One-step formation of a plasmonic grating with an ultranarrow resonance linewidth for sensing.

Nanograting-based plasmonic sensors are capable of real-time and label-free detection for biomedical applications. Simple and low-cost manufacturing methods of high-quality sensors are always demanding. In this study, we report on a one-step etch-free method achieved by directly patterning a photoresist on a copper substrate using laser interference lithography. Large area uniform gratings with a period of 600 nm were fabricated on the copper film, and its refractive index sensing performance was tested using glucose as analyte. By replacing the metallic grating ridges with photoresist ridges, the Ohmic absorption and radiative scattering losses of surface plasmons were greatly reduced. As a result, a much sharper resonance linewidth (∼ 10 nm) was experimentally obtained. Compared with pure metallic gratings, the reported structure is characterized by sharper resonance and a much easier fabrication process, making it a cost-effective plasmonic sensor with high quality.