Plasmonic Chiral Metasurfaces for Real-Time Refractive Index Sensing and In Situ Monitoring of Thin Film Growth

Molecular sensing plays a crucial role in biomedical, chemical, and environmental applications. Traditional plasmonic sensors based on surface plasmon resonance offer excellent sensitivity but face limitations in molecular specificity, scalability, and real-time operation. Here, we present a novel plasmonic chiral metasurface sensor fabricated via a scalable bottom-up approach using Layer-by-Layer (LbL) assembly and grazing incidence spraying of silver nanowires, and which exhibits a strong circular dichroism (CD) signal. Once integrated into a microfluidic flow cell, the sensor enables real-time spectroscopic measurements with high stability, reproducibility, and reusability. Refractive index sensing reveals a sensitivity based on the wavelength of the peak in the CD spectra of ∼56 nm·refractive index unit (RIU)^-1 and a sensitivity based on the CD intensity at a fixed wavelength of ∼18 700 mdeg·RIU^-1, yielding a limit of detection as low as 1.6 × 10^-4 RIU, i.e. 20 times lower than the conventional extinction-based methods. Moreover, the device enables in situ monitoring of polymer adsorption throughout the LbL assembly process, thereby providing a highly sensitive and label-free method for investigating interfacial phenomena. The present work establishes a robust and scalable platform for optical sensing by integrating the distinct advantages of chiral plasmonic materials with real-time fluidic control and cost-effective fabrication methodologies.