Abstract
Knowledge on the synthesis of cationically charged fluorescent gold nanoparticles (Au NPs) is limited because the electrostatic repulsion between cationic ligands on the surface of NP hinders the formation of small Au NPs (usually less than ca. 2 nm) during nucleation in solvents. We herein propose a novel methodology for a synthesis of water-dispersible, cationic–thiolate protected fluorescent Au NPs by the sputtering of Au into liquid matrix containing thiolate ligands. By controlling mercaptan concentration the size and photophysical characteristics of Au NPs were directly controlled, resulting in near IR fluorescence with a 0.9% of absolute quantum yield. Cationically charged fluorescent metal NPs are promising, especially in biological fields, and this work provides a novel methodology towards the synthesis of a new series of functional metal NPs.
Highlights
Knowledge on the synthesis of cationically charged fluorescent gold nanoparticles (Au NPs) is limited because the electrostatic repulsion between cationic ligands on the surface of NP hinders the formation of small Au NPs during nucleation in solvents
To the best of our knowledge, little is known about the synthesis of water-dispersible fluorescent Au NPs using cationic mercaptan ligands except for only a few reports[18], because the electrostatic repulsion between cationic ligands on the surface of NP hinders the formation of small Au NPs during nucleation in solvents
The cationic stabilizer molecule, thiocholine chloride (TC, Fig. 1), was synthesized by the hydrolysis of commercially available acetylthiocholine iodide and the counter ion was exchanged to Cl− according to a method described in a previous paper[29,30]
Summary
Knowledge on the synthesis of cationically charged fluorescent gold nanoparticles (Au NPs) is limited because the electrostatic repulsion between cationic ligands on the surface of NP hinders the formation of small Au NPs (usually less than ca. 2 nm) during nucleation in solvents. Liquid matrixes in group (a) resulted in very small (~1.3 nm) fluorescent Au NPs, while those in group (b) formed rather large Au NPs (2–5 nm) The difference in their size was attributed to the coordination property of mercapto groups in group (a) that can prevent the coalescence of Au NPs inside or on the interface of liquid matrices. This technique can be applied for various conductive materials such as Ag22 and Cu23 From these results, it is hypothesized that we can prepare metal NPs of various sizes of the order of a single nanometer, and can control the physical properties of NPs by matrix sputtering method.
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