Au-Ag Bimetallic Nanoclusters Research Articles

GSH-AuAg NCs based fluorescent probe for multiple indicators in tap water: Free chlorine and copper ion

In this work, fluorescent AuAg bimetallic nanoclusters (AuAg NCs) were synthesized using a simple green hydrothermal method taking GSH as template. The NCs exhibits high quantum yield and stable FL performance based on aggregation induced emission (AIE). The product was mainly characterized by microscopic measurements, X-ray photoelectron spectroscopy (XPS) analysis, and the quenching mechanism of free chlorine and Cu2+ was studied in detail. By optimizing detection conditions and incorporating masking agents, this fluorescent probe demonstrates specific detection capabilities for free chlorine and Cu2+ specifically with the limits of detection of 0.1 μM and 0.5 nM, respectively. The proposed detection method was validated included linearity, accuracy, precision, selectivity and stability, demonstrating satisfactory recovery rates for the detection of free chlorine and Cu2+ in tap water.

SiO2@AuAg/PDA hybrid nanospheres with photo-thermally enhanced synergistic antibacterial and catalytic activity.

Wastewater discharged from industrial, agricultural and livestock production contains a large number of harmful bacteria and organic pollutants, which usually cause serious harm to human health. Therefore, it is urgent to find a "one-stone-two-birds" strategy with good antimicrobial and pollutant degradation activity for treating waste water. In this paper, SiO2@AuAg/Polydopamine (SiO2@AuAg/PDA) core/shell nanospheres, which possessed synergistic "Ag+-release-photothermal" antibacterial and catalytic behaviors, have been successfully prepared via a simple in situ redox polymerization method. The SiO2@AuAg/PDA nanospheres showed good catalytic activity in reducing 4-nitrophenol to 4-aminophenol (0.576 min-1 mg-1). Since the AuAg nanoclusters contain both gold and silver elements, they provided a high photothermal conversion efficiency (48.1%). Under NIR irradiation (808 nm, 2.5 W-2), the catalytic kinetics were improved by 2.2 times. Besides the intrinsic Ag+-release, the photothermal behavior originating from the AuAg bimetallic nanoclusters and the PDA component of SiO2@AuAg/PDA also critically improved the antibacterial performance. Both E. coli and S. aureus could be basically killed by SiO2@AuAg/PDA nanospheres at a concentration of 90 μg mL-1 under NIR irradiation. This "Ag+-release-photothermal" coupled sterilization offers a straightforward and effective approach to antimicrobial therapy, and further exhibits high potential in nanomedicine for combating bacterial contamination in environmental treatment and biological fields.

Atomically precise Au15Ag23 nanoclusters co-protected by alkynyl and bromine: Structure analysis and electrocatalytic application toward overall water splitting

We report the structure analysis and electrocatalytic application toward overall water splitting of atomically precise Au15Ag23(tBuC ≡ C)18Br6 nanoclusters (Au15Ag23 in short). Au15Ag23 possesses a triple-layered core-shell-shell metal core structure of Au6@Au6Ag23@Au3, with the core centre being a tetragonal bipyramidal Au6 structure unit, and the outer layer of one Ag atom linked with two alkynyl ligands to form a linear structural motif covering the surface of the metal nucleus. Au15Ag23 is a superatom with 14 free electrons and it displays a unique absorption profile. Remarkably, the Au15Ag23 catalyst exhibits excellent electrocatalytic properties in hydrogen evolution reaction (HER), manifested by a low overpotential of 125 mV at 10 mA cm−2 and a negligible current decrease for 16 h in 0.5 M H2SO4, while the Au15Ag23/NiFe-LDH catalyst demonstrates outstanding electrocatalytic performance in oxygen evolution reaction (OER), evidenced by an ultralow overpotential of 250 mV at 10 mA cm−2 and a ∼5% current decrease for 30 h in 1.0 M KOH. Such promoting effect is ascribed by the electron transfer from NiFe-LDH to the Au15Ag23 clusters, which results in generating high valent Fe species as active sites. When using the two catalysts for overall water splitting (OWS), only 1.51 V was required to achieve a current density of 10 mA cm−2, and it performed well in the 50 h's stability test. This study enriches the family member of alkynyl-protected AuAg bimetallic nanoclusters, and further highlights the dual functionalities (catalyzing HER and promoting OER) that metal nanoclusters can make contribution for electrochemical energy conversion and beyond.

Fabrication of a ratiometric electrochemiluminescence biosensor using single self-enhanced nanoluminophores for the detection of spermine

A ratiometric electrochemiluminescence strategy using a single luminophore for accurate and sensitive biomolecule detection could be immensely valuable in bioanalysis. Herein, an ultrasensitive ratiometric electrochemiluminescence sensing system was fabricated using a self-enhanced luminophore with dual-signal emission for the detection of spermine. A nanocomposite was synthesized by the covalent attachment of N, N-diisopropylethylenediamine onto glutathione-protected Au–Ag bimetallic nanoclusters (DPEA-GSH@Au/Ag BNCs). The nanocomposite exhibited efficient intra-cluster charge transfer to produce strong anodic self-enhanced electrochemiluminescence emission at 0.8 V without external co-reactants. Interestingly, the DPEA@GSH@Au–Ag BNCs exhibited cathodic electrochemiluminescence emission upon the addition of the co-reactant potassium persulfate at −1.6 V, exhibiting stable and efficient dual-signal electrochemiluminescence emission features at a continuous potential window of −1.75 to 1.2 V. Thus, they were used to fabricate a single-luminophore electrochemiluminescence sensor with dual emission. The cathodic emission of the biosensor gradually increased with increasing concentrations of spermine, whereas the anodic electrochemiluminescence intensity remained almost constant, enabling the ratiometric detection of spermine. The fabricated biosensor, with an internal standard, significantly improved the accuracy and reliability of spermine detection in a wide concentration range of 0.85 pM–100 μM, with a low limit of detection of 0.12 pM (S/N = 3) under optimum conditions. This single-luminophore electrochemiluminescence sensing system could be used for the detection of spermine and could guide the construction of ratiometric electrochemiluminescence sensors in the future.

A novel FRET immunosensor for rapid and sensitive detection of dicofol based on bimetallic nanoclusters

To minimize the need of complex testing procedures, accurate, rapid and selective on-site determination of dicofol (DICO) is of vital importance. Herein, fluorescence immunosensing platforms based on the Förster resonance energy transfer (FRET) between Au–Ag bimetallic nanoclusters (Au–Ag NCs) and Au nanoflowers (Au NFs) were developed for the rapid detection of DICO in both liquid system and paper-based analytical devices (PADs). Conjugations of Au–Ag NCs and antigen (NCs-Agen) and Au–Ag NCs were regarded as energy donors in liquid system and PADs, respectively, while conjugations of Au NFs and antibody (NFs-Ab) were synthesized as energy acceptors. The overlapping spectrum and decrease of fluorescence lifetime of NCs-Agen proved that the fluorescence quenching mechanism was FRET effect. When DICO was captured by NFs-Ab, FRET effect was inhibited due to the long distance between NFs-Ab and NCs/NCs-Agen. Under optimal conditions, the FRET-based fluorescent immunosensors allowed for a rapid response toward DICO with considerable sensitivities of 0.185 ng/mL and 0.170 ng/mL in liquid system and PADs, respectively. Excellent specificity and satisfactory recovery in three kinds of tea samples were confirmed as well. This study opens an avenue for on-site, portable and sensitive detection methods.

Immunoassay based on Au-Ag bimetallic nanoclusters for colorimetric/fluorescent double biosensing of dicofol

The high toxicity of dicofol (DICO) to nontarget organisms has resulted in the contamination of food materials and caused a threat to human health. Developing a rapid and sensitive detection method of DICO in food samples is essential and still pursued. Fluorescent nanomaterials have been widely applied in biosensors to improve the sensitivity of detection. Herein, glutathione-capped Au-Ag bimetallic nanoclusters (Au-Ag NCs) exhibited the outstanding fluorescence characteristic with the average fluorescence lifetime of 1971.08 ns and photoluminescence quantum yield of 9.84% when the molar ratio of Au to Ag was 5:1. Polyethyleneimine modified gold nanoparticles (PEI-Au NPs) with the positive charge were prepared to generate a strong colorimetric signal. A dual-model colorimetric/fluorescent immune probe based on the Au-Ag NCs and PEI-Au NPs was successfully constructed by electrostatic force, and could be applied in both ic-ELISA and LFIA methods for rapid and ultrasensitive detection of DICO. In the ic-ELISA method, the introduction of fluorescence signal significantly increased the sensitivity of detection with the limit of detection (LOD) of 0.62 ng/mL and exhibited an excellent linear relationship within the range of 1.36 ng/mL-19.92 ng/mL. In the LFIA method, the fluorescence signal of Au-Ag NCs was accumulated on the test line and control line for the fluorescence model detection with a quantitative LOD at the level of 1.59 ng/mL. Such a dual-model colorimetric/fluorescent immunoassay serves as a promising candidate to develop new approaches in field detection.

Surface-Defect-Induced and Synergetic-Effect-Enhanced NIR-II Electrochemiluminescence of Au-Ag Bimetallic Nanoclusters and Its Spectral Sensing.

Aqueous electrochemiluminescence (ECL) in the second near-infrared biowindow (NIR-II, 900-1700 nm) was anticipated for ECL evolution and spectral multiplexing. Herein, aqueous and monochromatic ECL with a single emission peak beyond 900 nm was achieved by employing methionine (Met)-capped Au-Ag bimetallic nanoclusters (BNCs) as luminophores and triethanolamine (TEOA) as a coreactant. The Met-capped Au-Ag BNCs with surface-defect-induced PL around 756 nm were water-soluble and synthesized via doping Met-capped Au NCs with Ag in a doping-in-growth way. By extensively exploiting the red-shifting nature of surface-defect-induced ECL to PL and the synergetic-effect-enhanced ECL of BNCs, physically surface-confined Au-Ag BNCs exhibited efficient NIR-II ECL around 906 nm in aqueous medium. A spectrum-based NIR-II ECL immunoassay around 915 nm was also achieved by immobilizing the Au-Ag BNCs onto an electrode surface via forming a sandwich immunocomplex, which could selectively determine CA125 from 5 × 10-4 to 1 U/mL with a detection limit of 5 × 10-5 U/mL (S/N = 3). The combined strategy of surface-defect-induced ECL and synergetic-effect-enhanced ECL would enable promising biorelated application of NIR-II ECL.

Mechanistic investigations into synergistically enhanced radiative-charge-transfer in Au-Ag bimetallic nanoclusters.

Synergetic effects in Au-Ag bimetallic nanoclusters (BNCs) more favorably enhanced electrochemical redox induced electrochemiluminescence (ECL) over photoexcitation induced photoluminescence (PL); this not only led to Au-Ag BNCs with enhanced bandgap-engineered ECL compared to Au NCs, but it also generated surface-defect related ECL to enhance the total ECL intensity.

Synthesis and properties of Au–Ag bimetallic nanoclusters with dual-wavelength emission

Au–Ag bimetallic nanoclusters with dual-wavelength emission were facilely synthesized and the generation of dual-emission was probed.

Ultrabright gold-silver bimetallic nanoclusters: synthesis and their potential application in cysteine sensing

Photoluminescent nanomaterials with a high quantum yield (QY) is preferred in many applications. Up to the present date, only a few organo-soluble Au-Ag bimetallic nanoclusters (NCs) have ever reported to exhibit a QY of more than 20%. Herein, ultrabright Au-Ag NCs with a maximum QY of ca. 23.6% were synthesized with the assistance of mercaptosuccinic acid (MSA) and poly(N-vinylimidazole) (PVIm) through a two-step green route, which was almost two-fold higher than the corresponding mono-metallic Au NCs. Moreover, the as-prepared Au-Ag NCs had similar high QY both in solution and in solid state, which widened its potential applications from solution to solid form. The existence of Au0, Ag+ and Ag0 in the formed Au-Ag NCs was demonstrated by XPS. DLS showed that the PVIm and MSA stabilized Au-Ag NCs were still nanogel, just like its Au NCs precursor. Synergistic fluorescence enhancement effect existed with the Ag/Au ratio in the range of 0.1–0.4. Au-Ag NCs emitted strongest when Ag/Au ratio was between 0.2 (Au-Ag0.2) and 0.3 (Au-Ag0.3). Au-Ag0.2 exhibited mainly phosphorescent emission falling in the far-red/near infrared region (centered at ca. 718 nm). The phosphorescent property was supported by the marked large Stokes shift (> 400 nm) and two microsecond magnitude long life times (τ1 = 0.30 μs and τ2 = 6.65 μs). The λem,max of Au-Ag NCs could be modulated to ca. 666 nm when keeping a higher Ag/Au ratio in the Au-Ag NCs, but a side effect of PL depression was accompanied. Compared with the corresponding mono-metallic Au NCs, besides the stronger emission, Au-Ag NCs still had the following characters: (1) more stable during the shelf-storage; (2) selective probing for cysteine having a limit of detection value of 2.5 μM.

Gold-silver bimetallic nanoclusters with enhanced fluorescence for highly selective and sensitive detection of glutathione

Herein, a sensitive and selective “off-on” fluorescence sensor for the detection of glutathione (GSH) was fabricated based on Au-Ag bimetallic nanoclusters (NCs) with the assistance of persulfate (S2O82−). The as-prepared Au-Ag bimetallic NCs with enhanced fluorescent intensity about 2.7-folds higher than pure Au NCs was performed due to the synergistic effect of two atoms, which can be quenched by the strong oxidant of S2O82− damaging the structure of Au-Ag bimetallic NCs. However, in the presence of GSH, it can react with S2O82− and induce the restoration of fluorescence. Under optimum conditions, the restored fluorescence ratio was linearly with the concentration of GSH in the range of 1–100 μM and 100 μM–10 mM with a limit of detection of 200 nM. Notably, an IMPLICATION logic gate can be constructed based on this detection system. The proposed logical system for GSH detection is simple, highly sensitive and selective, and has the excellent recovery results for GSH detection in human serum, indicating its promising application in integrated biological detection system.

Evolution of Silver-Mediated, Enhanced Fluorescent Au-Ag Nanoclusters under UV Activation: A Platform for Sensing.

Here, we report the synthesis of dopamine (DA)-mediated Au–Ag bimetallic nanoclusters in aqueous solution under UV activation. The success story emerges from monometallic fluorescent nanocluster evolution from photoactivation of gold as well as silver precursor compounds along with DA. The intriguing fluorescence property of the nanocluster relates to facile incorporation of Ag in Au, showing a 6-fold enhancement of the emission profile than simply DA-mediated Au nanoclusters. Silver effect, which is classified under the synergism, is the main reason behind such enhancement of fluorescence. The as-synthesized nanoclusters are robust and can be vacuum-dried and redispersed for repetitive application. The intriguing fluorescence of bimetallic nanoclusters is found to be quenched selectively in the presence of sulfide ion in an aqueous medium, paving the way for nanomolar detection of sulfide in water. The utility of the sensing platform has been verified employing different environmental water effluents.

A novel and high performance enzyme-less sensing layer for electrochemical detection of methyl parathion based on BSA templated Au–Ag bimetallic nanoclusters

In the present manuscript, a modified glassy carbon electrode with BSA templated Au–Ag bimetallic nanoclusters (Au–Ag@BSA/GCE) was employed for the rapid, selective and sensitive determination of methyl parathion (MP) as an enzyme-less electrochemical biosensor.

One-Step Synthesis of DNA Templated Water-Soluble Au-Ag Bimetallic Nanoclusters for Ratiometric Fluorescence Detection of DNA.

DNA strands have been used as templates to form different sized silver nanoclusters. Although DNA templated silver nanoclusters (NCs) probes which show outstanding fluorescence properties have been widely applied in chemical sensing and cellular imaging, synthesis of DNA template Au-Ag bimetallic nanoclusters remains a challenge. A facile one-step synthesis method was thus developed in this study to form Au-Ag NCs using C4-ATAT-C4 as template. C4-ATAT-C4 acted as a stabilizer for preventing aggregation of the Au-Ag NCs. The obtained Au-Ag NCs stabilized by C4-ATAT-C4 showed bright fluorescence and high stability. A series of experiments showed that temperature, citrate-citric acid buffer, sequence and concentration of DNA played an important role in the synthesis of fluorescent Au-Ag NCs. In addition, a ratiometric fluorescence probe was designed through combining the nucleotide sequence (C4-ATAT-C4) and hybridization sequence in the presence of the double-strand-chelating dye Super SYBR Green (SG). The combination of prepared Au-Ag NCs, Super SG, and perfectly matched DNA emitted fluorescence at 500 and 590 nm, respectively, when the composite was excited at 290 nm. A gastric cancer gene was also selectively detected by our developed ratiometric fluorescence probe.

Fast microwave-assisted synthesis of AuAg bimetallic nanoclusters with strong yellow emission and their response to mercury(II) ions

A rapid, effective and environmental friendly method was developed for preparing strong yellow fluorescent AuAg bimetallic nanoclusters (BNCs). With microwave irradiation, bovine serum albumin (BSA)-stabilized AuAg BNCs could be synthesized in a one-pot procedure within several minutes. The synthesized BSA–AuAg BNCs were fully characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, infrared spectroscopy, and photoluminescence spectroscopy. The mechanism of the formation of BSA–AuAg BNCs was also discussed in detail. Because the as-prepared BSA–AuAg BNCs display a good response to Hg2+, they have been potentially developed for the fabrication of fluorescent Hg2+ sensor. More importantly, due to the silver effect of Ag in the AuAg BNCs, the sensitivity of sensor prepared with BSA–AuAg BNCs is 6.3-fold higher than that prepared with BSA–Au NCs. Thus, this work highlights a new approach for the preparation of strongly fluorescent BNCs for the fabrication of highly sensitive fluorescence sensors.