“…As a bridge between atom and nanoparticle, metal nanoclusters (metal NCs, mainly Au, Ag and Cu) which are composed of a few to hundreds of mental atoms and covered with organic ligands on the surface of the metal core, have been receiving extensive attention due to their important roles in the fields of catalysis, sensing, electrochemistry, energy transfer and biomedicine [ 1 , 2 , 3 , 4 , 5 ]. Among various applications, metal nanoclusters are widely used as sensors because of their sensitive responses to temperature, pH value, metal ions and small biological molecules [ 6 , 7 , 8 , 9 , 10 ]. For example, Hu et al utilized Cu-MOF as a precursor to prepare highly stable Cu NCs, which can be used to construct a pH ratiometric fluorescence sensor to monitor pH of microorganism [ 8 ].…”