Fluorescent Metal Nanoclusters for Detecting Biomarkers

Fluorescent metal nanoclusters (NCs), particularly gold (Au), silver (Ag), and copper (Cu) NCs, have emerged as revolutionary tools for biomarker detection due to their unique optical properties, biocompatibility, and tunable surface chemistry. These ultrasmall clusters (<2 nm) bridge the gap between atomic and nanoparticle behavior, exhibiting discrete electronic transitions and intense fluorescence, which surpass conventional organic dyes and quantum dots. Their high surface-to-volume ratio allows precise functionalization with ligands such as thiols, proteins, or DNA, enabling selective binding to disease-specific biomarkers, including proteins, nucleic acids, and metabolites. Advances in synthesis techniques—such as template-assisted reduction, microwave-assisted synthesis, and biomineralization—have enhanced the stability, quantum yield, and emission tunability of these NCs. These properties are critical for developing ultra-sensitive biosensors capable of detecting biomarkers at femtomolar concentrations, even in complex biological matrices. AuNCs, for instance, have been employed for early cancer diagnosis by detecting tumor-associated antigens, while DNA-stabilized AgNCs serve as nanoprobes for miRNA profiling in neurodegenerative diseases. CuNCs, with their cost-effectiveness and low toxicity, are gaining traction for detecting nucleic acids and small molecules. The integration of smartphone technology and portable diagnostic platforms further highlights the translational potential of NC-based biosensors in point-of-care and wearable applications.