Impact of yeast lipid pathway engineering and bioprocess strategy on cellular physiology and lipid content
2022 Annual Meeting
Theoretical Investigations into the Fluorescence of Au25@Ag Bimetallic Nanoclusters
Fluorescent Au nanoclusters have shown extensive applications in biomedicine for biological imaging and detection. For example, Au nanoclusters are ideal for cellular and in vivo imaging due to their high photostability and bioinert nature. Optical sensing schemes have been devised that utilize the quenching of the luminescence of fluorescent Au nanoclusters to detect the presence of certain biological molecules. Enhancement in photoluminescence and quantum yield is highly desirable to increase the efficacy of these nanoclusters. Recent research has shown significant photoluminescence enhancements of the Au25(SH)18- nanocluster (referred to as Au25) in the presence of Ag(I) ions, where it forms Au25@Ag bimetallic nanoclusters. However, little is known about the structure and optical properties of these bimetallic nanoclusters. It is known that luminescence in Au25 primarily arises from emission from the first singlet excited state (S1), but the emission mechanism of the Au25@Ag nanoclusters has yet to be determined. Using density-functional theory (DFT) and time-dependent density-functional theory (TD-DFT), we investigate the geometry, electronic structure, and emission properties of Au25 with one Ag(I) ion added (Au25@Ag1) and Au25 with six Ag(I) ions added (Au25@Ag6) to better understand the origin of this enhanced photoluminescence.
The Au25 nanocluster consists of an Au13 icosahedral core surrounded by six S-Au-S-Au-S ligand motifs distributed symmetrically on the surface of the core. The calculated geometries of Au25@Ag1 and Au25@Ag6 show that the Ag(I) ions prefer to be located in the outer shell of the nanocluster among the ligand motifs, which agrees with experiment, while still interacting closely with the surface of the core. Calculated electronic structure diagrams of Au25@Ag1 and Au25@Ag6 show smaller emission energies from the S1 excited state than Au25 and longer S1 lifetimes. This suggests that the bimetallic nanoclusters may emit through a different mechanism than the parent cluster, such as through phosphorescence or higher singlet states. Theoretical absorption spectra were also calculated and compared with the parent cluster. An improved understanding of the luminescence enhancement upon introduction of Ag(I) ions may help facilitate improvements in other nanocluster systems.
