Bimetallic Nanoshells Research Articles

Nanosensors sensitivity based on localized surface plasmons created in bimetallic nanoshells

Due to the increasing importance of nanosensors in the early diagnosis of diseases, the need for high-performance nanosensors is one of the goals of researchers. In this paper, a structure consisting of plasmonic nanoshells with spherical and ellipsoidal geometry has been proposed to calculate the refractive index (RI) changes in the range of 1–3. The sensitivity of the proposed nanosensor has been computed, and the effective factors on the performance of the nanosensor, including geometry, material, core dimensions, shell thickness, and RI of the surrounding environment are studied. To this end, various nanostructures have been modeled using the boundary element method. It has been shown that ellipsoidal nanoshells are more sensitive to RI changes than spherical nanoshells. Also, the results show that nanoshells with a core and shell made of plasmonic metals (bimetallic nanoshell) can exponentially increase the sensitivity of the nanosensor.

Metal-organic frameworks-based hierarchical heterojunction coupling with plasmonic nanoshells for self-powered photoelectrochemical immunoassay

Self-powered PEC immunoassays (AgAu/ZIF-8@ZnS@CdS), derived from MOFs-based semiconductor coupling with plasmonic AgAu bimetallic nanoshells, are designed and nano-engineered. The immunoassays exhibit superior detection ability for prostate-specific antigen because of the synergistic effect of the multi-heterostructure interfaces of ZIF-8@ZnS@CdS and enhanced electromagnetic field enabled by the MOFs-shells-encapsulated plasmonic AgAuNSs. • A plasmonic hierarchical structure (AgAu/ZIF-8@ZnS@CdS) was designed. • Plasmon-promoted MOFs-based PEC immunoassays were constructed. • The PEC performance was significantly boosted due to the synergistic effect. • The immunoassays exhibited excellent sensitivity, reproducibility and stability. Benefiting from the large specific areas and versatile designability, metal–organic frameworks (MOFs) based materials open a new avenue for the design of superior catalysts, whereas their applications in sensitive detection are still in their infancy. Herein, plasmon-promoted MOFs-based photoelectrochemical (PEC) immunoassays with hierarchical structures (AgAu/ZIF-8@ZnS@CdS) are prepared via a MOFs-engaged directional deposition method and ion-exchange reaction. As a result, the hierarchical structures exhibit excellent PEC performance with reinforced light absorption and charge separation efficiency. Reaction dynamics at the electron level and spatial-resolved simulations clarify that the multi-heterostructure interfaces of ZIF-8@ZnS@CdS and the plasmonic effect of AgAu nanoshells can synergistically improve the light absorption efficiency and promote the spatial separation of the electron-hole pairs. Notably, the MOFs shells are found to dramatically enhance the electromagnetic field and prevent the decay along the radial direction, which is favorable to the charge separation and transfer. Taking prostate-specific antigen as a representative analyte, both label-free and sandwich-type self-powered immunoassays exhibit superior detection performance with limits of detection (LODs) as low as 0.11 pg·mL −1 and 0.9 fg·mL −1 , respectively. This study offers a promising platform for the construction of ultrasensitive immunoassays and provides methodologies for the mechanism investigation beyond the PEC detection performance.

Improve the Effective Resonance Light Scattering of Three-Layered Plasmonic Au@Dielectric@Ag Bimetallic Nanoshells

The strong light scattering from SPR has received an extraordinary attention due to the useful applications in photodetectors and cell and biomedical imaging. However, the applications using light scattering require a high scattering cross-section along with low absorption losses near the resonance wavelength. In this paper, effective plasmonic scattering of three-layered Au–Ag bimetallic nanoshells with a dielectric separate layer has been studied using the quasi-static approximation of classical electrodynamics. Because of the surface plasmon resonance (SPR)-induced intense light absorption, the effective scattering intensity is much weaker than that of scattering cross-section. However, the effective scattering intensity could be improved by tuning the geometric dimension and local dielectric environment of the nanostructure. It has been found that the greatest effective scattering takes place when the outer Ag nanoshell has a thick thickness or the dielectric separate layer has a small dielectric constant. The effective scattering also depends on the inner Au sphere radius and outer surrounding dielectric constant. Because of the mode transformation of the SPR, the effective scattering could also be greatly improved when the inner Au sphere has a very small or large size. However, the effective scattering intensity changes non-monotonously as the surrounding dielectric constant increases. The greatest effective scattering could be obtained when the surrounding dielectric constant has an intermediate value. This tunable effective plasmonic scattering of Au@Ag three-layered nanoshells presents a potential for design and fabrication of plasmonic optical nanodevice based on resonance light scattering.

Lipase production from mutagenic strain of Fusarium Incarnatum KU377454 and its immobilization using Au@Ag core shells nanoparticles for application in waste cooking oil degradation.

In the present study, lipase production from mutated strain of Fusarium incarnatum KU377454 was optimized through central composite design (CCD) based response surface methodology (RSM). The maximum lipase production (4.01IU/mL) was obtained within 4days of incubation using 0.1% CaCl2 concentration and 8% wheat bran concentration. Further, salting out technique was applied for partial purification of lipase. The partially purified lipase was immobilized using Au@Ag bimetallic nanoshell. The characterization of immobilized lipase was carried out by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transformed infrared (FTIR), energy dispersive X-ray (EDX), X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). The immobilized lipase could retain its 95% of activity after 15days of storage at 4°C. Subsequently, Au@Ag immobilized lipase was used for the degradation of waste cooking oil (WCO), which showed higher WCO degradation (85%) compared to the free lipase mediated waste cooking oil degradation (71%). The immobilized lipase could be reused for five times without any loss of its activity.

Smart Plasmonic Nanozyme Enhances Combined Chemo-photothermal Cancer Therapy and Reveals Tryptophan Metabolic Apoptotic Pathway

Regulation of the tumor microenvironment is considered to be an intelligent strategy for cancer therapeutics, but the related metabolic pathways of cell apoptosis still remain a great challenge. Herein, by applying multifunctional carbon dot-decorated Ag/Au bimetallic nanoshells (CDs-Ag/Au NSs, CAANSs) nanoprobes as smart plasmonic nanozymes for combined chemo-photothermal cancer therapy, we achieved a high efficiency in cancer cell therapy and revealed a tryptophan (Trp) metabolic apoptotic pathway. In addition to high photothermal conversion efficiency, the CAANSs can act as a smart nanozyme to catalyze intracellular H2O2 to the cytotoxic reactive oxygen species (ROS) of superoxide anion (·O2-), in response to mild acidic cancerous cell microenvironment to damage cellular DNA. More importantly, the Trp metabolic pathway during the combined chemo-photothermal therapy has revealed that the Trp participates in an oxidative stress process, which can be decomposed to produce H2O2 and further formed into superoxide anions to kill cells under the catalytic nanomedicine process. The current work provides an effective platform for cancer therapeutics and is promising for cancer-related molecular biology studies.

Tunable local surface plasmon resonance and refractive index sensitivity ability of three-layered dielectric-silver bimetallic nanoshells

Optical properties and refractive index sensitivity abilities of three-layered silver/gold-dielectric-silver bimetallic nanoshells are investigated based on quasi-static theory. The results show that absorption spectra of silver/gold-dielectric-silver bimetallic nanoshells can be well tuned by changing the inner core radius, middle dielectric radius and outer shell layer thickness. Local surface plasmon resonance (LSPR) shifts of |ω−−〉 mode show a red-shift with increasing the inner core radius and the thickness of middle dielectric layer, while a blue-shift with increasing the thickness of outer shell. It is interesting to find that the shifts of |ω−+〉 mode are related to the ratio ε2∕ε4, the component of core and nanoshell. In addition, the refractive index sensitivity abilities of three-layered silver/gold-dielectric-silver bimetallic nanoshells are also reported. A higher refractive index sensitivity ability can be obtained by adjusting its geometric size and component. |ω−−〉 mode gets more intensity with increasing the surrounding medium dielectric function, while |ω−+〉 mode fades down. The intensity difference between |ω−−〉 mode and |ω−+〉 mode is mainly effected by the surrounding medium dielectric function, its geometric parameter, middle layer dielectric function, the component of core and nanoshell. Our study provides a way to analyze sensitivity application of nanoshells and broadens the application of nanoshells in sensor ability.

Vapreotide-mediated hierarchical mineralized Ag/Au nanoshells for photothermal anti-tumor therapy

A new type of vapreotide-templated Ag/Au bimetallic nanoshells (Vap@Ag/AuNSs) were successfully designed and fabricated based on polypeptide-directed mineralization and hierarchical self-assembly mechanisms under mild synthetic conditions. The nanoparticles with polypeptides serving as a core and coated Ag/Au bimetallic nanoshells exhibit diverse advantages, such as excellent biocompatibility, tumor targeting and low-cost. The Vap@Ag/AuNSs share excellent dispersibility, uniform size (120 nm) and a positive zeta potential (36.74 ± 4.49 mV), hence they easily accumulate in negatively charged tumor tissue. The results of thermal imaging, temperature variation assays and photothermal conversion efficiency (41.6%) indicated that Vap@Ag/AuNSs have excellent photothermal conversion capability. Based on their photothermal response, as well as biocompatibility determined by MTT assay, the prominent anti-tumor effects of Vap@Ag/AuNSs have been verified by fluorescein diacetate staining. Therefore, Vap@Ag/AuNSs are novel and promising candidates for photothermal tumor therapy.

Copper Template Design for the Synthesis of Bimetallic Copper–Rhodium Nanoshells through Galvanic Replacement

AbstractGalvanic replacement reactions are widely used in the synthesis of bimetallic nanoshells. Essential to these syntheses is the design of template materials with electrochemical potentials that are low enough to facilitate the replacement of a wide variety of metals. While Cu is an attractive template from this standpoint, it has only rarely been used due to its propensity for oxidation and the associated difficulties in achieving chemically stable colloids. Here, a synthetic scheme is demonstrated for the design of supported Cu templates and their subsequent replacement with Rh where the detrimental influences of oxidation are not only mitigated but used to place shape and compositional controls on the reaction product. It is shown that the CuRh nanoshells can be produced that are shaped as substrate‐truncated nanocubes or cuboctahedrons depending upon the degree of exposure that the Cu templates have to dissolved oxygen. Moreover, it is demonstrated that the intentional surface oxidation of the Cu template followed by Cu2O removal results in galvanic replacement reactions yielding porous nanoshells with far greater Rh replacement. The study forwards the design of Cu templates for galvanic replacement reactions and presents opportunities for their use in other template‐mediated syntheses.

Enlarge the biologic coating-induced absorbance enhancement of Au-Ag bimetallic nanoshells by tuning the metal composition

Surface plasmon resonance (SPR) absorption properties of biologic layer-coated Au-Ag core-shell nanoparticle have been studied theoretically. By comparing with pure Au and Ag nanoparticles, the absorption peak intensity of Au-Ag bimetallic nanoparticle is more dependent on the dielectric coating, and the longer wavelength peak corresponding to the Au-Ag interface is more sensitive to the coating thickness. As the Au-Ag composition ratio is increased, the dielectric coating-dependent peak intensity change is always non-monotonous, and the critical Au-Ag composition ratio corresponding to the greatest peak intensity increase could be further tuned by changing the dielectric constant of the coated dielectric layer. The physical mechanism of the non-monotonous sensitivity change has been attributed to the Au-Ag composition ratio-dependent separation and overlap of the two SPR peaks from Au-Ag interface and outer Ag surface. These results indicate that the plasmonic absorption intensity of Au-Ag core-shell nanoparticle could be used in refractive index sensing and biologic detection.

Surface-Enhanced Raman Scattering in Tunable Bimetallic Core-Shell

In this paper, optical properties of multilayer spherical core-shell nanoparticles based on quasi-static approach and plasmon hybridization theory are investigated. Calculations show that light absorption spectrum of bimetallic multilayer core-shell has three intense plasmon resonance peaks, which are more suitable for multiplex biosensing based on surface-enhanced Raman scattering (SERS) and localized surface plasmon resonance (LSPR). The plasmon resonance peaks in bimetal nanshells are optimized by tuning the geometrical parameters. In addition, the optimal geometry is discussed to obtain the Raman enhancement factor in bimetallic multilayer nanoshell. SERS enhancement factor is calculated with consideration of dampings due to both the electron scattering and the radiation at the boundary and modified Drude model in dielectric function of bimetallic nanoshell. It is shown that bimetallic nanoshell with the small size exhibits strong SERS enhancement factor (~6.63 × 105) with additional collision dampings and ~2.9 × 109 with modified Drude model which are suitable for biosensing applications. In addition, any variation in blood concentration and oxygen level can be detected by this bimetallic core-shell nanoparticle with sensitivity of Δλ/Δn = 264.91 nm/RIU.

Tunability of Multipolar Plasmon Resonances and Fano Resonances in Bimetallic Nanoshells

We study the multipolar surface plasmon modes and its link to Fano resonances in bimetallic nanoparticles. General expressions for the multipolar surface plasmon frequencies and damping rates are analytically derived by long-wave approximation. The results are in agreement with that from plasmon hybridization model for nanoshell system. Numerical results show that the surface plasmon resonances and damping rates for Au/Ag and Ag/Au nanoshells exhibit quite different behavior with the increase of shell thickness. In addition, both the near-field diagram and the far-field quantity are theoretically investigated. Fano resonances of scattering efficiency by Ag/Au core-shell nanoparticles occur due to the dipole-dipole coupling. The asymmetry of Fano profiles can be tuned by adjusting the size ratio of the core and the shell. Our results may found some potential applications in optical devices and biomedicine.

A Hybrid Plasmonic Bimetallic Nanoshell-Microsphere Sensor for Cancer Market Protein Detection

In this paper, the detection of a thyroid cancer market (Thyroglobulin, Tg) protein has demonstrated by using a hybrid plasmonic bimetallic nanoshell-microsphere sensor based on the reactive sensing principal (RSP). Tunable optical properties and plasmon resonances at three frequencies made a bimetallic nanoshell more special for sensing purposes. The rough surface of the bimetallic nanoshell affixed to the microsphere surface locally enhanced the electric field within the microcavity without significantly degrading a Q-factor (~ 7.59 × 105), at near infrared wavelength. The rough surface of the bimetallic nanoshell effectively enhanced a wavelength shift of the hybrid microcavity by the factor of ~300. At lower energy mode, the electric field enhancement of the hybrid plasmonic microsphere resonator increases by ~863% at the surface of the bump in comparison with a smooth nanoshell. This enhancement occurs in rough bimetallic nanoshell as localized surface Plasmon resonance (LSPR), which increases the Raman signal through the surface Raman scattering (SERS) effect in hybrid microcavity. Calculated results demonstrate that the hybrid plasmonic microsphere resonator can generate very strong SERS enhancement factor at a visible wavelength (~1.5 × 107).

The Effect of Bumpy Structure on Optical Properties of Bimetallic Nanoshells

In this paper, a sensitive bumpy bimetallic nanoshell for detection of thyroid cancer market (Thyroglobulin, Tg) and bovine serum albumin (BSA) proteins is reported. The physical origin of plasmonic properties of bimetal nanoshells is described by plasmon hybridization theory which indicates three intense and clearly separated plasmon modes. The electric field intensity enhancement of the bumpy bimetal nanoshell increases by ~559 %, at the surface of the bump in comparison with a smooth shell. The presence of bumpy structure on the nanoshell surface provides a high enhancement of the resulting Raman signal through an electromagnetic field of the order of 107 which leads to an increase in sensitivity detection of Tg and BSA proteins. In addition, a refractive index (RI) sensitivity of 332.54 nm/RIU is achieved for this bumpy bimetallic nanoshell.

Copper-gold nanoparticles: Fabrication, characteristic and application as drug carriers

In this investigation, the fabrication of porous core/shell nanostructures consisting of copper (core) and copper-gold nanoalloy (shell) for medical applications is presented. As a core triangular-shaped copper nanoparticles were used. The porous bimetallic nanoshell was prepared via galvanic reaction in the presence of oil-in water emulsion. It was proved that porous nanoalloy layer can be prepared at pH 7 and in the presence 0.1% and 0.5% oil-in water emulsion. The porous structure fabrication was mainly determined by volume fraction of hexadecane to acetone in the oil-in water emulsion and Zeta-potential of emulsion droplets (pH of emulsion). The influence of emulsion droplets size before galvanic reaction on porous structure preparation was negligible. It was found that doxorubicin could be easily introduced and released from porous core/shell nanostructures, due to spontaneous adsorption on the copper-gold nanoporous surface. The in vitro test showed that cytotoxic effect was more prominent once the doxorubicin was adsorbed on the porous copper-gold nanocarriers. It was demonstrated, that doxorubicin-loaded copper-gold nanostructures caused inhibition cell proliferation and viability of cancer cells, in a concentration-dependent manner. The results indicates that presented coper-gold nanocarrier have potential to be used in targeted cancer therapy, due to its porous structure and cytotoxic effect in cancer cells.

Bimetallic Nanoshells as Platforms for Metallo‐ and Biometallo‐Catalytic Applications

AbstractThe use of gold, silver, platinum and palladium for preparation of bimetallic nanoshells (AgAu, AgPt, and AgPdNSs, respectively) and their use for metallo‐ and bio‐metallo catalytic applications have been described. Bimetallic nanoshells (metallo‐catalysts) were employed for silane oxidation to silanols and hydrogen (H2) production. Fast and efficient oxidation of several silanes was observed after only 1 h at room temperature, by employing AgPd NSs as catalyst, acetone as solvent, and water as oxidant. Interestingly, bio‐metallo‐catalysts (NSs‐CALB) prepared from lipase attachment to the bimetallic nanoshells, displayed promising bi‐catalytic activities (enzymatic: transesterification; metallic: silane oxidation).

Self-assembled Monolayer Mediated Surface Environment Modification of Poly(vinylpyrrolidone)-Coated Hollow Au-Ag Nanoshells for Enhanced Loading of Hydrophobic Drug and Efficient Multimodal Therapy.

Hollow Au-Ag bimetallic nanoshell possessing hydrophobic interior space and hydrophilic exterior surface was prepared and its application as a chemo-thermo-gene therapeutic agent based on its high payload of multiple drugs having different water solubility was demonstrated. The multifunctional drug delivery system is based on the hydrophobic interior created by the self-assembled monolayer (SAM) of hexanethiol onto the inner surface of the hollow metallic nanoshells whereas the outer surface was mostly coated by hydrophilic biocompatible polymer. The nanoshells having surface environment modified by hexanethiol SAMs provided high capacity both for hydrophilic DNAzyme (Dz) to induce gene silencing and for hydrophobic SN38 (7-ethyl-10-hydroxycamptothecin), anticancer drug. The release of the loaded Dz and SN38 was independently triggered by an acidic environment and by photothermal temperature elevation upon irradiation, respectively. The chemo-thermo-gene multitherapy based on the present nanoshells having modified surface environment showed high efficacy in quantitative cell-based assays using Huh7 human liver cell containing hepatitis C viral NS3 gene replicon RNA.

Highly Asymmetric, Interfaced Dimers Made of Au Nanoparticles and Bimetallic Nanoshells: Synthesis and Photo‐Enhanced Catalysis

Synthesis of a class of exotic interfaced dimers with high asymmetries in terms of composition, morphology, structure (solid versus hollow), and dimension of the individual nanoscale components in the dimers is successfully accomplished. Typical examples include the interfaced dimers made of solid Au nanoparticles and hollow bimetallic nanoshells with different compositions, such as Au/Ag, Pt/Ag, and Pd/Ag. The success of the synthesis relies on the combination of asymmetric overgrowth of Ag nanodomains on the partially passivated Au nanoparticles and a following galvanic replacement reaction between the Ag nanodomains and appropriate noble metal precursors. The entire synthesis is processed on the unique superparamagnetic colloidal substrates that offer many advantages, such as time‐efficiency, scalability, and high yield. The Au nanoparticle and the bimetallic nanoshell in each interfaced dimer are in direct contact, resulting in the possible strong coupling between them as well as novel properties that cannot be observed in either the nanoparticle or the nanoshell. For example, dimers made of Au nanoparticles and Pd/Ag nanoshells exhibit enhanced catalytic performance toward Suzuki coupling reactions under illumination of visible light because the strong surface plasmon resonances in the Au nanoparticles can influence the catalytic activity of the Pd/Ag nanoshells through coupling between the nanoparticles and the nanoshells.

Excitation of Multiple Fano-Like Resonances Induced by Higher Order Plasmon modes in Three-Layered Bimetallic Nanoshell Dimer

The presence of plasmonic Fano-like resonances in the optical response of isolated and dimer metal-dielectric-metal nanostructures are investigated theoretically. The nanostructures are engineered in such a way to support multiple Fano-like resonances that are induced by the interference of bright and dark plasmon modes. It is found that the dimer resonators exhibit different types of Fano resonances for both the transverse and longitudinal polarizations unlike conventional nanodimers. Several configurations of the dimer Fano resonator are analyzed with special emphasis on the Fano spectral line shape. Breaking the symmetry of the dimer nanostructure in various directions control the asymmetric line shape and provides different kinds of unique Fano resonances. In certain cases, the Fano resonators exhibit multiple Fano resonances that are particularly significant for plasmon line shaping and can serve as platforms for multi-wavelength sensing applications.

Bimetallic Nanoshells for Metal-Enhanced Fluorescence with Broad Band Fluorophores

In this article, we reported the near-field interactions between the Ru(bpy)(3) (2+) complexes and plasmon resonances from the bimetallic nanoshells. The metallic nanoshells were fabricated on 20 nm silica spheres as cores by depositing 10 nm monometallic or bimetallic shells. There were approx. 15 Ru(bpy)(3) (2+) complexes in the silica core. The metal shells were constituted of silver or/and gold. The bimetallic shells could be generated in homogeneous or heterogeneous geometries. The homogeneous bimetallic shells contained 10 nm silver-gold alloys. The heterogeneous bimetallic shells contained successive 5 nm gold and 5 nm silver shells, or alternatively, 5 nm silver and 5 nm gold shells. Optical properties of metal nanoshells were studied on both the ensemble spectra and single nanoparticle imaging measurements. The heterogeneous bimetallic shells were found to have a large scale of metal-enhanced emission relative to the monometallic or homogeneous bimetallic shells. It is because the heterogeneous bimetallic shells may display split dual plasmon resonances which can interact with the excitation and emission bands of the Ru(bpy)(3) (2+) complexes in the silica cores leading to more efficient near-field interactions. The prediction can be demonstrated by the lifetimes. Therefore, it is suggested that both the compositions and geometries of the metal shells can influence the interactions with the fluorophores in the cores. This observation also offers us an opportunity for developing plasmon-based fluorescence metal nanoparticles as novel nanoparticle imaging agents which have high performances in fluorescence cell or tissue imaging.

Optimization of Three-Layered Au–Ag Bimetallic Nanoshells for Triple-Bands Surface Plasmon Resonance

Plasmonic light absorption properties of three-layered Au–Ag bimetallic nanoshells are investigated using the quasi-static electricity and plasmon hybridization theory. Comparing with Au-dielectric-Au and Ag-dielectric-Au multilayer nanoshells, Au-dielectric-Ag multilayer nanoshells are demonstrated more suitable for triple-bands surface plasmon resonance (SPR). Calculation results indicated that the triple plasmon resonance in Au-dielectric-Ag multilayer nanoshells could be optimized by choosing appropriate geometrical dimensions of the inner gold sphere and outer silver shell. The corresponding physical mechanism has also been illustrated by analyzing the surface charge distribution and intercoupling of the polarization fields from different metal–dielectric interfaces. This triple-bands SPR in the bimetallic multilayer nanostructure provides potential for multiplex biosensing based on SPR absorption, surface enhanced fluorescence, and surface enhanced Raman scattering (SERS).