Design and analysis of an efficient plasmonic sensor for sensing water-soluble CaCl₂ electrolyte

This paper presents a label-free optical refractive-index sensor to detect CaCl₂ electrolyte concentration in the water that can be applicable in the medicine, the food industry, and the environmental science. Its structure is based on a slot plasmonic nanodisk resonator with a radius of 350 nm and a small inner sub-disk. The numerical analysis based on the finite element method shows that the sensitivity and FOM have been improved compared to the previously designed sensors with the same size. The internal resonator improves the quality factor in the resonance wavelength; its radius can be adjusted to achieve the required free spectral range without increasing sensor dimensions. Additionally, gas phase sensing results show further improvements in the sensitivity and FOM. This sensor has much smaller dimensions than the previous CaCl₂ sensors.