Au-based Nanomaterials Research Articles

Gold Nanomaterials and their Composites as Electrochemical Sensing Platforms for Nitrite Detection.

Nitrite is one of the abundant toxic components existing in the environment and is likely to have a great potential to affect human health badly. For that reason, it has become crucial to build a reliable nitrite detection method. In recent years, several nitrite monitoring systems have been proposed. Compared with traditional analytical strategies, the electrochemical approach has a bunch of advantages, including low cost, rapid response, easy operation, simplicity, etc. In this case, noble metal nanomaterials, especially Au-based nanomaterials, have attracted attention in electrode modification because of higher catalytic activity, facile mass transfer, and broad active area for determining nitrite. This review is based on the state-of-the-art, which includes a variety of nanomaterials that have been coupled with gold nanoparticles (AuNPs) for the creation of nanocomposites, and the construction as well as development of electrochemical sensors for nitrite detection over the last few years (2016-2022). A background study on synthesizing different morphological AuNPs and nanocomposites has also been introduced. The fabrication methods and sensing capabilities of modified electrodes are given special consideration.

High Stability Au NPs: From Design to Application in Nanomedicine.

In recent years, Au-based nanomaterials are widely used in nanomedicine and biosensors due to their excellent physical and chemical properties. However, these applications require Au NPs to have excellent stability in different environments, such as extreme pH, high temperature, high concentration ions, and various biomatrix. To meet the requirement of multiple applications, many synthetic substances and natural products are used to prepare highly stable Au NPs. Because of this, we aim at offering an update comprehensive summary of preparation high stability Au NPs. In addition, we discuss its application in nanomedicine. The contents of this review are based on a balanced combination of our studies and selected research studies done by worldwide academic groups. First, we address some critical methods for preparing highly stable Au NPs using polymers, including heterocyclic substances, polyethylene glycols, amines, and thiol, then pay attention to natural product progress Au NPs. Then, we sum up the stability of various Au NPs in different stored times, ions solution, pH, temperature, and biomatrix. Finally, the application of Au NPs in nanomedicine, such as drug delivery, bioimaging, photothermal therapy (PTT), clinical diagnosis, nanozyme, and radiotherapy (RT), was addressed concentratedly.

Stellate Plasmonic Exosomes for Penetrative Targeting Tumor NIR-II Thermo-Radiotherapy.

Multifunctional gold (Au)-based nanomaterials with high atomic number (symbol Z) and strong absorbance in the second near-infrared window (NIR-II) property are emerging as promising candidates for tumor thermo-radiotherapy. The main limitations of applying Au-based nanomaterials to biomedical studies include the absence of active tumor-targeting ability, penetrating efficiency, and stability. In this study, we present a novel type of tumor cell-derived stellate plasmonic exosomes (TDSP-Exos) for penetrative targeted tumor NIR-II thermo-radiotherapy and photoacoustic imaging. The TDSP-Exos are abundantly and easily produced by the incubation of tumor cells with gold nanostars, based on which gold nanostars promote the exocytosis of exosomes from tumor cells. Compared with bare gold nanostars, the TDSP-Exos exhibit pronounced accumulation in deep tumor tissues and perform well in both PA imaging and NIR-II thermo-radiotherapy against the tumor. Moreover, the TDSP-Exos improve tumor hypoxia to enhanced radiotherapy by NIR-II photothermal therapy. This work indicates that the tumor cell-derived exosomes have the potential to function as a universal carrier of photothermal agents for targeted tumor NIR-II thermo-radiotherapy.

Application of Gold-Based Nanomaterials in Tumor Photothermal Therapy and Chemotherapy.

Photothermal therapy (PTT) is a minimally invasive tumor treatment method in which photothermal conversion agents (PTAs) can be enriched in tumor tissue by external light stimulation to convert photon energy into thermal energy to induce the temperature of tumor tissue higher than normal physiological, and can effectively kill tumor cells and tissues while avoiding damage to healthy tissue. As a well-known biocompatible nanomaterial, gold-based nanomaterials have high photothermal conversion efficiency and cross section, which can be used in tumor targeting therapy treatment as a potential photothermal conversion agent. Combining PTT and chemotherapy can be achieved by loading a chemotherapeutic drug modified on the surface of a gold nanomaterials. Therefore, this paper first reviews the preparation and surface functionalization of Au-based nanomaterials, such as Au nanorods, Au nanostars, Au nanoshells, and so on. Second, we have also introduced the application of Au-based nanomaterials in PTT, chemotherapy, and combination therapy. Finally, the limitations and challenges of Au-based photothermal conversion agents are summarized and the development prospects in this field are prospected.

Preparation of Au nanoparticles on a magnetically responsive support via pyrolysis of a Prussian blue composite

A strategy is described for the direct preparation of Au nanoparticles (AuNPs) on a Fe-based support, coated with porous carbon (PC), via pyrolysis of an AuCN functionalised Prussian Blue (PB) metal organic framework (MOF). The composite starting material was prepared with an even distribution of AuCN on the surface via galvanic exchange of PB with a gold salt in solution. The resulting structures after pyrolysis were shown to be active Au-based nanomaterials for model applications including catalysis (4-nitrophenol reduction) and electroanalysis (arsenic (III) detection), suggesting broad application where Au nanoparticles are required at a liquid-solid interface. The Fe based support was seen to consist of Fe, Fe3C and Fe4C phases, and the carbon coating increased the stability and improved the conductivity of the materials. The temperature of pyrolysis was seen to affect the activity of the supported nanoparticles, with an increased Au surface area obtained at the higher pyrolysis temperature (650 °C) tested. A general strategy is thus confirmed for preparation of noble metal nanoparticles evenly distributed on a magnetic support, allowing easy separation of catalysts from products in heterogeneous applications.

Enhanced catalytic reduction of nitrophenols by sodium borohydride over highly recyclable Au@graphitic carbon nitride nanocomposites

In this study, a photochemical green synthesis using thermal exfoliation process is developed to fabricate Au@graphitic carbon nitride (g-C3N4) nanocomposite, highly recyclable and reusable, for the catalytic reduction of nitrophenols by NaBH4. Au nanoparticles (Au NPs) in the diameter of 5–15 nm are deposited onto the surface of g-C3N4 in 3–6 layers of structure. The synthesized Au@g-C3N4 nanocomposites exhibit excellent catalytic activity and stability in the reduction of nitrophenols including 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-nitrophenol, and 2,4,6-nitriophenol. The catalytic performance of Au@g-C3N4 is highly dependent on the initial nitrophenol concentration, Au loading, inorganic anions, and pH. The rate constant of 4-nitrophenol reduction over Au@g-C3N4 (2 wt%) is 26.4 times that of pure Au NP in the presence of 7 mM of NaBH4 at pH 5. Moreover, Au@g-C3N4 can be reused for at least 10 consecutive cycles without considerable loss of catalytic activity. The presence of anions (0.1 M) such as H2PO4−, SO42-, HCO3−, and NO3− decreases the rate of 4-nitrophenol reduction by a factor of 1.2–8.8; whereas there is a 1.2-time increase in rate constant upon the addition of Cl− ion. The detection of H radical adducts indicates that Au NPs adsorbs BH4− ions and forms Au-H species. The porous and conductive g-C3N4 provides large surface area for nitroarene adsorption and subsequent electron transfer from the Au-H species to 4-nitrophenol, which results in accelerating the reduction of 4-nitrophenol. Results clearly demonstrate that Au@g-C3N4 is a promising green catalyst of enormous potential for nitroaromatic reduction, which provides a new venue for tailoring Au-based nanomaterials in elucidation of a wide variety of heterogeneous catalytic reactions.

Bare laser‐synthesized Au‐based nanoparticles as nondisturbing surface‐enhanced Raman scattering probes for bacteria identification

The ability of noble metal-based nanoparticles (NPs) (Au, Ag) to drastically enhance Raman scattering from molecules placed near metal surface, termed as surface-enhanced Raman scattering (SERS), is widely used for identification of trace amounts of biological materials in biomedical, food safety and security applications. However, conventional NPs synthesized by colloidal chemistry are typically contaminated by nonbiocompatible by-products (surfactants, anions), which can have negative impacts on many live objects under examination (cells, bacteria) and thus decrease the precision of bioidentification. In this article, we explore novel ultrapure laser-synthesized Au-based nanomaterials, including Au NPs and AuSi hybrid nanostructures, as mobile SERS probes in tasks of bacteria detection. We show that these Au-based nanomaterials can efficiently enhance Raman signals from model R6G molecules, while the enhancement factor depends on the content of Au in NP composition. Profiting from the observed enhancement and purity of laser-synthesized nanomaterials, we demonstrate successful identification of 2 types of bacteria (Listeria innocua and Escherichia coli). The obtained results promise less disturbing studies of biological systems based on good biocompatibility of contamination-free laser-synthesized nanomaterials.

Shape-Dependent Radiosensitization Effect of Gold Nanostructures in Cancer Radiotherapy: Comparison of Gold Nanoparticles, Nanospikes, and Nanorods.

The shape effect of gold (Au) nanomaterials on the efficiency of cancer radiotherapy has not been fully elucidated. To address this issue, Au nanomaterials with different shapes but similar average size (∼50 nm) including spherical gold nanoparticles (GNPs), gold nanospikes (GNSs), and gold nanorods (GNRs) were synthesized and functionalized with poly(ethylene glycol) (PEG) molecules. Although all of these Au nanostructures were coated with the same PEG molecules, their cellular uptake behavior differed significantly. The GNPs showed the highest cellular responses as compared to the GNSs and the GNRs (based on the same gold mass) after incubation with KB cancer cells for 24 h. The cellular uptake in cells increased in the order of GNPs > GNSs > GNRs. Our comparative studies indicated that all of these PEGylated Au nanostructures could induce enhanced cancer cell-killing rates more or less upon X-ray irradiation. The sensitization enhancement ratios (SERs) calculated by a multitarget single-hit model were 1.62, 1.37, and 1.21 corresponding to the treatments of GNPs, GNSs, and GNRs, respectively, demonstrating that the GNPs showed a higher anticancer efficiency than both GNSs and GNRs upon X-ray irradiation. Almost the same values were obtained by dividing the SERs of the three types of Au nanomaterials by their corresponding cellular uptake amounts, indicating that the higher SER of GNPs was due to their much higher cellular uptake efficiency. The above results indicated that the radiation enhancement effects were determined by the amount of the internalized gold atoms. Therefore, to achieve a strong radiosensitization effect in cancer radiotherapy, it is necessary to use Au-based nanomaterials with a high cellular internalization. Further studies on the radiosensitization mechanisms demonstrated that ROS generation and cell cycle redistribution induced by Au nanostructures played essential roles in enhancing radiosensitization. Taken together, our results indicated that the shape of Au-based nanomaterials had a significant influence on cancer radiotherapy. The present work may provide important guidance for the design and use of Au nanostructures in cancer radiotherapy.

Green Synthesis of Au-Based Nanomaterials Using an "All-in-One" Ionic Liquid and Their Electrocatalytic Properties for Glucose Electro-Oxidation

In a previous work, the ability of 2-hydroxyethylammonium formate ionic liquid to act as an “all-in-one” reaction medium was tested for Pd and Pd-NiO nanoparticles. In this work, the proof of its power to synthesize metallic nanoparticles was extended to the following materials: Au, AuPd, AuPt and AuCuO nanoparticles as well as Pd and CuO as controls. These materials were used as electrocatalysts for the glucose electro-oxidation reaction. According with XRD, crystallite sizes of 16.9, 11.8, 12.0, 12.6, 10.1 and 11 nm were obtained for Au/C, AuPd/C, AuPt/C, AuCuO/C, Pd/C and CuO/C, respectively. TEM micrographs showed nanoparticle sizes closed to crystallite sizes. For metallic mixtures, X-ray fluorescence revealed metallic compositions of Au60Pd40, Au90Pt10 and Au85CuO15. Moreover, thermogravimetric analyses showed metal mass contents between 24 to 32 wt. % (Vulcan carbon was used as support) for all materials except AuCuO which showed 4 wt. %. The electrocatalytic activity toward glucose electro-oxidation was tested as function of its concentration and temperature. All materials showed electrochemical response to the presence of glucose. For fuel cell applications, AuPt showed the most negative oxidation potential (-0.57 V vs. NHE at 40°C) and the highest peak current density (58.5 mA mg-1). For electrochemical non-enzymatic glucose detection, all materials showed good response to the successive addition of 1 mM glucose at short times (less than 10 seconds). However, due to its easiness to be synthesized, and its relative low cost, CuO/C can be an attractive option for non-enzymatic glucose sensors.

Sulfur radical species form gold deposits on Earth.

Current models of the formation and distribution of gold deposits on Earth are based on the long-standing paradigm that hydrogen sulfide and chloride are the ligands responsible for gold mobilization and precipitation by fluids across the lithosphere. Here we challenge this view by demonstrating, using in situ X-ray absorption spectroscopy and solubility measurements, coupled with molecular dynamics and thermodynamic simulations, that sulfur radical species, such as the trisulfur ion S3(-), form very stable and soluble complexes with Au(+) in aqueous solution at elevated temperatures (>250 °C) and pressures (>100 bar). These species enable extraction, transport, and focused precipitation of gold by sulfur-rich fluids 10-100 times more efficiently than sulfide and chloride only. As a result, S3(-) exerts an important control on the source, concentration, and distribution of gold in its major economic deposits from magmatic, hydrothermal, and metamorphic settings. The growth and decay of S3(-) during the fluid generation and evolution is one of the key factors that determine the fate of gold in the lithosphere.

Gold nanomaterials conjugated with indocyanine green for dual-modality photodynamic and photothermal therapy

Light-exposure-mediated higher temperatures that markedly accelerate the degradation of indocyanine green (ICG) in aqueous solutions by thermal decomposition have been a serious medical problem. In this work, we present the example of using gold nanorods (Au NRs) and gold nanoparticles (Au NPs) simultaneously serving as photodynamic and photothermal agents to destroy malignant cells. Au NRs and Au NPs were successfully conjugated with hydrophilic photosensitizer, indocyanine green (ICG), to achieve photodynamic therapy (PDT) and photothermal therapy (PTT). We also demonstrated that Au NRs and Au NPs conjugated with ICG displayed high chemical stability and acted as a promising diagnostic probe. Moreover, the photochemical destruction ability would have a gradually increase depending on different sizes of Au NPs. Due to its stability even via higher temperatures mediated by laser irradiation, the combination of PTT and PDT proved to be efficiently killing cancer cells as compared to PTT or PDT treatment alone and enhanced the effectiveness of photodestruction and was demonstrated to enhance its photostability. As a result, the preparation of Au-based nanomaterials conjugated with ICG as well as their use in biomedical applications is valuable developments in multifunctional nanomaterials.

Synthesis, characterization, and catalytic application of networked Au nanostructures fabricated using peptide templates

Bio-inspired-based methods represent new approaches for the fabrication and activation of nanomaterials, all under ambient and energy-neutral conditions. Recent advances have demonstrated the production of non-spherical materials of Pd and Pt; however, the production of similar Au materials remains challenging. Such fabrication routes are highly important as Au-based nanomaterials of selectable morphologies could have immediate applications in catalysis and energy storage. In this contribution, we demonstrate a peptide template-based methodology for the fabrication of Au nanoparticle networks, which are highly branched linear structures that are prepared in water at room temperature. The materials were fully characterized using UV-vis, TEM, XRD, and DLS, from which their catalytic activity was subsequently studied for the reduction of 4-nitrophenol. Using this approach, the materials were shown to be highly reactive as compared to comparable structures, which is likely due to their unique biological template. Together, this research represents a step forward in bio-based methodologies for the fabrication of functional and potentially sustainable materials.

Modulating cell-uptake behavior of Au-based nanomaterials via quantitative biomolecule modification

The pre-modification method provides a rapid and controllable amount of biomolecule conjugated to nanomaterials via quantitative creation of “activated sites” on biomolecules, modulating specific targeting rate toward cancer cells. In our studies, activating reagent, 2-iminothiolane, is introduced into the biomolecule structure as activated site for linking to Au nanomaterial. To fabricate Au-based magnetic nanoparticles, the amounts of Au nanoparticles are controllably conjugated to chitosan–Fe3O4 nanoparticles by increasing activated sites on chitosan, adjusted by 2-iminothiolane concentration. Further, to develop the biorecognition of Au–Fe3O4 nanoparticles toward target cells, pre-modified transferrin (Tf) is allowed to facilitate the conjugation with Au–Fe3O4 nanoparticles, and validations of bioactivity and specificity are examined in vitro using J5 cancer cells as well. The cell uptake analysis indicates that the high-degree Tf modified Au–Fe3O4 nanoparticles have rapid-targeting ability and easy internalization toward cancer cell, compared to low-degree ones. It implies that the efficiency of cell targeting can be improved or lowered by modulating Tf modification. The potential control of applications can be achieved by modulating Tf modification, such as rapid-targeting rate for signal enhancement, the long-term or rapid drug-treatment in circulation, etc. This concept of modulating by Tf modification can be extensively utilized in future designs of various biomolecule-conjugated Au-based nanomaterials.

Comparative efficiencies of photothermal destruction of malignant cells usingantibody-coated silica@Au nanoshells, hollow Au/Ag nanospheres and Au nanorods

Three Au-based nanomaterials (silica@Au nanoshells, hollow Au/Ag nanospheres andAu nanorods) were evaluated for their comparative photothermal efficiencies atkilling three types of malignant cells (A549 lung cancer cells, HeLa cervix cancercells and TCC bladder cancer cells) using a CW NIR laser. Photodestructiveefficiency was evaluated as a function of the number of nanoparticles required todestroy the cancer cells under 808 nm laser wavelength at fixed laser power. Ofthe three nanomaterials, silica@Au nanoshells needed the minimum number ofparticles to produce effective photodestruction, whereas Au nanorods neededthe largest number of particles. Together with the calculated photothermalconversion efficiency, the photothermal efficiency rankings are silica@Au nanoshells > hollow Au/Agnanospheres > Au nanorods. Additionally, we found that HeLa cells seem to present better heat tolerancethan the other two cancer cell lines.