Novel Au nano-grating for detection of water in various electrolytes

This paper reports an advanced and novel sensing idea by utilizing the concept of surface plasmon resonance. A numerically designed model of plasmonic-based sensor has been proposed that is capable of detecting the mixture of water in alcohol and in a variety of other electrolytes including milk, hemoglobin, octane, etc. The sensor uses gold as a recognition element with equidistant slits for the transmission of incoming light which give rise to plasmon polaritons on metal–dielectric–interface. The zeroth-order transmission spectra have been extracted for this investigation and optimization. A transverse magnetic wave illuminates the noble metal normally through a glass substrate generating surface plasmon polaritons (SPPs) on a particular wavelength which changes with respect to the refractive index of adjacent medium. The sensor model has been numerically solved after optimization of slit size by keeping other parameters fixed utilizing the fundamental plasmonic mode for efficient excitation of SPPs. In this sensing chip, a uniform spatial period of about 660 nm, a constant slit size of 320 nm, a gold thickness of 50 nm for sensing element and 500 nm for glass substrate are used. An appreciable increment in the value of refractive index sensitivity of 668.66 nm per RIU has been found which is noteworthy. Such sensors are likely been welcomed in biological investigation, along with chemical and environmental detection techniques.