Metal nanoclusters (NCs), composed of a few to roughly ahundred atoms, are a new type of nanomaterial that are beinginvestigated intensively at present . Metal NCs typically possess diameters below 2 nmand physicochemical properties that place them in-between iso-lated atoms and larger nanoparticles (NPs). For NC dimensionsapproaching the Fermi wavelength of electrons, the continuousdensity of states breaks up into discrete energy levels, leading tooptical, electronic and chemical properties that are markedly differ-ent from those of bulk metals . Most importantly,these ultrasmall metal NCs can exhibit strong photoluminescence(PL). Combined with other distinct advantages, including ultrasmallsize, attractive photophysical properties and facile synthesis, metalNCs show great promise for biological applications such as cellularimaging and cancer therapy.