By Marta Siek
Stirring allows for homogenization and efficient gas exchange - this fact we have known for decades. But were we aware that a properly chosen stirring bar can give us higher gas-liquid mass transfer than in an industrial reactor? And did we realize that the delivery of oxygen to the synthetic mixture at a proper time and rate can be a make-or-break factor for the result of the synthesis? We answer these and other questions in the manuscript recently published and featured as Editor's Choice in the journal Small (IF 13.3): "Stirring-Controlled Synthesis of Ultrastable, Fluorescent Silver Nanoclusters" by Olgierd Cybulski, Cristobal Quintana, Marta Siek,* and Bartosz A. Grzybowski* (doi: 10.1002/smll.202400306).
Our case study is the synthesis of fluorescent silver nanoclusters in the classical sodium borohydride/glutathione system. We demonstrate how to precisely tune the properties of obtained structures - from unstable and non-fluorescent to highly fluorescent for over two years - just by controlling the stirring conditions. Even a very small change in the stirring bar size, from 25 by 12 mm to 20 by 10 mm, while keeping the same stirring rate, systematically resulted in a non-fluorescent product. Moreover, we show an unprecedented property of oxygen as a factor dictating the structure and functional properties of silver nanoclusters.
"As a chemist, I was quite puzzled that oxygen did not simply "ruin"/oxidize silver - instead, the fluorescence became so lasting because oxygen incorporated into the silver lattice of the forming nanoclusters" - said Prof. Grzybowski, the head of the group.
As a result, we report the unprecedented stability of our silver nanoclusters - over 2 years - that may open the door for wider use in catalysis, biosensing, or bioimaging. Our study leads to a better understanding of the structure-properties relationship of created nanostructures. It will allow for more flexible design of properties of synthesized nanomaterials and for broadening the scope of their potential uses.
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