Exploration of optical nanosensors for environmental and biomedical applications: a comprehensive review

Optical nanosensors represent a rapidly developing class of analytical tools for biomedical diagnostics and environmental monitoring, offering high sensitivity and selectivity for detecting a wide range of analytes. This review explores the wide range of nanomaterials that underpin the current optical sensing technologies. The techniques behind nanosensors are critically reviewed, with an emphasis on how they enable the detection of biomarkers, pollutants, and other analytes at minute levels. Despite these achievements, several challenges remain. The long-term stability, biocompatibility, and reproducibility of nanosensors in complex biological and environmental matrices remain major challenges. Immunological reactions and the potential toxicity of these nanomaterials require extensive in vivo studies to ensure their safety and reliability for practical use. This review also identifies strategies to improve nanosensor performance, including surface functionalisation, heteroatomic doping, the use of complementary nanomaterials, and integration with microfluidic and machine learning systems. By evaluating the advantages, operations, constraints, and prospects of optical nanosensors, this article identifies key research gaps and opportunities to advance their real-world deployment. Stability, selectivity, reproducibility, and scalability are essential for ensuring that these technologies are integrated into clinically relevant diagnostics and robust environmental monitoring tools. Optical nanosensors have the potential to revolutionise precision sensing, providing transformative value.