Microwave-assisted Synthesis and Mechanistic Study of Multicolor Emissive Au Nanoclusters Using Thiol-Containing Biomolecules

Developing effective synthesis method for few-atom gold nanoclusters (AuNCs) with tunable emissions is vitally important to gain better understanding of their formation mechanism and provide more design flexibilities to suite for various applications such as multiplex cellular imaging and/or light-emitting diodes. This paper reports a fast method (<30 minutes) of preparing multicolour (red, orange, near infrared) emissive AuNCs via a microwave-assisted biotemplating synthesis approach. A series of analytical tools such as UV-vis and photoluminescence spectroscopies, transmission electron microscopy (TEM) and polyacrylamide gel electrophoresis (PAGE) have been utilized to characterize the resultant AuNCs and unravel the formation mechanism that lead to their multicolour emissive properties. It was found that the surface charge of the thiol-containing peptide reagent and the peptide-to-Au ratio are crucial factors to control the size and emission colour of the resultant AuNCs. By bringing the solution pH to near the isoelectric point of peptide ligand (~3), the red (em = 725 nm) emissive AuNC which is initially stable at alkaline conditions (pH12) tends to aggregate due to deficiency of surface charge, thus forming a larger and orange (em = 640 nm) emissive AuNC. By further applying an even lower peptide-to-Au ratio to fine-tune the protection power of thiolate ligands, a nearinfrared (em = 846 nm) emissive AuNC has been synthesized. Compared to other microwave-assisted synthesis of AuNCs, current study is featured by its simplicity, rapidity, and versatility to tune the emission wavelength of resultant AuNCs in a much broader range (up to 206 nm). Copyright © 2018 VBRI Press.