Achievements in the development of plasmonic waveguide sensors for measuring the refractive index

Optical sensors are widely used in the biomedical, chemical and food industries. They provide high sensitivity to changes in the refractive index of the environment due to a specific distribution of resonances across the field. The sensitivity of the sensor is highly dependent on its material and structure. In this review, we focused on the analysis of silicon waveguides as a promising component for optical sensor miniaturization, and plasmon refractive index sensors without fluorescent labeling. We presented the latest developments of special types of plasmon structures, such as metal-insulator-metal waveguides, and their application in refractive index sensors. We analyzed numerous types of plasmon waveguides, their geometry, materials and manufacturing processes, as well as possible energy losses. A discussion of the spectral characteristics of recently proposed refractive index sensors, with an emphasis on their sensitivity and quality indicators, is an important part of the review.