Defect-tuned ternary photonic platforms for ultra-sensitive refractochemical drug fingerprinting in biofluids

In this study, a defect-engineered one-dimensional ternary photonic crystal is proposed as an optical sensing platform for detecting illicit drug analytes in complex biological environments. The structure consists of a periodic multilayer arrangement of CYTOP/Ge/Si 3 N 4 layers with an embedded defect cavity that enhances light confinement and produces a sharp localized defect peak within the photonic band gap. Variations in the refractive index of the drug analytes introduced into the defect layer lead to measurable shifts in the resonance wavelength, enabling label-free optical detection. The optical response of the structure is theoretically investigated using the transfer matrix method (TMM) to evaluate the transmittance spectra and defect-peak behavior. A parametric analysis is performed to examine the influence of structural parameters such as defect layer thickness, lattice constant, incident angle, and the number of periods on the sensing performance. The proposed structure achieves an ultra-high sensitivity of up to 6310.52nmRIU −1 with low detection limits in the sub-10 −3 RIU regime. The sensing performance is further characterized by high Q-factors reaching 97.02, a figure of merit up to 95.97RIU −1 , and a dynamic range approaching 786.77 nm, demonstrating strong spectral selectivity and detection capability. These results establish defect-mediated ternary photonic structures as a promising class of scalable, label-free, and chemically responsive optical systems for next-generation forensic and biomedical drug screening technologies.