Au Nanocages Research Articles

High Catalytic Performance of Silver‐Doped Gold Nanocages for Methanol Electrooxidation

AbstractHollow or porous noble metal nanocrystals with large specific electrochemical surface area and stability hold stimulating technological applications in fuel cell catalysis. Here, a simple galvanic replacement reaction synthesis of Ag‐doped Au nanocages with a tunable Ag/Au atomic ratio is developed. Without surface ligands being used in the synthesis, the obtained AuAg nanocages with hollow cavity and opened nanoporous shell possess clean surface and enhanced electrocatalytic activity. In the electrocatalysis of the methanol oxidation reaction (MOR), the obtained AuAg nanocages possess high electrocatalysis properties and show morphology and composition‐dependent electrocatalytic property. The optimized AuAg cubic nanocages that have 5% Ag exhibit excellent electrocatalytic activity for MOR, and this is attributed to the unique geometric structure and the well‐controlled Ag content. The hollow and nanoporous structure can effectively promote the mass transfer and atomic utilization during the catalytic process for MOR. Density functional theory calculations indicate that introducing of a small amount of Ag facilitates methanol adsorption to the surface of catalysts and promotes the break of the OH bond during the MOR process, thus accordingly enhances the catalytic activity.

Bimetallic Au–Ag nanocages extended TPP conjugate structure for self-enhancing therapy of tumors

Bimetallic Au–Ag nanocages extended TPP conjugate structure for self-enhancing therapy of tumors

Improve the Hole Size–Dependent Refractive Index Sensitivity of Au–Ag Nanocages by Tuning the Alloy Composition

In this study, Au–Ag nanoboxes are converted into Au–Ag alloy nanocages by increasing the hole size. The extinction spectrum and the refractive index sensing characteristics of Au–Ag alloy nanocages with different geometric parameters are studied by using discrete dipole approximation method (DDA). With the increase of Au composition, the peak of local surface plasmon resonance (LSPR) shows approximately linear redshift and the sensitivity factor shows approximately linear decrease. The refractive index sensitivity can be effectively controlled by the Au–Ag ratio at large hole size because the hole and cavity surfaces distribute more environmental dielectric components. Therefore, increasing the hole size and decreasing the Au–Ag ratio can improve the refractive index sensitivity. These calculation results have also been verified experimentally. In order to illustrate the influence of alloy composition on the LSPR characteristics and the refractive index sensitivity, the local electric field distributions under different geometric parameters are plotted. We find that the electric field direction on the hole and cavity surfaces is controlled by the Au–Ag ratio and environmental dielectric constant. Moreover, the field vectors on the hole and cavity surfaces are formed by the superposition of the incident field, the electric field generated by the oscillating electrons on the outer surface, and the polarized field in the environmental dielectric constant.

Core-shell nanomaterials engineered to reverse cancer multidrug resistance by immunotherapy and promote photo-responsive chemotherapy

Cancer immunotherapy has already become a critical hallmark in clinical cancer therapy, especially through tumor associated macrophages (TAMs) polarization. Because multidrug resistance (MDR) hinders the efficiency of chemotherapy, immunotherapy was also incorporated in regulation of MDR. Herein, Au nanocages encapsulated with doxorubicin (Dox) by the phase change material were fabricated with a layer consisting of calcium and ferrous carbonates (FeCaC), and achieved DPAu@FeCaC NPs could reprogram TAMs from immunosuppressive M2 to immunostimulatory M1 based on the intrinsic property of FeCaC shell. Nitric oxide (NO) could be produced by M1 TAMs to inhibit P-glycoprotein (P-gp) expression. Then, FeCaC shell of DPAu@FeCaC NPs could be degraded at the acidic condition and NIR laser irradiation would further facilitate to thermally release Dox. A series of in vitro and in vivo assessments confirmed DPAu@FeCaC NPs could realize the immunotherapy-mediated highly efficient chemotherapy of MDR cancer.

Single-chain antibody-decorated Au nanocages@liposomal layer nanoprobes for targeted SERS imaging and remote-controlled photothermal therapy of melanoma cancer cells

The development of theranostic platforms combining surface-enhanced Raman spectroscopy (SERS) imaging with NIR-stimulated photothermal therapy (PTT) is of utmost importance for the precise diagnosis and selective treatment of cancers, especially in superficial solid tumors. For this purpose, a versatile theranostic nanoprobe of liposomal layer-coated Au nanocages (AuNCs) was decorated with an anti-MUC18 single-chain antibody (scFv). 4-mercapto benzoic acid (p-MBA)-labeled AuNCs (p-AuNCs) were coated by a liposomal layer (p-AuNCs@lip), followed by conjugating anti-MUC18 scFv via post-insertion method to form immuno-liposomal layer-coated AuNCs (p-AuNCs@scFv-lip). Physicochemical characterizations of the p-AuNCs@scFv-lip were investigated by transmission electron microscopy (TEM) and UV–vis and Raman spectroscopy. Furthermore, the targeting ability and theranostic efficiency of the nanoprobe were evaluated for specific diagnosis and treatment of cancerous melanoma cells by flow cytometry, SERS mapping, and live/dead assay. The formation of lipid layer on p-AuNCs surface was confirmed by TEM imaging. After decorating the liposomal layer with scFv, a relevant red shift was observed in the UV–vis spectrum. Moreover, p-AuNCs@lip presented characteristic peaks in the Raman spectrum, which exhibited only a minor change after scFv conjugation (p-AuNCs@scFv-lip). Interestingly, the cellular uptake of AuNCs@scFv-lip by A375 cell line (MUC18+) showed a 24-fold enhancement compared with SKBR3 cells (MUC18−). AuNCs@scFv-lip specifically identified A375 cells from SKBR cells via SERS mapping and effectively killed A375 cells through the PTT mechanism. Taken together, this theranostic platform can provide a promising tool for both in situ diagnosis and remote-controlled thermal ablation of cancer cells.

A multifunctional dual-shell magnetic nanocomposite with near-infrared light response for synergistic chemo-thermal tumor therapy.

The synergistic tumor therapy in single nanoplatform has always been the goal for high efficacy tumor treatment while still remains great challenge. This paper reports a versatile nanotheranostic platform enlisting magnetic iron oxide nanoparticles, polydopamine (PDA), gold nanocages (Au nanocage) and metal organic framework (MOF, MIL101-NH2 ) in order to achieve synergistic chemothermal tumor therapy both in vitro and in vivo. The prepared magnetic photothermal nanoparticles (MPNPs) exhibit high drug loading capacity (31.34 mg/g), superior photo-thermal capacity (11.5°C enhancement in 180 s), low bio-toxicity, good magnetic resonance with a low dosage of 22 μg/g, as well as high antitumor efficacy in vivo. Such a novel and multifunctional nanoplatform is expected to find promising applications in target tumor synergistic therapy.

Highly Stable Iron Carbonyl Complex Delivery Nanosystem for Improving Cancer Therapy.

Metal carbonyl complexes can readily liberate carbon monoxide (CO) in response to activation stimulus. However, applicability of metal carbonyl complexes is limited because they are unstable under natural ambient conditions of moisture and oxygen. Reported here is the rational design of an iron carbonyl complex delivery nanosystem for the improvement of cancer therapy. We demonstrated that iron pentacarbonyl (Fe(CO)5) can be encapsulated into the cavity of a Au nanocage under an oxygen-free atmosphere and then controllably form iron oxide on the surface of the Au nanocage under aerobic conditions. The formation of iron oxide efficiently avoids the leakage and oxidation of the caged Fe(CO)5. The resulting nanomaterial exhibits excellent safety, biocompatibility, and stability, which can be specifically activated under near-infrared (NIR) irradiation within the tumor environment to generate CO and iron. The released CO causes damage to mitochondria and subsequent initiation of autophagy. More importantly, during autophagy, the nanomaterial that contains iron and iron oxide can accumulate into the autolysosome and result in its destruction. The produced CO and iron show excellent synergistic effects in cancer cells.

Dynamic Detection of Endogenous Hydroxyl Radicals at Single-Cell Level with Individual Ag-Au Nanocages.

Hydroxyl radicals (•OH) are a type of short-lived radical which is the most aggressive reactive oxygen species due to its high reactivity to biomolecules. Dynamic measurement of •OH level in living cells is critical for understanding cell physiology and pathology. In this manuscript, we prepare individual Ag-Au@PEG/RGD nanocages for in situ determination of endogenous •OH at single-cell level, whose spectral shift rate correlate to the •OH concentration. The high-selective response to •OH relies on the specific oxidization of the conjugated PEG/RGD outside and the silver etching inside the nanocages that resulted in a significant LSPR signal and scattered color changes. The spectral red-shift rate of LSPR has a linear relationship with the logarithm of •OH concentration in range of 100 pM to 1 μM, suitable for the measurement of endogenous •OH. Thus, the individual nanocages were successfully used to monitor the dynamic intracellular •OH level of single tumor cells under oxidative stress. This strategy has great potential in promoting •OH mediated cell homeostasis and injury research.

Synthesis of octapod Cu–Au bimetallic nanocrystal with concave structure through galvanic replacement reaction

We synthesized octapod Cu–Au bimetallic alloy with a concave structure by employing a replacement reaction between AuPPh3Cl and Cu nanocubes. Using Cu nanocube as sacrificial templates, we have successfully generated high-active sites on alloy nanocrystals by carefully tuning the replacement reaction and growth. The key is to afford the proper concentration of AuPPh3Cl-TOP to the reaction solution. When the Au precursor with high concentration is injected into the galvanic replacement reaction, growth dominates the process, hollowed octapod Cu–Au alloy was obtained. In contrast, when the concentration of the Au precursor is low, the replacement reaction can only take place at the nanocrystals, leading to generated Cu–Au nanocages. This work provides an effective strategy for the preparation of hollow bimetallic nanocrystals with high-active sites.

Orientation Effects on Plasmonic Heating of Near-Infrared Colloidal Gold Nanostructures

Photothermal therapy assisted by plasmonic nanostructure relies on the absorption of light energy by the metallic nanoparticle. The manifestation of a rational use of plasmonic-assisted superficial laser thermal therapy procedures requires the analyses of the thermoplasmonic behavior of colloidal nanostructures in random orientation. A quantitative analysis of orientation effect on optically heating metallic nanostructures still unrevealed. Here, we evaluate the thermal properties of metallic nanoparticles (SiO2/Au core-shell particles, Au nanotriangles, Au nanorods, and Au nanocages) irradiated by polarized light. We perform 3D full-wave field analysis to compare absorption properties and temperature rise of these nanoparticles as a function of the nanostructure orientation with respect to applied field polarization. The analysis shows a major variation in joule number of asymmetrical nanostructures (up to 50%) due to orientation effects, which may limit its performance on colloidal photothermal applications. In contrast, the high degree of rotational symmetry of core-shell nanoparticles and nanocages provide greater potential in thermal-assisted phototherapy applications, as their absorption is largely independent (less than 2%) of their orientation in colloid. Our computational results establish new insights for the use of gold nanocages, as a high performance plasmonic structure for thermal applications with colloidal samples.

Nanomechanical Recognition and Discrimination of Volatile Molecules by Au Nanocages Deposited on Membrane-Type Surface Stress Sensors

Here we show that gold nanocages (AuNCs) can be used as receptor materials for nanomechanical Membrane-type Surface stress Sensor (MSS). The fabricated AuNCs-coated MSS (AuNCs_MSS) was employed suc...

Colorimetric determination and recycling of Hg2+ based on etching-induced morphology transformation from hollow AuAg nanocages to nanoboxes

Herein, we propose a selective and simple colorimetric sensing approach for the determination of Hg2+ ions based on bimetallic AuAg nanocages with partial hollow cavity and several pinholes on the wall, wherein the residual Ag atoms existing inside this AuAg nanocages can be directly etched by Hg2+ and the generated Hg depositing on inner surface of nanocages induces the morphology transformation from hollow AuAg nanocages to closed nanoboxes which consists of an AuAg shell and Hg core. This morphology transformation of “nanocage-to-nanobox” not only extends the detection range of Hg2+, but also cleans the Hg2+ in solutions by enriching it into the nanoboxes. With increasing Hg2+ concentrations, the blue shift of localized surface plasmon resonance (LSPR) peak position with multicolor changing from light-blue to light-brown is great for colorimetric determination of Hg2+. Under optimal conditions, the colorimetric sensing shows a linear response to Hg2+ ranging from 0.03 to 35 μM with a detection limit of 10 nM. Besides, interference study and real samples detection applying lake and tap water demonstrated that Hg2+ can be specifically and practically detected by utilizing this method.

Ambient Ammonia Electrosynthesis from Nitrogen and Water by Incorporating Palladium in Bimetallic Gold–Silver Nanocages

Electrosynthesis of ammonia using nitrogen and water provides a potential alternative to the thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way when electricity is generated from renewable sources. To enable the widespread commercialization of this technology, an electrocatalyst to convert nitrogen (N2) to ammonia (NH3) with high selectivity and activity must be developed. Here, we report our findings in the investigation into the role of incorporating palladium (Pd) in bimetallic Au-Ag nanocages on the electrocatalytic activity of the nitrogen reduction reaction (NRR) under ambient conditions. The localized surface plasmon resonance (LSPR) peak position of the resulting trimetallic nanoparticles is tuned with Pd concentration, achieving the highest electrocatalytic NRR activity (NH3 yield rate = 5.80 μg cm−2 h−1, Faradaic efficiency = 48.94%) using Au-Ag-Pd-850 nanoparticles at −0.3 V vs RHE. This activity corresponds to the production energy efficiency of 28.9% with an electrical energy input of 19.1 MWh / ton NH3. The enhanced NRR activity is attributed mainly to the formation of a highly porous Pd layer with remarkably high surface area active for NRR. In addition, operando surface-enhanced Raman spectroscopy (SERS) is used to probe the mechanism of NRR on the trimetallic nanostructures and to identify the intermediate species at the electrode-electrolyte interface.

A AuNP-capped cage fluorescent biosensor based on controlled-release and cyclic enzymatic amplification for ultrasensitive detection of ATP.

Gold nanodevices have attracted extensive interest in the detection of specific targets within cells. However, constructing gold sensing devices that can be activated by the simulation of remote applications remains a huge challenge. Here, we report a Au nanoparticle (AuNP)-capped cage fluorescent biosensor based on controlled-release and Exonuclease III (Exo III) assisted cyclic enzymatic amplification that can be activated by adenosine triphosphate (ATP). In the system, AuNPs were used as the building blocks to cap the pores of Au nanocages (AuNCs) loaded with Rhodamine B (RhB) molecules through the hybridization of DNA. The RhB fluorescent molecules were finally released with the help of Exo III in the presence of ATP for detection purposes. Ultimately, the biosensor leads to a wide linear ATP detection range from 1.0 × 10-9 to 1.0 × 10-7 M with a limit of detection (LOD) down to 0.88 nM. In addition, it also has good selectivity for ATP to distinguish between ATP and ATP analogues such as cytidine triphosphate (CTP), guanosine triphosphate (GTP), and uridine triphosphate (UTP). Therefore, as a convenient and sensitive biosensor, it is expected to be widely used in the biomedical field.

Ultrasensitive detection of NDM-1 resistant bacteria based on signal amplification with sandwich-type LNA electrochemical biochips

New Delhi metallo-β-lactamase-1 (NDM-1) is an identified metallo-β-lactamase that confers resistance to carbapenems and all other β-lactam antibiotics, with the exception of aztreonam. Herein, a novel electrochemical biochip was constructed based on a zinc oxide (ZnO) and reduced graphene oxide (rGO) complex (ZnO@rGO) supported by Au nanocages (Au NCs) for signal amplification for ultrasensitive detection of NDM-1 in early clinical diagnosis. A Au NC and a sulfhydryl (SH) modified locked nucleic acid-1 (Au NC@LNA-1) probe was synthesized with stable Au-S bonds to on the biochip surface. In hybridization solution, Au NCs and LNA-2 probes modified with SH groups formed stable Au NC@LNA-2 complexes. Au NC@LNA-1 and Au NC@LNA-2 were linked with the NDM-1 to form a Au NC@LNA-1/NDM-1/Au NC@LNA-2 “sandwich-like” complex through complementary base pairing, and this complex can bind additional copies of the target sequence to further amplify it’s the detection signal. Under optimized conditions, the system showed a linear range from 1 pg L−1 to 100 μg L−1, and the detection limit was 0.042 pg L−1. The time of biochip probe-modification was 45 min, incubation was 30 min, and electrochemical scanning detection was 1 min. In addition, the results indicate that the specific LNA probe identified single base mismatches and exhibited affinity for the target DNA molecule, resulting in the direct detection of the NDM-1 in complex clinical bacteria samples without PCR amplification. In conclusion, this novel electrochemical biochip method allows for the rapid, specific, and sensitive detection of the NDM-1, indicating its potential application in disease diagnostics.

Direct Visualization and Semi‐Quantitative Analysis of Payload Loading in the Case of Gold Nanocages

AbstractUpon incubation with Au nanocages, pyrrole (Py) molecules can enter the cavities by diffusing through the porous walls and then be polymerized to generate a polypyrrole (PPy) coating on the inner surface. The thicknesses of the PPy coating can serve as a direct indicator for the amount of Py molecules that diffuse into the cavity. Py molecules are able to diffuse into the cavities throughout the polymerization process, while a prolonged incubation time increases the amount of Py accumulated on both inner and outer surfaces of the nanocages. Furthermore, it is demonstrated that the dimensions of the cavity and the size of the pores in the wall are not critical parameters in determining the loading efficiency, as they do not affect the thickness of the PPy coating on the inner surface. These findings offer direct evidence to support the applications of Au nanocages as carriers for drug delivery and controlled release.

Porous SiO2@Ni@C and Au nanocages as surface-enhanced Raman spectroscopy platform with use of DNA structure switching for sensitive detection of uracil DNA glycolase

In this work, SiO2@Ni@C nanosphere and Au nanocages (AuNCs) platform with use of target-induced DNA structure switching strategy was utilized to construct a surface-enhanced Raman spectroscopy (SERS) biosensor to analyze trace amounts of uracil DNA glycolase (UDG). In details, we utilized NH2-functioned SiO2@Ni@C nanosphere to immobilize abundant hairpin DNA (R) due to the large surface area and abundant adsorption sites. In the presence of the target UDG, they could specifically recognize and hydrolyze the uracil bases, generating apyrimidinic (AP) sites to induce DNA structure switching process, which could reconfigure hairpin DNA (R) to hairpin DNA (R′). Then the generated R′ could capture complementary DNA S1 bonded to the toluidine blue-Au nanocages (AuNCs-TB). With the increasing amount of UDG, more SiO2@Ni@C-NH2-R′ would be obtained and coupled with TB-AuNCs-S1 to produce a stronger Raman signal. Based on this simple protocol, the SERS assay could achieve sensitive UDG detection in a concentration range from 5 × 10−5 U mL−1 to 1 U mL−1 with a detection limit down to 3.2 × 10−5 U mL−1. Therefore, this SERS-based assay gives a new strategy for SERS detection which may have potential application for ultrasensitive detection of other protein biomarkers.

Au nanocages saturable absorber for 3-µm mid-infrared pulsed fiber laser with a wide wavelength tuning range.

Au nanocages (Au-NCs) have attracted wide attention as low-dimensional materials with broadband absorption, ultrafast optical response, large third-order optical nonlinearity coefficient, and high photothermal stability and thermal tolerance. By employing Au-NCs as saturable absorbers, we demonstrate a widely tunable passively Q-switched erbium-doped fluoride fiber laser at the wavelength of 2.8 µm. When operates at 2778.0 nm, this laser delivers stable Q-switched pulses with a maximum average power of 584.6 mW at a pulse repetition rate of 80.6 kHz. The minimum pulse duration attained was 1.16 µs corresponding with the single pulse energy of 7.25 µJ. Our results present onefold increase in pulse energy over previously published values achieved from Au nanoparticles based 3-µm passively Q-switched fiber lasers. By introducing a plane ruled grating, a tuning rage of 57.0 nm from 2753.0 to 2810.0 nm is achieved, while maintaining stable Q-switched operation. To our knowledge, this is the first time to demonstrate that Au-NCs can realize mid-infrared pulsed laser. Our research results show that Au-NCs are promising broadband nonlinear modulators for mid-infrared pulse generation.

CeO2 -Encapsulated Hollow Ag-Au Nanocage Hybrid Nanostructures as High-Performance Catalysts for Cascade Reactions.

Inspired by bio-enzymes, multistep cascade reactions are highly attractive in catalysis. Despite extensive research in recent years, it remains a challenge to promote the stability and activity of catalysts. Here, well-defined core-shell structured Ag-Au nanocage@CeO2 (Ag-Au NC@CeO2 ) are designed by a simple and facile self-assembly method. The results indicate that the Ag-Au NC@CeO2 has glucose oxidase-like activity and intrinsic peroxidase-like activity at the same time. As expected, Ag-Au NC@CeO2 hybrid nanomaterials exhibit cascade reactions activity. Moreover, the hybrid materials are promising to detect glucose without bio-enzymes. This research has potential applications in biomedicine and biomimetic catalysis.

SERS immunoassay for detection of procalcitonion in serum from patients with premature rupture of membranes using hollow Au nanocages and Ag nanowires-decorated filter paper

Procalcitonion (PCT) have been proved to be disease-related markers of premature rupture of membranes (PROM) in serum of patients. Therefore, the profiling technology of rapid and sensitive is crucial for detecting the level of PCT in human serum, which is of great significance for early diagnosis and treatment of PROM. In this work, the surface-enhanced Raman scattering (SERS) detection platform combined with double antibody sandwich method was used to quantitatively detect PCT in serum of patients with PROM. A highly sensitive, uniform, and reliable SERS substrate was fabricated by assembling Ag nanowires (AgNWs) on the hydrophobic filter paper treated with alkyl ketene dimer (AKD). Then hollow Au nanocages (HAuNCs) with SERS activity were synthesized facilely. The SERS immunoassay system consists of SERS tags and capturing substrate. HAuNCs labled anti-PCT (labeling) were used as SERS tags. Filter paper modified with AgNWs and anti-PCT (coating) was used as capturing substrate. When the SERS immunoassay system were used to directly detect PCT antigen, Raman intensity at different PCT antigen concentrations (1 pg/mL-1 μg/mL) was linearly related to the logarithm of PCT antigen concentration. By establishing a calibration curve within a certain range, it can be concluded that the detection limits of PBS and human serum were as low as 2.86 pg/mL and 3.74 pg/mL respectively. Serum samples from PROM patients were detected by SERS, and the results were consistent with those of the enzyme-linked immunosorbent assay (ELISA). Furthermore, The high reproducibility and homogeneity of SERS immunoassay were confirmed. Above results demonstrated the feasibility and great potential for developing this new SERS immunosensor into a clinical tool for sensitive analysis of biomarkers in human serum.