Highly Sensitive Dual-Mechanism Photonic Crystal-Plasmonic Biosensors with Amplified Output

In this work, we designed two hybrid sensors by integrating a one-dimensional Si–SiO₂ photonic crystal with a defect layer into a metal–insulator-metal plasmonic structure. The addition of periodic plasmonic resonators with subwavelength periods and rectangular and triangular geometries for Sensors I and II, respectively, resulted in 20-fold and 50-fold enhancements in resonance transmission amplitude compared to the baseline structure. The sharp edges of the triangular resonators enabled stronger localized surface plasmon resonance, contributing to a higher degree of plasmonic coupling and a more significant amplification compared to the rectangular design. The proposed sensors employ dual sensing mechanisms: (1) resonance wavelength shifts and (2) changes in resonance transmission amplitude due to refractive index variations. Using the finite integration technique, by the first mechanism, Sensor I achieved sensitivity, quality factor, and figure of merit values of 219.8 nm/RIU, 899.16, and 91.58 RIU^-1, respectively, while Sensor II reached 227.1, 750.35, and 81.1. For the second mechanism, amplified transmission led to exceptional sensitivity and FOM values of 1418.5%/RIU and 591.4%/(RIU·nm) for Sensor I and 3311.6 and 1182.71 for Sensor II. These sensors are rapid, compact, and efficient for disease detection, requiring no amplifiers or expensive transmitters and detectors, making them ideal for biomedical applications.