Optimization of the metal-dielectric metasurface unit cell for sensitivity enhancement in determination of IgG concentration in solutions

This study focuses on developing a metal-dielectric sensor structure with optimized unit cell geometry for the determination of protein Immunoglobulin G (IgG) concentration in aqueous solutions. The research combines both experimental and theoretical investigations, utilizing the differential microwave dielectrometry method and numerical modeling with COMSOL software. Complex permittivity (CP) values dependence of IgG water solutions on the protein concentration was experimentally obtained at the microwaves using a microwave dielectrometer setup developed by our group. It was shown that increase of IgG concentration resulted in the decrease of CP values of the solutions studied. The experimentally obtained CP data for the IgG water solutions were used as a basis for microwave metal-dielectric metasurface unit cell numerical modeling. The metal-dielectric metasurface (consisting of two layers of Teflon and plane copper microresonators) was combined with a standard 96-well microplate used in clinical laboratories. Optimization of the obtained metasurface unit cell revealed that the size and position of the copper microresonators within the unit cell significantly impact the sensor sensitivity for determining the IgG concentration. The metasurface with the unit cell containing four copper microresonators provided the most sensitive platform for detecting variations in the IgG level in the sample. The frequency shift of the reflection coefficient was directly related to changes in the protein concentration that occurred due to the decrease in the CP values of the water-protein solution with increased protein concentration. The calibration graph was developed, and the sensitivity of the sensor structure was evaluated for effective determination of IgG concentrations in the aqueous solutions.