Synthesis, photophysics and dynamics of organically coated, dye-functionalised noble metal particles

Noble metal nanoparticles are well known for their interesting optical properties associated with the metal plasmon resonance. In particular, gold nanoparticles have met with a considerable interest, in part because of their stability in solution under ambient conditions and the possibility to protect and functionalise them using a wide range of organic molecules, especially thiols and disulfides. Here, we report the synthesis and photophysical study of noble metal nanoparticles of various sizes (5-50 nm, see Figure 1), shapes (sphere, rod, stars) and composition (gold, silver and gold-silver alloys). All particles were efficiently protected against aggregation in biologically relevant (aqueous) media using hydrophilic ligands. The use of fluorescent derivatives of the ligands provides useful insight in the dynamics of ligand adsorption and ligand desoprtion at low concentrations, as well as further demonstration of the highly efficient quenching of molecular fluorescence by noble metal particles in these systems. In addition to fluorescence spectroscopy, white-light scattering spectroscopy is demonstrated to be a highly sensitive technique for the detection and compositional analysis of noble metal particles in suspension.