Bright Future of Gold Nanoclusters in Theranostics.

Quantum-sized gold nanoclusters (AuNCs) are emerging as theranostic agents-those that combine diagnostics and therapeutic properties-given their ultrasmall size <3 nm, which makes them behave more like a molecule rather than a nanoparticle. This molecule-like behavior endows AuNCs with interesting properties including photoluminescence, catalytic activity, and paramagnetism-all without the presence of any toxic heavy metal. But despite these fundamental advances, scalable synthetic approaches to produce high-quality AuNCs with well-controlled and programmable properties for biological applications as well as methods to determine their structure-property relationships are not widely available. In this Perspective, we will discuss what is known so far about AuNCs as well as how to move forward to propel AuNCs as a theranostic agent of choice for many biomedical applications.