 directly linked to antigen-antibody interactions, enabling precise detection. The study validates this label-free detection method for small molecules, exemplified by 25-hydroxyvitamin D3 (calcidiol), and emphasizes its simplicity, cost-effectiveness, and portability, indicating its potential applications in virus detection and cancer diagnostics.