Au Nanoclusters Research Articles

Reduction of 4‐Nitrophenol Catalyzed by Gold Nanoclusters with Aggregation‐Induced‐Emission: Emission Intensity Correlated Activity and Mechanistic Exploration

AbstractThiolate‐protected Au nanoclusters (NCs) have developed as a promising class of model catalysts to achieve fundamental understanding of metal nanocatalysis. Whereas, the packing mode of peripheral ligand on metal core is changeful in the reaction medium and show elusive impact on catalytic activity. In this work, using glutathione (GSH) protected Au NCs (Au@GSH NCs) with aggregation‐induced‐emission (AIE) characteristics as model catalyst for the hydrogenation of 4‐nitrophenol (4‐NP), photoluminescence (PL) intensity correlated catalytic activity of Au@GSH NCs was successfully mediated by the addition of Ag+ in the preparation or poor solvent in the reaction medium, showing a relationship of “as one falls, another rises.” Au NCs with intense PL implied a dense packing of peripheral ligand, which hampered the accessibility of active site and thus exhibited slowest catalytic reaction kinetics of the reduction of 4‐NP and vice versa. Based on this methodology, a case study of the effect of salt additives on the catalytic activity is carried out, different mechanisms are distinguished by the change in the PL intensity, and with the combination of diagnostic deuterium isotope experiments, it has been demonstrated that the proton from water solvent is involved in the reaction and that the proton transfer process is the rate‐determining step, the contribution of ionic additives to the hydrogen bonding network determines their effect on the reaction kinetics. The correlation between PL intensity and catalytic activity of Au NCs could provide an efficient way to design highly active Au NC catalysts and give a new insight to understand the unique optoelectronic properties of Au NCs and reaction mechanism.

Atomically Precise Rhodium‐Gold Carbonyl Nanoclusters: In‐Depth Synthesis and Multivalence Investigation of [Rh16Au6(CO)36]6−, and its Correlation with [Rh10Au(CO)26]3−

AbstractThe synthesis of the previously‐reported atomically‐precise [Rh16Au6(CO)36]6− (1) nanocluster has been optimized by screening different reaction variables like solvent, stoichiometric ratio, counterion and atmosphere. Its multivalence properties have also been studied by means of electrochemical and spectroelectrochemical techniques; the results pointed out a remarkable electron‐sponge behaviour, as under such experimental conditions 1 is capable to release one electron and accept up to four more, while retaining its molecular structure. This scarce structural variation has been confirmed through DFT calculations on those species whose redox processes showed the maximum reversibility, namely [Rh16Au6(CO)36]7− and [Rh16Au6(CO)36]5−. Moreover, we report herein the isolation and characterization of the new [Rh10Au(CO)26]3− (2) nanocluster, which represents one of the major fallouts of the synthetic pathway investigation of 1. Finally, we disclosed the existence of further species that, from preliminary results, appear to be new large atomically‐precise Rh−Au nanoclusters, which will be the subject of future investigations. Cluster 2 has been identified via single‐crystal X‐ray diffraction analysis, and the characterization of both clusters 1 and 2 completed by infrared (IR) spectroscopy and Electrospray Ionization Mass Spectrometry (ESI‐MS).

Encapsulation of an Au25 Nanocluster inside a Porphyrin Nanoring Enhances Singlet Oxygen Generation and Photo‐Electrocatalytic CO2 Reduction

AbstractThe synthesis of molecular host–guest complexes with enhanced performance, relative to those of their components, is a central theme in supramolecular chemistry. Here we explore a host‐guest system consisting of an atomically precise gold nanocluster bound inside a zinc porphyrin nanoring. UV/Vis absorption and fluorescence titrations with different sized nanorings revealed strong binding between a pyridinethiol‐coated Au25 nanocluster and a nanoring consisting of six zinc porphyrin units, and complexation is confirmed by mass spectrometry. Formation of this assembly enhances the stability of the gold nanocluster. The host‐guest complex also exhibits remarkable activity and selectivity for photochemical CO2 to CO conversion and singlet oxygen generation.

Encapsulation of an Au25 Nanocluster inside a Porphyrin Nanoring Enhances Singlet Oxygen Generation and Photo-Electrocatalytic CO2 Reduction.

The synthesis of molecular host-guest complexes with enhanced performance, relative to those of their components, is a central theme in supramolecular chemistry. Here we explore a host-guest system consisting of an atomically precise gold nanocluster bound inside a zinc porphyrin nanoring. UV-vis absorption and fluorescence titrations with different sized nanorings revealed strong binding between a pyridinethiol-coated Au25 nanocluster and a nanoring consisting of six zinc porphyrin units, and complexation is confirmed by mass spectrometry. Formation of this assembly enhances the stability of the gold nanocluster. The host-guest complex also exhibits remarkable activity and selectivity for photochemical CO2 to CO conversion and singlet oxygen generation.

Au25 Cluster-Based Atomically Precise Coordination Frameworks and Emission Engineering through Lattice Symmetry.

The atomically precise metal nanoclusters (NCs) have attracted significant attention due to their superatomic behavior originating from the quantum confinement effect. This behavior makes these materials suitable for various photoluminescence-based applications, including chemical sensing, bioimaging, and phototherapy, owing to their intriguing optical properties. Especially, the manipulation of inter- or intracluster interaction through cluster-assembled materials (CAMs) presents significant pathways for modifying the photophysical properties of NCs. Herein, two distinct CAMs, Au25-Zn-Hex and Au25-Zn-Rod, were synthesized via forming a coordination bond between [Au25(p-HMBA)18]- (p-H2MBA = 4-mercaptobenzoic acid) and Zn2+. Au25-Zn-Rod exhibited a 6-fold higher luminescence intensity in the near-infrared region compared to Au25-Zn-Hex, attributed to synergistic inter- and intracluster interactions that induce exciton delocalization and structure rigidification at the atomic scale. This study highlights the potential of diverse lattice symmetries in cluster-based frameworks for tuning the photophysical properties, contributing to a deeper understanding of the structure-property relationship in Au NCs.

Raising Near-Infrared Photoluminescence Quantum Yield of Au42 Quantum Rod to 50% in Solutions and 75% in Films.

Highly emissive gold nanoclusters (NCs) in the near-infrared (NIR) region are of wide interest, but challenges arise from the excessive nonradiative dissipation. Here, we demonstrate an effective suppression of the motions of surface motifs on the Au42(PET)32 rod (PET = 2-phenylethanethiolate) by noncoordinative interactions with amide molecules and accordingly raise the NIR emission (875/1045 nm peaks) quantum yield (QY) from 18% to 50% in deaerated solution at room temperature, which is rare in Au NCs. Cryogenic photoluminescence measurements indicate that amide molecules effectively suppress the vibrations associated with the Au-S staple motifs on Au42 and also enhance the radiative relaxation, both of which lead to stronger emission. When Au42 NCs are embedded in a polystyrene film containing amide molecules, the PLQY is further boosted to 75%. This research not only produces a highly emissive material but also provides crucial insights for the rational design of NIR emitters and advances the potential of atomically precise Au NCs for diverse applications.

Au Cluster-Nanoparticle Dual Coupling for Photocatalytic CO2 Conversion.

CO2-selective photoreduction to value-added products is ideal, but its practical application suffers from weak photogenerated carrier separation and insufficient multielectron transport. Herein, we constructed the tricomponent AuNPs@SnO2-AuNCs hybrid by decorating Au nanoclusters (AuNCs) on the Au nanoparticle (AuNPs)@SnO2 core-shell structure. AuNC-NP dual coupling endowed AuNPs@SnO2-AuNCs with an excellent CO yield of 64.8 μmol g-1 h-1 during CO2 photoreduction, which was higher than the role of separate application of AuNCs (25.3 μmol g-1 h-1) and AuNPs (16.0 μmol g-1 h-1). It was mainly attributed that the coaction of AuNPs and AuNCs not only enhanced the visible light absorption capacity but also improved the photogenerated carrier separation/migration. As a result, the electron-rich AuNCs induced from plasmonic AuNPs and photoexcited SnO2 promoted the photocatalytic CO2-to-CO performance. This work provides a new perspective to design multicomponent photocatalysts for highly efficient CO2 conversion.

“Kill two birds with one stone” role of PTCA-COF: Enhanced electrochemiluminescence of Au nanoclusters via radiative transitions and electrochemical excitation for sensitive detection of cadmium ions

Au nanoclusters (AuNCs) have attracted significant attention in electrochemiluminescence (ECL) owing to their excellent luminescent properties; however, achieving high-efficient ECL remains a formidable challenge. Despite the extensively reported emphasis on enhancing radiative transitions, it is imperative to acknowledge that both radiation and excitation play crucial roles in ECL, thereby requiring a dual-enhanced strategy for improving ECL efficiency. Herein, we introduced PTCA-COF, a dual-functional covalent organic frameworks (COFs) with the effect of “kill two birds with one stone” to achieve this purpose. The PTCA-COF not only acted as a carrier to effectively suppress the rotational vibration of surface ligands and reduce self-quenching by minimizing non-radiative transitions, but also acted as an electrosensitiser that facilitated the generation of electrogenerated holes, thereby promoting efficient transfer of hot electrons and enhancing excitation of AuNCs due to favorable energy level alignment. As a proof of concept, by utilizing cadmium ions (Cd2+) as a model analyte, the ECL aptasensing platform fabricated based on the dual-enhancement AuNCs-COFs ECL system demonstrated a broad linear response spanning from 1 pM to 5 nM and achieved an impressive low detection limit of 0.66 pM (S/N=3) with exceptional reproducibility and selectivity. The findings of this study not only presented a novel approach for the rational dual-enhancement of ECL efficiency, but also contributed to the advancement of their potential applications in the field of environmental monitoring.

Anchoring ultrafine Au nanoclusters on sulfonate groups functionalized carbon matrix for efficient catalytic reduction of nitrophenol

Despite immense research efforts in the field of Au supported on carbon matrix, the rational design and fabrication of ultrafine Au/carbon matrix nanocatalysts with effective reactivity and high stability are still challenging. The main obstacles are faced with adjusting the size of Au nanoclusters and strengthening the bond of Au and carbon. In this work, sulfonate groups (−SO3H) introduced onto activated coke (AC) matrix was prepared for steadily anchoring ultrafine Au nanoclusters (∼2 nm). The obtained Au/SO3H-AC exhibited superior reactivity for 4-nitrophenol reduction within 3 min using NaBH4 as reducing agent. The superior performance and stability are attributed to the − SO3H groups with hydrophilic property, benefiting for substrates readily dispersion and for Au species (including oxidized Au+ and Au3+) bind and stabilization, possibly by tightly interacting with the O atoms bound to S atom of − SO3H. In addition, several lines of evidence demonstrate the oxidized Au species can serve as electron relay system, ensuring the sustained reaction. Given that the Au nanoclusters in this study have superior reactivity and stability, this work proposes a novel strategy for preparing other supported metal nanocomposites.

WS2 Moiré Superlattices Supporting Au Nanoclusters and Isolated Ru to Boost Hydrogen Production.

Maximizing the catalytic activity of single-atom and nanocluster catalysts through the modulation of the interaction between these components and the corresponding supports is crucial but challenging. Herein, guided by theoretical calculations, a nanoporous bilayer WS2 Moiré superlattices (MSLs) supported Au nanoclusters (NCs) adjacent to Ru single atoms (SAs) (Ru1/Aun-2LWS2) is developed for alkaline hydrogen evolution reaction (HER) for the first time. Theoretical analysis suggests that the induced robust electronic metal-support interaction effect in Ru1/Aun-2LWS2 is prone to promote the charge redistribution among Ru SAs, Au NCs, and WS2 MSLs support, which is beneficial to reduce the energy barrier for water adsorption and thus promoting the subsequent H2 formation. As feedback, the well-designed Ru1/Aun-2LWS2 electrocatalyst exhibits outstanding HER performance with high activity (η10=19mV), low Tafel slope (35mVdec-1), and excellent long-term stability. Further, in situ, experimental studies reveal that the reconstruction of Ru SAs/NCs with S vacancies in Ru1/Aun-2LWS2 structure acts as the main catalytically active center, while high-valence Au NCs are responsible for activating and stabilizing Ru sites to prevent the dissolution and deactivation of active sites. This work offers guidelines for the rational design of high-performance atomic-scale electrocatalysts.

Selectivity Modulation of Multistep Reduction Reactions by Gold Nanoclusters

The selective synthesis of valuable azo‐ and azoxyaromatic chemicals via transfer coupling of nitroaromatic compounds has been achieved by fine‐tuning the catalyst structure. Here, a direct method to modulate nitrobenzene reduction and selectively alter the product from azobenzene to azoxybenzene by employing the size effect of Au is reported. Au nanoclusters (NCs) with smaller sizes embedded in ZIF‐8 controllably converted nitrobenzene into azoxybenzene, while supported Au nanoparticles (NPs) catalyzed nitrobenzene reduction to azobenzene. X‐ray photoelectron spectroscopy (XPS) and Diffuse reflectance infrared Fourier transform spectroscopy on CO adsorption (CO‐DRIFTS) of Au NC/ZIF‐8 revealed a higher valence state and a lower electron density of Au than that of Au NP/ZIF‐8, combined with the desorption of azoxybenzene from the Au NC and Au NP surface, suggesting that the Au NCs with lower electron density exhibit stronger adsorption. Density functional theory (DFT) calculations and charge density difference maps indicated that azoxybenzene bonded to Au NC/ZIF‐8 with greater adsorption energy, resulting in more electron transfer between azoxybenzene and the generated Au sites, which inhibited further reduction of azoxybenzene and resulted in high azoxybenzene selectivity. The application of the size effect of Au particles to regulate nitrobenzene transfer coupling provided new insights into the structure‐selectivity relationships.

Selectivity Modulation of Multistep Reduction Reactions by Gold Nanoclusters.

The selective synthesis of valuable azo- and azoxyaromatic chemicals via transfer coupling of nitroaromatic compounds has been achieved by fine-tuning the catalyst structure. Here, a direct method to modulate nitrobenzene reduction and selectively alter the product from azobenzene to azoxybenzene by employing the size effect of Au is reported. Au nanoclusters (NCs) with smaller sizes embedded in ZIF-8 controllably converted nitrobenzene into azoxybenzene, while supported Au nanoparticles (NPs)catalyzed nitrobenzene reduction to azobenzene. X-ray photoelectron spectroscopy (XPS) and Diffuse reflectance infrared Fourier transform spectroscopy on CO adsorption (CO-DRIFTS) of Au NC/ZIF-8 revealed a higher valence state and a lower electron density of Au than that of Au NP/ZIF-8, combined with the desorption of azoxybenzene from the Au NC and Au NP surface, suggesting that the Au NCs with lower electron density exhibit stronger adsorption. Density functional theory (DFT) calculations and charge density difference maps indicated that azoxybenzene bonded to Au NC/ZIF-8 with greater adsorption energy, resulting in more electron transfer between azoxybenzene and the generated Au sites, which inhibited further reduction of azoxybenzene and resulted in high azoxybenzene selectivity. The application of the size effect of Au particles to regulate nitrobenzene transfer coupling provided new insights into the structure-selectivity relationships.

Golden Guardians: Advanced pH Sensors with Built‐in Antimicrobial Defense

AbstractGold nanoclusters (Au NCs) capped with a small biomolecule, namely (+)‐norephedrine, (Au@Nore) display exceptional performance as fluorescent pH sensors. They display high emission quantum yield (ΦPL of ≈33% in strongly basic media); absence of nanocluster (NC) aggregation and/or induced rigidification of the organic shell; a linear dependency of their emission on the pH in the 8.2–9.5 range; and reversible pH sensing. In addition, excitation at 310 nm, where both the NC and the ligand absorb, enables ratiometric sensing. Studies on the fungus Candida albicans and bacterium Bacillus subtilis demonstrate that while Au@Nore do not cause any impact on the growth of the fungus, it inhibited the growth of the Bacillus, showing the lowest cell viability of 18% at the highest pH values via a mechanism of action involving the disruption of the bacterial wall.

The photothermal effect induces M1 macrophage-derived TNF-α-type exosomes to inhibit bladder tumor growth

Bladder cancer presents a significant challenge for patient treatment and prognostic health due to its high recurrence and metastasis. Nanoparticle-based photothermal therapy offers a potential solution, as it can achieve thermal ablation of tumors through photothermal conversion, modulate cytokine and exosome secretion from macrophages to assist in treatment. Herein, a system that integrates gold-manganese nanomaterials and engineered macrophage-derived exosomes for the synergistic treatment of bladder tumors was developed. We encapsulated MnO2 on the surface of sea-urchin-like Au nanoclusters (AuNCs) to form a nanocomposite with a shell-and-core structure (Au@MnO2), effectively enhancing its stability and photothermal conversion efficiency. In vitro experiments showed that Au@MnO2 induced polarization of macrophages to secrete cytokines (e.g., TNF-α, iNOS, etc.) and TNF-α-rich exosomes of the M1 phenotype when exposed to near-infrared light. This M1 phenotype, combined with the nano-photothermal effect, significantly inhibited the proliferation of bladder tumor cells, and promoted apoptosis and cycle blockade. RNA sequencing revealed significant regulation of inflammation-related genes and pathways, including TNF, NF-κB, and cytokine receptor pathways, both in M1 macrophages and their exosomes. In vivo experiments confirmed that engineered macrophages combined with nano-photothermal effect inhibited subcutaneous tumor growth in mice and reduced the macrophage CD206/CD86 ratio in tissues. This study highlights the promise of engineered macrophages combining cytokines, M1-Exo, and the photothermal effects of Au@MnO2 to achieve synergistic treatment for bladder cancer.

An electrochemical point-of-care testing device for specific diagnosis of the albinism biomarker based on paradigm shift designs

L-tyrosine is a recognized biomarker of albinism, whose endogenous level in human bodies is directly linked to melanin synthesis while no attention has been paid to its specific diagnosis. To this end, we have developed an electrochemical point-of-care testing device based on a molecularly imprinted gel prepared by a universal paradigm shift design to achieve the enhanced specific recognition of the L-tyrosine. Interestingly, this theoretically optimized molecularly imprinted gel validates the recognition pattern of L-tyrosine and optimizes the structure of the polymer itself with the aid of computational chemistry. Besides, modified extended-layer MXene and Au nanoclusters have significantly improved the sensing activity. As a result, the linear diagnostic range of this electrochemical point-of-care testing device for L-tyrosine is 0.1–100 μM in actual human fluids, which fully covers the L-tyrosine levels of healthy individuals and people with albinism. The diagnosis is completed in 90 s and then the results are transmitted by Bluetooth low energy to the smart mobile terminal. Therefore, we are convinced that this electrochemical point-of-care testing device is a promising tool in the future smart medical system.

Multi-deformable interpenetrating network thermosensitive hydrogel fluorescent device for real-time and visual detection of nitrite

Functionalized thermosensitive hydrogel materials exhibit excellent properties for the fabrication of sensing devices that enable real-time visual detection of food safety duo to their good plasticity and powerful loading capacity. Here, a ratiometric fluorescent device based on an interpenetrating network (IPN) thermosensitive hydrogel was designed to embed functionalized Au nanoclusters (Au NCs) and Blue Carbon dots (BCDs) composites in a multi-network structure to build a sensitive hazardous material nitrite (NO2-) chemsensor. The hydrogel was utilized poloxamer 407 (P407), lignin and cellulose to form stable IPN structure, which resulted in complementation and synergy, thereby strengthening its porous network structure. The combination of fluorescent nanoprobes with the porous network structure has the potential to enhance stable fluorescence signals and improve sensing sensitivity. Moreover, the thermosensitive liquid-solid transition characteristics of the hydrogel facilitate its preparation into diverse sensing devices following curing at room temperature. The hydrogel device, when combined with a smartphone system, converted image information into data information, thereby enabling the accurate quantification of NO2- with a detection limit of 9.38 nM in 2 s. The designed multi-functional hydrogel device is capable of real-time differentiation of NO2- dosage with the naked eye, offering a high-contrast, rapid-response sensing methodology for visual assessment of food freshness. This research contributes to the expansion of hydrogel materials applications and the detection of hazardous materials in food safety.

Gold Clusters on Graphene/Graphite—Structure and Energy Landscape

Adopting an advanced microscopic model of the Au–graphite interaction, a systematic study of Au nanoclusters (up to sizes of 11 238 atoms) on graphene and on graphite is carried out to explore their structure and energy landscape. Using parallel tempering molecular dynamics, structural distribution as a function of temperature is calculated in the entire temperature range. Low‐energy structures are identified through a combination of structural optimization and Wulff–Kaischew construction which are then used to explore the energy landscape. The potential energy surface (PES), which is energy as a function of translation and rotation, is calculated for a few Au nanoclusters along specific directions on carbon lattice. Minimum‐energy pathways are identified on the PES indicating a reduced barrier for pathways involving simultaneous rotation and translation. Diffusion simulations of Au233 on graphite show that diffusion mechanism is directly related to the PES, and the information of the cluster pinning events is already present in the PES. Finally, a comparison of various interaction models highlights the importance of reasonably correct Au–C interactions which is crucial for studying the energy landscape and cluster sliding.

High-Efficient Electrochemiluminescence of DNA-Au Ag Nanoclusters with Au NPs@Ti3C2 as a Novel Coreaction Accelerator for Ultrasensitive Biosensing.

In this work, an ultrasensitive electrochemiluminescence (ECL) biosensor was constructed based on DNA-stabilized Au Ag nanoclusters (DNA-Au Ag NCs) as the efficient luminophore and Au NPs@Ti3C2 as a new coreaction accelerator for determining microRNA-221 (miRNA-221) related to liver cancer. Impressively, DNA-Au Ag NCs were stabilized by the high affinity of the periodic 3C sequence, exhibiting an excellent ECL efficiency of 27% compared with classical BSA-Au Ag NCs (16%). Moreover, the Au NPs@Ti3C2 nanocomposites, as a new coreaction accelerator, were first introduced to accelerate the production of abundant sulfate free radicals (SO4•-) for promoting the ECL efficiency of DNA-Au Ag NCs in the DNA-Au Ag NCs/Au NPs@Ti3C2/S2O82- ternary system due to the energy band of Au NPs@Ti3C2 being well-matched with the frontier orbital of S2O82-. Furthermore, the trace target (miRNA-221) could drive the rolling circle amplification to generate an amount of output DNA with periodic 3C and 10A sequences. Through covalent bonds on the surface of poly A and Au NPs, the distance between the luminophor and the coreaction accelerator could be narrowed to further enhance the detection sensitivity. As a result, the constructed sensor has been applied for the ultrasensitive detection of miRNA-221 with a low detection limit of 50 aM and successfully monitored miRNA-221 in MHCC-97L and HeLa cell lysates. This strategy could be utilized for guiding the synthesis of light-emitting DNA-metal NCs, which has great potential in the construction of ultrasensitive biosensors for the early diagnosis of diseases.

Au Nanoclusters Embedded in Polydopamine for Photothermal Radiotherapy on Non-Small-Cell Lung Cancer

Au Nanoclusters Embedded in Polydopamine for Photothermal Radiotherapy on Non-Small-Cell Lung Cancer

Photoresponse performance of Au (nanocluster and nanoparticle) TiO2: Photosynthesis, characterization and mechanism studies

In this study, gold (Au), nanoclusters (NC) and heterogeneous titanium dioxide (TiO2) were successfully synthesized by low-temperature photoelectron spectroscopy. The chemical structure of Au-TiO2 was characterized by XRD, EDX, XPS and HR-TEM. Optical properties were evaluated using PL and UV–Vis, and electrical properties were evaluated using CV, CP, UPS and EIS parameters. The results showed that Au nanocluster (NCs) were converted into Au nanoparticles (NPs) during high sunlight, and the transfer mechanism was examined. In addition, the produced nanoparticles can form a Schottky barrier with TiO2, which affects the band structure. Moreover, the simultaneous synthesis of nanoparticles and nanoclusters adds an extra dimension to the understanding of the photoelectronic behavior of structured photoelectrodes. Moreover, this research shows that good control of the photography process can result in more photos. This improvement is related to several factors, including the plasmonic field and coupling line bending.