DESIGN & MODELLING OF SYMMETRIC AND ASYMMETRIC PLASMONIC NANOGRATINGS FOR CHEMICAL/BIOLOGICAL SENSING

Abstract

When optical frequencies are incident on metal nanostructures with corrugations, such as nanoscale gratings with nanoscale gaps, light is coupled into plasmonic modes in these nanostructures. At certain special wavelengths- called the plasmon resonance wavelengths- light couples most strongly into these nanostructures creating electromagnetic hotspots in the grating gaps. This phenomenon of electromagnetic enhancement due to localized surface plasmons can be exploited to create chemical or biological sensors sensitive to nano-molar concentrations of the analytes. In this project, we aim to explore certain specific designs of nanogratings with nanogaps below 20 nm. Symmetric and asymmetric nanogratings will be modelled and simulated in the wavelength range of 400 nm to 1600 nm by employing Rigorous Coupled Wave Analysis. The reflectance spectra will be calculated ‘with’ and ‘without’ a biomolecule layer (different biomolecules will be analysed), and sensitivities will be reported as the shift in wavelength per unit refractive index (nm/RIU). We aim at sensors based on such nanogratings which can be tuned to the wavelength range of choice, and can provide multiple sensing wavelengths thus allowing their usage with multiple lasers.