احمد محمدی اسلامی

Plasmonicnano biosensors are powerful tool for identifying and analyzing in biomedical research, healthcare, environmental monitoring, homeland security, battlefields and food safety. These sensors, which are commonly known as surface plasmon resonance (SPR)sensors, are based on the excitation of surface plasmon at an interface between a metal and a dielectric. In this work, we present a nano biosensor based on multi-layers nanoplasmonic crystals. It consists of periodic arrays of plasmonic nanoparticles deposited on a dielectric layer below which there is a thin plasmonic layer coated on a dielectric substrate. The strong coupling between localized surface plasmon in the nanoparticles and the surface plasmonpolariton in the metal/dielectric interface can be used as a sensing tools for biosensors which is considerably sensitive to small changes in the surrounding optical properties. To investigate the optical properties of the proposed biosensor, we employ finite difference time domain (FDTD) method which is known as a powerful computational technique for solving Maxwell’s equations for complex geometries. The structure is illuminated by a pulsed plane wave and reflection is measured in the wavelength range of 400-1100 nm. A dip in the reflection spectrum is seen due to the excitation of SPP. The position of SPR can be tuned by varying the geometry parameters such as the period, the thickness and the material of metal and dielectric layers. We choose different geometries to show how one can tune the spectral range and sensitivity of the proposed sensor. We also investigate the sensitivity of multi-layers nanoplasmonic crystal to the variations of refractive index of surrounding medium. It is shown that this kind of biosensor can provide considerable sensitivity for biological applications.