Optical sensors are the most

Optical sensors are the most widely used class of biosensors because they have several advantages over conventional analytical techniques. They can be real-time with numerous features such as fast, cost-effective, compact size, immunity to electromagnetic interference and unlabeled remote sensing, the availability of multiple commercial organic dyes with diverse optical properties, and Appropriate optical instruments that detect several different analytes. They are very specific, sensitive, and small in size [38, 135, 136]. Because research and development in optical sensors have grown exponentially over the past decade, such sensors have great potential for applications in biotechnology, environmental sciences, and health care. Detection time, reusability, output accuracy, and cleaning needs of optical sensors can be adjusted according to the concentration and characteristics of the analyte [136]. Optical sensors are classified based on their transmission mechanisms, such as absorption, scattering, diffraction, reflection, refraction, and luminescence (including photo-, chemi-, electrochemi, or bioluminescence) [79]. Optical gas sensors detect changes in visible light or electromagnetic waves that result from the reaction of the analyte with the receptor part. In measurement, emission, scattering or absorption are the main mechanisms of optical gas sensors [141].