Fluorescent Metal Nanoclusters Research Articles

Ultra-Bright 2D Assembled Copper Nanoclusters: Fluorescence Mechanism Exploration and LED Application

Novel fluorescent nanomaterials have attracted enormous interests in the applications of illumination and display besides the traditional organic fluorophors. As potential alternatives, the environmental friendly fluorescent ultra-small organic-inorganic hybrid metal nanoclusters (size < 2 nm) is a series of powerful competitors used in illuminating field, on account of the non-poisonous, large amount of storage in earth, simple synthetic route, and relative low cost. The most important one, facile regulation of the fluorescence intensity and emission colors makes metal nanoclusters more attractive candidates for illumination application. Here, through ingeniously designing the structures of capping ligands, the highly bright copper nanoclusters are obtained, which further assemble into 2D ribbons with fluorescence quantum efficiency ascending to 36.4%. Last, the light emitting diodes with excellent performance are constructed, the emission wavelength locates at 650 nm in red region, which is suitable for plant illumination.

Polyvinyl Alcohol-Supported AuAgNCs-CDs Film as a Selective Sensor for Gas Hydrogen Sulfide Detection in Air.

A novel strategy is reported for the synthesis of glutathione (GSH)-protected bimetallic nanoclusters, Au-AgNCs@GSH, and its fabrication with polyvinyl alcohol (PVA) into a film sensor for H2 S gas detection. Meanwhile, carbon dots (CDs) synthesized from polyethyleneimine (PEI) are introduced as an internal standard to correct the photobleaching of Au-AgNCs@GSH and uniformity of film. The joining of it greatly improves the chemical and structural stability of the composite film via multi cross-linking between PEI, PVA, and GSH. The PVA-AuAgNCs-CDs film exhibits an emission-quenching response to H2 S gas at atmosphere, which is highly repeatable, fast, sensitive, and can distinguish H2 S from other poisonous gases. Finally, the in-depth mechanism investigations reveal that the quenching response is attributed to decomposition of Au-AgNCs@GSH and the formation of Au2 S and Ag2 S in the composite film. As a sensor, the PVA-supported film combines the functions of fluorescent metal nanoclusters and polymer CDs, providing a portable device for the rapid detection of H2 S gas in air.

Development of a near infrared Au-Ag bimetallic nanocluster for ultrasensitive detection of toxic Pb2+ ions in vitro and inside cells.

Although the research activities pertaining to the synthesis of fluorescent noble metal nanoclusters (NCs) and their applications in biological optics have been growing, only limited information is available in the near IR (NIR) region. However, fluorescence spectroscopy and microscopy in the NIR region offer significant advantages over UV and visible wavelengths. In this manuscript, we demonstrate bio-mineralized synthesis of stable Au–Ag bimetallic NCs with tunable NIR fluorescence using bovine serum albumin (BSA) as a protein template. We also demonstrate its application in the detection of toxic heavy metal ions Pb2+in vitro and inside cells. The tunability of the fluorescence emission between 680 nm and 815 nm is achieved by systematically varying the ratio of Au and Ag in the composite NCs. The bimetallic NCs when interacting with Pb2+ offered a large increase in fluorescence intensity, which enabled sensitive detection of Pb2+. We determined a limit of detection (LOD) of 96 nM for the detection of Pb2+ under in vitro conditions, which is significantly less than the safe level in drinking water. Its applicability has also been demonstrated successfully in real water samples collected from local water bodies.

Green Synthesis of Fluorescent Palladium Nanoclusters.

Metal nanoclusters, with dimensions between atomic and nanoparticles, have attracted a great deal of attention due to their significantly unusual properties. Water-soluble palladium nanoclusters (Pd NCs) with blue-green fluorescence were synthesized by a water bath heating method, with methionine as a stabilizer and ascorbic acid as a reducing agent. We investigated the optimal synthesis conditions, stability, and pH response of the obtained products in detail. The synthesized materials were characterized by ultraviolet-absorption spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. These experimental results showed that the Pd NCs had a small size of ~1.91 nm, with a uniform size distribution. Additionally, the Pd NCs emitted blue-green fluorescence under ultraviolet light with a quantum yield of 5.47%. Notably, both stabilizers and reducing agents used in this synthesis method are nutrients for humans, non-toxic, and harmless. This method could be viewed as a biologically friendly and green way of preparing fluorescent metal nanoclusters. The as-prepared fluorescent Pd NCs also possessed excellent fluorescence detection ability and were very sensitive to low concentrations of hemoglobin, with a linear response in the range of 0.25–3.5 μM and a detection limit of 50 nM.

Emerging applications of near-infrared fluorescent metal nanoclusters for biological imaging

Fluorescent metal nanoclusters (MNCs) have recently emerged as a novel kind of promising fluorescent probes for biological imaging because of their ultrasmall core size (<2nm), strong photoluminescence, facile availability and good biocompatibility. In this review, we provide an update on recent advances in the development of near infrared (NIR)-emitting MNCs in terms of synthesis strategies and bioimaging applications. We mainly focus on the utilization of NIR-emitting MNCs (including Au, Ag, Cu and alloy NCs) either as single modal imaging (fluorescence intensity-based imaging, fluorescence lifetime imaging, two-photon imaging) probes or as multimodal imaging (such as NIR fluorescence/X-ray computed tomography/magnetic resonance imaging, NIR fluorescence/photoacoustic imaging/magnetic resonance imaging, NIR fluorescence/single photon emission computed tomography) probes in biological cells and tissues. Finally, we give a brief outlook on the future challenges and prospects of developing NIR-emitting MNCs for bioimaging.

Fluorescent Metal Nano-Clusters as Next Generation Fluorescent Probes for Cell Imaging and Drug Delivery

Abstract Fluorescent metal nano-clusters with size-dependent properties have emerged as the next generation fluorophores with versatile applications. In this article, we give a brief overview on three fluorescent metal nano-clusters, (gold, silver and copper). Because of their non-toxicity and solubility in water they are highly suitable for biological systems and in particular, live cell imaging. We show that they may be used for distinguishing cancer and non-cancer cells and selective killing of cancer cells. We also discuss their effect on enzyme catalysis.

Understanding the Effect of Single Cysteine Mutations on Gold Nanoclusters as Studied by Spectroscopy and Density Functional Theory Modeling.

Fluorescent metal nanoclusters have generated considerable excitement in nanobiotechnology, particularly in the applications of biolabeling, targeted delivery, and biological sensing. The present work is an experimental and computational study that aims to understand the effects of protein environment on the synthesis and electronic properties of gold nanoclusters. MPT63, a drug target of Mycobacterium tuberculosis, was used as the template protein to synthesize, for the first time, gold nanoclusters at a low micromolar concentration of the protein. Two single cysteine mutants of MPT63, namely, MPT63Gly20Cys (mutant I) and MPT63Gly40Cys (mutant II) were employed for this study. The experimental results show that cysteine residues positioned in two different regions of the protein induce varying electronic states of the nanoclusters depending on the surrounding amino acids. A mixture of five-atom and eight-atom clusters was generated for each mutant, and the former was found to be predominant in both cases. Computational studies, including density functional theory (DFT), frontier molecular orbital (FMO), and natural bond orbital (NBO) calculations, validated the experimental observations. The as-prepared protein-stabilized nanoclusters were found to have applications in the imaging of live cells.

Protein-Guided Formation of Silver Nanoclusters and Their Assembly with Graphene Oxide as an Improved Bioimaging Agent with Reduced Toxicity.

As an emerging category of fluorescent metal nanoclusters (NCs), protein-based NCs are considered as one of the promising candidates for the biomedical applications because of their luminescent properties and inherent biocompatibilities. Protein-capped silver NCs impregnated onto graphene oxide (GO) sheets can be internalized into the K562 cell, a human erythroleukemic cell line, and the Ag NCs/GO assembly can act as a synergistic drug carrier for Imatinib, a first-generation tyrosine kinase inhibitor. Further, Ag NCs adsorbed on GO have a great potential to be used as X-ray computer tomography (CT) imaging contrasting agents, and CT images show significant contrast enhancement of bone tissues in mice models. Overall, this assembly can exhibit great potential in the field of biomedical application and therapeutic studies.

Synthesis and Characterization of PEGylated Luminescent Gold Nanoclusters Doped with Silver and Other Metals

Doping of fluorescent noble metal nanoclusters is being pursued to manipulate the structure of such materials along with improving physicochemical characteristics such as long-term stability and photoluminescence quantum yield. Here, we synthesize metal-doped and alloyed ultrasmall gold nanoclusters (AuNCs) directly in water using a facile one-step coreduction reaction with bidentate dithiolane PEGylated ligands that terminate in different functional groups including a methoxy, carboxy, amine, and azide. Two primary types of cluster materials were the focus of synthesis and characterization: first, a series of doped/alloyed Ag-doped AuNCs, where the ratio of Au:Ag was varied across a wide range including 99:1, 98:2, 90:10, 80:20, 50:50, 20:80, 10:90, and 2:98 along with pure AuNC and AgNC controls; second, doped Au:D NCs, where D included Pt, Cu, Zn, and Cd. Physical characterization of the modified AuNCs included TEM analysis of size, XPS/EDX analysis of dopant content, and a detailed analysis of photoph...

DNA-templated silver nanocluster as a label-free fluorescent probe for the highly sensitive and selective detection of mercury ions

We have constructed a label-free fluorescent probe using ssDNA-templated silver nanoclusters (Ag NCs), and its quantum yield (QY) was significantly higher (∼29%) compared to traditional water-soluble fluorescent metal nanoclusters. The proposed approach is simple, non-toxic, sensitive, and selective for the detection of mercuric ion (Hg2+). The fluorescence intensity of ssDNA-Ag NCs was quenched significantly in the presence of Hg2+, which might be attributed to the strong interactions between them including the dynamic and static quenching mechanisms. Though Ag+ induced a moderate interference to Hg2+, there was a negligible quenching in the presence of other metal cations. In addition, Hg2+ could be detected as low as 4.5nM, within a good linear range from 0 to 150nM (R2=0.995). More importantly, this method has also been successfully applied to the detection of Hg2+ in the real water samples. Thus, the ssDNA-Ag NCs detection system is potentially suitable for Hg2+ sensing in environmental samples.

Dumbbell-shaped metallothionein-templated silver nanoclusters with applications in cell imaging and Hg2+ sensing

Metallothionein (MT) is a cysteine-rich, low-molecular-weight protein, which adopts a unique dumbbell-shaped structure with a stable C-terminal α-domain and a reactive N-terminal β-domain. The specific configuration serves as a unique scaffold for the synthesis of ultra-small fluorescent metal nanoclusters (NCs). For the first time, MT-templated Ag NCs (MT-Ag NCs) with excellent antioxidant capacity and superior biocompatibility were facilely synthesized. The NCs were thoroughly characterized by various techniques. Zn2+ in the β-domain was preferentially replaced by Ag+, which was then reduced by NaBH4 to yield Ag NCs, while Zn2+ in the α-domain was intactly tetrahedrally-coordinated through thiolate ligands in MT. Fluorescent imaging of HeLa cells was achieved by attaching folic acid (FA) to MT-Ag NCs. Due to the strong binding capacity toward the thiolate ligands in the α-domain, Hg2+ was assayed via quenching the fluorescence of Ag NCs by an energy transfer process. The methodology described herein may be extended to the synthesis of other metal NCs with potential applications in biosensing and cell imaging.

Photophysical Characterization of Fluorescent Lysozyme Stabilized Gold Nanoclusters and their Applications

Fluorescent metal nanoclusters show great potential to be used as imaging and sensing agents. Among such nanoclusters, noble metal nanoclusters such as gold and silver have gained importance owing to their small size and non-toxicity. These metal nanoclusters can be synthesized easily via reduction using a protein template, which yields nanoclusters with a stable protein backbone incorporating tens of metal atoms. On the basis of previous studies, it has been established that proteins rich in cysteine residues are ideally suited for noble metal nanocluster synthesis. Thus, such nanoclusters can be customized to serve as probes specific to biomarkers or enzymes of interest. For this study, we synthesized gold nanoclusters using lysozymes. The nanoclusters have an emission peak at 670nm, and their lifetime was determined to be greater than 1 µs. This work explores the photophysical characteristics of lysozyme gold nanoclusters (LyAuNc) in different solvents, and their potential use as an imaging and sensing agent in cells.

DNA assembled metal nanoclusters: synthesis to novel applications

In this review, we have discussed the emergence of promising environmental-benign DNA assembled fluorescent metal nanoclusters and their unique electronic structures, unusual physical and chemical properties.

Designed Modular Proteins as Scaffolds To Stabilize Fluorescent Nanoclusters.

Proteins have been used as templates to stabilize fluorescent metal nanoclusters thus obtaining stable fluorescent structures, and their fluorescent properties being modulated by the type of protein employed. Designed consensus tetratricopeptide repeat (CTPR) proteins are suited candidates as templates for the stabilization of metal nanoclusters due to their modular structural and functional properties. Here, we have studied the ability of CTPR proteins to stabilize fluorescent gold nanoclusters giving rise to designed functional hybrid nanostructures. First, we have investigated the influence of the number of CTPR units, as well as the presence of cysteine residues in the CTPR protein, on the fluorescent properties of the protein-stabilized gold nanoclusters. Synthetic protocols to retain the protein structure and function have been developed, since the structural and functional integrity of the protein template is critical for further applications. Finally, as a proof-of-concept, a CTPR module with specific binding capabilities has been used to stabilize gold nanoclusters with positive results. Remarkably, the protein-stabilized gold nanocluster obtained combines both the fluorescence properties of the nanoclusters and the functional properties of the protein. The fluorescence changes in nanoclusters fluorescence have been successfully used as a sensor to detect when the specific ligand was recognized by the CTPR module.

Enzyme-free detection of sequence-specific microRNAs based on nanoparticle-assisted signal amplification strategy

Developing direct and convenient methods for microRNAs (miRNAs) analysis is of great significance in understanding biological functions of miRNAs, and early diagnosis of cancers. We have developed a rapid, enzyme-free method for miRNA detection based on nanoparticle-assisted signal amplification coupling fluorescent metal nanoclusters as signal output. The proposed method involves two processes: target miRNA-mediated nanoparticle capture, which consists of magnetic microparticle (MMP) probe and CuO nanoparticle (NP) probe, and nanoparticle-mediated amplification for signal generation, which consists of fluorescent DNA–Cu/Ag nanocluster (NC) and 3-mercaptopropionic acid (MPA). In the presence of target miRNA, MMP probe and NP probe sandwich-capture the target miRNA via their respective complementary sequence. The resultant sandwich complex (MMP probe–miRNA–CuO NP probe) is separated using a magnetic field and further dissolved by acidolysis to turn CuO NP into a great amount of copper (II) ions (Cu2+). Cu2+ could disrupt the interactions between thiol moiety of MPA and the fluorescent Cu/Ag NCs by preferentially reacting with MPA to form a disulfide compound as intermediate. By this way, the fluorescence emission of the DNA–Cu/Ag NCs in the presence of MPA increases upon the increasing concentration of Cu2+, which is directly proportional to the amount of target miRNA. The proposed method allows quantitative detection of a liver-specific miR-221-5p in the range of 5pM to 1000pM with a detection limit of ∼0.73pM, and shows a good ability to discriminate single-base difference. Moreover, the detection assay can be applied to detect miRNA in cancerous cell lysates in excellent agreement with that from a commercial miRNA detection kit.

ChemInform Abstract: Protein‐ and Peptide‐Directed Approaches to Fluorescent Metal Nanoclusters

AbstractReview: [85 refs.

Phosphorothioate DNA Stabilized Fluorescent Gold and Silver Nanoclusters.

Unmodified single-stranded DNA has recently gained popularity for the templated synthesis of fluorescent noble metal nanoclusters (NCs). Bright, stable, and biocompatible clusters have been developed primarily through optimization of DNA sequence. However, DNA backbone modifications have not yet been investigated. In this work, phosphorothioate (PS) DNAs are evaluated in the synthesis of Au and Ag nanoclusters, and are employed to successfully template a novel emitter using T15 DNA at neutral pH. Mechanistic studies indicate a distinct UV-dependent formation mechanism that does not occur through the previously reported thymine N3. The positions of PS substitution have been optimized. This is the first reported use of a T15 template at physiological pH for AgNCs.

Protein‐ and Peptide‐directed Approaches to Fluorescent Metal Nanoclusters

AbstractFluorescent metal nanoclusters (FMNCs), one of the promising functional nanomaterials, have aroused great interest in diverse areas due to their unique characteristics, such as ultrasmall size, high fluorescence, excellent photophysical and chemical stability, good biocompatibility, and tuneable emissions. Many methods have been developed to prepare the FMNCs. Among them, the biomolecule‐directed approach, which could produce FMNCs with high water‐solubility, good biocompatibility, enhanced fluorescence, and rich surface chemistry for conjugation has attracted enormous attention. In this review, we highlight the substantial progress in protein‐ and peptide‐directed approaches to varieties of FMNCs. The synthetic protocols and potential formation mechanisms are well summarized. Selected key applications, ranging from biological and chemical detection to cellular and in vivo imaging, are also discussed. Finally, the current challenges, as well as future perspectives, are briefly discussed. The lessons from these case studies would provide a valuable guide to designing nanomaterials with desired or even personalized functions in the future.

Recent developments on nanomaterials-based optical sensors for Hg2+ detection

Mercuric ion (Hg2+), released from both natural and industrial sources, has severe adverse effects on human health and the environment even at very low concentrations. It is very important to develop a rapid and economical method for the detection of Hg2+ with high sensitivity and selectivity. Nanomaterials with unique size and shape-dependent optical properties are attractive sensing materials. The application of nanomaterials to design optical sensors for Hg2+ provides a powerful method for the trace detection of Hg2+ in the environment, because these optical sensors are simple, rapidly responsive, cost-effective and highly sensitive. This review summarizes the recent advances on the development of optical assays for Hg2+ in aqueous solution by using functionalized nanomaterials (including noble metal nanoparticles, fluorescent metal nanoclusters, semiconductor quantum dots and carbon nanodots). Detection strategies based on the Hg2+-induced changes in spectral absorbance, fluorescence intensity and surface-enhanced Raman scattering signals were described. And the design principles for each optical assay were presented. In addition, the future challenge and the prospect of the development of nanomaterial optical sensors for Hg2+ detection were also discussed.

Fluorescent Au nanoclusters: recent progress and sensing applications

Recent progress in nanotechnology has given rise to a new class of fluorescent nanomaterials: fluorescent noble metal nanoclusters. The noble metal nanoclusters include Ag, Au, Cu and Pt and typically consist of a ligand shell and a metal core, which incorporates various numbers of atoms ranging from only a few to several hundred, with diameters <2 nm. Au nanoclusters are the most intensely studied of these materials because of their attractive features, including convenient synthesis, ultra-small size, fluorescent properties, excellent optical/colloidal stability and biocompatibility. This paper summarizes the common synthesis strategies for obtaining water-soluble, highly fluorescent Au nanoclusters using different capping agents, and highlights recent advances in their fluorescent sensing applications with an emphasis on the sensing mechanisms. We also consider the prospects, opportunities and challenges for the synthesis and application of Au nanoclusters.