Single-Molecule Optical Biosensing: Recent Advances and Future Challenges

In recent years, the sensitivity and specificity of opticalsensorshas improved tremendously due to improvements in biochemical functionalizationprotocols and optical detection systems. As a result, single-moleculesensitivity has been reported in a range of biosensing assay formats.In this Perspective, we summarize optical sensors that achieve single-moleculesensitivity in direct label-free assays, sandwich assays, and competitiveassays. We describe the advantages and disadvantages of single-moleculeassays and summarize future challenges in the field including theiroptical miniaturization and integration, multimodal sensing capabilities,accessible time scales, and compatibility with real-life matricessuch as biological fluids. We conclude by highlighting the possibleapplication areas of optical single-molecule sensors that includenot only healthcare but also the monitoring of the environment andindustrial processes.