The proof of concept of a simple sensing platform based on the fl uorescence of agold cluster consisting of eight atoms, which is easily manipulated by reduction andoxidation of a specifi c molecule in the absence of chemical linkers, is demonstrated.Without using any coupling reagents to arrange the distance of the donor–acceptorpair, the fl uorescence of the Au 8 -cluster is immediately switched off in the presenceof 2-pyridinethiol (2-PyT) quencher. Through an upward-curving Stern–Volmerplot, the system shows complex fl uorescence quenching with a combination of staticand dynamic quenching processes. To analyze the static quenching constant ( V ) bya “sphere of action” model, the collisional encounter between the Au 8 -cluster and2-PyT presents a quenching radius ( r ) ≈5.8 nm, which is larger than the sum of theradii of the Au 8 -cluster and 2-PyT. This implies that fl uorescence quenching canoccur even though the Au 8 -cluster and 2-PyT are not very close to each other. Thequenching pathway may be derived from a photoinduced electron-transfer processof the encounter pair between the Au 8 -cluster (as an electron donor) and 2-PyT (asan electron acceptor) to allow effi cient fl uorescence quenching in the absence ofcoupling reagents. Interestingly, the fl uorescence is restored by oxidation of 2-PyTto form the corresponding disulfi de compound and then quenched again after thereduction of the disulfi de. This redox-switchable fl uorescent Au 8 -cluster platform isa novel discovery, and its utility as a promising sensor for detecting H 2 O 2 -generatingenzymatic transformations is demonstrated.
