Synthesis of Fluorescent Silver Nanoclusters: Introducing Bottom- Up and Top-Down Approaches to Nanochemistry in a Single Laboratory Class Lin Zhu, †,⊥ Mustafa Gharib, †,‡,⊥ Charline Becker, † Yuan Zeng, † Anna R. Ziefuß, § Lizhen Chen, † Alaaldin M. Alkilany, †,∥ Christoph Rehbock, § Stephan Barcikowski, § Wolfgang J. Parak, † and Indranath Chakraborty* ,† † Faculty of Physics, Center for Hybrid Nanostructures (CHyN), Universitä t Hamburg, 22761 Hamburg, Germany ‡ Radiation Biology Department, Egyptian Atomic Energy Authority (EAEA), 11787 Cairo, Egypt § Technical Chemistry I and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitaetsstrasse 7, 45141 Essen, Germany ∥ Department of Pharmaceutics & Pharmaceutical Technology, School of Pharmacy, The University of Jordan, Amman 11942, Jordan * S Supporting Information ABSTRACT: 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: dihy- drolipoic 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. KEYWORDS: Nanotechnology, Physical Chemistry, Materials Science, Upper-Division Undergraduate, Interdisciplinary/Multidisciplinary, Fluorescence Spectroscopy, Kinetics, Synthesis, UV−Vis Spectroscopy ■ INTRODUCTION Noble metal nanoparticles (NPs) have shown their tremen- dous applicability in broad directions of science owing to their size- and shape-dependent optical properties. 1 Nanoclusters (NCs) are a subset of these materials which bridge the gap between NPs and atoms. 2,3 Because of their ultrasmall size (1− 2 nm), they show unusual optical and photophysical properties. These NCs may be atomically precise with a well-defined molecular formula, e.g., Au 25 (SR) 18 , Ag 29 (SR) 12 (SR represents the thiolate which acts as the ligand), etc. 4−7 More than 100 such NCs are currently known, and extensive research has already been done to explore their promising properties and applications. 2,3 Over the past few years, fluorescent NCs became more popular because of their intrinsic fluorescence properties which can be used in many biological and sensor-based applications. 2,8 While the synthesis and characterization of metal NPs have appeared in many chemical education publications, 9−17 there are few didactic reports to transfer the knowledge of NC synthesis, character- ization, and application. One example in this direction described a microwave-based synthesis of Au NCs using proteins as a stabilizing agent. 18 Thus, more reports will be beneficial for students to understand the evolving science of metal NCs. This would involve educational materials 19 in which students learn to understand the transition between NPs and NCs. Herein, we adapt a facile synthesis of silver NPs/ NCs that involves two stages during their growth: (1) formation of silver NPs with plasmonic properties starting from silver ions (bottom-up), followed by (2) etching of the formed Ag NPs to form smaller Ag NCs that exhibit bright red Received: April 8, 2019 Revised: October 11, 2019 Laboratory Experiment pubs.acs.org/jchemeduc Cite This: J. Chem. Educ. XXXX, XXX, XXX-XXX © XXXX American Chemical Society and Division of Chemical Education, Inc. A DOI: 10.1021/acs.jchemed.9b00342 J. Chem. Educ. XXXX, XXX, XXX−XXX Downloaded via GARDNER WEBB UNIV on November 6, 2019 at 14:48:03 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.