Protein oligomerization contributes to Alzheimer’s disease development (AD). A nanoparticle that can speed up the oligomerization of proteins is generally considered harmful. Gold nanoparticles (AuNPs) have been reported to be making headway in biological platforms, but they may also have the capacity to stimulate protein oligomerization. Our goal herein was to investigate the neurotoxicity and oligomerization of amyloid-β-1-42 (Aβ1-42) in the presence of AuNPs. The precipitation approach was used to create AuNPs, which were then analyzed using transmission electron microscopy (TEM), ThT, Congo red, and CD spectroscopy. The results demonstrated that the 50-nm-sized fabricated AuNPs guided acceleration in Aβ1-42. In addition, cytotoxicity studies on PC 12 cells showed that Aβ1-42 with AuNPs were less toxic than untreated oligomers Aβ1-42 in terms of inducing cell death, oxidative apoptosis, stress, and membrane leakage. In conclusion, our investigation sheds light on how AuNPs stimulate the development of cytotoxic oligomers by binding to proteins in Alzheimer’s disease.

This report provides a method to estimate how much the photocurrents can be increased by adding gold nanoparticles in P3HT:PCBM films, without having to carry out the complex process of fabricate a whole cell. The tuning effect of varying the gold nanoparticle concentration on optical properties of these films was analyzed by measuring optical absorption. To estimate the contribution of the optical absorption variation, theoretical photocurrents generated for these films as active layers were calculated using a photonic flux density equation. With this methodology, it is possible to estimate the amount of energy that can be harvest with a given gold nanoparticle concentration. Improvements up to 26% were obtained compared with films without added gold nanoparticles.

One-step laser-assisted fabrication of elongated Au nanoparticles (NPs) and their subsequent fragmentation and agglomeration are experimentally studied. The generation of elongated Au NPs is carried out via laser ablation of a solid Au target in water using an ytterbium-doped fiber laser source with pulse duration of 200 ns and pulse energy of 1 mJ. Extinction spectrum of the resulting particles exhibits an increase in the absorption in visible red and near IR spectral regions. This change in absorption is accounted for by the longitudinal plasmon resonance of the electrons in elongated Au NPs and is corroborated by the TEM images. The effect of additional laser exposure on the elongated Au NPs produced using this method is studied, as well. Laser pulse energies and exposure times are varied. Possible processes of laser-assisted formation of elongated Au NPs in aqueous solutions of calcium chloride and magnesium sulfate and their following interaction with pulsed laser radiation are discussed.

Gold exchange traded funds help investors to generate the returns based on the movements of underlying commodity. In current scenario, gold ETFs are emerging as one of the best ETFs for the investments. The present study intended to determine the causal relationship between spot prices of gold, SENSEX, and ten selected BSE listed Gold ETFs. The closing prices gold ETFs, SENSEX and spot prices of gold was collected during 2015–2018. The study applied ADF root test, co-integration test, and Granger causality test to study the causal relationship. The results of the study revealed that out of ten, six gold ETFs has significant causal relationship with gold price and only two schemes has significant relationship with BSE SENSEX during 2015–2018. The study concluded that gold ETFs are largely affected by the spot price movements of gold. Therefore, an investor must understand the pricing dynamics of the underlying asset of ETF.

The age hardenability of 22 karat gold (Au-5.8wt.%Cu-2.5wt.%Ag) alloyed with Ti at various concentrations (0.5, 0.75, and 1 wt.%) was studied. The addition level of Ti is compensated with Ag to maintain the purity of gold in 22 karat, i.e., 91.75 wt.%. The Ti containing 22 karat gold was prepared by melting Au, Cu, and Ag and adding Ti via Au-6wt.%Ti master alloy. The castings obtained were cold-rolled into thin sheet (90% reduction). Both the cast and cold-rolled sheets were subjected to age hardening treatment (solutionizing and artificial aging). Artificial aging was performed as a function of time at 550 °C to identify the peak aging. At all addition level of Ti, the 22 karat gold responded well to the age hardening treatment. The cold-worked sheet samples showed faster peak aging within 30 min. and higher peak hardness than their cast counterpart. Increasing the Ti concentration increases the peak hardness of both cold-rolled sheet and casting samples. Transmission electron microscopic analysis of the peak aged cold-rolled sheet samples shows uniformly distributed coherent Au4Ti precipitates in Au matrix which contribute to the higher hardness.

The present study attempted to analyse the random-walk characteristics of the gold spot price of the London Bullion Market Association (LBMA) by using several linear and nonlinear models. The research collects two decades of daily data from 3rd February 2000 to 2nd October 2020. Econometric tests such as serial correlation test, unit-root tests, multiple variance ratio (MVR), and the BDS test were applied to examine the linear and nonlinear dependence of return series. Further, we employed all the tests from ARCH family to examine the volatility clustering of the gold return series. The results of serial correlation and the unit-root test suggest that the gold return is stationary, therefore does not follow the random-walk benchmark, and hence the gold market is inefficient. EGARCH results indicate that the positive news has a more significant impact on the gold return than the negative news. The findings have important implications for the efficient portfolio investments, and better hedging opportunities for the investors.

The influence of the orientation of gold nanorods in different assemblies has been investigated using the finite difference time domain (FDTD) simulation method. To understand the relative orientation, we vary the size and angle in dimer geometries. Significant effects of plasmon coupling emerged in longitudinal resonances having end-to-end configurations of gold nanorods. The effect of orientational plasmon coupling in dimers gives rise to both bonding and anti-bonding plasmon modes. Effects of various geometries like primary monomer, dimer, trimer, and tetramer structures have been explored and compared with their higher nanorod ensembles. The asymmetric spectral response in a 4 × 4 gold nanorods array indicates a Fano-like resonance. The variation of gap distance in ordered arrays allowed modulation of the Fano resonance mode. The plasmon modes’ resonance wavelength and field enhancement have been tuned by varying the gap distance, angular orientation, size irregularity between the nanorods, and nanorod numbers in an array. The integrated nanostructures studied here are not only significant for fundamental research but also applications in plasmon-based devices.

This article reports a simple one-step method for anisotropic gold nanoparticle synthesis for plasmonic photothermal therapy medical purposes, using 1,4-bis[(2-ethylhexyl) oxy]-1,4-dioxo-2-butanesulfonic acid-sodium (AOT) reverse micelles as nanoreactor, where under specific condition, AOT acts as both a reducing and stabilizing agent. Obtained AuNPs were functionalized by attaching compounds derived from 2-aminopteridin-4(3H)-ona (pterin family) such as (2S)-2-[(4-{[(2-amino-4-hydroxypteridin-6-yl) methyl] amino} phenyl) formamido] pentanedioic acid (folic acid/FA) and 2-amino-4-hydroxypteridine-6-carboxylic acid (PCA) in order to evaluate its effect as targets for folate receptor-mediated cellular uptake in HeLa and normal human endocervical cells. The nanoconjugates were characterized through transmission electron microscopy (TEM), ultraviolet-visible, fluorescence, and Fourier transform infrared spectroscopies. Results showed an effective photothermal response of AuNPs in solution under NIR exposure with concentration dependence and none effect of the conjugation. In vitro studies in HeLa cells showed a concentration-dependent cytotoxicity of AuNPs; thus, conjugation to biomolecules such as FA or PCA has provided a biocompatible coating onto AuNPs and made them highly cytocompatible. Results demonstrated despite AF and PCA are analogue molecules, the folate receptors in HeLa cells are specific, and the different chemical groups available on the AuNPs surface have drastically different cell membrane penetration properties. The specific cell uptake through folate receptor (FR) was observed for short treatment time, while for a long treatment time, other mechanisms as penetration or adhesion were shown involved. In the particular case, of AF@AuNPs, the cell uptake through FR-mediated endocytosis was evidenced to have been decreasing cell viability in 24% after 2 h of treatment and 5 min under NIR exposure. This was confirmed by morphological changes in cells, as well the selective uptake of the FA@AuNPs by HeLa cells compared to normal cells, due folate receptor overexpression in HeLa cells. The findings from this study will have implications in the chemical design of nanostructures for plasmonic photothermal therapy. The obtained results provide evidences at in vitro level to support the fact that AF@AuNP nanoconjugate will accumulate in the affected tissue preferentially through the EPR (enhanced permeability and retention) effect by folate-targeting mechanism which will significantly enhance the efficacy of NIR-induced local photothermal effects.

This study reports a new detection process for sensing ultra-low concentrations of tetracycline (TC), using a hot spot surface-enhanced Raman scattering (SERS) sensor. A gold nanoparticles/ macroporous silicon (Au NPs/macroPSi) hot spot SERS sensor was fabricated using a very simple and low cost method. The SERS signal was investigated using Au NPs/macroPSi hot spot SERS sensor for efficient detection of TC antibiotics at lower concentrations of (10 −3 –10 −9 ) mol/L. The sensor showed an excellent performance for TC detection with an enhancement factor (EF) of 2 × 10 8 , ultra-low detection limit of 10 −9 mol/L, and very high reproducibility with a relative standard deviation of 2%. The effect of the pH value on the behavior of the SERS spectra for TC antibiotic was evaluated, and it was found that pH values of 5 and 6 were the best for the detection process of TC antibiotic.

Fixed laser pulse duty cycle at 20% using short laser wavelength (405 nm) at different values of laser power density (300–600 mW/cm2) were used to form Si nano-columns as based SERS layer. The idea was to synthesize SERS devices with excellent reproducibility and high enhancement factor to detect ultra-low residence of chlorpyrifos pesticide. The results indicated that the morphological aspects of silicon nano-columns layer and; hence, the performance of SERS devices could be well-regulated through the adjustment of laser power density. The SERS detection of ultra-low chlorpyrifos concentrations displayed an excellent reproducibility with less than 5% error. The highest chlorpyrifos enhancement factor (EF = 1.1 × 106) and minimum detection limit (LOD = 22 × 10−8 M) were obtained from high altitude Si nano-columns; partly populated with three dimensions AuNPs layer, and the use of 500mW/cm2 laser power density.

The transitioning of nanotechnology from laboratory to industrial-scale manufacturing poses various challenges in nanoparticle realization. From this perspective, beside the conventional synthetic procedure, based on the seed-mediated growth approach, a reshaping thermal strategy has been investigated to improve the control on gold nanorods aspect ratio, with the aim to point out a potential and encouraging way to better manage the scalability and reproducibility of nanoparticles. For this purpose, nanorods covered with CTAB and nanorods enclosed within a silica shell of tuned thickness have been synthesized and submitted to a post-thermal treatment at various temperatures, up to 300 °C for CTAB recovered gold nanorods (AuNR@CTAB), and up to 500 °C for silica-shell embedded gold nanorods (AuNR@SiO2). For AuNR@CTAB, through accurate temperature control, the longitudinal plasmonic band can be moved very close to the transversal one upon slight reduction of their length. Instead, for AuNR@SiO2, owing to the fully inorganic shell, a higher temperature of treatment can be reached leading to the possibility of reshaping the nanorods into spheres without the observation of any by-products.

The miR-21 detection is essential for the accurate and early diagnosis or prognosis of most diseases. In the current study, the miR-21 detection method was performed based on the exploitation of the simple colorimetric biosensor due to the unique surface plasmon resonance (SPR) absorption of gold nanoparticles. AuNPs were functionalized with the specific DNA probes on the gold surface by Au-SH bond. Two strategies are proposed to detect the miR-21. In the first strategy, probes (DNA1 and DNA2) were complementary to the sequence of the miR-21. When miR-21 is introduced, the hybridization reaction is triggered between the golden nanoparticles- (GNP)-DNA conjugates and targets, resulting in changes in SPR absorption band and macroscopic color of the AuNPs solution. In the second strategy, we used a fluorescence sequence (DNA3-FAM), which was complimentary of DNA1. The DNA3-FAM was released after hybridization of miR-21 with DNA1 and DNA2. The free DNA3-FAM sequences in plate wells containing 1% agarose gel were assessed by fluorescent microscope. The combination of two strategies and conventional equipment such as UV–Vis spectrometers and fluorescent microscopes could be useful in detecting the desired miRNAs (miR-21).

Gold nanorod (AuNR) nanocomposite hydrogels have attracted increasing attention due to the photothermal effect of AuNRs. However, a facile strategy that avoids multi-step surface modification for synthesis of AuNR crosslinkers is still a critical challenge. Here, AuNRs crosslinking PNIPAM hydrogels were prepared by polymerization of NIPAM with N , N ′-bis(acryloyl)cystamine (BACA)-modified AuNRs as crosslinkers. BACA contains a disulfide bond in the structure. Dynamic and reversible Au-thiolate bonding was formed by directly mixing AuNRs and BACA to facilely prepare AuNR crosslinkers before hydrogel formation. The addition of AuNRs gives hydrogels their photothermal effect and remarkable mechanical behaviors. Hydrogels could repeatedly adhere to the surface of pigskin, metal, plastic, and glass with a relatively stable adhesion. The damaged hydrogels heal within 2 min with near-infrared (NIR) laser (808 nm, 300 mW∙cm −2 ) irradiation. This work provides a line of thinking for improvement of PNIPAM hydrogels, making them promising for further applications in biomedicine.

Stable solutions of gold nanoparticles with an average diameter of 13 nm and C Au = 5×10 –4 M were obtained by the reduction of HAuCl 4 with an equivalent amount of sodium sulfite at 80–100 °C in the presence of 2% PEG 6000 as a stabilizer: AuCl 4 – + 3/2 SO 3 2– + 3/2 H 2 O → Au 0 + 3/2 SO 4 2– + 3 H + + 4 Cl – . The resulting solutions of nanoparticles do not contain additional components capable of complexation, redox, and acid-based interactions. The effect of additives of thiourea, cysteine, thiomalate, and glutathione at various pH on the stability of such solutions to the aggregation has been studied. It was shown that the values of the protonation constants and charges of species of a thiol-containing component are not the only factors determining stability. Using thiomalate (HTM 2– ) as an example, it was shown also that at pH 7–8, the chemisorption is not followed by the release of H + ions into the solution.

Brazing of CoCrFeNi and CoCrFeMnNi equiatomic alloys using 70Au-8Pd-22Ni (AuPdNi) filler foil by infrared and traditional furnaces was investigated. The wettability of AuPdNi filler on both CoCrFeNi and CoCrFeMnNi substrates is excellent at 1050 °C. CoCrFeNi/AuPdNi/CoCrFeNi joints brazed using infrared and traditional furnaces are composed of Au/Ni-rich solid solutions of different sizes. CoCrFeMnNi/AuPdNi/CoCrFeMnNi joints brazed with an infrared furnace are composed of large globular CoCrFeNi/Ni-rich particles in AuMn intermetallic matrix. In traditional furnace brazed CoCrFeMnNi/AuPdNi/CoCrFeMnNi joints, the AuMn intermetallic compound is uniformly distributed in CoCrFeNi-based and Ni-rich phases. The average shear strengths of both infrared and traditional furnace brazed CoCrFeNi/AuPdNi/CoCrFeNi joints exceed 300 MPa, and all joints fractured at the brazed zone present dimple dominated fracture. In contrast, the traditional furnace brazed CoCrFeMnNi/AuPdNi/CoCrFeMnNi joint has a much lower average shear strength of 173 MPa because of the existence of many solidification shrinkage voids in the brazed zone.

Gold, used for jewelry and ornaments at times, is now considered a safe metal for investment. In addition to buying and selling gold physically, some markets offer electronic trade in gold. Trade volume is on surge in these bullion markets with each passing day. Daily opening and closing gold prices are used for analysis for 7740 days. Data series of daily return on investment in gold is split into two data series; first when the price goes up and second when the price goes down, at the day’s end. Statistical properties of three data series are analyzed and probabilities to earn profits are calculated during any day regardless of what types of decisions are going to be made that day. Probabilities of daily return, for both long and short positions, are presented in the form of tables. The expected daily profit of a trader with associated probability is explained in an illustrative example.

In the present work, sulfur-doped carbon nanotubes (SCNTs) have been prepared using chemical vapor deposition method and various cobalt-containing catalysts. In this line, simple and silica-supported cobalt nanoparticles (Co and Co/SiO 2 ) and 5 cobalt spinels (MCo 2 O 4 , M = Ni, Cu, Mn, Fe, Cr, and Mg) were used as the growth catalysts and four different temperatures (600, 650, 700, and 750 °C) were used to obtain the optimized condition for the preparation of SCNTs. Among the employed catalysts, Co/SiO 2 at 600 °C showed the higher abilities for the preparation of desired SCNTs. All products were characterized using FESEM, EDS, XRD, Raman, static contact angle, TGA, and DTA analyzes. The electrochemical behaviors of the two best products (SCNTs-Co/SiO 2 and SCNTs-Co) in hydrogen evolution reaction (HER) were examined, which confirmed the higher ability of SCNTs-Co/SiO 2 . This best product was decorated with 2, 5, and 10% of gold nanoparticles to examine the effect of gold decoration of the properties and electrochemical abilities of the product. All decorated products exposure the higher electrochemical potencies versus the simple SCNTs and among the decorated products, 10% Au-SCNT was the most appropriate product for this purpose with small differences with the other ones.

Au(I)/Au(III) redox catalysis, also known as redox gold catalysis, has evolved as a new technique in the past decade, opening up possibilities for the cross-coupling and 1,2-difunctioalization reactions of C–C multiple bonds that were previously inaccessible with gold(I) or gold(III) catalysis. However, the enantioselective Au(I)/Au(III) redox catalysis was missing until recently. The research group of Patil and Shi independently developed new hemilabile chiral (P,N)-ligands to achieve enantioselective redox gold catalysis for the first time.Graphical abstract

Gold oxides with thicknesses of less than 1 nm that were prepared by an oxygen-dc glow discharge over various periods (0.5–10 min) from gold films at room temperature were characterized by X-ray photoelectron spectroscopy (XPS), and a preservation method was developed for these oxides. The O 1s spectra show three oxygen species comprising components I, II, and III in the gold oxides. Components I and II are both stable and assigned to hydroxyl groups. The angular dependence of the XPS spectra of the gold oxides indicates that the oxygen species of components I and II are present in this order from the top surface of the gold oxide (component III). The gold oxides decompose after 36 h at room temperature and decompose immediately at temperatures exceeding 121 °C in a dark atmosphere. These gold oxides also decompose under ultraviolet (UV) light irradiation (254, 302, and 365 nm) at room temperature and decompose more rapidly in water vapor at the shorter wavelengths. These findings indicate that the gold oxide decomposition is accelerated via a reaction with excited water molecules produced by UV light absorption. The gold oxide decomposes after 6 h in water but decomposes more slowly in hydrocarbons (hexane, octane, and dodecane) at room temperature in a dark atmosphere. The gold oxide can be preserved in the oxidized state for 84 days in anhydrous dodecane. This simple preservation method of a gold oxide immersed in a hydrocarbon with low water content will be helpful for practical use in future applications.