Optical biosensors have shown great potential in biosensing due to their high sensitivity, reusability, and ultrafast sensing capabilities. This review summarizes recent advancements in optical biosensors, focusing on plasmonic and metasurface-based biosensors, which have gained significant attention for their performance in bioassays and potential in lab-on-a-chip and point-of-care devices. Plasmonic biosensors, such as surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR), along with surface-enhanced Raman spectroscopy (SERS), are highlighted for their ability to perform diverse bioassays. Metasurface-based biosensors are also discussed, emphasizing their unique optical sensing properties. The review addresses current challenges, opportunities, and future prospects in optical biosensing, noting that optical biosensors are becoming a robust and widespread platform for early disease diagnostics. Key topics include the principles of optical biosensing, recent developments in various platforms, and applications in bioassays. The review also discusses the importance of sensor parameters such as sensitivity, specificity, signal-to-noise ratio, and detection limit in optical biosensing. The review highlights the potential of optical biosensors in biomedical applications, including their ability to detect single biomolecule interactions without labeling. The review also discusses the role of microfabrication and microfluidic technologies in reducing the size of optical sensors, making them suitable for point-of-care (POC) devices. The review covers various types of optical biosensors, including whispering gallery mode (WGM) biosensors, photonic crystal array (PhA) biosensors, and nano-plasmonic biosensors. The review also discusses the use of metasurfaces in biosensing, emphasizing their ability to confine light into the nanoscale and generate EM hotspots for detecting a wide range of bioassays. The review concludes with a discussion on the future of optical biosensing, highlighting the potential of these technologies in biomedical applications.Optical biosensors have shown great potential in biosensing due to their high sensitivity, reusability, and ultrafast sensing capabilities. This review summarizes recent advancements in optical biosensors, focusing on plasmonic and metasurface-based biosensors, which have gained significant attention for their performance in bioassays and potential in lab-on-a-chip and point-of-care devices. Plasmonic biosensors, such as surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR), along with surface-enhanced Raman spectroscopy (SERS), are highlighted for their ability to perform diverse bioassays. Metasurface-based biosensors are also discussed, emphasizing their unique optical sensing properties. The review addresses current challenges, opportunities, and future prospects in optical biosensing, noting that optical biosensors are becoming a robust and widespread platform for early disease diagnostics. Key topics include the principles of optical biosensing, recent developments in various platforms, and applications in bioassays. The review also discusses the importance of sensor parameters such as sensitivity, specificity, signal-to-noise ratio, and detection limit in optical biosensing. The review highlights the potential of optical biosensors in biomedical applications, including their ability to detect single biomolecule interactions without labeling. The review also discusses the role of microfabrication and microfluidic technologies in reducing the size of optical sensors, making them suitable for point-of-care (POC) devices. The review covers various types of optical biosensors, including whispering gallery mode (WGM) biosensors, photonic crystal array (PhA) biosensors, and nano-plasmonic biosensors. The review also discusses the use of metasurfaces in biosensing, emphasizing their ability to confine light into the nanoscale and generate EM hotspots for detecting a wide range of bioassays. The review concludes with a discussion on the future of optical biosensing, highlighting the potential of these technologies in biomedical applications.