Two-photon active graphene quantum dots (GQDs) are obtained from extracts of the neem root.

This review discusses the advantages of using luminescent d⁶-transition-metal complexes as cell probes for optical microscopy. In particular it focusses on the Thomas group's use of specific complexes as “building blocks” toward the construction of biomolecular binding substrates, with DNA being a particular target. Using this approach, a range of new imaging probes for conventional optical microscopy, nanoscopy and transmission electron microscopy have been identified. Through selection of specific metal centres and by substitution of coordinated ligands we illustrate how new chemotherapeutics, photo-therapeutics, and theranostics have been identified and developed from the original architectures.