Ultrasmall Au Nanoparticles Research Articles

Gapped and Rotated Grain Boundary Revealed in Ultra-Small Au Nanoparticles for Enhancing Electrochemical CO2 Reduction.

Although gapped grain boundaries have often been observed in bulk and nanosized materials, and their crucial roles in some physical and chemical processes have been confirmed, their acquisition at ultrasmall nanoscale presents a significant challenge. To date, they had not been reported in metal nanoparticles smaller than 2 nm owing to the difficulty in characterization and the high instability of grain boundary (GB) atoms. Herein, we have successfully developed a synthesis method for producing a novel chiral nanocluster Au78(TBBT)40 (TBBT=4-tert-butylphenylthiolate) with a 26-atom gapped and rotated GB. This nanocluster was precisely characterized using single-crystal X-ray crystallography and mass spectrometry. Additionally, an offset atomic defect linked to the peripheral Au(TBBT)2 staple was found in the structure. Comparing it to similarly face-centered cubic-structured Au36(TBBT)24, Au44(TBBT)28, Au52(TBBT)32, Au92(TBBT)44, and ~5 nm nanocrystals, the bridging Au78(TBBT)40 nanocluster exhibited higher catalytic activity in the electroreduction of CO2 to CO. This enhanced activity was explained through density functional theory calculations and X-ray photoelectron spectroscopy analysis, which highlight the impact of GBs and point defects on the surface properties of metal nanoclusters in balancing intermediate adsorption and product desorption.

Expanding the Toolbox of Oxidants: Controllable Etching of Ultrasmall Au Nanoparticles toward Tailorable NIR-II Luminescence and Ligand-Mediated Biodistribution and Clearance.

Oxidant-driven and controllable etching of small-sized nanoparticles (NPs, d < 3 nm) and tailorable modulation of their optical properties are challenging due to the high reactivity and complicated surface chemistry. Herein, we present a facile strategy for highly controllable oxidative etching of ultrasmall AuNPs and tailorable modulation of luminescence. The proper choice of a moderate oxidant, ClO-, could not only selectively etch the Au(I)-thiolate motifs from the nanoparticle surface at the subnanometer scale but also retained a stable metallic core structure without aggregation, which impressively prompted the wide-range luminescent switching from the visible to second near-infrared (NIR-II) region. The resultant oxidized AuNPs displayed highly luminescent NIR-II emission with a quantum yield of 3.0%, excellent monodispersed stability, ideal biocompatibility, and tunable shielding effects against protein adsorption. With those outstanding features, oxidized AuNPs could be utilized as nanoprobes for long-lasting and in vivo bioimaging of associated metabolic behaviors with distinguishable organ-specific targeting capabilities and ligand-mediated kinetics in nanoparticle clearance. These findings expand the toolbox of oxidants for the controllable synthesis of NIR-II nanoprobes and open up a path for exploring diverse ligand interactions on ultrasmall AuNPs with organs or tissues that might advance their monitoring applications for a wide range of clinically important diseases.

Multifunctional nanoplatform based on tetragonal BaTiO3-Au@polydopamine for computed tomography imaging-guided photothermal synergistic and enhanced piezocatalytic cancer therapy

Non-centrosymmetric tetragonal barium titanate nanocrystals have the potential to serve as piezoelectric catalysts in cancer therapy. When exposed to ultrasound irradiation, BaTiO3 can generate reactive oxygen species with a noninvasive and deep tissue-penetrating approach. However, the application of BaTiO3 in cancer nanomedicine is limited by their biosafety, biocompatibility, and dosage efficiency. To explore the potential application of BaTiO3 in nanomedical cancer treatment, we introduced ultra-small Au nanoparticles onto the surface of BaTiO3 to enhance the piezoelectric catalytic performance. Additionally, we also coated the BaTiO3 with polydopamine to improve their biosafety and biocompatibility. This led to the preparation of a novel multifunctional BaTiO3-based nanoplatform called BTAPs. In vitro and in vivo experiments demonstrated that the incorporation of Au dopants and polydopamine coating successfully improved the piezoelectric catalysis properties and biocompatibility of BaTiO3. Compared with unmodified BaTiO3, BTAPs achieved a similar piezoelectric catalytic effect at a low dose (0.3 mg ml−1 in vitro and 10 mg kg−1 in vivo). Moreover, BTAPs also exhibited enhanced properties in computed tomography imaging and photothermal effects in vivo. Therefore, BTAPs offer valuable insights into the advantages and limitations of piezoelectric catalytic nanomedicine in cancer treatment.

Clay-based durable catalyst membranes of porous layered double hydroxide and gold nanoparticle nanocomposites for fast and continuous-flow reactions

We synthesized the hybrid catalyst of a porous layered double hydroxide (LDH) decorated with ultrasmall Au nanoparticles. The porous LDH was prepared by coprecipitation and ethanol washing, producing thin LDH nanoplatelets. Thereafter, spray drying was carried out, affording a few hundred nm of the hydrangea-like structure of the LDH with an extensive open network and a Brunauer–Emmett–Teller surface area of 386 m2/g. Its sizable open frame and active hydroxide surface enabled the uniform decoration of average 4-nm-diameter Au nanoparticles (Au/P-LDH) through one-pot chemical reduction using NaBH4 at room temperature. We applied the Au/P-LDH for the fabrication of catalyst membranes, which are potentially valuable for the continuous flow of catalytic reactions, e.g., the hydrogenation of p-nitrophenol. This study suggested that their porous structure and active Au nanoparticle catalyst allowed fast and mass catalytic functions by simple filtration without washing or catalyst recovery steps. We found no significant damage to the hybrid membrane during the reactions with a few liters; thus, we expect strong bindings of the Au nanoparticles on the surface of the porous LDH.

Rational fabrication of Ti0.69Zr0.31O2 modified Au-loaded halloysite core-shell catalyst for highly efficient reduction of 4-nitrophenol and dye pollutants

Catalytic reduction method can reductively degrade some highly toxic and harmful pollutants and transform them into useful chemical resources with low toxicity and easy biodegradability, owning the advantages of environmental friendliness, economic effectiveness and mild conditions. This study reported the rational fabrication of the HNTs-Au@Ti0.69Zr0.31O2 hollow tubular core-shell catalyst for facile reductive degradation of aqueous 4-nitrophenol and azo dye pollutants. The catalyst employed the interfacial reaction strategy for aminopropyl-functionalization of halloysite nanotubes as core, amino electrostatic adsorption and in situ redction of ultrasmall Au nanoparticles with good dispersibility, and sol-gel deposition of Ti0.69Zr0.31O2 shell. The obtained HNTs-Au@Ti0.69Zr0.31O2 catalyst manifested superior catalytic performance and atom utilization efficiency of Au active sites for reduction of 4-nitrophenol, methylene blue and methyl orange in comparison to those control samples. The integration of TiO2 and ZrO2 within Ti0.69Zr0.31O2 shell enriched the porosity of the catalyst, and generated the extraordinary interfacial chemical effect on Au NPs with improved surface electronic state. The interlayer-embedded Au nanoparticles were effectively solidified and avoided from agglomeration and loss, where the reactive electron migration rate from BH4- to target pollutants upon Au surfaces was elevated for prominent catalytic reaction rate. The unique structural characteristics and synergistic enhancement effect of catalyst components created excess catalytic active sites at the hybrid interface surrounded Au nanoparticles due to the strong metal-carrier chemical effect, and contributed to the construction of the high-performance catalytic system, which endowed the HNTs-Au@Ti0.69Zr0.31O2 catalyst with remarkable catalytic capability, reusability and structural stability. The reaction mechanism and structure-property relationship were finally proposed.

Bifunctional Cascading Nanozymes Based on Carbon Dots Promotes Photodynamic Therapy by Regulating Hypoxia and Glycolysis.

Photodynamic therapy (PDT) still faces great challenges with suitable photosensitizers, oxygen supply, and reactive oxygen species (ROS) accumulation, especially in the tumor microenvironment, feathering hypoxia, and high glucose metabolism. Herein, a carbon dots (CDs)-based bifunctional nanosystem (MnZ@Au), acting as photosensitizer and nanozyme with cascading glucose oxidase (GOx)- and catalase (CAT)-like reactivity, was developed for improving hypoxia and regulating glucose metabolism to enhance PDT. The MnZ@Au was constructed using Mn-doped CDs (Mn-CDs) as a core and zeolitic imidazolate framework-8 (ZIF-8) as a shell to form a hybrid (MnZ), followed by anchoring ultrasmall Au nanoparticles (AuNPs) onto the surface of MnZ through the ion exchange and in situ reduction methods. MnZ@Au catalyzed glucose consumption and oxygen generation by cascading GOx- and CAT-like nanozyme reactions, which was further enhanced by its own photothermal properties. In vitro and in vivo studies also confirmed that MnZ@Au greatly improved CDs penetration, promoted ROS accumulation, and enhanced PDT efficacy, leading to efficient tumor growth inhibition in the breast tumor model. Besides, MnZ@Au enabled photoacoustic (PA) imaging to provide a mapping of Mn-CDs distribution and oxygen saturation, showing the real-time catalytic process of MnZ@Au in vivo. 18F-Fluorodeoxyglucose positron emission tomography (18F-FDG PET) imaging also validated the decreased glucose uptake in tumors treated by MnZ@Au. Therefore, the integrated design provided a promising strategy to utilize and regulate the tumor microenvironment, promote penetration, enhance PDT, and finally prevent tumor deterioration.

Potentiating Tweezer Affinity to a Protein Interface with Sequence-Defined Macromolecules on Nanoparticles.

Survivin, a well-known member of the inhibitor of apoptosis protein family, is upregulated in many cancer cells, which is associated with resistance to chemotherapy. To circumvent this, inhibitors are currently being developed to interfere with the nuclear export of survivin by targeting its protein-protein interaction (PPI) with the export receptor CRM1. Here, we combine for the first time a supramolecular tweezer motif, sequence-defined macromolecular scaffolds, and ultrasmall Au nanoparticles (us-AuNPs) to tailor a high avidity inhibitor targeting the survivin-CRM1 interaction. A series of biophysical and biochemical experiments, including surface plasmon resonance measurements and their multivalent evaluation by EVILFIT, reveal that for divalent macromolecular constructs with increasing linker distance, the longest linkers show superior affinity, slower dissociation, as well as more efficient PPI inhibition. As a drawback, these macromolecular tweezer conjugates do not enter cells, a critical feature for potential applications. The problem is solved by immobilizing the tweezer conjugates onto us-AuNPs, which enables efficient transport into HeLa cells. On the nanoparticles, the tweezer valency rises from 2 to 16 and produces a 100-fold avidity increase. The hierarchical combination of different scaffolds and controlled multivalent presentation of supramolecular binders was the key to the development of highly efficient survivin-CRM1 competitors. This concept may also be useful for other PPIs.

A multifunctional nanocatalytic system based on Chemodynamic-Starvation therapies with enhanced efficacy of cancer treatment

A multi-functional nanocatalytic system based on combined therapies has attracted considerable research attention in recent years due to its potential in the treatment of cancer. Herein, ZnO2@Au@ZIF-67 nanoparticles (NPs) based on hydroxyl radical (•OH) mediated chemodynamic therapy (CDT) and glucose-exhausting starvation therapy (ST) were constructed. Specifically, in the acidic tumor microenvironment (TME), the pH responsive decomposition of the shell ZIF-67 triggered the release of the Fenton-like catalyst Co2+, after which the exposed zinc peroxide (ZnO2) reacted with H2O (H+) to generate O2 and hydrogen peroxide (H2O2). The generated O2 could alleviate hypoxia in the TEM and interact with ultra-small Au NPs originally coated on ZnO2 to catalyze intracellular glucose and to produce another source of H2O2. While the glucose consumption caused the starvation of tumor cells, the generated H2O2 from dual sources reacted with the catalyst Co2+ to generate highly toxic •OH for CDT. Systematic in vitro and in vivo experiments were carried out to evaluate this nanocatalytic system, and the results showed an enhanced efficacy of this cancer therapy.

Mussel-Inspired Surface Modification of α-Zirconium Phosphate Nanosheets for Anchoring Efficient and Reusable Ultrasmall Au Nanocatalysts

The shortage of powerful functionalities on scalable α-zirconium phosphate (ZrP) materials blocks the facile preparation of highly dispersed and immobilized metal nanocatalysts. We herein present a mild and facile mussel-inspired strategy based on polydopamine (PDA) for the surface modification of ZrP, and hence, the generation of powerful functionalities at a high density for the straightforward reduction of chloroauric acid to Au nanoparticles (AuNPs) and the immobilization of AuNPs. The resulting ternary ZrP@PDA/Au exhibited ultra-small AuNPs with a particle size of around 6.5 nm, as estimated based on TEM images. Consequently, the ZrP@PDA/Au catalyst showed significant activity in the catalytic conversion of 4-nitrophenol (4NP) to 4-aminophenol (4AP), a critical transformation reaction in turning the hazard into valuable intermediates for drug synthesis. The PDA was demonstrated to play a critical role in the fabrication of the highly efficient ZrP@PDA/Au catalyst, far outperforming the ZrP/Au counterpart. The turnover frequency (TOF) achieved by the ZrP@PDA/Au reached as high as 38.10 min−1, much higher than some reported noble metal-based catalysts. In addition, the ZrP@PDA/Au showed high stability and reusability, of which the catalytic efficiency was not significantly degraded after prolonged storage in solution.

Modulating luminescence and assembled shapes of ultrasmall Au nanoparticles towards hierarchical information encryption.

Because of their intriguing luminescence performances, ultrasmall Au nanoparticles (AuNPs) and their assemblies hold great potential in diverse applications, including information security. However, modulating luminescence and assembled shapes of ultrasmall AuNPs to achieve a high-security level of stored information is an enduring and significant challenge. Herein, we report a facile strategy using Pluronic F127 as an adaptive template for preparing Au nanoassemblies (AuNAs) with controllable structures and tunable luminescence to realize hierarchical information encryption through modulating excitation light. The template guided ultrasmall AuNP in situ growth in the inner core and assembled these ultrasmall AuNPs into intriguing necklace-like or spherical nanoarchitectures. By regulating the type of ligand and reductant, their emission was also tunable, ranging from green to the second near-infrared (NIR-II) region. The excitation-dependent emission could be shifted from red to NIR-II, and this significant shift was considerably distinct from the small range variation of conventional nanomaterials in the visible region. In virtue of tunable luminescence and controllable structures, we expanded their potential utility to hierarchical information encryption, and the true information could be decrypted in a two-step sequential manner by regulating excitation light. These findings provided a novel pathway for creating uniform nanomaterials with desired functions for potential applications in information security.

Ultrasmall Au nanoparticles modified 2D metalloporphyrinic metal-organic framework nanosheets with high peroxidase-like activity for colorimetric detection of organophosphorus pesticides

Ultrasmall Au nanoparticles (UsAuNPs) in the size range of 4.0–7.0 nm was successfully immobilized on the surface of 2D metalloporphyrinic metal–organic framework nanosheets (2D MOF). Firstly, The obtained hybrid nanomaterial, UsAuNPs/2D MOF, was fully characterized by TEM, HRTEM, element mapping images and XPS. Then, the peroxidase-like activity of UsAuNPs/2D MOF was comparatively studied with other hybrid nanozyme to explore the influence of AuNPs size on peroxidase-like activity. Further, UsAuNPs/2D MOF with outstanding peroxidase-like activity was selected to form ternary cascade enzyme reaction with acetylcholinesterase (AChE) and choline oxidase (ChOx). Based on the inhibitory effect of organophosphorus pesticides on AChE, a fast and sensitive colorimetric method was established for trichlorfon detection with the advantages of simple operation, low detection limit (1.7 μM), good linear range (1.7–42.4 μM) and high accuracy (recovery rate of 96.6–105.3%). Finally, this method was applied to visual analysis of trichlorfon concentration in tomatoes, cucumbers and eggplants.

Truly-Biocompatible Gold Catalysis Enables Vivo-Orthogonal Intra-CNS Release of Anxiolytics.

Being recognized as the best-tolerated of all metals, the catalytic potential of gold (Au) has thus far been hindered by the ubiquitous presence of thiols in organisms. Herein we report the development of a truly-catalytic Au-polymer composite by assembling ultrasmall Au-nanoparticles at the protein-repelling outer layer of a co-polymer scaffold via electrostatic loading. Illustrating the in vivo-compatibility of the novel catalysts, we show their capacity to uncage the anxiolytic agent fluoxetine at the central nervous system (CNS) of developing zebrafish, influencing their swim pattern. This bioorthogonal strategy has enabled -for the first time- modification of cognitive activity by releasing a neuroactive agent directly in the brain of an animal.

Size-Controlled Au Nanoparticles Incorporating Mesoporous ZnO for Sensitive Ethanol Sensing.

Zinc oxide (ZnO) as a commonly used semiconductor material has aroused extensive research attention in various fields, such as field-effect transistors, solar cells, luminescent devices, and sensors, because of its excellent light-electrical features and large exciton bonding energy. Herein, ultrasmall Au nanoparticles with tunable size decorated mesoporous ZnO nanospheres were synthesized via facile formaldehyde-assisted metal-ligand cross-linking strategy, where these active Au species could be transferred into Au nanoparticles in the frameworks by various reduction strategies. Typically, mesoporous ZnO-Au with a photoreduction technique showed superior ethanol sensing performance (ca. 159 for 50 ppm at 200 °C) because of its high surface area, dual-mesoporous structure, and interface effect (electron effect, surface catalytic/adsorption). Moreover, the mesoporous ZnO-Au composites by photoreduction show much better performance than those via H2 reduction and NaBH4 reduction, which is ascribed to the providential size of Au nanoparticles (ca. 6.6 nm) and abundant oxygen defects in the composites. In particular, the selectivity and sensitivity of mesoporous ZnO-Au far exceeds those of materials loaded with other noble metals (Pt, Pd, and Ag). The sensing mechanism of mesoporous ZnO-Au for ethanol is attributed to classical surface adsorption/catalytic reaction, where strong sensitization effect (electron and chemical) and the spillover effect of Au nanoparticles in the catalytic reaction cause superior ethanol sensing performances. In situ FTIR and GC-MS measurement revealed that the catalytic oxidation of ethanol follows the process of dehydrogenation and deep oxidation, that is, dehydrogenation to acetaldehyde, and then further oxidation to carbon dioxide and water.

Programmable Metal Nanoclusters with Atomic Precision

With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1-3nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X-ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum-confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold-thiolate nanoclusters (Aun (SR)m ) are revealed to contain an inner kernel, Au-S interface (motifs), and surface ligand (-R) shell. Programming the atomic packing into various crystallographic structures of the metal kernel can be achieved, which plays a significant role in determining the optical properties and the energy gap (Eg ) of NCs. When the size increases, a general trend is observed for NCs with fcc or decahedral kernels, whereas those NCs with icosahedral kernels deviate from the general trend by showing comparably smaller Eg . Comparisons are also made to further demonstrate the more decisive role of the kernel structure over surface motifs based on isomeric Au NCs and NC series with evolving kernel or motif structures. Finally, future perspectives are discussed.

Highly Selective Conversion of Glycerol to Formic Acid over a Synergistic Au/Phosphotungstic Acid Catalyst under Nanoconfinement

Converting surplus glycerol into the hydrogen storage material, formic acid, can meet the increasing energy demand, yet its commercial production is hindered by the low efficiency. Herein, a nano-confined catalytic system with multiple active sites that consists of ultrasmall Au nanoparticles (NPs) and highly dispersed phosphotungstic acid (PTA) within the nanochannels of mesoporous silica nanoparticles (Au-PTA/MSN) was demonstrated to directly convert glycerol to formic acid in a one-step operation under the mild condition with a selectivity of up to 79.2%. The time-course experiment revealed that such a one-pot process involves synergistic catalysis from glycerol to a triose, followed by the breakdown of the C–C bond of trioses into glycolic acid and formic acid, as well as further oxidative cleavage of glycolic acid to formic acid, which eventually contributed to the highly selective formic acid production. Characterizations showed that the nano-confined Au-PTA/MSN catalytic system incorporated the catalytic actions of Au NPs and phosphotungstic acid in one operation, thus offering a high activity for converting glycerol to formic acid.

In-situ synthesis of ultrasmall Au nanoparticles on bimetallic metal-organic framework with enhanced electrochemical activity for estrone sensing

In this work, ultrasmall Au nanoparticles decorated bimetallic metal-organic framework (US Au NPs@AuZn-MOF) hybrids were facilely prepared by a sequential ion exchange and in-situ chemical reduction strategy. Numerous of Au nanoparticles with size less than 5 nm was homogeneously dispersed on the surface of the whole bimetallic AuZn-MOF polyhedrons. The integration of ultrasmall Au nanoparticles greatly enhanced the electron transfer capacity and electrochemical active surface area of the metal-organic framework host. Compared with the pristine Zn-MOF, bimetallic AuZn-MOF, the as-synthesized US Au NPs@AuZn-MOF hybrids exhibited remarkably promoted electrochemical activity toward the oxidation and sensing of endocrine-disrupting chemical (EDC) estrone. As a result, a highly sensitive electrochemical sensing platform was developed for the detection of estrone in the range of 0.05 μM–5 μM with limit of detection of 12.3 nM (S/N = 3) and sensitivity of 101.3 μA−1 μM−1 cm−2. Considering the structural diversity of MOFs and superior property of ultrasmall Au nanoparticles, the strategy proposed here may open a new avenue for the design and synthesis of other high-activity nanomaterials for electrochemical sensing or other challenging fields.

Stabilization of ultra-small gold nanoparticles in a photochromic organic cage: modulating photocatalytic CO2 reduction by tuning light irradiation

A DTE based photochromic organic cage was used for stabilization of ultra-small Au nanoparticles and the resulting hybrid nanocomposite showed irradiated light regulated photocatalytic CO2 reduction to CO.

Bio-genic synthesis of ultra-small Au particles loaded silica nanoparticles for effective wound healing agent for the nursing care in the femoral fracture during surgery

In this study, Au?SiO2 materials were synthesized by a simple biogenic approach using ultra-small Au nanoparticles (NPs) loaded on mesoporous SiO2 NPs. The functional groups, crystalline behavior, morphological structure, and elemental compositions of synthesized nanomaterials were characterized and confirmed by various techniques such as ultraviolet-visible (UV-Vis), X-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, transmission electron microscope (TEM) with energy dispersive X-ray (EDX) mapping, Zeta potential, and dynamic light scattering (DLS) analysis. The cell viability results also indicated that the nano Au NPs loaded on mesoporous SiO2 NPs exhibited highly efficient biocompatibility and low toxicity. The wound healing rate of mesoporous SiO2 and Au?SiO2 NPs were 82% and 96%, respectively, at the end of 14 days, which were higher than that of the control samples. These results strongly support the possibility of using these Au particles loaded on mesoporous SiO2 NPs as a promising wound healing agent for nursing care during femoral fracture surgery.

In Situ Anchoring Ultra Small Au Nanoparticles by Conformal Coating of Carbon Layer within the Micro-Environments of Mesoporous Silica for Highly Efficient Catalytic Reduction of 4-nitrophenol

For the noble-metal based catalysts, the metal dispersion and sinter resistance of the metal nanoparticles (NPs) are the most vital factors for their application in series catalytic reactions. However, in the most noble-metal based catalysts, the weak interaction between metal NPs and support would be negative for these factors, and the poor catalytic performance would be obtained relatively. Committed to overcome these, in this work, the catalyst of Au@C/AMS would be designed and fabricated by the hydrothermal and calcinations process, in which the ultra small Au NPs are formed and stabilized in situ by the conformal coating of carbon layer in the micro-environment of mesoporous silica. The results demonstrate that the carbon layer would be directly formed in the mesoporous channels by calcinations in nitrogen atmosphere, and the ultra small Au NPs would be in situ anchored in the carbon layer. The average particle size of Au in Au@C/AMS is as small as 1.8 nm from TEM results, which is much smaller than those in the sample of Au/AMS without the protection of carbon layer. Besides, compared with the samples that the Au NPs are deposited on the outer and inner surface of mesoporous silica, a strong interaction would be built between Au NPs and support in the target Au@C/AMS sample. As expected, the catalyst of Au@C/AMS displays superior catalytic activity and stability in the liquid-phase reduction of 4-nitrophenol. The construction of this special architecture for Au-based catalysts could provide new sights for the design and fabrication of noble metal-based mesoporous materials with desirable catalytic activity and stability. In this work, the catalyst of Au@C/AMS would be designed and fabricated by the hydrothermal and calcinations process, in which the ultra small Au NPs are formed and stabilized in situ by the conformal coating of carbon layer in the micro-environment of mesoporous silica. Compared with the samples that the Au NPs are deposited on the outer and inner surface of mesoporous silica, a strong interaction would be built between Au NPs and support in the target Au@C/AMS sample. As expected, the catalyst of Au@C/AMS displays superior catalytic activity and stability in the liquid-phase reduction of 4-nitrophenol. The construction of this special architecture for Au-based catalysts could provide new sights for the design and fabrication of noble metal-based mesoporous materials with desirable catalytic activity and stability.

Rod-shape inorganic biomimetic mutual-reinforcing MnO2-Au nanozymes for catalysis-enhanced hypoxic tumor therapy

Biomimetic nanozymes possessing natural enzyme-mimetic activities have been extensively applied in nanocatalytic tumor therapy. However, engineering hybrid biomimetic nanozymes to achieve superior nanozyme activity remained to be an intractable challenge in hypoxic tumors. Herein, a rod-like biomimetic hybrid inorganic MnO2-Au nanozymes are developed, where MnO2 and ultrasmall Au nanoparticles (NPs) are successively deposited on the mesoporous silica nanorod to cooperatively improve the O2 content and thermal sensitivity of hypoxic solid tumors guided by multi-modal imaging. Under the catalyzing of MnO2, the intratumoral H2O2 is decomposed to greatly accelerate O2 generation, which could boost the curative effect of radiation therapy (RT) and further enhance the Au-catalyzed glucose oxidation. Mutually, the Au NPs can steadily and efficiently catalyze the oxidation of glucose in harsh tumor microenvironment, thus sensitizing tumor cells to thermal ablation for mild photothermal therapy and further promoting the catalytic efficiency of MnO2 with the self-supplied H2O2/H+. As a result, this mutual-reinforcing cycle can endow the nanoplatform with accelerated O2 generation, thus alleviating hypoxic environment and further boosting RT effect. Furthermore, acute glucose consuming can induce downregulation expression of heat shock protein (HSP), achieving starvation-promoted mild photothermal therapy. This synthesized hybrid nanozymes proves to be a versatile theranostic agent for nanocatalytic cancer therapy.