Au Shell Research Articles

Intensity-dependent optical nonlinearities of composite materials made of ionic liquid crystal glass and bimetallic nanoparticles

ABSTRACT Although isotropic glass materials are ubiquitous in everyday life, the properties and applications of anisotropic liquid crystal glasses stable at room temperature are still insufficiently explored. In this paper, nonlinear-optical properties of unconventional glass nanocomposites made of mesogenic cadmium octanoate and bimetallic nanoparticles are reported. Two types of bimetallic nanoparticles (Ag/Au core – Au shell and Ag/Au homogeneous alloy) are synthesised utilising an ionic liquid crystal phase of cadmium octanoate as a nanoreactor. A nonlinear-optical characterisation of the studied samples is performed by means of a Z-scan technique and using nanosecond laser pulses at 1064 nm excitation wavelength. The studied nanocomposites exhibit a strong nonlinear-optical response with the magnitude of the third-order nonlinear optical susceptibility within a 2.81 × 10−8 - 2.19 × 10−7 esu range. The measured values of the effective nonlinear refractive indices and nonlinear absorption coefficients depend on the laser beam intensity. The physical mechanisms of the observed intensity-dependent optical nonlinearities are discussed.

Cu12@Au30Ag12: a magnetic pentakis icosidodecahedron molecule with core-shell configuration.

A 54-atom trimetallic core-shell Cu12@Au30Ag12 molecule has been identified by using first-principles calculations. This molecule with Ih symmetry consists of an icosahedral 12-atom Cu core (Cu12) coated by a pentakis icosidodecahedral 42-atom Au-Ag shell (Au30Ag12) composed of an icosidodecahedral Au30 and an icosahedral Ag12. Both the molecular dynamics simulations and vibrational frequency analysis demonstrate the high stability of Cu12@Au30Ag12. The analyses for electronic properties indicate that there exists spd hybridization which is crucial to maintain the geometrical configuration of Cu12@Au30Ag12. Moreover, a total spin magnetic moment of Cu12@Au30Ag12 is found to be 4 µB, which chiefly arises from the 6s states of Au atoms. A new type of sugar gourd-like [Cu12@Au30Ag11]n nanowire is also proposed; the results demonstrate that the nanowire exhibits metallic and magnetic behaviors. The magnetic Cu12@Au30Ag12 molecule and [Cu12@Au30Ag11]n nanowire can be promising candidates of novel magnetic nanomaterials and nanodevices.

High-Yield 99mTc Labeling of Gold Nanoparticles Carrying Atropine and Adrenaline.

This work focuses on the synthesis, purification, and analytical characterization of novel multifunctional Au NPs radiolabeled with 99mTc. These mixed-ligand shell Au NPs represent pharmacologically relevant samples for potential application in theragnostics. A ligand using a plain linker with a rather long chain consisting of 10 CH2 groups and a thiol moiety along with the PADA chelator has been used for both the attachment to the Au NP surface and for the 99mTc(CO)3+ complexation. We have combined this with our approach of stabilizing Au NP without any PEG or other stabilizing groups. Thus, monoligand shell Au NPs were radiolabeled by different strategies (prelabeling and postlabeling). Additionally, pharmacologically relevant Au NPs were synthesized carrying both a biofunctionalization with either atropine or adrenaline and the 99mTc radiolabel. All samples were obtained in very good yields (up to 80% of the total activity loaded onto the column) and completely/particularly purified using desalting columns. Detailed analytical characterization of the Au NPs before and after radiolabeling has proven the NPs' robustness throughout the process. Their intact functionalization, shape, and stability was confirmed by transmission electron microscopy (TEM), ultraviolet/visible (UV/vis) spectroscopy, dynamic light scattering (DLS), and infrared (IR) spectroscopy. The presented strategy represents a versatile building block system that can be adapted to a variety of bioactive molecules and may be of high relevance for theragnostic applications.

Synthesis and characterization of Au:CdO nanoparticles using laser ablation in liquid as gases sensors

Laser ablation technique in solution has been advanced to achieve single step synthesis of varied gold: oxide nanocomposites with uniform morphology and supreme dispersibility. The core:shell Au:CdO nanoparticles were manufactured by using fundamental Nd:YAG laser (1064 nm) at several energy of laser 600, 800 and 1000 mJ/100pulses, after that deposited on surface of porous-Si (PS). PS is prepared by using photo-electrochemical etching (PECE) method of n-type Si wafer in 16% hydrofluoric acid (HF).Current density 12 mA/cm2 and time of etching was 15 min. The characteristics of Au:CdO NPs that have been synthesized were studied. The structural properties were investigated using X-ray diffraction (XRD). Furthermore, the results of the AFM “atomic force microscope” test indicated a 26.34 nm surface roughness for Au:CdO NPs, TEM “transmission electron microscope) revealed that the fabricated particles of Au:CdO were spherical shape, and Photoluminescence (PL) test. Finally, the effects of different operation temperatures on the gas sensor sensitivity, recovery, and response times of NO2 and H2S gas sensors which created from synthesized samples were investigated. The maximum sensitivity of Au:CdO NPS/PS ablated by energy laser 800 mJ is approximately 93.5% and 67.81% of gas H2S and NO2 respectively.

Ag Nanoparticles with Ultrathin Au Shell-Based Lateral Flow Immunoassay for Colorimetric and SERS Dual-Mode Detection of SARS-CoV-2 IgG.

Immunoglobulin detection is essential for diagnosing progression of SARS-CoV-2 infection, for which SARS-CoV-2 IgG is one of the most important indexes. In this paper, Ag nanoparticles with ultrathin Au shells (∼2 nm) embedded with 4-mercaptobenzoic acid (MBA) (AgMBA@Au) were manufactured via a ligand-assisted epitaxial growth method and integrated into lateral flow immunoassay (LFIA) for colorimetric and SERS dual-mode detection of SARS-CoV-2 IgG. AgMBA@Au possessed not only the surface chemistry advantages of Au but also the superior optical characteristics of Ag. Moreover, the nanogap between the Ag core and the Au shell also greatly enhanced the Raman signal. After being modified with anti-human antibodies, AgMBA@Au recognized and combined with SARS-CoV-2 IgG, which was captured by the SARS-CoV-2 spike protein on the T line. Qualitative analysis was achieved by visually observing the color of the T line, and quantitative analysis was conducted by measuring the SERS signal with a sensitivity four orders of magnitude higher (detection limit: 0.22 pg/mL). The intra-assay and inter-assay variation coefficients were 7.7 and 10.3%, respectively, and other proteins at concentrations of 10 to 20 times higher than those of SARS-CoV-2 IgG could hardly produce distinguishable signals, confirming good reproducibility and specificity. Finally, this method was used to detect 107 clinical serum samples. The results agreed well with those obtained from enzyme-linked immunosorbent assay kits and were significantly better than those of the colloidal gold test strips. Therefore, this dual-mode LFIA has great potential in clinical practical applications and can be used to screen and trace the early immune response of SARS-CoV-2.

Fiber Optic Plasmonic Sensors Based on Nanodome Arrays with Nanogaps.

In this study, a high-performance fiber optic surface plasmon resonance (FO-SPR) sensor using a dome array with nanogaps (DANG) is proposed for label-free real-time detection of biomolecules. A novel and simple method using polymer beads enables high sensitivity by allowing hotspots with nanometer spacing between the Au dome and the surrounding film. The nanodome structure, which comprises a polymer core and a Au shell, induces a localized surface plasmon, expands the sensing area, and extensively enhances the electromagnetic field. The refractive index sensitivity of the FO-SPR sensor with nanostructures, i.e., with nanogaps and nanodomes, was found to be 7.8 times higher than that of the FO-SPR sensor without nanostructures. The proposed sensor achieved a low detection limit of 38 fg/mL while quantifying thyroglobulin antibody-antigen interactions and exhibited excellent selectivity. In addition, it helped detect serum samples with a 103% recovery rate.

Fabrication of Pt–Ag–Au heterogeneous truncated hollow sub-microspheres for chemically self-propelled colloidal motors

Colloidal motors with cavity structure, which have advantages over solid motors in catalytic efficiency, cargo capacity and biocompatibility, are still expected. Here, we design and fabricate a type of truncated hollow sub-microsphere via organic colloidal template etching/heating and layer-by-layer isotropic deposition. The as-prepared truncated hollow sphere is of one circular open pore through the shell layer and built of Pt, Ag and Au shell layers from inside to outside. They are controllable in sphere diameter, circular open pore size and shell thickness, which depend on the template and deposition conditions. Further experiments have shown that the Ag sandwich layer and post-deposition ageing process are crucial to obtaining strong and complete truncated hollow sub-microspheres. Their formation is attributed to the template geometry and nearly isotropic deposition. Due to the catalytic Pt layer on the inner surface and the truncated hollow spherical structure, such Pt–Ag–Au hollow spheres are demonstrated to be chemically propelled colloidal motors, which can directionally move in H2O2-containing solutions. This study presents a controllable route for mass-fabricating heterogeneous multi-layer truncated hollow sub-microspheres, and provides a new type of chemically self-propelled colloidal motor.

Enhanced refractive index sensitivity of localized surface plasmon resonance inflection points in single hollow gold nanospheres with inner cavity

Hollow gold nanoparticles have great potential for localized surface plasmon resonance (LSPR) sensing. In this study, we investigated the refractive index (RI) sensitivities of single hollow gold nanosphere (HAuNS) with thin Au shell and inner cavity and single solid gold nanosphere (AuNS) in media with different RIs. The HAuNS exhibited a remarkable improvement in the RI sensitivity than the AuNS of similar size. The increased RI sensitivity of HAuNSs was ascribed to plasmon coupling between the inner and outer surface of the Au nanoshell. We then investigated the homogeneous LSPR scattering inflection points (IFs) to better understand the RI sensitivity of single HAuNS. The LSPR IF at the long wavelength side exhibited a better RI sensitivity compared to the wavelength shift of its counterpart LSPR maximum peak. Furthermore, the single HAuNS showed a remarkable improvement in the RI sensitivity at the LSPR IFs when compared to the AuNS of similar size. Therefore, we provided a new insight into the effect of inner cavity of HAuNS on the RI sensitivity of homogeneous LSPR IFs for use in LSPR-based biosensors.

Multimodal bioimaging using nanodiamond and gold hybrid nanoparticles

Hybrid core–shell nanodiamond-gold nanoparticles were synthesized and characterized as a novel multifunctional material with tunable and tailored properties for multifunctional biomedical applications. The combination of nanostructured gold and nanodiamond properties afford new options for optical labeling, imaging, sensing, and drug delivery, as well as targeted treatment. ND@Au core–shell nanoparticles composed of nanodiamond (ND) core doped with Si vacancies (SiV) and Au shell were synthesized and characterized in terms of their biomedical applications. Several bioimaging modalities based on the combination of optical and spectroscopic properties of the hybrid nano-systems are demonstrated in cellular and developing zebrafish larvae models. The ND@Au nanoparticles exhibit isolated ND’s Raman signal of sp3 bonded carbon, one-photon fluorescence of SiV with strong zero-phonon line at 740 nm, two-photon excited fluorescence of nanogold with short fluorescence lifetime and strong absorption of X-ray irradiation render them possible imaging agent for Raman mapping, Fluorescence imaging, two-photon Fluorescence Lifetime Imaging (TP-FLIM) and high-resolution hard-X-ray microscopy in biosystems. Potential combination of the imaging facilities with other theranostic functionalities is discussed.

New Insights into the Magnetic Properties of CoFe2O4@SiO2@Au Magnetoplasmonic Nanoparticles

We report the successful synthesis and a complete magnetic characterization of CoFe2O4@SiO2@Au magnetoplasmonic nanoparticles. The CoFe2O4 magnetic nanoparticles were prepared using the hydrothermal method. A subsequent SiO2 shell followed by a plasmonic Au shell were deposited on the magnetic core creating magnetoplasmonic nanoparticles with a core–shell architecture. A spin-glass-type magnetism was shown at the surface of the CoFe2O4 nanograins. Depending on the external magnetic field, two types of spin-glass were identified and analyzed in correlation with the exchange field acting on octahedral and tetrahedral iron sites. The magnetization per formula unit of the CoFe2O4 core is not changed in the case of CoFe2O4@SiO2@Au nanocomposites. The gold nanoparticles creating the plasmonic shell show a giant diamagnetic susceptibility, dependent on their crystallite sizes.

Photo-thermal-induced response of VO2@Au@Au-seeds nanovesicle: A highly efficient NIR tunable nanoscatterer

Gold nanoparticles (AuNPs) are capable of localizing and enhancing light on a nano-sized scale, making these particles a unique structure to overcome the diffraction limit to allow for higher optical resolution in photonic devices. The optical response of AuNPs is controlled by their size, shape, and the refractive index contrast with the surrounding medium. Using phase change materials (PCMs) in the AuNP design introduces a dynamic tunability to the optical response without any modification to the geometrical properties. In this work, we have studied the induced photothermal response of the vesicle nanoparticle (VNP) consisting of a vanadium dioxide (VO2) core (80 nm), as a PCM, and an Au shell (10 nm) covered by Au-seeds (10 nm). When the VNP is irradiated by a CW laser, the light energy absorbed by the particle provides enough heat for the VO2 core to undergo a phase change from the semiconductor state to the metallic state. To do this, we simultaneously solve a self-consistent multiphysics problem consisting of electromagnetism and thermodynamics. Our calculations show that the maximum tunability of the extinction cross section corresponds to the scattering part achieved at the near-infrared wavelength of λ = 790 nm for the incident threshold intensity of 101.5 kW/cm2 at which the VO2 core experiences the semiconductor-metal phase change. We also show how the temperature is localized inside the VNP at both the semiconductor and metal phases of the VO2 core. It is expected that our results will offer a promising potential application in active photonic devices, near infrared imaging, detectors, and tunable scatterers.

Magnetic-plasmonic properties of CoFe2O4@Au nanocomposite

Cobalt ferrite-gold nanocomposite (CoFe2O4@Au), were synthesized using for the first time the synthetic route that involved (i) the polyol method to produce cobalt ferrite nanoparticles (CoFe2O4), (ii) the surface of CoFe2O4 functionalized with APTES to obtain amino groups, (iii) decorated cobalt ferrite nanoparticles with the ultra-small gold nanoparticles produced by the reduction of THPC, and (iv) using the platy solution method whereby the CoFe2O4 nanoparticles were decorated with a gold shell through crystal growth. X-ray diffraction (XRD) experiments showed that CoFe2O4 particles crystallized in a spinel structure (6 nm diameter). The XRD experiments for CoFe2O4@Au nanocomposite showed the presence of cubic gold nanocrystals confirming the presence of gold. Further experiments conducted using Fourier-transformed infrared (FTIR) spectroscopy showed the typical bands observed for the coordination around the tetrahedral and octahedral sites of CoFe2O4 particles. The evolution of the synthesis was also tracked through FTIR by observing the peaks attributed to the silica stretching bands on the surface of the APTES functionalized CoFe2O4 nanoparticles and the displacement of the ferrite peaks suggest the gold shell on the surface of the cobalt ferrite nanoparticles throughout the nanocomposite. UV–Vis spectroscopy showed a red shift in the spectra for CoFe2O4@Au when compared to spectra produced for CoFe2O4. Transmission electron microscope (TEM) images were obtained for both CoFe2O4 nanoparticles and CoFe2O4@Au nanocomposite. The images showed a difference in the size of the particles after the formation of the nanocomposite. Physical property measurements (PPMS) were performed to study the magnetic properties for both newly synthesized gold-coated nanocomposite and those without the gold. The study revealed superparamagnetic behavior for both samples and demonstrated that the addition of the Au shell has no influence on the block temperature, thus the particle growth is due to the gold coating. The magnetic properties were further examined using the Langevin model. This study found that the plasmonic gold behavior did not alter the magnetic properties of the particles and that instead the magnetic properties of CoFe2O4@Au are maintained which can be useful to magnetic-plasmonic applications.

Highly sensitive characteristic of surface enhanced Raman scattering for CuO/Au core/shell nanowires substrate

In this paper, we report a facile process to fabricate CuO/Au core/shell nanowires, where CuO core and Au shell were prepared by thermal oxidation and sputtering, respectively. The as-prepared CuO/Au nanowires are highly sensitive surface-enhanced-Raman-scattering (SERS) substrates, which can detect methylene blue down to a very low concentration of 10 −13 M. The major advantages of SERS substrates based on CuO/Au core/shell nanowires compared with others SERS substrates are the high sensitivity, uniformity, and purity due to the absence of any organic surfactants in the synthesis process.

Fe3O4@Au core-shell hybrid nanocomposite for MRI-guided magnetic targeted photo-chemotherapy.

The combination of multiple therapeutic and diagnostic functions is fast becoming a key feature in the area of clinical oncology. The advent of nanotechnology promises multifunctional nanoplatforms with the potential to deliver multiple therapeutics while providing diagnostic information simultaneously. In this study, novel iron oxide-gold core-shell hybrid nanocomposites (Fe3O4@Au HNCs) coated with alginate hydrogel carrying doxorubicin (DOX) were constructed for targeted photo-chemotherapy and magnetic resonance imaging (MRI). The magnetic core enables the HNCs to be detected through MRI and targeted towards the tumor using an external magnetic field, a method known as magnetic drug targeting (MDT). The Au shell could respond to light in the near-infrared (NIR) region, generating a localized heating for photothermal therapy (PTT) of the tumor. The cytotoxicity assay showed that the treatment of CT26 colon cancer cells with the DOX-loaded HNCs followed by laser irradiation induced a significantly higher cell death as opposed to PTT and chemotherapy alone. The in vivo MRI study proved MDT to be an effective strategy for targeting the HNCs to the tumor, thereby enhancing their intratumoral concentration. The antitumor study revealed that the HNCs can successfully combine chemotherapy and PTT, resulting in superior therapeutic outcome. Moreover, the use of MDT following the injection of HNCs caused a more extensive tumor shrinkage as compared to non-targeted group. Therefore, the as-prepared HNCs could be a promising nanoplatform for image-guided targeted combination therapy of cancer.

Flexible and transparent electrodes imprinted from metal nanostructures: morphology and opto-electronic performance.

We directed the self-assembly of nanoscale colloids via direct nanoimprint lithography to create flexible transparent electrodes (FTEs) with metal line widths below 3 μm in a roll-to-roll-compatible process. Gold nanowires and nanospheres with oleylamine shells were imprinted with soft silicone stamps, arranged into grids of parallel lines, and converted into metal lines in a plasma process. We studied the hierarchical structure and opto-electronic performance of the resulting grids as a function of particle geometry and concentration. The performance in terms of optical transmittance was dominated by the line width. Analysis of cross-sections indicated that plasma sintering only partially removed the insulating ligands and formed lines with thin conductive shells and a non-conductive core. We provide evidence that the self-assembly of high-aspect nanowires can compensate for defects of the stamp and substrate irregularities during imprinting, while spheres cannot. The wire-based electrodes thus outperformed the sphere-based electrodes at ratios of optical transmittance to sheet resistance of up to ≈ 0.9% Ωsq−1, while spheres only reached ≈ 0.55% Ωsq−1.

Green synthesis of biocompatible core-shell (Au-Ag) and hybrid (Au-ZnO and Ag-ZnO) bimetallic nanoparticles and evaluation of their potential antibacterial, antidiabetic, antiglycation and anticancer activities.

The fabrication of bimetallic nanoparticles (BNPs) using plant extracts is applauded since it is an environmentally and biologically safe method. In this research, Manilkara zapota leaf extract was utilized to bioreduce metal ions for the production of therapeutically important core–shell Au–Ag and hybrid (Au–ZnO and Ag–ZnO) BNPs. The phytochemical profiling of the leaf extract in terms of total phenolic and flavonoid content is attributed to its high free radical scavenging activity. FTIR data also supported the involvement of these phytochemicals (polyphenols, flavonoids, aromatic compounds and alkynes) in the synthesis of BNPs. Whereas, TEM and XRD showed the formation of small sized (16.57 nm) spherical shaped core–shell Au–Ag BNPs and ZnO nano-needles with spherical AuNPs (48.32 nm) and ZnO nano-rods with spherical AgNP (19.64 nm) hybrid BNPs. The biological activities of BNPs reinforced the fact that they show enhanced therapeutic efficacy as compared to their monometallic components. All BNPs showed comparable antibacterial activities as compared to standard tetracycline discs. While small sized Au–Ag BNPs were most effective in killing human hepato-cellular carcinoma cells (HepG2) in terms of lowest cell viability, highest intracellular ROS/RNS production, loss of mitochondrial membrane potential, induction of caspase-3 gene expression and enhanced caspase-3/7 activity. BNPs also effectively inhibited advanced glycation end products and carbohydrate digesting enzymes which can be used as a nano-medicine for aging and diabetes. The most important finding was the permissible biocompatibility of these BNPs towards brine shrimp larvae and human RBCs, which suggests their environmental and biological safety. This research study gives us insight into the promise of using a green route to synthesize commercially important BNPs with enhanced therapeutic efficacy as compared to conventional treatment options.

Flexible and transparent electrodes imprinted from Au nanowires: stability and ageing.

We study the stability of flexible transparent electrodes (FTEs) that were self-assembled from ultra-thin gold nanowires (AuNW) by direct nanoimprinting of inks with different particle concentrations (1 to 10 mg mL−1). The resulting lines were less than 3 μm wide and contained bundles of AuNW with oleylamine (OAm) ligand shells. Small-angle X-ray scattering confirmed a concentration-independent bundle structure. Plasma sintering converted the wire assemblies into lines with a thin metal shell that contributes most to electrical conductivity and covers a hybrid core. We studied the relative change in sheet resistance and the morphology of the FTEs with time. The sheet resistance increased at all concentrations, but at different rates. The metal shell aged by de-wetting and pore formation. The hybrid core de-mixed and densified, which led to a partial collapse of the shell. Residual organics migrated through the shell via its pores. Lines formed at low concentration (cAu = 2 to 3 mg mL−1) contained less residual organics and aged slower than those formed at high cAu ≥ 5 mg mL−1. We passivated the conductive shell with thin, adsorbed layers of PEDOT:PSS and found that it decelerated degradation by slowing surface diffusion and hindering further rupture of the shell. Thick capping layers prevented degradation entirely and stopped pore formation.

Core-shell Au-Ag nanoparticles as colorimetric sensing probes for highly selective detection of a dopamine neurotransmitter under different pH conditions.

Dopamine (DA) is a vital biomarker for the early diagnosis of dopaminergic dysfunction; therefore, it is important to establish a direct and selective detection tool for DA neurotransmitters. This work reports facilely synthesized Au-Ag core-shell nanoparticles (Au@Ag NPs) as colorimetric sensing probes for highly selective detection of the DA neurotransmitter. Our sensing strategy is based on DA-mediated aggregation of the Au@Ag NPs, which can show a distinct color transition from yellow to greenish grey. With the increase of pH from 6 to 10, the response time of colorimetric transition was significantly reduced by a factor of 10 and the limit of detection (LOD) for DA by a spectroscopic device was estimated to be 0.08 μM. Notably, optimized sensing probes of Au@Ag NPs at pH 10 demonstrated an excellent selectivity to DA against various interfering components (including catecholamines (norepinephrine and epinephrine), lysine, glutamic acid, glucose, or metal ions). Our sensing system also exhibited the reliable detection of DA in spiked human serum with the relative standard deviation lower than 4.0%, suggesting its possible application to the direct detection of DA in biological fluids.

Realization of the dehydrogenation pathway of formic acid oxidation by ultra-small core–shell Au–Pt nanoparticles with discrete Pt shells

Ultra-small core–shell structured Au–Pt nanoparticles with discrete Pt shells can realize the oxidation of formic acid in the dehydrogenation pathway.

Impact of capping agent removal from Au NPs@MOF core–shell nanoparticle heterogeneous catalysts

Core–shell Au NPs@MOF-808 architecture has been synthesized using sustainable conditions. Au NPs capping agent removal has been optimized to boost the catalytic efficiency of the composite material.