Highly Luminescent Gold Nanocluster Frameworks

Abstract

cytotoxic and are restricted in their use in nanomedicine. [6] Organic dyes, on the other hand, suffer from toxicity and poor photostability. [7] Therefore, the large potential of appropriate luminophores in biomedical applications has prompted intensive efforts toward the development of alternative nanomaterials with reduced toxicity and increased biocompatibility. A promising new approach is to exploit the photoluminescence of noble metal nanoclusters (NCs), having emissions in visible or near-IR regions, depending on their size, chemical environments, and surface ligands. [8] Few-atom metal NCs, with a core diameter of ≤1 nm, possess unique optical properties, stemming from quantum confinement of the electrons, unlike larger plasmonic nanoparticles. [1,9] Among the metal nanoclusters, atomically precise gold nanoclusters (GNCs) have gained remarkable interest over the last decade due to their high stability and biocompatibility. [9,10] However, low photoluminescence (PL) quantum efficiency restricts their potential applications. [11,12] PL can be amplified to a certain extent by the reduced rotational degree of freedom of the ligands surrounding the metal core, restrictions of intramolecular motions, or preventing nonradiative relaxations through aggregation. [13][14][15][16] However, controlling the aggregation behavior of the NCs to obtain superstructures of defined morphology in aqueous media has been a challenge. [17] Therefore, it is relevant to ask whether controlled self-assemblies can be designed to achieve colloidal superstructures based on luminescent NCs with enhanced PL and quantum yields in aqueous dispersion. Despite their dispersion behavior being similar to supramolecular complexes, self-assembly of monolayer protected NCs is a challenging task, as the inter-nanocluster interactions are close to the thermal fluctuations of the surroundings. Recently, it has been shown that atomically precise gold nanoclusters with surface carboxylic acid functionalities offer control over self-assemblies in aqueous medium to 2D or 3D superstructures. [18][19][20] We have discovered that a controlled assembly of water soluble luminescent GNCs having surface carboxylic groups by introducing metal ions might offer a new avenue to achieve superstructures, consisting of GNCs, metal ions, and ligands, akin to metal-organic frameworks. Such cluster frameworks would allow restricted motion of the surface ligands, thus potentially enhancing the PL. To test this hypothesis, we used water-soluble glutathione (GSH) capped luminescent Metal nanoclusters (NCs) are being intensely pursued as prospective luminophores because of their tunable electronic and optical properties. Among the various fluorescent NCs, gold nanoclusters (GNCs) are attractive due to their biocompatibility and excellent photostability, even if so far, they have had limited application potential due to poor quantum yield (QY). In this context, a facile route is demonstrated to tune up the photophysical and photochemical activities of water-borne luminesce...

Luminescent Gold Nanocluster‐Methylcellulose Composite Optical Fibers with Low Attenuation Coefficient and High Photostability

“…The Au4f7/2 XPS spectrum of CNC‐Au@GSH confirmed typical peak positions of gold nanoclusters with Au(0) core and Au(I) surfaces at 83.9 and 84.8 eV, respectively (Figure S3c, Supporting Information). [ 79 ]…”

“…[ 67–73 ] Among AuNCs, bovine serum albumin (BSA) coated gold nanoclusters (Au@BSA) and reduced glutathione (GSH) capped gold nanoclusters (Au@GSH) have been explored for sensors, catalysis, bioimaging, and pathogen detection. [ 74–86 ] However, their potential in biopolymer‐based composite fibers for optical amplification and waveguiding is unexplored to date.…”

Luminescent gold nanoclusters for bioimaging applications

“…However, there are challenges because the number of luminescent gold NCs is limited and the PL quantum yield is low compared to organic dyes, lanthanide complexes and SCQD-based nanomaterials. To improve the quantum yield and PL, various approaches have been developed including ligand engineering, selective doping to create alloy clusters, aggregation-induced emission, selective etching and self-assembly [48][49][50][51][52][53][54][55][56][57][58].…”

“…The NC assemblies have been used to encapsu- late poorly water-soluble fluorinated drugs through nanoconfinement [97]. Chandra et al recently reported highly luminescent gold nanocluster frameworks (AuNCFs) using selfassembly through metal chelation [53]. Glutathione-capped AuNCs [Au 25 (SG) 18 ] spontaneously self-assembled into spherical AuNCFs upon controlled addition of SnCl 2 ( Figure 6C).…”

Self‐Assembly of Precision Noble Metal Nanoclusters: Hierarchical Structural Complexity, Colloidal Superstructures, and Applications

“…reported the fabrication of highly luminescent Au NC frameworks (GNCFs) by coordinating divalent cations with carboxylate anions present on the NC surface. [ 319 ] [Au@SG] NCs were prepared by heating the presynthesized Au‐thiolates at 70 °C for 24 h. Surprisingly, the addition of Sn 2+ ions into the above prepared NCs has shown a seven‐fold enhancement in their PL due to the coordination‐assisted assembly. Interaction of negatively charged carboxylate group of SG with divalent Sn 2+ cations resulted in the formation of GNCFs via inter‐NC crosslinking, which was confirmed by observing 3D spherical colloidal structures in STEM and ET ( Figure ).…”