Gold-silver Nanoclusters Research Articles

Maturing conditions of bimetallic nanocomposites as a new factor influencing Au-Ag synergism and impact of Cu(II) and/or Fe(III) on luminescence.

Gold-silver synergism has been well documented in many scientific works dealing with luminescent nanostructures that are exploitable in biomedical and environmental application. Frequently, the ratio of Au : Ag in synthetic mixtures was varied to influence the extent of Au-Ag synergism of the resulting luminescent gold-silver nanoclusters (GSNCs). However, in our approach, a new step, maturing under differing conditions using the same Au : Ag ratio (5 : 1), has been investigated systematically for the very first time. As referent systems, monometallic gold nanoclusters (AuNCs) and protein treated by the conditions of synthesis and maturing were prepared and investigated. The selected types of maturing conditions led to distinct changes in fluorescence characteristics and, consequently, Au-Ag synergism extent (evaluated as the ratio of fluorescence quantum yields of GSNCs versus AuNCs). The best synergism was obtained for GSNCs matured at 37°C for 2.5 h. The stability of luminescent signal of these GSNCs was tested in the presence of an excess (to 20 mM) of Cu(II) and/or Fe(III) ions (crucial cofactors in living systems). The same metallic ion concentration caused different extents of GSNC luminescence quenching, for which a plausible reasoning is suggested.

Controllable fabrication of high-quantum-yield bimetallic gold/silver nanoclusters as multivariate sensing probe for Hg2+, H2O2, and glutathione based on AIE and peroxidase mimicking activity

The grave threat posed by heavy metals and food hazards has increased the urgency of rapid and precise detection for food security and human health. Efficient multivariate sensing probes are imperatively required for sensing heavy metals and tumor markers, which are still facing great challenge in terms of multi-functional integration. Here, bimetallic gold-silver nanoclusters (NG-AuAgNCs) were developed with unique aggregation-induced-emission (AIE) property and peroxidase (POD) mimicking activity towards the efficient multivariate sensing via optimization of the precursors. The NG-AuAgNCs emitted at 614 nm and enable AIE feature with lifetime of 12.61 μs and high quantum yield of 40.5%. Possessing AIE and POD activity, the NG-AuAgNCs show great potential as fluorimetric and colorimetric dual-mode probe for multivariate sensing Hg2+, H2O2 and GSH, with good recoveries in real samples. The NG-AuAgNCs paper sensors further integrating with smartphone, achieved portable detection of Hg2+ with limit of detection (LOD) of 19 nM, while the colorimetric-mode presented consecutive response to H2O2 and GSH via a reversible oxidase tetramethylbenzidine process with LODs of 7.02 and 0.45 μM, respectively. This work not only demonstrates a multivariate probe for environment and human health, but also provides valuable insights for the function integration of the nanocluster via synthetic manipulation.

“Silver effect” enhanced fluorescence for sensitive detection of crystal violet utilizing long wavelength emission bimetallic gold-silver nanoclusters

Crystal violet (CV), widely used as a fungicide in aquaculture, is susceptible to enrichment in fish and thus poses a threat to human health. Therefore, there is an urgent need for a simple, sensitive and cost-effective method to detect CV. To this need, duck egg white-stabilized gold-silver nanoclusters (DEW-AuAgNCs) with long wavelength fluorescence emission were synthesized via microwave method in 1 min. The raw materials used were easily available and environmentally friendly. And based on the Fluorescence resonance energy transfer (FRET) between DEW-AuAgNCs and CV, a fluorescence quenching method was established for CV detection. The detection limit of this method was 1.7 × 10−8 mol/L, which was lower than most of the reported methods. In addition, prominent performance of DEW-AuAgNCs with long wavelength emission can be applied for the detection of CVs in real organism.

Highly Efficient Fabrication of Fluorescent "Turn-On" Lateral Flow Strips for Highly Sensitive Detection of Small Molecules Based on Self-Assembly of AuAg Nanoclusters.

Currently, fluorescent "turn-on" lateral flow assay (FONLFA) has shown enhanced "naked eye" detection sensitivity for small molecules, while it is urgent to adopt biocompatible fluorescent nanomaterials and needs new strategies to simplify the preparation process. In this study, a highly effective method was proposed to produce FONLFA strips for the detection of small molecules. The gold-silver nanoclusters (AuAgNCs) were immobilized onto the nitrocellulose membrane of the strips by the self-assembly of poly(sodium 4-styrenesulfonate), antigen, and AuAgNCs. The immobilization process entails a straightforward mixing of the three components, taking merely 1 min, thereby bypassing the necessity for chemical modification of fluorescent nanomaterials. The strategy offers a significantly simplified process, which substantially enhances the efficiency of the strip fabrication. Utilizing this method, a FONLFA was developed for carbendazim with a visual limit of detection (vLOD) reduced by 40-fold compared with the conventional colorimetric lateral flow assay (LFA). Furthermore, the approach demonstrates versatility by enabling the immobilization of AuAgNCs and streptavidin, which facilitates the development of aptamer-based FONLFAs. The designed aptamer-based FONLFA for kanamycin exhibited a 50-fold reduction in the vLOD compared with conventional colorimetric LFAs. Therefore, FONLFA holds promising potential for widespread applications in the analysis of small molecules.

Marrying luminescent metal nanoclusters to C3N4 for efficient photocatalytic hydrogen peroxide production

Photocatalytic oxygen (O2) reduction has been considered a promising method for hydrogen peroxide (H2O2) production. However, the poor visible light harvesting and low-efficient separation and generation of charge carriers of conventional photocatalysts strongly limited their photocatalytic H2O2 generation performance. Herein, we design a highly efficient photocatalyst in this work by marrying luminescent gold-silver nanoclusters (AuAg NCs) to polyethyleneimine (PEI) modified C3N4 (C3N4-PEI). The key design in this work is the utilization of highly luminescent AuAg NCs as photosensitizers to promote the generation and separation of charge carriers of C3N4-PEI, thereby ultimately producing abundant e− for O2 reduction under visible light illumination (λ ≥ 400 nm). As a result, the as-designed photocatalyst (C3N4-PEI-AuAg NCs) exhibits excellent photocatalytic activity with an H2O2 production capability of 82 μM in pure water, which is 3.5 times higher than pristine C3N4 (23 μM). This interesting design provides a paradigm in developing other high-efficient photocatalysts for visible-light-driven H2O2 production.

A Ratiometric Fluorescent Sensor for Penicillin G Based on Color-Tunable Gold-Silver Nanoclusters.

Excessive administration of penicillin G and improper disposal of its residues pose a serious risk to human health; therefore, the development of convenient methods for monitoring penicillin G levels in products is essential. Herein, novel gold-silver nanoclusters (AuAgNCs) were synthesized using chicken egg white and 6-aza-2-thiothymine as dual ligands with strong yellow fluorescence at 509 and 689 nm for the highly selective detection of penicillin G. The AuAgNCs were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible absorption spectrophotometry, and fluorescence spectrophotometry. Under optimum conditions, the fluorescence intensity decreased linearly with the concentration of penicillin G from 0.2 to 6 μM, with a low detection limit of 18 nM. Real sample analyses indicated that a sensor developed using the AuAgNCs could detect penicillin G in urine and water samples within 10 min, with the recoveries ranging from 99.7 to 104.0%. The particle size of the AuAgNCs increased from 1.80 to 9.06 nm in the presence of penicillin G. We believe the aggregation-induced quenching of the fluorescence of the AuAgNCs was the main mechanism for the detection of penicillin G. These results demonstrate the ability of our sensor for monitoring penicillin G levels in environmental and clinic samples.

Synthesis of Bimetallic Gold-Silver Nanoclusters and Its Application as Pb (II) Sensing Based on Fluorescence Technique

Much research has been done on gold nanoclusters stabilized by biomolecules because of their remarkable fluorescence properties and potential biological applications. Here, we synthesize bimetallic gold-silver nanoclusters in a protein template using Galvanic Exchange (GE) Method. The samples were analyzed using UV-visible spectroscopy, a fluorolog (fluorescence spectrometer), and a lifetime kit using Time-Correlated Single-Photon Counting method. It is found that the bimetallic gold-silver nanoclusters emit bright red fluorescence with a long fluorescence lifetime in the range of microseconds. The bimetallic gold nanoclusters were used for Pb (II) detection using fluorescence technique. The fluorescence intensity of nanoclusters increased as the concentration of added Pb (II) increased. This work suggests that bimetallic gold-silver nanoclusters can be used for Pb detection with a detection limit of 15 nmol/L and this sensing will contribute to providing clean water without Pb contamination.

Complementary imaging of nanoclusters interacting with mitochondria via stimulated emission depletion and scanning transmission electron microscopy

The emerging stress caused by nanomaterials in the environment is of great concern because they can have toxic effects on organisms. However, thorough study of the interactions between cells and diverse nanoparticles (NPs) using a unified approach is challenging. Here, we present a novel approach combining stimulated emission depletion (STED) microscopy and scanning transmission electron microscopy (STEM) for quantitative assessment, real-time tracking, and in situ imaging of the intracellular behavior of gold–silver nanoclusters (AuAgNCs), based on their fluorescence and electron properties. The results revealed an aggregated state of AuAgNCs within the mitochondria and an increase in sulfur content in AuAgNCs, presumably owing to their reaction with thiol-containing molecules inside the mitochondria. Moreover, AuAgNCs (100 μg/mL) induced a 75% decline in mitochondrial membrane potential and a 12-fold increase of mitochondrial reactive oxygen species in comparison to control. This mitochondrial damage may be triggered by the reaction of AuAgNCs with thiol, which provides direct imaging evidence for uncovering the action mechanism of AuAgNCs on the mitochondria. The proposed dual-imaging strategy using STED and STEM is a potential tool to offer valuable insights into cytotoxicity between subcellular structures and diverse NPs, and can serve as a key strategy for nanomaterial biosafety assessment.

A ratiometric fluorescence sensor based on gold silver nanoclusters and tungsten disulfide quantum dots with simple fabrication for the detection of copper ions in river water.

Copper plays a key role in the human body; meanwhile, excess Cu2+ ions can result in various diseases. Nanoclusters (NCs) are often used to measure Cu2+ ions, but there are two difficulties. On the one hand, a single probe of NCs is easily affected by environmental factors. On the other hand, it is difficult to mask the interference of Pb2+ ions and Cd2+ ions in the process of detecting Cu2+ ions. As a new type of quantum dots (QDs), tungsten disulfide quantum dots (WS2-QDs) have some advantages of simple synthesis and stable luminescence properties. Stable WS2-QDs with blue fluorescence are used as a reference probe, while gold silver nanoclusters (AuAgNCs) with red fluorescence are used as a response probe. A ratiometric fluorescent sensor was constructed by mixing the two styles of fluorescent probes, which is abbreviated as NCs/QDs. This nano-sensor can be used to detect the concentration of Cu2+ ions, in which the fluorescence of QDs does not change significantly, while the fluorescence of NCs can be quenched by Cu2+ ions. The concentration of Cu2+ ions can be determined as low as 0.12 μM with a linear range from 0.3 to 3 μM. The common interference caused by Pb2+ and Cd2+ ions can be eliminated by the phosphate buffer solution (PBS). This sensor was used to detect the concentration of Cu2+ in river water with satisfactory results.

Determination of dopamine based on its enhancement of gold-silver nanocluster fluorescence

Dopamine (DA) is one of the most important neurotransmitters in human bodies and its sensitive detection remains a challenge. Herein, protein stabilized gold-silver nanoclusters (Au-AgNCs) were synthesized at first. It was found that the introduction of dopamine lead to a significant enhancement of the fluorescence from the nanoclusters, together with a red-shift of the peak. Through related spectroscopic and electrochemical studies, the fluorescence enhancement was attributed to the reduction of the nanoclusters by dopamine. This enhancement was then adopted for quantitative measurements, and linear responses toward dopamine in the ranges 0.01–1.7 μM and 1.7–10 μM were constructed. A limit of detection was obtained at 6.9 nM. The present study provided a facile and efficient method for the determination of dopamine, and the method was successfully applied for related measurements in serum samples.

Application of Biomimetic Nanomaterials in Biological Detection and the Intelligent Recognition Method of Nanoparticle Images

New nanomaterials (metal nanoclusters, graphene, etc.) are favored by researchers due to their unique properties and are widely used in biomedical detection. The excellent fluorescence characteristics of gold nanoclusters are utilized to develop a fast and highly sensitive bionic nanomaterial with non-label and dual functions, which can detect silver ions and mercury ions and study the particularity of TEM nanoparticle images. The particle segmentation of TEM nanoparticle images is studied to compare the traditional watershed algorithm and watershed transformation algorithm. The experiment results show that silver ions can enhance the fluorescence of gold nanoclusters to form gold-silver nanoclusters with strong yellow fluorescence, and mercury ions can quickly weaken the fluorescence of gold-silver nanoclusters. Based on the biomimetic nanomaterials, a dual-function fluorescent probe is designed to detect silver ions and mercury ions in lake with detection accuracy of 8 nM and 33 nM respectively; the sensing excitation of the fluorescent probe is further analyzed. Because the metal-enhanced fluorescence (MEF) effect enables the silver element and Au nanoparticles to form fluorescence-enhancing effect, the high metalphilic interaction between mercury ions and silver ions quenches the fluorescence effect of gold nanocluster; the rapid watershed transformation/region fusion method can achieve better particle image segmentation combined with the image segmentation algorithms of different TEM nanoparticles, which can be better applied to the characterization analysis of the preparation of gold nanomaterials.

Near-infrared emitting gold-silver nanoclusters with large Stokes shifts for two-photon in vivo imaging.

Near-infrared emitting bi-metallic gold/silver nanoclusters with large Stokes shifts were manufactured through one-pot synthesis. The gold/silver nanoclusters exhibit strong NIR fluorescence due to the silver effect, which can be applied as a two-photon fluorescent contrast agent for in vivo bioimaging.

Surface functionalized red fluorescent dual-metallic Au/Ag nanoclusters for endoplasmic reticulum imaging.

Anefficient method is reportedto prepare endoplasmic reticulum-targetable dual-metallic gold-silver nanoclusters, denoted as ER-Au/Ag nanoclusters (NCs), by virtue of a rationally designed molecular ligand. The prepared ER-Au/Ag NCs possesses red-emitting fluorescence with a strong emission at 622nm and a high fluorescence quantum yield of 5.1%, which could avoid the influence of biological auto-fluorescence. Further investigation results showed that ER-Au/Ag NCs exhibited superior photostability, minimal cytotoxicity, and ER-targeting capability. Enabled by these meritorious features, ER-Au/Ag NCs have been successfully employed for long-term bioimaging of ER in living cells.Graphical abstract A sensitive non-enzymatic fluorescent glucose probe-based ZnO nanorod decorated with Au nanoparticles.

A paper-based fluorescent test for determination and visualization of cysteine and glutathione by using gold-silver nanoclusters

A method is described for fluorometric determination of cysteine (Cys) and glutathione (GSH), either in solution by using a fluorescence spectrometer, or by using a paper-based test with visual observation. The method is based on the finding that the yellow fluorescence of the gold/silver nanoclusters (AuAg NCs), with excitation/emission maxima of 358/574 nm, is quenched by Cys and GSH via NCs aggregation. The method is selective for Cys and GSH. The limits of detection for both Cys and GSH are 0.74 nM in solution state and 5.0 μM on paper-based test. Response is linear in the range from 2.3 nM to 110 μM and from 2.3 nM to 63 μM in solution for Cys and GSH, respectively. The method is not interfered by other amino acids even if their concentrations are 10 times higher. It was successfully applied to the determination of Cys in spiked serum samples.

Photonic crystal enhanced gold-silver nanoclusters fluorescent sensor for Hg2+ ion

Luminescent nanoclusters (NCs) have attracted much attention because of their good photostability and low toxicity, however, the low quantum yield is still a deficiency, and many increasing efforts are being devoted to enhance the luminescence intensity of NCs. In this paper, a method of enhancing the fluorescent signal of gold-silver nanoclusters (AuAgNCs) by photonic crystals (PhCs) was proposed. The fluorescent intensity of AuAgNCs on PhCs can be enhanced 8.0-fold in comparison to the control sample without PhCs. Furthermore, a novel fluorescence sensor of AuAgNCs based on PhCs is used for the sensitive and selective detection of Hg2+ ion in the aqueous solution, the detection limit is 0.35 nM due to the PhCs enhancement effect for the fluorescence. This proposed method may not only develop a highly sensitive method for determination of Hg2+ ion, but also expand the application of AuAgNCs in ultra-trace analysis.

Surface motifs regulated aggregation induced emission in gold-silver nanoclusters.

Aggregation-induced emission (AIE) is a recently developed strategy to design highly luminescent metal nanoclusters (NCs), which can be controlled by the surface motifs [M(i)-SR] of NCs. This communication is an account to understand the AIE in gold silver (AuAg) NCs, where the Au(i)-thiolate motif is engineered by doping different amount of Ag in Au NCs. Investigation revealed the great impact of Au(i)-thiolate motifs on the AIE of AuAg NCs.

A dual-model strategy for fluorometric determination of ascorbic acid and of ascorbic acid oxidase activity by using DNA-templated gold-silver nanoclusters.

Methods are described for the fluorometric and colorimetric determination of ascorbic acid (AA) and the activity of ascorbic acid oxidase (AA-Ox). The method for AA is based on AA-induced growth and aggregation of DNA-templated gold/silver nanoclusters (DNA-Au/Ag NC), which is accompanied by quenching of fluorescence emission at 605nm upon 260nm excitation and a visible color change of the solution from colorless transparent to yellow. The determination of the activity of AA-Ox is based on the finding that it catalyzes the oxidation of AA which results in the inhibition of growth and aggregation. AA can be determined with a 0.6μmol·L-1 detection limit over the 5 to 150μmol·L-1 concentration range. AA-Ox can be determined with a 0.0048U·mL-1 detection limit over the 0.01 to 0.20U·mL-1 range. Graphical abstract Schematic of a novel fluorometric and colorimetric platform for determination of ascorbic acid and ascorbic acid oxidase activity based on the use ofDNA-templated gold-silver nanoclusters.

Fluorescence red-shift of gold-silver nanoclusters upon interaction with cysteine and its application

In this work, gold-silver alloy nanoclusters (AuAg NCs) were demonstrated as a novel probe for fluorescent detection of cysteine (Cys). The alloy nanoclusters were fabricated by bovine serum albumin as a template and NaBH4 as a reducer. They showed a red emission at 650 nm. The interaction between AuAg NCs and Cys was investigated. The thiol group in Cys molecules has strong affinity on the surface of metals, which results in variation of fluorescence peak wavelength. It was further demonstrated that this red-shift of fluorescence had a good linear relationship with the concentration of Cys in the range of 2–100 μM. The method was successfully applied for human plasma analysis with satisfactory results. This novel strategy was expected to provide a potential opportunity for extending the application of novel metal nanoclusters in fluorescence.

Tip-Selective Growth of Silver on Gold Nanostars for Surface-Enhanced Raman Scattering

Nanogaps as "hot spots" with highly localized surface plasmon can generate ultrastrong electromagnetic fields. Superior to the exterior nanogaps obtained via aggregation and self-assembly, interior nanogaps within Au and Ag nanostructures give stable and reproducible surface-enhanced Raman scattering (SERS) signals. However, the synthesis of nanostructures with interior hot spots is still challenging because of the lack of high-yield strategies and clear design principles. Herein, gold-silver nanoclusters (Au-Ag NCs) with multiple interior hot spots were fabricated as SERS platforms via selective growth of Ag nanoparticles on the tips of Au nanostars (Au NSs). Furthermore, the interior gap sizes of Au-Ag NCs can be facilely tuned by changing the amount of AgNO3 used. Upon 785 nm excitation, single Au-Ag NC350 exhibits 43-fold larger SERS enhancement factor and the optimal signal reproducibility relative to single Au NS. The SERS enhancement factors and signal reproducibility of Au-Ag NCs increase with the decrease of gap sizes. Collectively, the Au-Ag NCs could serve as a flexible, reproducible, and active platform for SERS investigation.

Dually emitting gold-silver nanoclusters as viable ratiometric fluorescent probes for cysteine and arginine.

Glutathione coated gold and silver nanoclusters (GSH-Au/AgNCs) were synthesized by one-pot reduction methods and are found to be viable fluorescent nanoprobes for cysteine (Cys) and arginine (Arg), with good selectivity over other amino acids. The GSH-Au/AgNCs have two emissions at 616nm and 412nm when excited at 360nm. With the increased concentration of Cys, the ratio of the emission intensities (I616/I412) linearly decreases with Cys inconcentration ranging from 0.05 to 10μM and from 10 to 50μM, respectively. With increased concentrations of Arg, the ratio of I616/I412 linearly decreases with Arg concentration ranging from 0 to 50μM and from 50 to 100μM, respectively. The probe was applied to the determination of Cys and Arg in spiked samples of serum and urine where it gave good recoveries. Graphical abstract Glutathione-coated gold and silver nanoclusters (GSH-Au/AgNCs) were synthesized by one-pot reduction and are found to be viable fluorescent nanoprobes for cysteine (Cys) and arginine (Arg).