Synthesis of Fluorescent Silver Nanoclusters: Introducing Bottom-Up and Top-Down Approaches to Nanochemistry in a Single Laboratory Class

A laboratory class was developed and evaluated to illustrate the synthesis of metal nanoclusters (NCs) and to explain their photoluminescence properties for the case of silver. The described experiment employs a synthetic protocol that consists of two sequential phases in a single reaction pot: the reduction of silver ions into plasmonic silver nanoparticles (NPs) (bottom-up), followed by etching the formed silver NPs into ultrasmall atomically precise fluorescent silver NCs (top-down), Ag-29(DHLA)(12) (DHLA: dihydrolipoic acid). UV-vis absorption and fluorescence spectroscopy were employed as a function of reaction time to confirm the development of the plasmonic character of silver NPs (reaction intermediate) and, later on, the onset of fluorescence emission of the silver NCs (final product). Collectively, this experiment was found to be simple to carry out, safe, reproducible, and cost-effective, and it achieved the intended learning outcomes. Participating students found this laboratory class suitable to be implemented into an upper-division undergraduate or graduate curriculum.