Sonosynthesis of gold nanoparticles from a geranium leaf extract

A rapid in situ biosynthesis of gold nanoparticles (AuNPs) is proposed in which a geranium (Pelargonium zonale) leaf extract was used as a non-toxic reducing and stabilizing agent in a sonocatalysis process based on high-power ultrasound. The synthesis process took only 3.5 min in aqueous solution under ambient conditions. The stability of the nanoparticles was studied by UV–Vis absorption spectroscopy with reference to the surface plasmon resonance (SPR) band. AuNPs have an average lifetime of about 8 weeks at 4 °C in the absence of light. The morphology and crystalline phase of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The composition of the nanoparticles was evaluated by electron diffraction and X-ray energy dispersive spectroscopy (EDS). A total of 80% of the gold nanoparticles obtained in this way have a diameter in the range 8–20 nm, with an average size of 12 ± 3 nm. Fourier transform infrared spectroscopy (FTIR) indicated the presence of biomolecules that could be responsible for reducing and capping the biosynthesized gold nanoparticles. A hypothesis concerning the type of organic molecules involved in this process is also given. Experimental design linked to the simplex method was used to optimize the experimental conditions for this green synthesis route. To the best of our knowledge, this is the first time that a high-power ultrasound-based sonocatalytic process and experimental design coupled to a simplex optimization process has been used in the biosynthesis of AuNPs.     

Effect of gold nanoparticle size on acoustic cavitation using chemical dosimetry method

When a liquid is irradiated with high intensities of ultrasound irradiation, acoustic cavitation occurs. Acoustic cavitation generates free radicals from the breakdown of water and other molecules. Cavitation can be fatal to cells and is utilized to destroy cancer tumors. The existence of particles in liquid provides nucleation sites for cavitation bubbles and leads to decrease the ultrasonic intensity threshold needed for cavitation onset. In the present investigation, the effect of gold nanoparticles with appropriate amount and size on the acoustic cavitation activity has been shown by determining hydroxyl radicals in terephthalic acid solutions containing 15, 20, 28 and 35 nm gold nanoparticles sizes by using 1 MHz low level ultrasound. The effect of sonication intensity in hydroxyl radical production was considered.The recorded fluorescence signal in terephthalic acid solutions containing gold nanoparticles was considerably higher than the terephthalic acid solutions without gold nanoparticles at different intensities of ultrasound irradiation. Also, the results showed that the recorded fluorescence signal intensity in terephthalic acid solution containing finer size of gold nanoparticles was lower than the terephthalic acid solutions containing larger size of gold nanoparticles. Acoustic cavitation in the presence of gold nanoparticles can be used as a way for improving therapeutic effects on the tumors.     

Effect of surface acoustic waves on activity in heterogeneous catalysis

A synopsis of the recent developments in acoustically influencing and controlling gas-surface interactions is presented. The cleaning effect of ultrasound and its surface activation play an important role for the sonochemical enhancement of reactivity in chemical processes involving solid and liquid phases. So far, there have only been a few studies on the effects of surface acoustic waves on surface chemical reactions under high-vacuum conditions by the application of piezoelectric surface acoustic wave transducers. Very recently, metal films deposited between InterDigital Transducer (IDT) electrodes on a LiNbO₃ substrate have shown a significant inerease in catalytic activity during surface acoustic excitation and Edge-Bonded Transducers (EBT) with a metal single crystal as a substrate have been used to acoustically influence the rate in the oscillatory reaction for CO oxidation. Tunable narrowband surface acoustic excitation is anticipated to be an efficient route to control catalytic processes, and in our work this approach is being used to investigate the physical basis of this process.     

Ultrasound technology for food fermentation applications

Fermentation processes involve the participation of enzymes and organic catalysts, generated by range of microorganisms to produce chemical transformations. Ultrasound can be used in such processes to either monitor the progress of fermentation or to influence its progress. High frequency ultrasound (>2 MHz) has been extensively reported as a tool for the measurement of the changes in chemical composition during fermentation providing real time information on reaction progress. Low frequency ultrasound (20–50 kHz) can influence the course of fermentation by improving mass transfer and cell permeability leading to improved process efficiency and production rates. It can also be used to eliminate micro-organisms which might otherwise hinder the process. This review summarises key applications of high and low frequency ultrasound in food fermentation applications.     

Ultrasound-assisted cyanide extraction of gold from gold concentrate at low temperature

A sonochemical reactor was developed to study the ultrasound-assisted cyanide extraction of gold from gold ore at low temperature. The effects of ultrasound on gold leaching in low temperature and conventional conditions were investigated. At the low temperature of 10 °C, ultrasound-assisted extraction increased extraction rate of gold by 0.6%–0.8% and reduced the gold content of cyanide tailings to 0.28 g/t in the leaching of gold concentrate and cyanide tailings, respectively. At the conventional temperature of 25 °C, ultrasound-assisted extraction obtained a 0.1% higher extraction rate of gold compared with conventional extraction, with the unit consumption of NaCN reduction of 15%. The analysis of kinetic model also demonstrated that sonication indeed improved the reaction of gold leaching greatly. The mineralogy and morphology of ore were further analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and particle size analyzer to explore the strengthening mechanism of gold leaching. The results showed that the ore particles were smashed, the ore particle surface was peeled, the passive film was destroyed and the reaction resistance decreased under ultrasonic processing. Therefore, the extraction rate of gold was improved and the extraction time was shortened significantly in ultrasound-assisted cyanide extraction.     

Raman spectroscopy as a tool for long‐term energetic material stability studies

Raman spectroscopy is shown to be useful as a tool for long‐term stability studies. The stability of a novel submicron‐size γ‐polymorph form of the explosive HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) was monitored up to 1 year using Raman spectroscopy. The preparation and characterization of this submicron HMX has been previously discussed. It is important to know the long‐term stability of this submicron γ‐polymorph material under ambient conditions for its eventual utilization. This submicron HMX material has been found to be stable both chemically and polymorphically (to the order of 1% impurity level), even though HMX normally converts to the β‐polymorph at ambient conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Ripening of nanowire-supported gold nanoparticles

Gold nanoparticles have applications ranging from catalysts for low temperature oxidation of CO to solar energy capture in the infrared. For all these applications, particle size and shape are critical. In this study, nanoparticle gold formed on GaN nanowires by plasma-enhanced chemical vapor deposition was annealed at temperatures ranging from 150 to 270 °C for 24 h. Particle size was measured before and after annealing using a field emission scanning electron microscope. Ripening of the gold particles was observed even at the lowest annealing temperatures of the study. The particle growth kinetics showed an Arrhenius relationship with activation energy of 27.38 kJ/mol. This value suggests that ripening occurs by particle migration and coalescence rather than adatom diffusion.     

Lysozyme microspheres incorporated with anisotropic gold nanorods for ultrasound activated drug delivery

We report on the fabrication of lysozyme microspheres (LyMs) incorporated with gold nanorods (NRs) as a distinctive approach for the encapsulation and release of an anticancer drug, 5-Fluorouracil (5-FU). LyMs with an average size of 4.0 ± 1.0 µm were prepared by a sonochemical method and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). The LyMs were examined using hydrophobic (nile red) as well as hydrophilic (trypan blue) dyes under confocal laser scanning microscopy (CLSM) to obtain information about the preferential distribution of fluorescent molecules. Notably, the fluorescent molecules were accumulated in the inner lining of LyMs as the core was occupied with air. The encapsulation efficiency of 5-FU for LyMs-NR was found to be ∼64%. The drug release from control LyMs as well as LyMs incorporated with NRs was investigated under the influence of ultrasound (US) at 200 kHz. The total release for control LyMs and LyMs incorporated with gold NRs was found to be ∼70 and 95% after 1 h, respectively. The density difference caused by NR incorporation on the shell played a key role in rupturing the LyMs-NR under US irradiation. Furthermore, 5-FU loaded LyMs-NR exhibited excellent anti-cancer activity against the THP-1 cell line (∼90% cell death) when irradiated with US of 200 kHz. The enhanced anti-cancer activity of LyMs-NR was caused by the transfer of released 5-FU molecules from bulk to the interior of the cell via temporary pores formed on the surface of cancer cells, i.e., sonoporation. Thus, LyMs-NR demonstrated here has a high potential for use as carriers in the field of drug delivery, bio-imaging and therapy.     

Microwave assisted one pot synthesis of biocompatible gold nanoparticles in Triton X-100 aqueous micellar medium using tryptophan as reducing agent

The present work reports an environmentally benign process for the synthesis of gold nanoparticles via microwave-assisted heating method, using a basic amino acid l-Tryptophan as reducing agent. The synthesis was carried out in the presence of a nonionic surfactant Triton X-100 (TX-100) aqueous micellar system. Influence of various reaction parameters such as microwave irradiation time and concentrations of precursor ion were analyzed. The effect of pH on the plasmonic properties and stability of synthesized AuNPs were studied in detail. The various size distributions of gold nanostructures obtained were characterized and analyzed by ultraviolet visible spectroscopy (UV-Vis), TEM and DLS analysis. Fourier transform infrared (FT-IR) measurements were carried out to identify the interaction sites responsible for capping and efficient stabilization by the amino acid as well as the surfactant. The synthesized gold nanoparticles were stable for more than 6 months at ambient conditions.     

Extracellular biosynthesis of monodispersed gold nanoparticles by a SAM capping route

Monodispersed gold nanoparticles capped with a self-assembled monolayer of dodecanethiol were biosynthesized extracellularly by an efficient, simple, and environmental friendly procedure, which involved the use of Bacillus megatherium D01 as the reducing agent and the use of dodecanethiol as the capping ligand at 26 °C. The kinetics of gold nanoparticle formation was followed by transmission electron microscope (TEM) and UV-vis spectroscopy. It was shown that reaction time was an important parameter in controlling the morphology of gold nanoparticles. The effect of thiol on the shape, size, and dispersity of gold nanoparticles was also studied. The results showed that the presence of thiol during the biosynthesis could induce the formation of small size gold nanoparticles (<2.5 nm), hold the shape of spherical nanoparticles, and promote the monodispersity of nanoparticles. Through the modulation of reaction time and the use of thiol, monodispersed spherical gold nanoparticles capped with thiol of 1.9 ± 0.8 nm size were formed by using Bacillus megatherium D01.     

Intensification of heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction using ultrasound: Understanding effect of operating parameters

Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction is a significant reaction for obtaining industrially important products. The current research work deals with intensification of reaction of 4-bromoanisole and phenylboronic acid catalyzed with 5 wt% Pd/C (5% by weight Pd supported on C available as commercial catalyst) using ultrasound and more importantly, without use of any additional phase transfer catalyst. Heterogeneous catalyst has been selected in the present work so as to harness the benefits of easy separation and the possible limitations of heterogeneous operation are minimized by introducing ultrasonic irradiations. The effect of operating parameters such as ultrasound power, temperature, catalyst loading and molar ratio on the progress of reaction has been investigated. It has been observed that an optimum power, temperature and catalyst loading exist for maximum benefits whereas higher molar ratio was found to be favourable for the progress of the reaction. Also, the use of ultrasound reduced the reaction time from 70 min required in conventional approach to only 35 min under conditions of frequency of 22 kHz, power dissipation of 40 W and catalyst loading as 1.5 mol% (refers to total quantum of catalyst used in the work) in ethanol-water system under ambient conditions. The work also demonstrated successful results at ten times higher volume as compared to the normally used volumes in the case of simple ultrasonic horn. Overall, the work has successfully demonstrated process intensification benefits obtained due to the use of ultrasound for heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction.     

Photochemical synthesis of polygonal gold nanoparticles

In this paper, we propose a method to generate gold nanoparticles capable of absorbing near infrared light (NIR) radiation through a photochemical reaction. This approach does not require the use of either surfactants or polymers, reducing the difficulties that may arise in further chemical modifications for the gold nanoparticles. The gold nanoparticles with either triangular or hexagonal shapes were generated using the photo-reduction method, mixing hydrogen tetrachloroaurate with sodium oxalate, a reducing agent, in aqueous solution under illumination of a mercury lamp (λ_max = 306 nm) for more than 10 min. The size of the gold nanoparticles varies from 25 to 200 nm, which mainly depends on the duration of light illumination and the concentration of sodium oxalate. Furthermore, we demonstrate that the presence of the gold nanoparticles in aqueous solutions can effectively elevate the temperature of the solutions under irradiation of NIR light (808 nm) within a few minutes. The gold nanoparticles can be potentially used as suitable photothermal agents for hyperthermia.     

Sonochemical preparation of carbon spheres

Spherical morphology of carbon with 150–400 nm size is produced by sonication (480 kHz, 2.5 W) of toluene with water under ambient conditions. Medium range of frequency and weak power of ultrasound is found to be the appropriate conditions for preparing the carbon spheres. Morphological and structural analysis of the product is carried out with TEM, SEM, elemental analysis, TGA, and FT-IR spectroscopy.     

DFT study of CO and NO adsorption on low index and stepped surfaces of gold

Adsorption energies and vibrational frequencies of CO and NO adsorbed on gold (1 1 1), (1 0 0), (1 1 0) and (3 1 0) surfaces, as well as on adatoms on Au(1 0 0) have been calculated using density functional theory. The results clearly show that the adsorption energy of the molecules increases considerably with increasing the degree of coordinative unsaturation of the gold atoms to which the molecules bind, and thus support the view that defects, steps and kinks on the surface determine the activity of gold catalysts.     

Synthesis of monodisperse spherical AgNPs by ultrasound-intensified Lee-Meisel method,and quick evaluation via machine learning

Due to the high reactivity of Ag⁺ and uncontrolled growth process, the AgNPs produced by conventional Lee-Meisel method always exhibited larger particle size (30–200 nm) and polydisperse morphology (including spherical, triangular, and rod-like shape). An ultrasound-intensified Lee-Meisel (UILM) method is developed in this study to environmental-friendly and controllable synthesize monodisperse spherical AgNPs (~3.7 nm). Effects of Ag:citrate ratio (1:3 or 5:4), ultrasound power (300 to 1200 W) and reaction time (4 to 24 min) on the physical–chemical properties of AgNPs are investigated systematically. The transmission electron microscope (TEM) images, UV–Vis spectra, average particle size, zeta potential and pH value all demonstrate that crystallization and digestive ripening processes are facilitated in the presence of ultrasound irradiation. Therefore, both chemical reaction rate and mass transfer rate are enhanced to accelerate primary nucleation and inhibit uncontrolled particle growth, leading to the formation of monodisperse spherical AgNPs. Moreover, a machine learning approach - Decision Tree Regressor in conjunction with Shapley value analysis reveal the concentration of reactants is a more important feature affecting the particle.     

Effects of pores and temperature on mechanics of gold nanowires using molecular dynamics

The deformation mechanisms of gold nanowires with different nanopores under tension were simulated by molecular dynamics (MD). The stress–strain curves varied from different porous defects, and the tension caused dislocations to take place and slip along plane (1 1 1). Moreover, the tensile strength of the nanoporous monocrystalline gold was decreased when the simulated temperature increased. The stress concentrations factors of porous nanowires were calculated, and it was found that there was a great influence of size and model effects on the stress concentration factors.     

Ultrasound-assisted green synthesis of gold nanoparticles using citrus peel extract and their enhanced anti-inflammatory activity

Ultrasound and plant extract are two green approaches that have been used to synthesize gold nanoparticles (AuNPs); however, how the combination of ultrasound and citrus peel extract (CPE) affects the structure characteristics and the bioactivity of AuNPs remains unknown. Here we investigated the effects of ultrasound conditions on the particle size, stability, yield, phenolic encapsulation efficacy, and the anti-inflammatory activity of AuNPs. The results showed that temperature was positively correlated to the particle size and the anti-inflammatory activity of synthesized AuNPs. Increasing the power intensity significantly decreased the particle size, while increased the change of total phenolic content (ΔTPC) in the reaction mixture. The increase of ΔTPC caused the enhanced anti-inflammatory activity of AuNPs. The AuNPs synthesized with or without ultrasound treatment were characterized using UV–Vis, DLS, SEM, TEM, EDS, XRD, and FT-IR. The result verified the formation of negatively charged, spherical, stable, and monodispersed AuNPs. AuNPs synthesized with ultrasound (AuNPs-U) has smaller particle size (13.65 nm vs 16.80 nm), greater yield and anti-inflammatory activity (IC₅₀, 82.91 vs 157.71 μg/mL) than its non-ultrasound counterpart (AuNPs-NU). HPLC analysis showed that hesperidin was the key reductant for the synthesis of AuNPs. AuNPs-U also inhibited the mRNA and protein expression of iNOS and COX-2 in the LPS-induced Raw 264.7 cells. Our research elucidates the relationship between the reaction conditions and the structure characteristics and the anti-inflammatory activity of AuNPs synthesized using CPE with the help of ultrasound, thereafter, provides a feasible and economic way to synthesize AuNPs that can be used to ameliorate inflammation.     

Ultrasound assisted enzymatic conversion of non edible oil to methyl esters

Conventional and ultrasound-assisted hydrolysis and subsequent esterification of Nagchampa oil under mild operating conditions have been investigated with an objective of intensification of methyl esters production using a sustainable approach. The effect of ratio of reactants, temperature, enzyme loading, pretreatment of enzyme (using ultrasonic irradiations) on the hydrolysis and esterification reaction has been studied. Optimum conditions for hydrolysis were observed to be 1:1 weight ratio of oil: water for Lip Z and 1:3 for Lip 2 enzymes, enzyme loading of 400 units for Lip Z and 800 mg for Lip 2 enzymes and reaction time of 6 h. In the case of esterification reaction, optimum conditions obtained were oil to methanol molar ratio of 1:2, enzyme loading of 1000 mg and reaction time of 20 h. Use of pretreated enzyme (using ultrasonic irradiations) was found to increase the extent of esterification reaction from 75% to 92.5%. It was observed that use of ultrasound in the reaction significantly intensified the esterification reaction with time requirement reducing from 20 h for conventional stirring based approach to only about 7.5 h in the presence of ultrasound. The extent of esterification obtained with sonicated enzyme also increased to 96% from 75% with unsonicated enzyme.     

Interaction between fullerene-wheeled nanocar and gold substrate: A DFT study

Since the successful synthesis of nanocar and its surprising movement on the gold surface, several theoretical investigations have been devoted to explain the interaction properties as well as its movement mechanism on the substrate. All of them failed, however, to gain a clear theoretical insight into the respected challenges because of the weak computational methods implemented for this complex system including heavy metal atoms and giant size of the whole system. In this work, we have investigated the adsorption of fullerene-wheeled nanocar onto a Au (1 1 1) substrate using the comprehensive first-principles density functional theory (DFT) simulations. The binding energy between the nanocar and Au (1 1 1) surface was determined to be −9.43 eV (−217.45 kcal/mol). The net charge transfer from the nanocar to the gold substrate was calculated to be about 9.56 electrons. Furthermore, the equilibrium distances between the Au surface and the C₆₀ molecule and nanocar chassis were estimated to be 2.20 Å and 2.30 Å, respectively. The BSSE correction was also considered in the binding energy estimation and the result show that the BSSE correction significantly affects the calculated binding energy for such systems.Finally, we have performed ab initio molecular dynamics simulation for a single C₆₀ fullerene on the gold surface at room temperature. Our first-principles result shows that ambient condition affect remarkably on the adsorption property of fullerene on the gold surface. We also observed that the C₆₀ fullerene wheel slips by approximately 3.90 Å within 5 ps of simulation time at 300 K.     

Sonothrombolysis with an acoustic net-assisted boiling histotripsy: A proof-of-concept study

Whilst sonothrombolysis is a promising and noninvasive ultrasound technique for treating blood clots, bleeding caused by thrombolytic agents used for dissolving clots and potential obstruction of blood flow by detached clots (i.e., embolus) are the major limitations of the current approach. In the present study, a new sonothrombolysis method is proposed for treating embolus without the use of thrombolytic drugs. Our proposed method involves (a) generating a spatially localised acoustic radiation force in a blood vessel against the blood flow to trap moving blood clots (i.e., generation of an acoustic net), (b) producing acoustic cavitation to mechanically destroy the trapped embolus, and (c) acoustically monitoring the trapping and mechanical fractionation processes. Three different ultrasound transducers with different purposes were employed in the proposed method: (1) 1-MHz dual focused ultrasound (dFUS) transducers for capturing moving blood clots, (2) a 2-MHz High Intensity Focused Ultrasound (HIFU) source for fractionating blood clots and (3) a passive acoustic emission detector with broad bandwidth (10 kHz to 20 MHz) for receiving and analysing acoustic waves scattered from a trapped embolus and acoustic cavitation. To demonstrate the feasibility of the proposed method, in vitro experiments with an optically transparent blood vessel-mimicking phantom filled with a blood mimicking fluid and a blood clot (1.2 to 5 mm in diameter) were performed with varying the dFUS and HIFU exposure conditions under various flow conditions (from 1.77 to 6.19 cm/s). A high-speed camera was used to observe the production of acoustic fields, acoustic cavitation formation and blood clot fragmentation within a blood vessel by the proposed method. Numerical simulations of acoustic and temperature fields generated under a given exposure condition were also conducted to further interpret experimental results on the proposed sonothrombolysis. Our results clearly showed that fringe pattern-like acoustic pressure fields (fringe width of 1 mm) produced in a blood vessel by the dFUS captured an embolus (1.2 to 5 mm in diameter) at the flow velocity up to 6.19 cm/s. This was likely to be due to the greater magnitude of the dFUS-induced acoustic radiation force exerted on an embolus in the opposite direction to the flow in a blood vessel than that of the drag force produced by the flow. The acoustically trapped embolus was then mechanically destructed into small pieces of debris (18 to 60 μm sized residual fragments) by the HIFU-induced strong cavitation without damaging the blood vessel walls. We also observed that acoustic emissions emitted from a blood clot captured by the dFUS and cavitation produced by the HIFU were clearly distinguished in the frequency domain. Taken together, these results can suggest that our proposed sonothrombolysis method could be used as a promising tool for treating thrombosis and embolism through capturing and destroying blood clots effectively.