Multi-hotspot coupled metasurface for fingerprint identification of trace carcinoembryonic antigen molecules

Cancer remains a major global health challenge, highlighting the need for effective biomarker monitoring. Carcinoembryonic antigen (CEA), a widely used tumor-associated marker, is crucial for cancer diagnosis. Surface-enhanced infrared absorption (SEIRA) spectroscopy, which detects unique molecular vibrations, offers a promising approach for trace cancer biomarker detection. However, conventional nanoantenna-based SEIRA is limited by small high-field regions and weak molecule-metasurface coupling, restricting signal enhancement. To address these challenges, this work presents a multi-hotspot coupled metasurface with high degrees of freedom, optimized via a particle swarm algorithm. By expanding the effective hotspot area and optimizing the loss ratio of the metasurface, we significantly enhanced the molecule-metasurface normalized coupling strength (μ_eff) and amplified the CEA molecular enhancement signal (ΔA). This ΔA enhancement results from the combined effects of μ_eff and the optimized loss ratio (ξ). Experimental results demonstrate excellent linearity for CEA detection across a wide concentration range from 0.1 ng/mL to 10 μg/mL, with a minimum distinguishable concentration as low as 0.1 ng/mL. This performance represents an order-of-magnitude improvement over conventional nanoantenna-based SEIRA sensors. This strategy offers promising potential for sensitive detection of other disease biomarkers, advancing human health monitoring.