The metallophilic bond is a weak interaction between closed-shell ions and has been widely used a probe for various sensing of toxic chemicals for environmental safety concerns. Here, the interaction between Au nanoclusters (NCs) and metallic ions (mercury (Hg2+) and copper (Cu2+) ions) is explored using steady-state and time-resolved luminescence and transient absorption measurements. For Hg2+ ions, the delayed fluorescence (DF) of bovine serum albumin (BSA) protected Au25 (Au25@BSA) NCs is quenched via an effective triplet state electron transfer through the metallophilic bond. However, the Cu2+ ions do not alter the DF in Au25@BSA NCs because of the absence of the metallophilic interaction. Furthermore, for Au8@BSA and Au10@histidine, in which there are no Au+ ions on the surface, the fluorescence is not quenched by Hg2+ ions. Such a novel triplet electron transfer process through metallophilic bonds are observed and reported for the first time. The reduction of the reverse intersystem crossing is the crucial for Hg2+ ion sensing in the fluorescent Au25@BSA NCs.