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 (μeff) and amplified the CEA molecular enhancement signal (ΔA). This ΔA enhancement results from the combined effects of μeff 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.