CHAPTER 13. Synthesis of Fluorescent Platinum Nanoclusters for Biomedical Imaging

Abstract

Noble metal nanoclusters consisting of several atoms have been gaining much attention as novel fluorescent markers due to their optical properties, similar to semiconductor quantum dots, such as discrete electronic state and size-dependent emission wavelength. Metal nanoclusters are supposedly superior to semiconductor quantum dots due to their smaller size and lower cytotoxicity. So far, several groups have reported biological application of noble metal nanoclusters (Au and Ag) as fluorescent probes in cellular imaging. An alternative noble metal, platinum (Pt), is another promising candidate as a noble metal fluorescent nanocluster for bioimaging probing. In our research, we prepared green-emitting Pt8 nanoclusters (excitation: 460 nm, emission: 520 nm), which exhibited a quantum yield of 28% in water, and found that the nanoclusters emit a brighter fluorescence than Au and Ag nanoclusters. Furthermore, we achieved the isolation of Pt nanoclusters by ligand-exchange with mercaptoacetic acid and by using high performance liquid chromatography. Therefore, the synthesized Pt nanoclusters were atomically monodispersed and we determined their precise composition. In this review, we describe synthesis strategies of fluorescent water-soluble Pt nanoclusters, their optical properties and biocompatibility, and discuss capabilities for cellular imaging.