Hollow Au Research Articles

Sophisticated Construction of Hollow Au–Ag–Cu Nanoflowers as Highly Efficient Electrocatalysts toward Ethylene Glycol Oxidation

Direct ethylene glycol fuel cells represent promising advanced portable energy storage and conversion devices, which can be well applied to serve as advanced sustainable energy technology to overcome the formidable challenges of ecological crisis and environmental pollution. However, many drawbacks of the newly established catalysts such as poor corrosion resistance and antipoisoning make them exhibit limited electrocatalytic performances. For addressing these issues, we herein combined both morphological and component advantages to engineer an advanced Au–Ag–Cu trimetallic electrocatayst with fascinating hollow nanoflowers structures. By virtue of such unique structure, the as-obtained Au–Ag–Cu hollow nanoflowers displayed unprecedentedly excellent electrocatalytic activity toward ethylene glycol oxidation with the highest mass activity of 5493.4 mA mgAu–1, 5.9-fold enhancement than that of pure Au. We postulate that the strategy and electrocatalysts we engineered in this work will greatly boost the comm...

Hollow Au-Ag Alloy Nanorices and Their Optical Properties.

Hollow noble metal nanoparticles have excellent performance not only in surface catalysis but also in optics. In this work, the hollow Au–Ag alloy nanorices are fabricated by the galvanic replacement reaction. The dark-field spectrum points out that there is a big difference in the optical properties between the pure Ag nanorices and the hollow alloy nanorices that exhibit highly tunable localized surface plasmon resonances (LSPR) and that possess larger radiative damping, which is also indicated by the finite element method. Furthermore, the surface enhanced Raman scattering (SERS) and oxidation test indicate that hollow Au–Ag alloy nanorices show good anti-oxidation and have broad application prospects in surface-plasmon-related fields.

Plasmonic Particles – Now Tailored to Your Needs

Plasmonic Particles – Now Tailored to Your Needs

Food Quality Monitor: Paper-Based Plasmonic Sensors Prepared Through Reversal Nanoimprinting for Rapid Detection of Biogenic Amine Odorants.

This paper describes the fabrication of paper-based plasmonic refractometric sensors through the embedding of metal nanoparticles (NPs) onto flexible papers using reversal nanoimprint lithography. The NP-embedded papers can serve as gas sensors for the detection of volatile biogenic amines (BAs) released from spoiled food. Commercial inkjet papers were employed as sensor substrates-their high reflectance (>80%) and smooth surfaces (roughness: ca. 4.9 nm) providing significant optical signals for reflection-mode plasmonic refractometric sensing and high particle transfer efficiency, respectively; in addition, because inkjet papers have lightweight and are burnable and flexible, they are especially suitable for developing portable, disposable, cost-effective, eco-friendly sensing platforms. Solid silver NPs (SNPs), solid gold NPs (GNPs), and hollow Au-Ag alloyed NPs (HGNs) were immobilized on a solid mold and then transferred directly onto the softened paper surfaces. The particle number density and exposure height of the embedded NPs were dependent on two imprinting parameters: applied pressure and temperature. The optimal samples exhibited high particle transfer efficiency (ca. 85%), a sufficient exposure surface area (ca. 50% of particle surface area) presented to the target molecules, and a strong resonance reflectance dip for detection. Moreover, the HGN-embedded paper displayed a significant wavelength dip shift upon the spontaneous adsorption of BA vapors (e.g., Δλ = 33 nm for putrescine; Δλ = 24 nm for spermidine), indicating high refractometric sensitivity; in contrast, no visible spectroscopic responses were observed with respect to other possibly coexisting gases (e.g., air, N2, CO2, water vapor) during the food storage process, indicating high selectivity. Finally, the plasmonic sensing papers were used to monitor the freshness of a food product (salmon).

A novel label-free electrochemical immunosensor based on the enhanced catalytic currents of oxygen reduction by AuAg hollow nanocrystals for detecting carbohydrate antigen 199

Herein, bimetallic alloyed AuAg hollow nanocrystals (AuAg HNCs) were prepared by a simple one-pot aqueous method using polycytidysic acid (PCA) as the green growth-directing agent. The novel immunosensor for carbohydrate antigen 199 (CA199) was further constructed based on the enhanced catalytic currents of oxygen reduction reaction (ORR) by AuAg HNCs. By virtue of the good biocompatibility and catalytic activity of AuAg HNCs, the immunosensor exhibited superior analytical performance for the assay of CA199 under the optimal experimental conditions, the ORR signals linearly decreased with the increased CA199 concentrations in the range of 1 ~ 30UmL–1, with the low detection limit of 0.228UmL–1, improved stability, reproducibility and selectivity.

Annealing temperature on photocatalytic activity of (hollow Au−Ag nanoparticles)/TiO2 composites prepared from block copolymer-stabilized bimetallic nanoparticles

ABSTRACTComposite containing a TiO2 and hollow Au−Ag nanoparticles (H−AuAg−NPs) have been prepared by using H−AuAg−NPs with block copolymer shells as templates, and the influence of annealing temperature on structure, surface property, and the photocatalytic activity has been investigated. The structures of H−AuAg−NPs/TiO2 Composites were examined by X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The carbon content was measured by thermogravimetric analyses (TGA). The specific surface areas and pore volumes of the H−AuAg−NPs/TiO2 composites after annealing at different temperature were characterized using the nitrogen gas sorption technique. The photocatalytic activities of the H−AuAg−NPs/TiO2 composite were investigated by the photodecomposition of methylene blue (MB). The results show that the TiO2 in H−AuAg−NPs/TiO2 composite is amorphous upon annealing at 400°C. Anatase phase appears as annealing temperature is increased to 450°C, and the crystallinity is further increased if the annealing temperature is raised to 500°C. The specific surface area decreases with annealing temperature from 400°C to 500°C. It is found that the H−AuAg−NPs/TiO2 composite annealed at 450°C shows the highest photocatalytic activity.

Metal-Enhanced Ratiometric Fluorescence/Naked Eye Bimodal Biosensor for Lead Ions Analysis with Bifunctional Nanocomposite Probes.

A novel metal-enhanced ratiometric fluorescence/naked eye bimodal biosensor based on ZnFe2O4@Au-Ag bifunctional nanocomposite and DNA/CeO2 complex for lead ions (Pb2+) has been successfully developed. The nanocomposite probe was composed of a magnetic ZnFe2O4 core and a Au-Ag hollow nanocube shell. Upon bioconjugation, bifunctional magnetic nanocomposites could not only make the probe possess excellent recyclability but also provide an enrichment of "hot spots" for surface enhanced fluorescence detection of Pb2+ by a metal-enhanced fluorescence effect. Typically, the bifunctional nanocomposites conjugated with double-stranded DNA (included Pb2+-specific DNAzyme strand and corresponding substrate strand) to form a Pb2+ biosensor. Nanoceria as a fluorescence quencher strongly adsorbed DNA. Therefore, the formation of double-stranded DNA brought the labeled nitrogen sulfur doped carbon dots (N,S-CDs) and CeO2 into close proximity, which significantly quenched the fluorescence of N,S-CDs. The presence of Pb2+ led to the breakage of the DNAzyme strand, resulting in the fluorescence signal of Cy3 decreasing, while the fluorescence intensity of N,S-CDs aggrandized. First, a preliminary test of Pb2+ was performed by the naked eye. The disengaged DNA/CeO2 complex could result in color change after adding H2O2 because of autocatalysis of CeO2, resulting in real-time visual detection of Pb2+. If further accurate determination was required, the fluorescence intensity ratio of these two fluorescence indicators was measured at 562 and 424 nm (I562/I424). A good linear correlation exists between the log(I562/I424) and the logarithm of Pb2+ concentrations ranging from 10-12 to 3 × 10-6 M. Remarkably, the detection limit of this ratiometric biosensor was 3 × 10-13 M, which ascribed to its superior fluorescence enhancement. Interestingly, the developed bifunctional nanocomposite probe manifests good recyclability and selectivity. More importantly, the biosensor provided potential application of on-site and real-time unknown Pb2+ ions in real systems.

Synthesis and characterization of hollow ZrO2–TiO2/Au spheres as a highly thermal stability nanocatalyst

A novel binary-metal-oxide-coated hollow microspheres-titanium dioxide-zirconium dioxide-coated Au nanocatalyst was prepared via a facile hydrothermal synthesis method. SEM, TEM, EDX, FTIR, XRD, UV–vis and XPS analyses were employed to characterize the composition, structure, and morphology of ZrO2–TiO2 hollow spheres. The size of Au nanoparticles was found to be 3–5nm in diameter before being immobilized on the aforementioned mesoporous ZrO2–TiO2 layer and used as catalysts in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. Compared with TiO2/Au and ZrO2/Au, ZrO2–TiO2/Au NPs showed a higher catalytic activity because of due to mixed oxide synergistic effect. Besides, the sample gets the highest thermal stability and reactivity at 550°C, after calcining the hollow ZT/Au NPs at 550°C, 300°C and room temperature, respectively. Finally, a possible reaction mechanism was also proposed to explain the reduction of 4-nitrophenol to 4-aminophenol over ZrO2–TiO2/Au catalyst.

Hollow Au-Ag Nanoparticles Labeled Immunochromatography Strip for Highly Sensitive Detection of Clenbuterol

The probe materials play a significant role in improving the detection efficiency and sensitivity of lateral-flow immunochromatographic test strip (ICTS). Unlike conventional ICTS assay usually uses single-component, solid gold nanoparticles as labeled probes, in our present study, a bimetallic, hollow Au-Ag nanoparticles (NPs) labeled ICTS was successfully developed for the detection of clenbuterol (CLE). The hollow Au-Ag NPs with different Au/Ag mole ratio and tunable size were synthesized by varying the volume ratio of [HAuCl4]:[Ag NPs] via the galvanic replacement reaction. The surface of hollow Ag-Au NPs was functionalized with 11-mercaptoundecanoic acid (MUA) for further covalently bonded with anti-CLE monoclonal antibody. Overall size of the Au-Ag NPs, size of the holes within individual NPs and also Au/Ag mole ratio have been systematically optimized to amplify both the visual inspection signals and the quantitative data. The sensitivity of optimized hollow Au-Ag NPs probes has been achieved even as low as 2 ppb in a short time (within 15 min), which is superior over the detection performance of conventional test strip using Au NPs. The optimized hollow Au-Ag NPs labeled test strip can be used as an ideal candidate for the rapid screening of CLE in food samples.

Near-IR-Absorbing Gold Nanoframes with Enhanced Physiological Stability and Improved Biocompatibility for In Vivo Biomedical Applications.

This paper describes the synthesis of near-infrared (NIR)-absorbing gold nanoframes (GNFs) and a systematic study comparing their physiological stability and biocompatibility with those of hollow Au-Ag nanoshells (GNSs), which have been used widely as photothermal agents in biomedical applications because of their localized surface plasmon resonance (LSPR) in the NIR region. The GNFs were synthesized in three steps: galvanic replacement, Au deposition, and Ag dealloying, using silver nanospheres (SNP) as the starting material. The morphology and optical properties of the GNFs were dependent on the thickness of the Au coating layer and the degree of Ag dealloying. The optimal GNF exhibited a robust spherical skeleton composed of a few thick rims, but preserved the distinctive LSPR absorbance in the NIR region-even when the Ag content within the skeleton was only 10 wt %, 4-fold lower than that of the GNSs. These GNFs displayed an attractive photothermal conversion ability and great photothermal stability, and could efficiently kill 4T1 cancer cells through light-induced heating. Moreover, the GNFs preserved their morphology and optical properties after incubation in biological media (e.g., saline, serum), whereas the GNSs were unstable under the same conditions because of rapid dissolution of the considerable silver content with the shell. Furthermore, the GNFs had good biocompatibility with normal cells (e.g., NIH-3T3 and hepatocytes; cell viability for both cells: >90%), whereas the GNSs exhibited significant dose-dependent cytotoxicity (e.g., cell viability for hepatocytes at 1.14 nM: ca. 11%), accompanied by the induction of reactive oxygen species. Finally, the GNFs displayed good biocompatibility and biosafety in an in vivo mouse model; in contrast, the accumulation of GNSs caused liver injury and inflammation. Our results suggest that GNFs have great potential to serve as stable, biocompatible NIR-light absorbers for in vivo applications, including cancer detection and combination therapy.

Surfactant-Free Preparation of Au@Resveratrol Hollow Nanoparticles with Photothermal Performance and Antioxidant Activity.

Nanocomposites based on hollow Au nanostructures have gained considerable attention in theranostics applications because of their unique plasmonic structures and attractive physicochemical properties. The exploration of feasible and facile methods for constructing multifunctional nanocomposites combined with bioactive molecules is greatly needed for the development of multifunctional theranostics platforms. In this work, resveratrol, a natural polyphenol with antioxidant activity and cancer-chemopreventive propertyies is employed as the reducing agent cum coating agent for the surfactant-free preparation of Au@resveratrol hollow NPs (Au@Res HNPs). The as-prepared Au@Res HNPs were found to present good photothermal performance and chemical inhibition for cancer therapy. In vitro experiments indicated that the Au@Res HNPs can block cell cycles to inhibit cell division and lead to cell apoptosis after 808-nm laser irradiation. Because no toxic surfactants are introduced, the current protocol avoids the tedious surfactant separation and surface modification processes that are necessary for most theranostics materials.

Hollow AuxAg/Au core/shell nanospheres as efficient catalysts for electrooxidation of liquid fuels.

One plausible approach to endow nanocrystals with both enhanced catalytic activity and stability for the electrooxidation of liquid fuels is to chemically control the crystal structures of nanoparticles. To date, core-shell and alloy structures have been demonstrated to offer generally two precious opportunities to design highly efficient nanocatalysts for the electrooxidation reaction of organic molecules. We herein combine these two advantages and develop a general method to successfully synthesize hollow AuxAg/Au core/shell nanospheres with a high yield approaching 100% via a combined seed mediated and galvanic replacement method. The results from the electrochemical measurements have revealed that this as-obtained hollow AuxAg/Au core/shell nanosphere exhibited considerably high electrocatalytic performance towards ethylene glycol and glycerol oxidation with mass activity of 4585 and 3486 mA mgAu-1, which were 5.3- and 5.8-fold higher than that of pure Au. We trust this strategy may be extended to the syntheses of other multimetallic nanocatalysts with such fascinating nanostructures and the as-obtained hollow AuxAg/Au core/shell nanospheres can be well applied to serve as highly desirable anode catalysts for the electrooxidation of ethylene glycol and glycerol.

A galvanic replacement-based Cu2O self-templating strategy for the synthesis and application of Cu2O–Ag heterostructures and monometallic (Ag) and bimetallic (Au–Ag) hollow mesocages

Polyhedral Cu2O microparticles as self-templates have been well-demonstrated for the synthesis of Cu2O–M heterostructures (M = Au, Pd, Pt) and Au nano/mesocages utilizing the galvanic replacement reaction (GRR) strategy. However, reports on GRR-based fabrication of Cu2O–Ag heterostructures and the ensuing Ag mesocages are scanty. There is no report that describes the phenomenon of facet selectivity during the GRR-based deposition of Ag on Cu2O template particles. Here, we have identified the underlying rationale behind the observed difficulty in nucleating Ag nanoparticles on an octahedral Cu2O self-template particle. Utilization of an appropriately chosen surfactant/complexant for the silver precursor helps in demonstrating the successful fabrication of Cu2O–Ag heterostructures (octahedral, cubic) with a tunable loading density of Ag NPs on the Cu2O surfaces. This is achieved using Cu2O template particles that undergo GRR with silver nitrate in the presence of nitric acid, and 5-sulfosalicylic acid as the surfactant (key role players). We provide evidence that supports facet selectivity during the deposition of Ag NPs on Cu2O cuboctahedral particles. Hollow octahedral Ag and Au–Ag bimetallic mesocages are fabricated that have rough surfaces, uniform morphology, and excellent shape retention. The fabricated heterostructures and mesocages act as an excellent SERS substrate. This is the first report on the rational synthesis of octahedral Cu2O–Ag heterostructures and octahedral hollow metallic mesocages utilizing the Cu2O self-templating strategy along with the demonstration of facet selectivity of Ag deposition on Cu2O template particles through GRR. The current approach offers a facile and versatile protocol for the synthesis of Cu2O–metal heterostructures and hollow noble metal mesocages.

Preparation of TiO2–ZrO2/Au/CeO2 hollow sandwich-like nanostructures for excellent catalytic activity and thermal stability

This work reports a novel type of sandwich-like hollow Au-based nanocatalyst, including a TiO2–ZrO2 shell, a hollow CeO2 core and Au nanoparticles of 2–5 nm.

Hollow Au nanoflower substrates for identification and discrimination of the differentiation of bone marrow mesenchymal stem cells by surface-enhanced Raman spectroscopy.

Bone marrow mesenchymal stem cells (BMSCs) are multipotent stem cells, which play an important role in the repair of bone injury, angiogenesis, immune diseases, cancer invasion and metastasis. Therefore, increasing attention has been focused on the study of BMSCs. However, the identification and discrimination of the undifferentiated and differentiated BMSCs, which are closely related and morphologically similar, are still a challenge using traditional methods. In this study, we report a novel surface-enhanced Raman scattering (SERS) substrate based on hollow gold nanoflower (HAuNF)-decorated silicon wafers for distinguishing the differentiation of BMSCs. The flower-like, hollow Au nanoparticles were successfully synthesized by a seed-mediated growth approach. We demonstrated that fabricated HAuNF substrates had very good reproducibility, homogeneous SERS activity and a high SERS effect. Using HAuNF substrates as a high-performance in vitro sensing platform allowed us to monitor the changes in the cellular biochemical composition during the differentiation of BMSCs. SERS spectra were analyzed using principal component analysis (PCA), which successfully segregated the subtypes of BMSCs. Furthermore, the results of biological assay suggested that the adipogenic inductor and the osteogenic inductor could induce the differentiation of BMSCs into adipocytes and osteocytes, respectively. The SERS technique based on HAuNF substrates provides a sensitive, efficient and non-invasive detection method for studying the differentiation of stem cells.

Hollow Au loaded with kanamycin for pharmacological and laser-triggered photothermal sterilization

Anti-E. coli-conjugated and kanamycin-loaded hAuNPs (hAuNPs-anti-E. coli-kana) were prepared for sterilization.

3D structure-preserving galvanic replacement to create hollow Au microstructures

3D hollow Au microstructures (HL-AuMSs) are fabricated via a galvanic replacement approach. 3D nanoporous Ag microstructures (np-AgMSs) are sacrificed as a template to control the structural complexity of HL-AuMSs.

Rapid Detection and Identification of miRNAs by Surface-Enhanced Raman Spectroscopy Using Hollow Au Nanoflowers Substrates

MicroRNAs (miRNAs) are recognized as regulators of gene expression during the biological processes of cells as well as biomarkers of many diseases. Development of rapid and sensitive miRNA profiling methods is crucial for evaluating the pattern of miRNA expression related to normal and diseased states. This work presents a novel hollow Au nanoflowers (HAuNFs) substrate for rapid detection and identification of miRNAs by surface-enhanced Raman scattering (SERS) spectroscopy. We synthesized the HAuNFs by a seed-mediated growth approach. Then, HAuNFs substrates were fabricated by depositing HAuNFs onto the surfaces of (3-aminopropyl)triethoxysilane- (APTES-) functionalized ITO glass. The result demonstrated that HAuNFs substrates had very good reproducibility, homogeneous SERS activity, and high SERS effect. The substrates enabled us to successfully obtain the SERS spectra of miR-10a-5p, miR-125a-5p, and miR-196a-5p. The difference spectra among the three kinds of miRNAs were studied to better interpret the spectral differences and identify miRNA expression patterns with high accuracy. The principal component analysis (PCA) of the SERS spectra was used to distinguish among the three kinds of miRNAs. Considering its time efficiency, being label-free, and its sensitivity, the SERS based on HAuNFs substrates is very promising for miRNA research and plays an important role in early disease detection and prevention.

Synthesis and Assembly of Gold and Iron Oxide Particles Within an Emulsion Droplet; Facile Production of Core@Shell Particles

Here we report a method for synthesising and assembling nanomaterials at the liquid-liquid interface of an emulsion droplet, resulting in a simple strategy for producing hollow Au shells, or Fe3O4@Au core@shell particles. Mercaptododecanoic acid stabilised Au nanoparticles were added to the aqueous continuous phase, in order to stabilise hexane emulsion droplets formed within a microfluidic chip. The diameters of Au Pickering emulsions could be controlled by varying the flow rates, this produce hollow particles. The addition of a second nanoparticle, Fe3O4 (average diameter of 12nm), into the organic phase produced core@shell particles. The diameter of the resultant material was determined by the concentration of the Fe3O4. This report is the first to demonstrate Pickering emulsions within a microfluidics chip for the production of Fe3O4@Au particles, and it is believed that this could be a versatile platform for the large scale production of core@shell particles.

Reversible Shape and Plasmon Tuning in Hollow AgAu Nanorods.

The internal structure of hollow AgAu nanorods created by partial galvanic replacement was manipulated reversibly, and its effect on optical properties was mapped with nanometer resolution. Using the electron beam in a scanning transmission electron microscope to create solvated electrons and reactive radicals in an encapsulated solution-filled cavity in the nanorods, Ag ions were reduced nearby the electron beam, reshaping the core of the nanoparticles without affecting the external shape. The changes in plasmon-induced near-field properties were then mapped with electron energy-loss spectroscopy without disturbing the internal structure, and the results are supported by finite-difference time-domain calculations. This reversible shape and near-field control in a hollow nanoparticle actuated by an external stimulus introduces possibilities for applications in reprogrammable sensors, responsive materials, and optical memory units. Moreover, the liquid-filled nanorod cavity offers new opportunities for in situ microscopy of chemical reactions.