Helicoid Grating-Coupled Surface Plasmon Resonance Sensor.

Ultrasensitive, rapid, and reliable biomolecular sensing is essential for biomedical diagnostics, requiring real-time monitoring and detection of trace samples. Optical sensing, particularly plasmonic biosensing, meets these demands through noninvasive, high-sensitivity detection based on the interaction between light and molecules. Here, we present novel plasmonic metamaterial-based sensing strategy, utilizing the circular dichroism (CD) response of grating-coupled surface plasmon resonance (SPR) from chiral nanoparticle grating structure (i.e., 2D helicoid crystal) on gold substrate. Strong chiroptic response of helicoids has been effectively expanded to produce a remarkable CD/ response in the SPR mode, achieved by spectral coupling of SPR with localized surface plasmon resonance (LSPR) in helicoids. This CD response, derived from the differential of left and right circularly polarized light, corrects optical fluctuations, enhancing sensitivity and reliability. Our SPR-CD-based approach achieves a sensitivity of 379.2 nm/RIU and detection limit of a few mM for d-glucose, offering a new paradigm for high-performance optical biosensors.