Insights into the synthesis of NHC-stabilized Au nanoclusters through real-time reaction monitoring

Luminescence Fingerprint of Intracellular NIR-II Gold Nanocluster Transformation: Implications for Sensing and Imaging

Gold nanoclusters emitting in the second biological window (NIR-II-AuNCs) have gained significant interest for their potential in deep-tissue bioimaging and biosensing applications due to the partial transparency and reduced autofluorescence of tissues in this spectral range. However, the limited understanding of how the biological environment affects their luminescent properties might hinder their use in bioimaging and biosensing. In this study, we investigated the emission properties of NIR-II-AuNCs when interacting and internalizing into live cells including macrophages, fibroblasts, and cancer cell lines, revealing substantial alterations in their luminescence. A systematic comparison between control and in vitro experiments concluded that the disruption of surface ligands is the main factor responsible for these alterations. NIR-II-AuNCs within cellular environments may also be influenced by other interactions, including aggregation or complexation with proteins. Furthermore, we also corroborated these spectroscopic modifications at the in vivo level, providing additional evidence of the environmental sensitivity of NIR-II-AuNCs. The results obtained in this study contribute to a deeper understanding of the luminescence mechanisms of NIR-II-AuNCs in biological environments in cells and in living tissues and are crucial for their optimization as reliable tools in biological environment for in vitro and in vivo imaging and diagnostics.

Spatial Confinement-Enhanced Electrochemiluminescence of Gold Nanoclusters on 3D Porous ZrO2 Hollow Nanospheres for the Assessment of Acute Myocardial Infarction Protein Markers

Herein, the gold nanoclusters@three-dimensional (3D) porous ZrO2 hollow nanospheres (Au NCs@ZrO2) with spatial confinement-enhanced electrochemiluminescence (SCE-ECL) were first prepared to fabricate a biosensing platform for the ultrasensitive detection of insulin-like growth factor 1 (IGF-1), which was associated with cardiovascular disease, malignant tumor, and neuropathic pain. Specifically, the confinement of Au NCs in a 3D microenvironment significantly boosted the optical radiation of excited Au NCs because the vibration of ligand molecules was restricted, and the recombination of holes and electrons of excited Au NCs was facilitated in the optical process for enhancing ECL efficiency, resulting in 5.1-fold stronger ECL efficiency than Au NCs. As a proof of concept, based on Au NCs@ZrO2 as an emitter and an orderly and localized catalytic hairpin self-assembly (OL-CHA) system as a signal amplifier, the built ECL biosensing platform achieved fast and trace determination of IGF-1 with the detection limit (LOD) down to 0.36 fg/mL. Moreover, the ECL platform realized the assessment of the IGF-1 expression of acute myocardial infarction (AMI) patients and exhibited a more prominent accuracy than the enzyme-linked immunosorbent assay (ELISA). This work proposed a neoteric avenue for developing highly efficient ECL emitters, which presented a promising prospect in ultrasensitive bioanalysis for early diagnosis of diseases.

Surface Charge Redistribution-Induced Electrochemiluminescence Enhancement of Gold Nanoclusters: The Novel Generation of Efficient Illuminants

Herein, we developed the agmatine/6-aza-2-thiothymine templated gold nanoclusters (Agm/ATT-Au NCs) as a novel electrochemiluminescence (ECL) illuminant, which exhibited high ECL in the annihilation path via the newly defined surface charge redistribution-induced ECL enhancement (SCRIE). Impressively, the electrochemical redox reaction of Agm/ATT-Au NCs was enhanced owing to the boosted electron transfer kinetics of the illuminant by the positively charged Agm-triggered surface charge redistribution of ATT-Au NCs, resulting in an ∼110-fold higher ECL signal of Agm/ATT-Au NCs than ATT-Au NCs. This work digs deep into the electrogenerated process of the annihilation mechanism to direct the rational design of an efficient illuminant. Moreover, the Agm/ATT-Au NCs as a powerful illuminant was successfully applied in a highly sensitive bioassay platform for detecting glial fibrillary acidic protein (GFAP) with the detection limit down to 27.5 ag/mL, an intense organic light-emitting diode (OLED), and high-definition ECL imaging.

When Metal Nanoclusters Meet Smart Synthesis

Atomically precise metal nanoclusters (MNCs) represent a fascinating class of ultrasmall nanoparticles with molecule-like properties, bridging conventional metal-ligand complexes and nanocrystals. Despite their potential for various applications, synthesis challenges such as a precise understanding of varied synthetic parameters and property-driven synthesis persist, hindering their full exploitation and wider application. Incorporating smart synthesis methodologies, including a closed-loop framework of automation, data interpretation, and feedback from AI, offers promising solutions to address these challenges. In this perspective, we summarize the closed-loop smart synthesis that has been demonstrated in various nanomaterials and explore the research frontiers of smart synthesis for MNCs. Moreover, the perspectives on the inherent challenges and opportunities of smart synthesis for MNCs are discussed, aiming to provide insights and directions for future advancements in this emerging field of AI for Science, while the integration of deep learning algorithms stands to substantially enrich research in smart synthesis by offering enhanced predictive capabilities, optimization strategies, and control mechanisms, thereby extending the potential of MNC synthesis.

Size disproportionation among nanocluster transformations

Controllable transformation is a prerequisite to the in-depth understanding of structure evolution mechanisms and structure-property correlations at the atomic level. Most transformation cases direct the directional evolution of nanocluster sizes, i.e., size-maintained, size-increased, or size-reduced transformation, while size disproportionation was rarely reported. Here, we report the Au-doping-induced size disproportionation of nanocluster transformation. Slight Au-doping on the bimetallic (AgCu)43 nanocluster produced its trimetallic derivative, (AuAgCu)43, following a size-maintained transformation. By comparison, the (AgCu)43 nanocluster underwent a size-disproportionation transformation under heavy Au alloying, leading to the formation of size-reduced (AuAgCu)33 and size-increased (AuAgCu)56 nanoclusters simultaneously. Such a size disproportionation among the nanocluster transformations was verified by the thin-layer chromatography analysis. This work presented a novel nanocluster transformation case with a size disproportionation characteristic, expected to provide guidance for the understanding of cluster size evolutions.

Synthesis and crystallization of a carboxylate functionalized N-heterocyclic carbene-based Au13 cluster with strong photo-luminescence

Here we report the synthesis and crystallization of a -COOH-capped N-heterocyclic carbene (NHC)-protected Au13 cluster. The single-crystal structure of the -COOH-capped NHC-Au13 cluster reveals a classic icosahedral core with one Au atom in its center. The icosahedral core is surrounded by five NHC ligands with pseudo C5 symmetry and exposed carboxyls in a pentagonal antiprism fashion. The detailed formula of the Au cluster was identified as Au13(bi-NHC carboxyl)5Cl2 (hereafter abbreviated as Au13-c). The density functional theory (DFT) calculations confirm that Au13-c is an electronically stable eight-electron super-atom cluster and elucidate its optical transitions in the UV-Vis range. The Au13-c cluster exhibits excellent thermal and chemical stability under bio-relevant conditions. Additionally, this cluster shows a strong red emission in DMF and H2O with an excellent quantum yield (QY) of 40% and 12.6%, respectively. The high QY of Au13-c enables its use in cell imaging on both cancer and noncancerous cells.

If the Crown Fits: Sterically Demanding N-Heterocyclic Carbene Promotes the Formation of Au8Pt Nanoclusters

While N-heterocyclic carbenes (NHCs) have recently been shown to be effective ligands for gold nanoclusters, very few examples of heterometallic clusters incorporating nongroup 11 metals are known. We present herein an Au-Pt NHC cluster featuring a crown-shaped [Au8Pt(NHC)8]2+ core, produced in high yield without the need for chromatographic purification. The method was largely independent of the substitution pattern of the NHC backbone; however, bulky wingtip groups were needed for clean conversion to the Au8Pt cluster. Clusters were characterized using single crystal X-ray diffraction, multinuclear nuclear magnetic resonance, electrospray ionization mass spectroscopy, and ultraviolet-visible spectroscopy, and electrochemical features of the cluster are also presented. A detailed analysis of the in-progress reaction mixture by ESI-MS supports the direct involvement of Au-H species as intermediates in cluster formation. These studies further demonstrate that NHC wingtip sterics play a key part in determining the nature of the initial cluster species, providing critical information for the generation of new NHC-stabilized nanoclusters.

Electron-Accelerator-Induced Fast Electron Transfer for Enhancing Electrochemiluminescence of Gold Nanoclusters and Its Bioanalysis Application: A Novel Avenue for Developing High-Efficient Emitters

Herein, the gold nanoclusters/CaFe2O4 nanospheres (Au NCs/CaFe2O4) heterostructure as a novel electrochemiluminescence (ECL) emitter was developed. Excitingly, Au NCs/CaFe2O4 displayed highly efficient and greatly stable ECL based on the newly defined electron-accelerator p-type semiconductor CaFe2O4 NS-induced fast electron transfer; it solved one key obstacle of metal NC-based ECL emitters: sluggish through-covalent bond electron transport kinetics-caused inferior ECL performance. Specifically, on account of the energy level matching between emitter Au NCs and electron-accelerator CaFe2O4 NSs, the valence band (VB) of the electron-accelerator could provide abundant holes for rapidly transporting the electrogenerated electron from the highest occupied molecular orbital (HOMO) of Au NCs to the electrode, generating massive excited species of Au NCs for strong ECL emission. Notably, Au NCs/CaFe2O4 emerged 5.4-fold higher ECL efficiency with 3.5-fold higher electrochemical oxidation current in comparison with pure Au NCs, exhibiting great prospects in extensive lighting installations, ultrasensitive biosensing, and high-resolution ECL imagery. As applications, an ECL bioassay platform was constructed with Au NCs/CaFe2O4 as an emitter and U-like structure-fueled catalytic hairpin assembly (U-CHA) as a signal amplifier for fast and trace analysis of aflatoxin B1 (AFB1) with the detection limit (LOD) down to 2.45 fg/mL, which was 3 orders of magnitude higher than that of the previous ECL biosensors with much better stability. This study developed an entirely new avenue for enlarging the ECL performance of metal NCs, and it is a very attractive orientation for directing the reasonable design of prominent metal NC-based ECL emitters and broadening the practical application of metal NCs.

N-Heterocyclic Carbene-Stabilized Atomically Precise Metal Nanoclusters

This perspective highlights advances in the preparation and understanding of metal nanoclusters stabilized by organic ligands with a focus on N-heterocyclic carbenes (NHCs). We demonstrate the need for a clear understanding of the relationship between NHC properties and their resulting metal nanocluster structure and properties. We emphasize the importance of balancing nanocluster stability with the introduction of reactive sites for catalytic applications and the importance of a better understanding of how these clusters interact with their environments for effective use in biological applications. The impact of atom-scale simulations, development of atomic interaction potentials suitable for large-scale molecular dynamics simulations, and a deeper understanding of the mechanisms behind synthetic methods and physical properties (e.g., the bright fluorescence displayed by many clusters) are emphasized.