Theoretical investigation of fast illicit drug detection via ternary photonic crystals.

This study presents a theoretical investigation of a highly sensitive optical sensor based on a one-dimensional ternary photonic crystal (1D-TPC) for rapid detection of illicit drugs. The proposed structure consists of alternating layers of polyaniline (PANI), lead sulfide (PbS), and AlₓGa₁₋ₓN quantum dots, incorporating a central defect layer that serves as the sensing region. The detection mechanism relies on monitoring shifts in the defect-mode wavelength induced by variations in the refractive index of different illicit substances. Numerical simulations were carried out using the transfer matrix method (TMM) to analyze the transmission characteristics of the structure under various operating conditions. The influence of key parameters—including aluminum mole fraction, defect layer thickness, incident angle, and number of periods—was systematically investigated. The results demonstrate pronounced tunability of the defect mode and a strong dependence of sensor performance on structural optimization. A maximum sensitivity of 5219.29 nm/RIU was achieved under optimal conditions, indicating excellent detection capability. The obtained results confirm that the proposed photonic crystal sensor offers high sensitivity, strong spectral response, and reliable performance, making it a promising platform for label-free and rapid detection of illicit drugs in forensic and biomedical applications.