Au Nanostructures Research Articles

Novel metal enhanced dual-mode fluorometric and SERS aptasensor incorporating a heterostructure nanoassembly for ultrasensitive T-2 toxin detection.

Fluorescent gold (Au) nanostructures have emerged as burgeoning materials to fabricate nanomaterial assemblies which play a vital role in improving the detection sensitivity and specificity for various biomolecules. In this work, a fluorescence labelled (Rhodamine-B-Isothiocyanate) silica shell with Au metal core (AuNPs@PVP@RITC@SiO2) and a graphene-Au nanostar nanocomposite (rGO-AuNS) are presented as a metal enhanced fluorescence (MEF) material and Raman signal enhancer, respectively. Their composite (AuNPs@PVP@RITC@SiO2NPs/rGO-AuNS) was employed as a dual-mode fluorescence (FL) and surface-enhanced Raman scattering (SERS) nanoprobe for selective and sensitive detection of T-2 toxin. To comprehend the dual-modality, a core-shell nanostructure, AuNPs@PVP@RITC@SiO2, was functionalized with an aptamer (donor) and adsorbed on the surface of rGO-AuNS through electrostatic forces and π-π stacking which act as a FL quencher and SERS signal enhancer. When exposed to T-2 toxin, the apt-AuNPs@PVP@RITC@SiO2NPs move away from the surface of rGO-AuNS, resulting in the restoration of FL and reduction of the SERS signal. There was distinct linearity between the T-2 toxin concentration and the dual FL and SERS signals with lower limits of detection (LOD) of 85 pM and 12 pM, as compared to the previous methods, respectively. The developed FL and SERS aptasensor presented excellent recovery ratio and RSD in wheat and maize, respectively, as compared with the standard ELISA method. The complementary performances of the developed stratagem revealed a high correlation between the FL and SERS sensing modes with exquisite detection properties.

Plasmon coupling using eigenmode expansion and its sensing applications

Plasmonic nanostructures providing enormous diversified applications are always a boon for the nanomaterial researchers. The light-matter interaction additionally provides various plasmonic modes, which are studied, in general, with the optical spectra along with the near field enhancement plots. Further, to visualize all the hybrid plasmonic modes between any two coupled nanostructures, the eigenmode expansion is employed as it’s an analytical calculation for optical response of interacting nanostructures. Herein, we have simulated the optical spectra for various morphology of Au nanostructures and also the Au-Au dimer nanospheres using MATLAB based Boundary element method (BEM), which requires less computing space and time. Different plasmonic modes and their respective coupling decay was calculated by modifying the interparticle gap and incident angle of the plane wave. These modes were further overviewed using the eigenmode determination which provides the properties of plasmonic lattices. The refractive index sensing was also analyzed, representing the individual sensitivity for the corresponding nanostructures.

Spatially confined (Au core)/CeO2–(Au nanoclusters) hierarchical nanostructures as highly active and stable catalysts for CO oxidation

Developing highly active and stable catalysts is still extremely desirable, but represents a great challenge. Herein, we report a feasible one-pot approach to prepare in large scale Au core)/CeO2–(Au nanoclusters) (denoted as Au/CeO2–Au) nanostructures through a spontaneous chemical redox reaction without any surfactants, in which the Au nanoclusters were embedded into stacked CeO2. Such special architecture can offer abundant exposed Au atoms and oxygen vacancies, provide much more CeO2–Au interfaces, ensure the effective transfer of reactants and have clean exposed atoms. The Au/CeO2–Au nanostructures therefore exhibit a significantly improved activity of 100 % CO conversion at a much lower temperature of 115 °C compared with their counterparty. More importantly, the Au nanoclusters are spatially confined into CeO2, hindering the aggregation or further growth during catalysis. The conversion is therefore still kept at 100 % without any decay even the reaction was performed for as long as 300 h (12.5 days) and 20 cycles. We believed that this work is a new pathway to design effective catalysts with high activity and stability, especially for that involves small-sized metal nanoclusters.

Green Synthesis of Near-Infrared Plasmonic Gold Nanostructures by Pomegranate Extract and Their Supramolecular Assembling with Chemo- and Photo-Therapeutics.

Au nanostructures exhibiting a localized surface plasmon resonance in the near-infrared spectral window are obtained in a single, green step at room temperature by pomegranate extract in the presence of a highly biocompatible β-cyclodextrin branched polymer, without the need of preformed seeds, external reducing and sacrificial agents, and conventional surfactants. The polymeric component makes the Au nanostructures dispersible in water, stable for weeks and permits their supramolecular assembling with the chemotherapeutic sorafenib and a nitric oxide (NO) photodonor (NOPD), chosen as representative for chemo- and photo-therapeutics. Irradiation of the plasmonic Au nanostructures in the therapeutic window with 808 nm laser light results in a good photothermal response, which (i) is not affected by the presence of either the chemo- or the phototherapeutic guests and (ii) does not lead to their photoinduced decomposition. Besides, irradiation of the hybrid Au nanoassembly with the highly biocompatible green light results in the NO release from the NOPD with efficiency similar to that observed for the free guest. Preliminary biological experiments against Hep-G2 hepatocarcinoma cell lines are also reported.

TiO2 Nanowires on TiO2 Nanotubes Arrays (TNWs/TNAs) Decorated with Au Nanoparticles and Au Nanorods for Efficient Photoelectrochemical Water Splitting and Photocatalytic Degradation of Methylene Blue

In this study, TiO2 nanowires on TiO2 nanotubes arrays (TNWs/TNAs) and Au-decorated TNWs/TNAs nanostructures are designed and fabricated as a new type of photoanode for photoelectrochemical (PEC) water splitting. The TNWs/TNAs were fabricated on Ti folds by anodization using an aqueous NH4F/ethylene glycol solution, while Au nanoparticles (NPs) and Au nanorods (NRs) were synthesized by Turkevich methods. We studied the crystal structure, morphology, and PEC activity of four types of nanomaterial photoanodes, including TNWs/TNAs, Au NPs- TNWs/TNAs, Au NRs-TNWs/TNAs, and Au NPs-NRs-TNWs/TNAs. The TiO2 and Au-TiO2 samples exhibited pure anatase phase of TiO2 with (0 0 4), (1 0 1), and (1 0 5) preferred orientations, while Au-TiO2 presented a tiny XRD peak of Au (111) due to a small Au decorated content of 0.7 ± 0.2 at.%. In addition, the samples obtained a well-defined and uniformed structure of TNAs/TNWs; Au NPs (size of 19.0 ± 1.9 nm) and Au NRs (width of 14.8 ± 1.3 nm and length of 99.8 ± 15.1 nm) were primarily deposited on TNWs top layer; sharp Au/TiO2 interfaces were observed from HRTEM images. The photocurrent density (J) of the photoanode nanomaterials was in the range of 0.24–0.4 mA/cm2. Specifically, Au NPs-NRs- decorated TNWs/TNAs attained the highest J value of 0.4 mA/cm2 because the decoration of Au NPs and Au NRs mixture onto TNWs/TNAs improved the light harvesting capability and the light absorption in the visible-infrared region, enhanced photogenerated carriers’ density, and increased electrons’ injection efficiency via the localized surface plasmon resonance (LSPR) effect occurring at the Au nanostructures. Furthermore, amongst the investigated nanophotocatalysts, the Au NPs-NRs TNWs/TNAs exhibited the highest photocatalytic activity in the degradation of methylene blue with a high reaction rate constant of 0.7 ± 0.07 h−1, which was 2.5 times higher than that of the pristine TNWs/TNAs.

Hybrid Au-star@Prussian blue for high-performance towards bimodal imaging and photothermal treatment

In recent years, branched or star-shaped Au nanostructures composed of core and protruding arms have attracted much attention due to their unique optical properties and morphology. As the clinically adapted nanoagent, prussian blue (PB) has recently gained widespread attention in cancer theranostics with potential applications in magnetic resonance (MR) imaging. In this article, we propose a hybrid star gold nanostructure（Au-star@PB）as a novel theranostic agent for T1-weighted magnetic resonance imaging (MRI)/ photoacoustic imaging（PAI） and photothermal therapy (PTT) of tumors. Importantly, the Au-star@PB nanoparticles function as effective MRI/PA contrast agents in vivo by increasing T1-weighted MR/PAI signal intensity and as effective PTT agents in vivo by decreasing the tumor volume in MCF-7 tumor bearing BALB / c mouse model as well as in vitro by lessening tumor cells growth rate. Interestingly, we found the main photothermal effect of Au-star@PB is derived from Au-star, but not PB. In summary, the hybrid structure of Au-star@PB NPs with good biological safety, significant photostability, dual imaging capability, and high therapeutic efficiency, might offer a novel avenue for the future diagnosis and treatment of cancer.

Spontaneous Hetero-attachment of Single-Component Colloidal Precursors for the Synthesis of Asymmetric Au-Ag2X (X = S, Se) Heterodimers.

Finding simple, easily controlled, and flexible synthetic routes for the preparation of ternary and hybrid nanostructured semiconductors is always highly desirable, especially to fulfill the requirements for mass production to enable application to many fields such as optoelectronics, thermoelectricity, and catalysis. Moreover, understanding the underlying reaction mechanisms is equally important, offering a starting point for its extrapolation from one system to another. In this work, we developed a new and more straightforward colloidal synthetic way to form hybrid Au-Ag2X (X = S, Se) nanoparticles under mild conditions through the reaction of Au and Ag2X nanostructured precursors in solution. At the solid-solid interface between metallic domains and the binary chalcogenide domains, a small fraction of a ternary AuAg3X2 phase was observed to have grown as a consequence of a solid-state electrochemical reaction, as confirmed by computational studies. Thus, the formation of stable ternary phases drives the selective hetero-attachment of Au and Ag2X nanoparticles in solution, consolidates the interface between their domains, and stabilizes the whole hybrid Au-Ag2X systems.

Surface Plasmon-Induced Hot Carriers: Generation, Detection, and Applications.

ConspectusDuring surface plasmon-mediated light-matter interactions, external energies on plasmonic metal nanostructures undergo energy dissipation via elastic e-e scattering, radiative luminescence, and nonradiative processes such as thermal relaxation (phonon) and electronic excitation (electron-hole pairs). In this process, surface plasmon decays dominantly through nonradiative recombination when the metal is smaller than 25 nm, forming hot carriers, including hot electrons and hot holes, with high kinetic energy of 1-3 eV. Although the ultrafast dynamics of hot carriers are on time scales ranging from femtoseconds to picoseconds, these fast-disappearing hot carriers can be collected as the steady-state photocurrent or chemicurrent by adopting the metal-semiconductor (M-S)-based platform for detecting hot carrier flow. Plasmonic hot carriers, especially as they convert to an electrochemical signal, are a promising topic, and their energy conversion mechanisms are being actively studied in the fields of renewable energy, optoelectronics, and photocatalysis. Recent studies have demonstrated that these hot carriers can both improve the performance of solar energy conversion and control the catalytic activity or selectivity by directly participating in the photoelectrochemical (PEC) reaction.In this Account, we describe the inherent relationship between hot carriers and surface plasmon as well as what role hot carriers play throughout the catalytic reaction. The recent experimental work and the theoretical analysis of in situ hot carrier generation on Au nanostructures were conducted with photoconductive atomic force microscopy and finite-difference time-domain (FDTD) simulations, respectively. We highlight the recent nanoscale visualization of hot carrier flow occurring through light-matter interactions and that the localized surface plasmon field surrounding the Au nanostructure leads to boosted hot carrier generation. In addition, we highlight the recent demonstration that plasmonic hot carriers prolong the lifetime of photoexcited carriers in the MAPbI3/Au/TiO2 hybrid nanodiode by the synergistic effect between plasmonic Au and perovskites. From this work, the solar-to-electron conversion performance of this nanodiode significantly increases due to the amplification of light absorption, which helps to design hybrid platforms for efficient hot carrier photovoltaics. We discuss the application of surface plasmon-driven hot electron generation, including hot electron-based photovoltaic devices and photocatalysts. We highlight the recent photoelectrochemical measurements on the Au/p-GaN heterostructures that are controlled by participating plasmonic hot carriers in the water splitting reaction. Furthermore, controlling the flow of both hot electrons and holes by developing hybrid platform configurations for hot carrier applications has promising opportunities for regulating the catalytic activities of hot carrier-based photocatalysis and improving the photoconversion efficiency of hot carrier-based optoelectronic devices.

Improving charge transfer in phosphate ion-modified hematite photoanode via decoration with gold nanostructures

Herein, we report a unique synergistic behavior between the phosphate ions (Pi) layer and the plasmonic gold nanostructures to enhance the PEC performance of the hematite photoanode. Under such a combined effect, the lifetime of the photogenerated holes is enhanced by a factor of 3-fold relative to that of pristine hematite. The Au/Pi–hematite photoanode illustrates a stable photocurrent of 1.32 mA cm–2 at 1.23 VRHE under standard illumination conditions, which is 3.1, 2.1, and 1.7 times higher than those of pristine hematite, Au/hematite, and Pi–modified hematite photoanodes, respectively. The enhanced photocurrent of Au/Pi–hematite is attributed to the improved hole lifetime and charge transfer kinetics as confirmed by transient photocurrent (TPC), photoelectrochemical impedance spectroscopy (PEIS), and intensity-modulated photocurrent spectroscopy (IMPS) measurements. Au nanostructures have a dual function. They enhance the light absorption ability and more importantly improve the charge transfer efficiency.

CuO nanorods decorated gold nanostructures as an ultra-sensitive and recyclable SERS substrate

Conventional surface-enhanced Raman scattering (SERS) substrates require complicated fabrication techniques and precious nanometals to achieve high sensitivity and reproducibility. Furthermore, since SERS requires the adsorption of analytes on the substrate, the reusability of the substrate is still challenging. Herein, CuO nanorods decorated with gold nanostructure have been developed as a highly sensitive, recyclable, and cost-effective SERS substrate. For the fabrication, CuO nanorods were simply constructed on Cu wire by thermal oxidation at 500 °C. Then, Au nanostructures were decorated on the CuO nanorod's surface by UV photoreduction approach. The prepared Au–CuO substrate enabled the identification of methylene blue at a concentration as low as 0.1 pM. Furthermore, the SERS activity of Au–CuO substrate was still maintained at approximately 80% after 3 times recycling by illuminating the substrate with UV irradiation. The long-term surface stability of the substrate was also evaluated, and the decrease of SERS signal was only 4.7% after three days of exposing the substrate to the ambient environment.

Facile approach for surfactant-free synthesis of Au@ginsenoside Rh2 nanoparticles and researches on anticancer activity

BackgroundInorganic nanocomposites especially Au nanostructures have exhibited outstanding physicochemical properties in biomedical fields. For further clinical applications on theranostics, especially drug delivery, numerous explorations of green and facile synthesis methods combining with pharmacoactive natural components have been investigated to construct safe and multifunctional bioactive Au nanoparticles (NPs). Ginsenoside Rh2 is protopanaxadiol type compound isolated from plants of genus Panax, with excellent anticancer effect and antioxidant activity. In this research, we prepared the novel Au nanoparticles using ginsenoside Rh2 as both reducing and stabilizing agents.ResultsThe synthesized Au@ginsenoside Rh2 NPs were proved to exhibit desirable inhibitory effect on different cancer cell lines, which benefited from the inherent anticancer effect of the ginsenoside Rh2. Investigations in vitro indicated that Au@ginsenoside Rh2 NPs inhibited cell proliferation, cell migration and invasion, induced cell cycle arrest, enhanced the reactive oxygen species (ROS) generation, and regulated the protein expressions of caspase-3, 8, 9 to trigger cell apoptosis as well.ConclusionsBecause of the absence of toxic chemical surfactants, the eco-friendly synthesis method of Au NPs modified by natural phytochemicals avoided tedious separation and modification processes. On the other hand, Au@ginsenoside Rh2 NPs also improved water solubility and bioavailability of the hydrophobic drug ginsenoside Rh2. It broadened minds for preparation and application of traditional Chinese medicines (TCMs) modified metal nanoparticles and deserved further study.

AuPd nanoporous dendrites: High electrocatalytic activity and surface plasmon-enhanced stability for ethanol electrooxidation

The design of electrocatalysts with high activity and enhanced durability for ethanol oxidation reaction (EOR) is critical for the commercialization of direct ethanol fuel cells (DEFCs). Herein, a AuPd nanoporous dendritic (AuPd NPD) catalyst was reported, which exhibited high electrocatalytic activity and stability for EOR by dealloying the ternary alloy AuxPdyNi95 with a low atom content of noble metals (5 at.%). The morphologies of AuPd nanopores varied from islands to dendrites by adjusting the Ni content from 80 at.% to 95 at.%. The activity of AuPd NPD was improved up to 8.2 A mg–1Pd by tuning the Au/Pd atomic ratio, which was 16.4 times higher than commercial Pd/C (0.5 A mg–1Pd). The current of all AuPd NPD catalysts remained above 85 % of their initial values after 500 CV cycles, indicating the good electrocatalytic cycle durability of NPD structures. Density functional theory (DFT) calculations revealed that the improved activity stemmed from the upshift of Pd d-band center. The CA long-term stability of Au3.5Pd1.5 NPD was further improved to 2.05 A mg–1Pd even after 6000 s of operation under simulated solar irradiation, which was 3.6 times higher than that without simulated solar irradiation (0.57 A mg–1Pd). The enhanced stability was attributed to the surface plasmon resonance effect of Au nanostructures excited by visible light excitation.

A Versatile Synthetic Pathway for Producing Mesostructured Plasmonic Nanostructures.

Highly branched gold (Au) nanostructures with sharp tips are considered excellent substrates for surface-enhanced Raman scattering (SERS)-based sensing technologies. Here, a simple synthetic route for producing Au or Au-Ag bimetallic mesostructures with multiple sharpened tips in the presence of carbon quantum dots (CQDs) is presented. The morphologies of these mesostructured plasmonic nanoparticles (MSPNs) can be controlled by adjusting the concentration of CQDs, reaction temperatures, and seed particles. The optimal molar ratio for [HAuCl4 ]/[CQDs] is found to be ≈25. At this molar ratio, the diameters of MSPNs can be tuned from 80 to 200nm by changing the reaction temperature from 25 to 80 °C. In addition, it is found that hierarchical MSPNs consisting of multiple Au nanocrystals can be formed over the entire seed particle surface. Finally, the SERS activity of these MSPNs is examined through the detection of rhodamine 6G and methylene blue. Of the different mesostructures, the bimetallic MSPNs have the highest sensitivity with the ability to detect 10-7 m of rhodamine 6G and 10-6 m of methylene blue. The properties of these MSPN particles, made using a novel synthetic process, make them excellent candidates for SERS-based chemical sensing applications.

High‐Performance and Stable Plasmonic‐Functionalized Formamidinium‐Based Quasi‐2D Perovskite Photodetector for Potential Application in Optical Communication

AbstractPhotodetectors play an important role in optical communication systems and are essential to achieve high‐fidelity signal transmission. The emerging formamidinium‐based quasi‐2D layered perovskites have attracted attention in the field due to their excellent photoelectric performance and moisture stability. By optimizing film quality and device engineering a high‐performance flexible photodetector based on formamidinium‐based perovskites ((BA)2FAPb2I7) is developed, which shows fast response and excellent air‐stability. By introducing the formamidinium chloride as an additive the quality and the crystallinity of the film are improved. In addition, localized surface plasmonic resonances (LSPRs) are introduced by embedding Au nanostructures on the substrate, the LSPRs, in turn, enhance light and matter interaction, which further increases the performance of the device. The optimized devices show an ultimate response speed ≈9 µs as well as outstanding long‐term environmental stability (environmental conditions > 1000 h). Achieving such high dynamic range and stability is to the best of authors knowledge rarely reported. The device shows the highest responsivity of 2.3 A W−1, detectivity of 3.2 × 1012 Jones, and outstanding flexibility stability. Finally, the prepared photodetector is successfully integrated into an optical communication system and tested. The results suggest that formamidinium‐based quasi‐2D perovskite photodetectors have great potential in optical communication applications.

Plasmonic enhancement in PTB7-Th:PC71BM organic photovoltaics

Organic photovoltaics struggles with limited exciton diffusion rate and low light absorption rates. The trade-off between these deficiencies limits the thickness of the active layer around 100–200 nm range. Plasmonic light management was introduced as one of the solutions to these problems in the last decade. The plasmonic metal nanostructures can manipulate light in subwavelength regime such as thin-film organic photovoltaics. In this work, we introduced a controllable and reproducible method to incorporate quasi-hexagonal arrays of Au nanostructure on the electron transport layer (ETL), which can directly facilitate light management in the active layer. The inverted PTB7-Th:PC71BM OPVs were selected as the model system, and Au nanostructure arrays were introduced in selected interfaces. In order to match the work function of Au nanostructures and the LUMO level of the PC71BM fullerene component of the bulk heterojunction, PEI was utilized to modify the work function of such surfaces. The plasmon-enhanced inverted OPV devices showed up to 22% higher power conversion efficiencies than reference devices. In order to elucidate the underlying reason for such high improvement, finite-difference time-domain simulations of whole OPV devices under AM1.5G solar illumination were performed. The results revealed up to 25 times higher local exciton generation rate in close proximity to the Au nanostructures and ETLs.

Nonenzymatic Sweat-Based Glucose Sensing by Flower-like Au Nanostructures/Graphene Oxide

The development of a nonenzymatic glucose sensor working in real human body conditions through a noninvasive sampling approach has attracted considerable attention. Hence, this work focuses on the development of a new nonenzymatic glucose sensor based on flower-like Au nanostructures (F-AuNTs) and graphene oxide (GO) as a supporting matrix. The F-AuNTs–GO hybrid was synthesized by simple drop casting of the GO suspension onto the graphite sheet (GS) followed by electrodeposition of F-AuNTs on GO nanosheets at 3 V in a two-electrode system. The electrocatalytic activity of the F-AuNTs–GO/GS sensor toward glucose electrooxidation was initially evaluated in a 0.1 M buffer phosphate solution (pH 7.4). The fabricated electrode shows a linear range (5 nM to 5 μM), a fast response time (6 s), a low detection limit (385 nM), and high sensitivity (162,210 μA mM–1 cm–2). Furthermore, this sensor exhibits very good selectivity in the presence of interferences such as lactic acid, uric acid, NaCl, dopamine, ascorbic acid, and inorganic salts. After obtaining the desired results, a screen-printed electrode (SPE) modified by the F-AuNTs–GO hybrid was prepared for the determination of glucose concentration from artificial sweat to evaluate the noninvasive capability of the proposed sensor. The F-AuNTs–GO/SPE exhibits good behavior for glucose detection with a long linear range of 160 nM to 82 μM and 160 μM to 5 mM, a high sensitivity of 474,617 μA mM–1 cm–1, and a low detection limit of 123 μM. Therefore, the electrochemical experiments demonstrated that F-AuNTs–GO possessed the excellent ability for electrochemically catalysis of glucose oxidation in both buffer solution and artificial sweat. Finally, the capability of the fabricated electrode was successfully investigated for glucose measurement in sweat samples. The outstanding performance of the F-AuNTs–GO-based sensor can be attributed to the superior catalytic activity of the F-AuNTs well dispersing onto GO nanosheets, which provides an excellent sensing platform owing to the enhanced electrical conductivity and large surface area. This study demonstrates that the F-AuNTs–GO hybrid is a promising candidate for the detection of glucose in sensor applications.

Suppression of adipogenesis by Au nanostructures-conjugated Sargassum seaweed extracts in 3 T3-L1 adipocytes

Recently, with the development of metal nanostructure synthesis technology, Au nanostructures (AuNPs) are synthesized using seaweed extract without using an organic solvent and applied to the pharmaceutical field. In this regard, in this study, AuNPs biosynthesis was mediated through extracts of two brown algae (Sargassum siliquastrum [SS] and Sargassum horneri [SH]) without the use of stabilizers or surfactants. In addition, we investigated the effects of SS-AuNPs (SS-functionalized AuNPs) and SH-AuNPs (SH-functionalized AuNPs) on adipogenesis in adipocytes and their underlying molecular mechanisms. A rapid and simplified synthesis of SS-AuNP and SH-AuP was achieved using aqueous extracts of SS and SH. The morphology, structure and composition of SS-AuNPs and SH-AuNPs were characterized by DLS, FTIR, UV–Vis spectroscopy, HR-TEM and EDS analysis. The stable monodisperse SS-AuNPs and SH-AuPs were synthesized with mean sizes of 17.47 ± 0.13 nm and 21.0 ± 2.74 and zeta potentials of −31.9 ± 0.75 and −34.57 ± 4.43, the biosynthetic AuNPs with the face-centered structure of SS-AuNPs and SH-AuPs had crystalline characteristics, and many functional groups that play an important role in the biological reduction present in the SS and SH extracts were adsorbed on the surfaces of the SS-AuNPs and SH-AuPs. This study was conducted to investigate the effect of SS-AuNPs and SH-AuPs on adipogenesis in adipocytes. SS-AuNPs and SH-AuPs reduced morphological changes and increased lipid accumulation by approximately 80% compared with that in mature adipocytes (MDI-induced). This result was accompanied by a reduction in the triglyceride content. SS-AuNPs and SH-AuPs suppressed lipid accumulation by downregulating C/EBPα, PPARγ, SREBP 1, FAS, and aP2 mRNA and protein expression. Furthermore, SS-AuNPs and SH-AuPs induced the mRNA and protein expression of UCP1, PRDM16, and PGC1α to increase mitochondrial biogenesis in mature adipocytes and effectively induced brown adipogenesis. SS-AuNPs and SH-AuPs have potent anti-adipogenic effects and can be used as potential therapeutic agents for obesity.

Three-dimensional flexible and stretchable gold foam scaffold for real-time electrochemical sensing in cells and in vivo

Compared with typical two-dimensional electrodes, the three-dimensional (3D) cell culture platform can simulate the real cell survival environment for cell growth to accurately reproduce cell functions. Moreover, considering that living cells are exposed to various of mechanical force in the microenvironment, the construction of 3D electrodes with excellent flexible, stretchable, and biocompatibility is of great significance to real-time monitor mechanically evoked biomolecule release from cells. Herein, we demonstrated a straightforward and effective three-step approach to fabricate three-dimensional flexible and stretchable gold foam scaffold (3D Au foam scaffold) for construction of 3D cell culture integrated electrochemical sensing platform. The excellent biological and electrical properties of Au nanostructures and porous networks of the 3D scaffold endow the platform with desirable biocompatibility and sensitive electrochemical sensing performance. As a proof of concept, the 3D Au foam scaffold functionalized with cobalt based nanocubes (Co NCs/Au foam scaffold) was validated to provide 3D culture for human umbilical vein endothelial cells (HUVECs), and synchronously real-time monitor superoxide anion (O2•-) released by HUVECs under mechanical stretching. Furthermore, 3-mercaptopropionic acid (3-MPA) modified 3D Au foam (3-MPA/Au foam scaffold) was successfully used for real-time monitoring of catecholamines in rat brain. The results demonstrate the great potential of this 3D Au foam scaffold for real-time electrochemical monitoring biomolecules in vitro and in vivo, providing convenience for future research on mechanotransduction relevant processes.

Surface engineering of Pt surfaces with Au and cobalt oxide nanostructures for enhanced formic acid electro-oxidation

A novel n-CoOx/n-Au/n-Pt nanocatalyst assembled onto a glassy carbon (GC) substrate is recommended for efficient formic acid electro-oxidation (FAEO), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). • A catalyst composed of Pt nanoparticles was engineered with Au and cobalt oxide nanostructures. • It showed a promising catalytic performance toward the formic acid electro-oxidation. • Adjusting its loading hierarchy drove the reaction mechanism to the desirable dehydrogenation pathway. • Geometric and electronic enhancements were elucidated and quantified. This study aims to mitigate the CO poisoning of platinum (Pt) surfaces during formic acid electro-oxidation (FAEO), the essential anodic reaction in the direct formic acid fuel cells (DFAFCs). For this purpose, a glassy carbon (GC) electrode was amended sequentially with Pt (n-Pt), gold (n-Au), and cobalt oxide (n-CoOx) nanostructures. Fascinatingly, the ternary modified n-CoOx/n-Au/n-Pt/GC catalyst (for which n-Pt, n-Au, and n-CoOx were sequentially and respectively assembled onto the GC surface) exhibited a remarkable electrocatalytic enhancement toward FAEO, which surpassed ca. 53 times that of the Pt/GC catalyst. Additionally, it exhibited a much (ca. 18 times) higher stability after 3000 s of continuous electrolysis. The observed enhancement was proven to originate from driving the reaction mechanism principally to the desirable direct dehydrogenation pathway on the expense of the poisoning dehydration path. The impedance and CO stripping measurements confirmed the prevailing of both the electronic and third body effects in the catalytic enhancement.

Elucidating Sensitivity and Stability Relationship of Gold-Carbon Hybrid LSPR Sensors Using Principal Component Analysis.

Sensitive localized surface plasmon resonance (LSPR) sensing is achieved using nanostructured geometries of noble metals which typically have dimensions less than 100 nm. Among the plethora of geometries and materials, the spherical geometries of gold (Au) are widely used to develop sensitive bio/chemical sensors due to ease of manufacturing and biofunctionlization. One major limitation of spherical-shaped geometries of Au, used for LSPR sensing, is their low refractive index (RI) sensitivity which is commonly addressed by adding another material to the Au nanostructures. However, the process of addition of new material on Au nanostructures, while retaining the LSPR of Au, often comes with a trade-off which is associated with the instability of the developed composite, especially in harsh chemical environments. Addressing this challenge, we develop a Au-graphene-layered hybrid (Au-G) with high stability (studied up to 2 weeks here) and enhanced RI sensitivity (a maximum of 180.1 nm/RIU) for generic LSPR sensing applications using spherical Au nanostructures in harsh chemical environments, involving organic solvents. Additionally, by virtue of principal component analysis, we correlate stability and sensitivity of the developed system. The relationship suggests that the shelf life of the material is proportional to its sensitivity, while the stability of the sensor during the measurement in liquid environment decreases when the sensitivity of the material is increased. Though we uncover this relationship for the LSPR sensor, it remains evasive to explore similar relationships within other optical and electrochemical transduction techniques. Therefore, our work serves as a benchmark report in understanding/establishing new correlations between sensing parameters.