Optical Biosensors: A Comprehensive Review of Their Applications in Photoplethysmography, Environmental Monitoring, and Medical Diagnostics.

Medical diagnostics, environmental monitoring, and food safety are key domains being transformed by the ongoing revolution in optical biosensors. These light sensors are highly sensitive and specific for detecting specific biological interactions, allowing for real-time, label-free detection. Biorecognition elements (such as enzymes, antibodies, or nucleic acids), following interaction with the target analyte, generate optical signals based on the same key principles as optical biosensors. Surface plasmon resonance (SPR), fluorescence-based sensors, and fiber optic sensors offer a wide range of biosensors capable of detecting a broad spectrum of biological and chemical agents at trace concentrations. Diagnostic capability has become efficient and rapid with advances in nanotechnology and microelectronics, particularly in nanopores. Monitoring of cardiovascular health using wearable optical biosensors, such as photoplethysmography (PPG), is a non-invasive method. It has also been recently improved to better track heart rate and blood pressure, as well as evaluate mental and vascular health. Wearable optical biosensors support technologies, such as continuous monitoring and early detection of anomalies, which help in personalized healthcare. Optical biosensors are particularly suitable for detecting pathogens, biomarkers, and pollutants in clinical settings, as well as for environmental monitoring and food safety assessments. These applications range from biopharmaceuticals to biotechnology and personalized care, which are used to monitor diseases, discover drugs, and detect pathogens. Despite progress, matrix interference with the sample matrix, sensor stability, and miniaturization remain challenges to be overcome. However, with future progress in materials science, nanotechnology, and increased integration with the Internet of Things (IoT), the potential for optical biosensors will continue to rise as portable, cost-effective, real-time data-analyzing diagnostic tools that expand accessibility to those in underserved regions. Developed using optical and electrochemical approaches, the biosensors reviewed in this article are discussed in terms of their principles, types, applications, and prospects, including their roles in healthcare and environmental sectors.