Analysis and detection of women's reproductive hormones using a bistable and reconfigurable 1D annular photonic crystal composed of the Ge2Sb2Te5 phase-change material

Abstract

In this study, the reconfigurable biosensing capabilities of the one-dimensional annular photonic structure, (AB)⁵CDC(AB)⁵, was examined theoretically. The proposed structure was made of concentric cylindrical layers of periodically modulated refractive indices, which were restricted in one direction only. Germanium antimony telluride (GST), which belongs to the class of phase-change materials (PCMs), was used in the fabrication of the proposed biosensing design. The entire study was carried out in the near-infrared region of the electromagnetic spectrum. The suggested biosensing structure was constructed by depositing alternate periodic cylindrical layers of SiO₂ and Si with a central air core. An air cavity coated on both sides by a phase-change chalcogenide material (Ge₂Sb₂Te₅) was introduced at the centre of the 1D annular photonic crystal to realize the (AB)⁵CDC(AB)⁵ structure. The simulation results of the proposed work were obtained using the MATLAB computational tool taking into consideration the modified transfer matrix method. The primary focus of this study was to measure the change in the position and intensity of the defect mode with respect to the change in the concentration levels of analytes containing progesterone and estradiol reproductive hormones separately in the amorphous and crystalline phases of the Ge₂Sb₂Te₅ material. Interestingly, a strong tunability in the position of the central wavelength of the defect mode inside the photonic band gap (PBG) was noticed during the phase transition of the GST material from amorphous to crystalline and back. In both the phases of the GST material, our design could identify minute refractive index variations in blood samples containing reproductive hormones at different concentrations for monitoring various gynaecological disorders in women. Besides sensitivity, other important parameters such as the limit of detection, signal-to-noise ratio, and quality factor were estimated to evaluate the biosensing capabilities of the proposed design.