Rapid and highly sensitive detection using Fano resonances in ultrathin plasmonic nanogratings

We developed a nanoplasmonic sensor platform employing the extraordinary optical properties of one-dimensional nanogratings patterned on 30 nm-thick ultrathin Ag films. Excitation of Fano resonances in the ultrathin Ag nanogratings results in transmission spectra with high amplitude, large contrast, and narrow bandwidth, making them well-suited for rapid and highly sensitive sensing applications. The ultrathin nanoplasmonic sensor chip was integrated with a polydimethylsiloxane microfluidic channel, and the measured refractive index resolution was found to be 1.46 × 10−6 refractive index units with a high temporal resolution of 1 s. This compares favorably with commercial prism-based surface plasmon resonance sensors, but is achieved using a more convenient collinear transmission geometry and a significantly smaller sensor footprint of 50 × 50 μm2. In addition, an order-of-magnitude improvement in the temporal and spatial resolutions was achieved relative to state-of-the-art nanoplasmonic sensors, for comparable detection resolutions.