Researchers discover that fluorescence in ligand-protected gold nanoclusters is an intrinsic property of the gold particles themselves
With their remarkable electrical and optical properties, along with biocompatibility, photostability and chemical stability, gold nanoclusters are gaining a foothold in a number of research areas, particularly in biosensing and biolabeling.
These gold nanoclusters are chemically protected by ligands, which also steer the binding to biological target molecules. There is still much that researchers don't know about the luminescent properties of ligand-protected gold nanoclusters, including the origin of their fluorescence.
An international research team from Switzerland, Italy, the United States and Germany has now shown that the fluorescence is an intrinsic property of the gold nanoparticles themselves. The researchers used Au20, gold nanoparticles with a tetrahedral structure. Their findings were reported this week in the Journal of Chemical Physics, from AIP Publishing.
"We present the first optical absorption, excitation and fluorescence spectra of bare Au20," said Harald Brune, head of the Institute of Physics at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and corresponding author of the paper. "Our results strongly suggest that the metal core in the ligand-protected clusters used for biosensing and biolabeling is at the origin of their fluorescence."
The researchers created a beam of bare Au20 clusters by combining a cluster aggregation source with a custom-designed ion optic and mass selection process. It is difficult to probe the optical properties of these clusters in the gas phase, given the poor signal-to-noise ratio. To address this issue, the researchers embedded them into a solid neon matrix. This was achieved by depositing the cluster beam with a neon background gas that condensed onto a cold surface held at 6 kelvins (about -267 degrees Celsius) while the clusters were landing there.
Neon, a noble gas, provides a weak interacting medium. As the first-principles calculations accompanying the experiment show, in neon the intrinsic structural and optical cluster properties are preserved.
"Therefore, the presented experimental results are the best possible approximation to the optical properties of free Au20 clusters," Brune said.
The Au20 absorption data was obtained by subtracting an Ne matrix reference spectrum from one of the Au20/Ne matrices. The fluorescence spectra were produced by laser excitation. The researchers found that excitation within the entire UV-to-visible range leads to intense and sharp fluorescence at a wavelength of 739.2 nanometers.
"[B]are Au20 strongly fluoresces, making it very likely that the origin of fluorescence in Au-based biomarkers comes from the Au core itself rather than from its interaction with the organic ligands," said Wolfgang Harbich, senior scientist at the EPFL and co-author of the paper.
The discovery could enable the design of new gold-based biomarkers, and the experiment serves as benchmark for the elaborate, time-dependent density functional theory calculations of optical cluster properties -- a topic gaining interest in fundamental chemistry and physics fields.
"The agreement between experiment and theory in the present case of Au20 is encouraging," Brune said, "and will enable a deeper understanding of theory-supported biomarker research."
The article, "Intense fluorescence of Au20," is authored by Chongqi Yu, Wolfgang Harbich, Luca Sementa, Luca Ghiringhelli, Edoardo Aprá, Mauro Stener, Alessandro Fortunelli and Harald Brune. The article appeared in the Journal of Chemical Physics August 15, 2017 [DOI: 10.1063/1.4996687] and can be accessed at http://aip.
ABOUT THE JOURNAL
The Journal of Chemical Physics publishes concise and definitive reports of significant research in the methods and applications of chemical physics. See http://jcp.
Julia Majors | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
17.07.2018 | Power and Electrical Engineering