Monolayer-protected metal nanoparticles (NPs) have gained a great deal of attention in the past decade because of their unique electronic properties and potential optical-sensing applications. [1] Gold nanoparticles (AuNPs) exhibit sizedependent surface plasmon resonance (SPR) absorption properties when their conducting electrons in both the ground and excited states are confined to dimensions smaller than the electron mean free path (ca. 20 nm). [2] This simple and practical theory predicts the spectra of AuNPs that have diameters larger than 3 nm, but fails for smaller particles. [2] Confinement of electrons within metallic nanostructures at sizes comparable to the Fermi wavelength of the electron (ca. 0.7 nm) results in electronic energy states that exhibit molecule-like transitions because the density of these states is too low to reproduce bulk metallic properties. [3] The photoluminescence (PL) quantum yields (QYs) of Au monolayerprotected clusters (MPCs) can be enhanced by up to eight orders of magnitude with respect to that of bulk gold (10 Γ10 ). [4] Alkanethiol-protected Au nanoclusters ranging in size from several atoms to small particles (smaller than 1.2 nm) fluoresce (QY % 10 Γ5 -10 Γ2 ) in the blue to near-IR region. [4] Upon decreasing the sizes of homologous stabilizer-protected Au nanoclusters, the emission wavelength undergoes a blue shift. [3a, 4f, 5a, 6] Recently, AuNPs emitting stronger fluorescence signals than those of AuMPCs have been prepared. [5] With their exceptional fluorescence properties, these fluorescent AuNPs are also called Au nanodots. AuNPs that are encapsulated and stabilized by polyamidoamine (PAMAM) dendrimers or polyethylenimine (PEI) exhibit stable fluorescence properties and high QYs (greater than 10 %), which probably result from the lower density of energy states present in the very small Au nanodots (smaller than Au 31 ), thus minimizing the number of internal nonradiative relaxation pathways. Additionally, the