In a recent study, researchers from the Chinese University of Hong Kong (CUHK) have found that the sensing sensitivity of a hybrid SP-waveguide mode (SWG) sustained by one-dimensional gold gratings with deep grooves significantly exceeds that of pure SP modes (SSP) in shallow grooves. More importantly, the team found that while SSP is mainly controlled by the periodicity of the grating, the shape of the groove governs SWG. By properly designing the groove shape, such as its width and height, SWG can be increased up to 1500 nm/RIU.

The scientists have derived a simple but useful analytical expression to describe SWG, which not only reveals the origin of waveguide mode’s sensitivity, but also provides useful guidance for the theoretical design and experimental realization of high-sensitivity metallic grating-based biosensors.

The concept of employing a hybrid plasmon-waveguide mode has opened up a completely new perspective in improving the sensing sensitivity of plasmonic nanosensors. This hybridization concept can also be applied to tune and optimize other parameters such as the spectral contrast and the resonance linewidth, which are also of critical importance to increase the overall sensing figure of merit for a general class of plasmonic nanostructures including nanoparticle clusters and hybrid metallodielectric nanostructures.

Additional information can be found in the journal Nanotechnology.