Search

The transition from molecular to plasmonic behaviour in metal nanoparticles with increasing size remains a central question in nanoscience. We report that the giant 246-gold-atom nanocluster (2.2 nm in gold core diameter) protected by 80 thiolate ligands is surprisingly non-metallic based on UV/Vis and femtosecond transient absorption spectroscopy as well as electrochemical measurements. Specifically, the Au246 nanocluster exhibits multiple excitonic peaks in transient absorption spectra and electron dynamics independent of the pump power, which are in contrast to the behaviour of metallic gold nanoparticles. Moreover, a prominent oscillatory feature with frequency of 0.5 THz can be observed in almost all the probe wavelengths. The phase and amplitude analysis of the oscillation suggests that it arises from the wavepacket motion on the ground state potential energy surface, which also indicates the presence of a small band-gap and thus non-metallic or molecular-like behaviour. [ABSTRACT FROM AUTHOR]

Near-infrared electrochemiluminescence (ECL) from Au-thiolate nanoclusters is activated by electrode reactions and enhanced by ethylenediamine tetraacetic acid (EDTA). The enhancement effect is higher at pH 7.4 than at more basic or acidic pHs. Magnesium ions are found to modulate the ECL signals through complexation with EDTA and the interaction with the Au nanoclusters. The chemical system and the signal modulation mechanism are believed to be generalizable and advantageous for future sensing and analysis applications with the following merits: 1) Ambient ECL without oxygen removal, 2) high enhancement at physiological pH values, 3) in the near-IR spectrum window with low interference, 4) rich and tunable redox activity of the Au nanoclusters, and 5) EDTA representing other ionophores or chelaters as versatile coreactants. [ABSTRACT FROM AUTHOR]

In stark contrast to organic systems, insight of the electrochemical properties is rather limited in aqueous solution for Au clusters, which have received extensive research attention recently. We demonstrate phase transfer as an efficient strategy to shuttle the Au nanoclusters between aqueous and organic solvents cyclically. The ability to phase transfer the Au clusters circumvents the limitations of potential window and high dielectric constant of water for electrochemistry studies. Two types of ligand molecular structures were employed with different hydrophilicity/hydrophobicity: mercaptosuccinic acid and lipoic acid, the latter featuring a longer hydrophobic portion and disulfide group (for Au bonding). The transfer efficiency was evaluated at different pHs. Additional redox activities from the Au22LA12 cluster that could not be seen from aqueous measurements were successfully resolved. Reversible and controllable transfer between aqueous and organic phases is believed to be a generalizable approach that could enable broader applications. [ABSTRACT FROM AUTHOR]

The article presents the back cover of the journal depicting near-infrared electrochemiluminescence from the nanoclusters of gold.