Catenane Structures of Homoleptic Thioglycolic Acid-Protected Gold Nanoclusters Evidenced by Ion Mobility-Mass Spectrometry and DFT Calculations

Peptide-Directed Synthesis of Aggregation-Induced Emission Enhancement-Active Gold Nanoclusters for Single- and Two-Photon Imaging of Lysosome and Expressed αvβ3 Integrin Receptors

This study explores the synthesis and characterization of aggregation-induced emission enhancement (AIEE)-active gold nanoclusters (AuNCs), focusing on their near-infrared luminescence properties and potential applications in biological imaging. These AIEE-active AuNCs were synthesized via the NaBH4-mediated reduction of HAuCl4 in the presence of peptides. We systematically investigated the influence of the peptide sequence on the optical features of the AuNCs, highlighting the role of glutamic acid in enhancing their quantum yield (QY). Among the synthesized peptide-stabilized AuNCs, EECEE-stabilized AuNCs exhibited the maximum QY and a pronounced AIEE effect at pH 5.0, making them suitable for the luminescence imaging of intracellular lysosomes. The AIEE characteristic of the EECEE-stabilized AuNCs was demonstrated through examinations using transmission electron microscopy, dynamic light scattering, zeta potential analysis, and single-particle imaging. The formation of the EECEE-stabilized AuNCs was confirmed by size-exclusion chromatography and mass spectrometry. Spectroscopic and electrochemical examinations uncover the formation process of EECEE-stabilized AuNCs, comprising EECEE-mediated reduction, NaBH4-induced nucleation, complex aggregation, and subsequent cluster growth. Furthermore, we demonstrated the utility of these AuNCs as luminescent probes for intracellular lysosomal imaging, leveraging their pH-responsive AIEE behavior. Additionally, cyclic arginylglycylaspartic acid (RGD)-modified AIEE dots, derived from cyclic RGD-linked peptide-induced aggregation of EECEE-stabilized AuNCs, were developed for single- and two-photon luminescence imaging of αvβ3 integrin receptor-positive cancer cells.

Ligand impact on reactive oxygen species generation of Au10 and Au25 nanoclusters upon one- and two-photon excitation

In photodynamic therapy (PDT), light-sensitive photosensitizers produce reactive oxygen species (ROS) after irradiation in the presence of oxygen. Atomically-precise thiolate-protected gold nanoclusters are molecule-like nanostructures with discrete energy levels presenting long lifetimes, surface biofunctionality, and strong near-infrared excitation ideal for ROS generation in PDT. We directly compare thiolate-gold macromolecular complexes (Au₁₀) and atomically-precise gold nanoclusters (Au₂₅), and investigate the influence of ligands on their photoexcitation. With the ability of atomically-precise nanochemistry, we produce Au₁₀SG₁₀, Au₁₀AcCys₁₀, Au₂₅SG₁₈, and Au₂₅AcCys₁₈ (SG: glutathione; AcCys: N-acetyl-cysteine) fully characterized by high-resolution mass spectrometry. Our theoretical investigation reveals key factors (energetics of excited states and structural influence of surface ligands) and their relative importance in singlet oxygen formation upon one- and two-photon excitation. Finally, we explore ROS generation by gold nanoclusters in living cells with one- and two-photon excitation. Our study presents in-depth analyses of events within gold nanoclusters when photo-excited both in the linear and nonlinear optical regimes, and possible biological consequences in cells.

Controlling the Chemistry of Nanoclusters: From Atomic Precision to Controlled Assembly

Metal nanoclusters have gained prominence in nanomaterials sciences, owing to their atomic precision, structural regularity, and unique chemical composition. Additionally, the ligands stabilizing the clusters provide great opportunities for linking the clusters in higher order dimensions, eventually leading to the formation of a repertoire of nanoarchitectures. This makes the chemistry of atomic clusters worth exploring. In this mini review, we aim to focus on the chemistry of nanoclusters. Firstly, we summarize the important strategies developed so far for the synthesis of atomic clusters. For each synthetic strategy, we highlight the chemistry governing the formation of nanoclusters. Next, we discuss the key techniques in the purification and separation of nanoclusters, as the chemical purity of clusters is deemed important for their further chemical processing. Thereafter which we provide an account of the chemical reactions of nanoclusters. Then, we summarize the chemical routes to the spatial organization of atomic clusters, highlighting the importance of assembly formation from an application point of view. Finally, we raise some fundamentally important questions with regard to the chemistry of atomic clusters, which, if addressed, may broaden the scope of research pertaining to atomic clusters.

Exploration of Formation and Size-Evolution Pathways of Thiolate-Gold Nanoclusters in the CO-Directed [Au25 (SR)18 ]- Synthesis

An intermolecular association and decarboxylation mechanism is proposed to understand the experimental evidence of the stepwise 2e^- hopping in the reductant-assisted thiolate-gold cluster synthesis. Based on the newly proposed intermolecular reaction mechanism, a total of 19 molecular-like reaction equations are deduced to account for the bottom-up formation of 2e^- -8e^- gold nanoclusters in the CO-directed [Au₂₅ (SR)₁₈ ]^- synthesis. With these established reaction equations, atomic pathways of three prototype cluster-size evolution reactions are comprehensively explored in the course of [Au₂₅ (SR)₁₈ ]^- synthesis, namely, the conversion of 0e^- homoleptic Au^(I) -SR complexes to the 2e^- intermediate Au₁₅ (SR)₁₃ cluster, the size-evolution of 2e^- Au₁₅ (SR)₁₃ cluster to the 4e^- -8e^- cluster (stepwise 2e^- -hopping), and the isoelectronic addition reaction of [Au₂₃ (SR)₁₆ ]^- to the [Au₂₅ (SR)₁₈ ]^- . The studies reveal that the CO can combine with the Au(I)-complex to form [Au_x (SR)_x -COOH]^- species in the alkaline condition, which acts as the active precursors in the 2e^- hopping cluster-size evolution process. Lastly, as a conceptual extension of the mechanistic studies of the CO-reduction system, a similar intermolecular reaction mechanism is proposed for the 2e^- reduction in the conventional "NaBH₄ reduction" system.

Four orders-of-magnitude enhancement in the two-photon excited photoluminescence of homoleptic gold thiolate nanoclusters following zinc ion-induced aggregation

Herein we report unprecedented determination of the molar mass of zinc mediated assemblies of homoleptic gold nanoclusters, based on charge detection mass spectrometry measurements. The accurate determination of the molar mass of zinc coordinated assemblies of gold clusters has further allowed unambiguous determination of the two-photon excited photoluminescence cross section of the same. Furthermore, in line with one-photon excited photoluminescence measurements, four orders-of-magnitude enhancement in two-photon excited photoluminescence of gold nanoclusters has been observed following complexation with zinc ions. The study reported herein is envisioned to not only deepen the fundamental understanding of the multiphoton excitation properties of atomic clusters but also widen their application potential as luminescence markers.

Covalent anchoring of atomically precise glutathione-protected gold nanoclusters on graphene oxide nanosheets

This paper describes the development of a novel method of producing nanocomposites consisting of gold nanoclusters anchored on graphene oxide nanosheets in a cost-effective and reproducible manner. The novelty of the technique hinges on the covalent functionalization of atomically precise subnanometer gold clusters protected by glutathione (Au15SG13 and Au25SG18) on to graphene oxide (GO) nanosheets according to the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride crosslinking method, using the existing carboxylic groups present both at the surfaces of the nanoclusters and the GO nanosheets. The atomic precision of glutathione-protected gold nanoclusters was evidenced by electrospray ionization mass spectrometry. The formed hybrid nanocomposites were characterized by TEM measurements and exhibit nonlinear optical properties characteristic of GO, in particular a strong second harmonic scattering response as well as a multi-photon excited fluorescence spectrum characterized by a broad band in the visible range between 350 and 700 nm. Atomically precise nanoclusters covalently linked to GO nanosheets are therefore promising for new applications in the areas of optoelectronics and photovoltaics.

Supramolecular Gold Chemistry: From Atomically Precise Thiolate-Protected Gold Nanoclusters to Gold-Thiolate Nanostructures

Supramolecular chemistry is defined as chemistry beyond the molecule [...].

Ligand shell size effects on one- and two-photon excitation fluorescence of zwitterion functionalized gold nanoclusters

Gold nanoclusters (Au NCs) are an emerging class of luminescent nanomaterials but still suffer from moderate photoluminescence quantum yields. Recent efforts have focused on tailoring their emission properties. Introducing zwitterionic ligands to cap the metallic kernel is an efficient approach to enhance their one-photon excitation fluorescence intensity. In this work, we extend this concept to the nonlinear optical regime, i.e., two-photon excitation fluorescence. For a proper comparison between theory and experiment, both ligand and solvent effects should be considered. The effects of ligand shell size and of aqueous solvent on the optical properties of zwitterion functionalized gold nanoclusters have been studied by performing quantum mechanics/molecular mechanics (QM/MM) simulations.