Study of tryptophan assisted synthesis of gold nanoparticles by combining UV–Vis, fluorescence, and SERS spectroscopy

We developed a rapid and non-toxic method for the preparation of colloidal gold nanoparticles (GNPs) by using tryptophan (Trp) as reducing/stabilizing agent. We show that the temperature has a major influence on the kinetics of gold ion reduction and the crystal growth, higher temperatures favoring the synthesis of anisotropic nanoparticles (triangles and hexagons). The as-synthesized nanostructures were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), fluorescence, and surface-enhanced Raman scattering (SERS) spectroscopy. The UV–Vis measurements confirmed that temperature is a critical factor in the synthesis process, having a major effect on the shape of the synthesized GNPs. Moreover, fluorescence spectroscopy was able to monitor the quenching of the Trp fluorescence during the in situ synthesis of GNPs. Using Trp as molecular analyte to evaluate the SERS efficiency of as-prepared GNPs at different temperatures, we demonstrated that the Raman enhancement of the synthesized gold nanoplates is higher than that of the gold spherical nanoparticles.     

Trapping and release of citrate-capped gold nanoparticles

An electrical method to trap and release charged gold nanoparticles onto and from the surface of gold electrodes modified by an alkanethiol self-assembled monolayer (SAM) is presented. To form electrodes coated with gold nanoparticles (GNPs), amine-terminated SAMs on gold electrodes were immersed in a solution of negatively charged citrate-capped GNPs. Accumulation of GNPs on the electrode surface was monitored by a decrease in the impedance of the SAM-modified electrode and by an increase in the electrochemical activity at the electrode as shown through cyclic voltammetry (CV). Electrostatic interactions between the GNPs and the amine-terminated SAM trap the GNPs on the electrode surface. Application of a subsequent negative bias to the electrode initiated a partial release of the GNPs from the electrode surface. Impedance spectroscopy, cyclic voltammetry, ultraviolet-visible (UV-Vis) spectroscopy and atomic force microscopy (AFM) were used to monitor and confirm the attraction of GNPs to and release from the aminealkanethiolated gold electrodes. This work describes a method of trapping and release for citrate-capped GNPs that could be used for on-demand nanoparticle delivery applications such as in assessing and modeling nanoparticle toxicology, as well as for monitoring the functionalization of gold nanoparticles.     

Investigation the effects of nano golds on the fluorescence properties of the sectorial poly(amidoamine) (PAMAM) dendrimers

The influence of nano golds on fluorescence properties of sectorial Polyamidoamine dendrimers (G4 s-PAMAM) was investigated in this paper. It was found that gold nanoparticles (GNPs) with definite surface plasmon absorption can quench the fluorescence of G4 s-PAMAM dendrimers. With the increasing of the concentration of GNPs, the fluorescence intensity of G4 s-PAMAM decreased correspondingly, and varied linearly at low concentration of GNPs. This phenomenon was owing to the fluorescence resonance energy transfer (FRET) between the dendrimers and GNPs. In contrast, the complex with smaller gold nanodots (GNDs) encapsulated in the interior of the G4 s-PAMAM presented greatly enhanced emission. Those results show that the size of nano golds may be used to adjust the fluorescence properties of sectorial PAMAM dendrimers and may extend potential applications of PAMAM dendrimers and nano golds.     

Real-time SAXS and ultraviolet-visible spectral studies on size and shape evolution of gold nanoparticles in aqueous solution

Gold nanoparticles were synthesized with seed mediated wet growth method. A coexistent system with gold nanorods and nanospheres was prepared. In-situ real-time small angle X-ray scattering (SAXS) and ultraviolet-visible (UV-vis) absorption were used to monitor the growth process of Au nanoparticles in the aqueous solution. Combining SAXS measurement and UV-vis spectra, the contribution of gold nanorods was separated from that of gold nanospheres. The growth behavior of the gold nanorods and the gold nanospheres was studied. The size and shape evolution of both gold nanoparticles as well as their volume fractions were obtained. After adding the seed-solution into the growth solution to form a particle suspension, within the first 18 min, a mutual competitive growth occurred between the gold nanorods and nanospheres. And their average particle sizes always increased with growth time. 18-min later, the evolution of size and shape of gold nanoparticles was almost stopped. The results demonstrate that the aspect ratio of gold nanorods in the particle suspension follows an exponential decay change after the initial 5-min growth. The evolution process of size and shape of gold nanoparticles in the particle suspension has been discussed.     

Biosynthesis of gold nanoparticles using Capsicum annuum var. grossum pulp extract and its catalytic activity

Biological synthesis approach has been regarded as a green, eco-friendly and cost effective method for nanoparticles preparation without any toxic solvents and hazardous bi-products during the process. This present study reported a facile and rapid biosynthesis method for gold nanoparticles (GNPs) from Capsicum annuum var. grossum pulp extract in a single-pot process. The aqueous pulp extract was used as biotic reducing agent for gold nanoparticle growing. Various shapes (triangle, hexagonal, and quasi-spherical shapes) were observed within range of 6–37 nm. The UV–Vis spectra showed surface plasmon resonance (SPR) peak for the formed GNPs at 560 nm after 10 min incubation at room temperature. The possible influences of extract amount, gold ion concentration, incubation time, reaction temperature and solution pH were evaluated to obtain the optimized synthesis conditions. The effects of the experimental factors on NPs synthesis process were also discussed. The produced gold nanoparticles were characterized by transform electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDS) and Fourier Transform infrared spectroscopy (FTIR). The results demonstrated that the as-obtained GNPs were well dispersed and stable with good catalytic activity. Biomolecules in the aqueous extract were responsible for the capping and stabilization of GNPs.     

VEGFR-2 targeted cellular delivery of doxorubicin by gold nanoparticles for potential antiangiogenic therapy

We report a novel gold nanobioconjugate system that achieves targeted delivery of the small molecule drug doxorubicin to endothelial cells using anti-VEGFR-2 antibody conjugated gold nanoparticles (GNPs). The reported nanobioconjugate system combines the inherent ability of GNPs to undergo high levels of derivatization with the precision of antibody recognition of a cell surface antigen. Transmission electron microscopy (TEM) and surface-enhanced Raman spectroscopy (SERS) confirmed intracellular presence of the GNPs. Using a VEGFR-2 expressing cell line and a cell line that is negative for the receptor, in combination with competition assay we established the cell specific targeted delivery of the nanobioconjugate. The nanobioconjugate system described here may have potential drug delivery applications for antiangiogenic cancer therapy.     

金纳米棒标记HepG2人肝癌细胞的荧光成像及其AFM探测

金纳米棒具有独特的光学性质,在生物医学领域有着广泛而重要的应用前景.本文制备了长径比为8∶1的金纳米棒,其在480 nm波长激发下,在560 nm和707 nm波长处有两个荧光发射峰.基于金纳米棒的荧光性质,将其标记于HepG2人肝癌细胞表面,利用激光扫描共聚焦显微镜对标记后的细胞进行荧光成像.在488 nm激发下,获...     

金纳米粒子的电化学合成及光谱表征

采用电化学方法合成各种形状的金纳米粒子,生成的金纳米粒子形貌与施加电流有关,通过匀速递增电流电解的方法,可制备得到哑铃形,球形以及棒状金纳米粒子,采用恒电流电解方法主要获得球形及哑铃形纳米粒子。利用透射电镜、紫外-可见光谱及拉曼光谱对金纳米粒子进行相关表征。紫外-可见光谱研究发现金纳米棒出现位于近红外区间的吸收峰(985 nm),由此推测棒的长径比约为6。以结晶紫为探针分子,研究了金纳米粒子的表面增强拉曼光谱(SERS)效应,并分析得出其平躺的吸附模式。根据形貌表征的结果推断了纳米粒子的生长机理。     

Direct monitoring of gold nanorod growth

The seed-mediated growth of gold nanorods is shown to be strongly dependent on the reaction time and chemical environment of the reaction solution. The versatile seed-mediated approach in aqueous surfactant solutions has been used in this study for the synthesis of gold nanorods. Changes in the aspect ratio of gold nanorods were reflected in shifts of the plasmon resonance peaks and were monitored using UV-Visible absorption spectroscopy (UV-Vis) to follow the different stages of gold nanorod formation as a function of time and varying amounts of silver ion. Unlike the use of strong reducing agents to make spherical gold nanoparticles, the growth of gold nanorods requires weak reducing conditions, leading to an unknown degree of gold reduction. Therefore, cyclic voltammetry was used to electrochemically interrogate the entire reaction from gold seed to gold nanorod as a function of time. Data obtained revealed that time-dependent gold species are involved in gold nanorod formation.     

An anisotropic snowflake-like structural assembly of polymer-capped gold nanoparticles

Snowflake-like structural assembly of isotropic gold nanoparticles (GNPs) is reported. A modified polyamine method has been employed to synthesize positively charged GNPs in presence of a polymeric metaphosphate. This process yields fascinating dendritic self-assembled morphologies. Structural characterization revealed that there was aggregation of crystalline GNPs. The aggregates of GNPs formed in the initial stage of synthesis are assumed to act as the bulging seeds for final growth of complex morphologies at nanometer to micrometer length scale. Self-assembly of GNPs was found to be greatly influenced by the concentration of gold precursor. Diffusion limited aggregation of GNPs is suggested as the plausible mechanism for this nanoparticle self-organization process.     

A Correlative Analysis of Gold Nanoparticles Internalized by A549 Cells

Fluorescently labeled nanoparticles are widely used to investigate nanoparticle cell interactions by fluorescence microscopy. Owing to limited lateral and axial resolution, nanostructures (<100 nm) cannot be resolved by conventional light micro­scopy techniques. Especially after uptake into cells, a common fate of the fluorescence label and the particle core cannot be taken for granted. In this study, a correlative approach is presented to image fluorescently labeled gold nanoparticles inside whole cells by correlative light and electron microscopy (CLEM). This approach allows for detection of the fluorescently labeled particle shell as well as for the gold core in one sample. In this setup, A549 cells are exposed to 8 nm Atto 647N‐labeled gold nanoparticles (3.3 × 10⁹ particles mL^?1, 0.02 μg Au mL^?1) for 5 h and are subsequently imaged by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). Eight fluorescence signals located at different intracellular positions are further analyzed by TEM. Five of the eight fluorescence spots are correlated with isolated or agglomerated gold nanoparticles. Three fluorescence signals could not be related to the presence of gold, indicating a loss of the particle shell.     

Facile Functionalization of Gold Nanoparticles with PLGA Polymer Brushes and Efficient Encapsulation into PLGA Nanoparticles: Toward Spatially Precise Bioimaging of Polymeric Nanoparticles

Nanocarriers prepared from poly(lactide‐co‐glycolide) (PLGA) have broad biomedical applications. Understanding their cellular uptake and distribution requires appropriate visualization in complex biological compartments with high spatial resolution, which cannot be offered by traditional imaging techniques based on fluorescent or radioactive probes. Herein, the encapsulation of gold nanoparticles (GNPs) into PLGA nanoparticles is proposed, which should allow precise spatial visualization in cells using electron microscopy. Available protocols for encapsulating GNPs into polymeric matrices are limited and associated with colloidal instability and low encapsulation efficiency. In this report, the following are described: 1) a facile protocol to functionalize GNPs with PLGA polymer followed by 2) encapsulation of the prepared PLGA‐capped GNPs into PLGA nanocarriers with 100% encapsulation efficiency. The remarkable encapsulation of PLGA‐GNPs into PLGA matrix obeys the general rule in chemistry “like dissolves like” as evident from poor encapsulation of GNPs capped with other polymers. Moreover, it is shown that how the encapsulated gold nanoparticles serve as nanoprobes to visualize PLGA polymeric hosts inside cancer cells at the spatial resolution of the electron microscope. The described methods should be applicable to a wide range of inorganic nanoprobes and provide a new method of labeling pharmaceutical polymeric nanocarriers to understand their biological fate at high spatial resolution.     

Brownian diffusion of gold nanoparticles in an optical trap studied by fluorescence correlation spectroscopy

The effect of thermal-induced Brownian motion on gold nanoparticles (Au NPs) in optical traps is studied by fluorescence correlation spectroscopy (FCS) method. The Brownian motion and optical trapping potential are investigated by the decay time of the FCS curve and the laser power. It is shown that that the probability of finding a gold nanoparticle in the trap depends on the ratio of the optical energy of the particle to its thermal energy. A power threshold is observed by the decay time as a function of laser power. The experimental studies show that the temperature rise does not seriously affect the average number of particles in the focal spot, but the average residence time is more sensitively affected by the temperature.     

Sonication-assisted layer-by-layer deposition of gold nanoparticles for highly conductive gold patterns

Sonication-assisted layer-by-layer (LBL) deposition of gold nanoparticles (GNPs) was carried out in an attempt to prepare highly conductive gold patterns on polyimide substrates. First, sonication time was optimized with GNPs (12.8 nm) whose size was large enough to be analyzed by FE-SEM in order to evaluate the surface coverage. Next, multilayer formation (4, 8 and 12 layer) was confirmed using ethanedithiol (EDT) as linker molecules under optimized conditions by measuring their UV absorption, near-IR (NIR) transmittance, thickness, and electrical conductivity. Finally, 20-layer films using small GNPs (2.5 nm) were prepared with or without patterning, followed by sintering at 150 °C for 1 h, which provided clean gold patterns with high electrical conductivity (2.5 × 10⁵ Ω⁻¹ cm⁻¹).     

PdNi-decorated manganite nanocatalyst for electrooxidation of ethylene glycol in alkaline media

PdNi bimetallic nanoparticles coated onto manganite (MN) nanocatalyst was used for ethylene glycol (EG) and glycerol (Gly) electrooxidation in alkaline media. The MN nanorods were prepared by hydrothermal method, and the PdNi was coated on the rods by an in situ reduction method. The prepared nanocomposite was characterized by scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS), and electrochemical methods. The SEM and TEM images exhibit the formation of nanorods of 10?nm and also show the formation of nanocrystalline PdNi on the walls of the MN nanorods. This study shows that the MN nanorods can be excellent support material and they supply oxygen to the catalyst, by which the catalytic activity is enhanced. The electrooxidation reactions in strong alkaline condition containing various concentrations of EG have been studied. Among the different concentrations, 9?M KOH/6?M EG exhibits the highest activity. PdNi/MN nanocatalyst exhibits better activity even in higher electrolytic concentrations of EG and alkali.     

Quasi 3D imaging of DNA-gold nanoparticle tetrahedral structures

Verification by imaging of the structure of 3D DNA constructs, both bare and conjugated to metal nanoparticles, is challenging. We demonstrate here two transmission electron microscopy (TEM) based methods to distinguish between fully formed tetrahedra, synthesized from DNA conjugated with gold nanoparticles (GNPs) at their vertices, and structures which are only partially formed. When deposited on a surface, fully formed tetrahedra are expected to retain their 3D pyramidal structure, while partially formed structures are expected to form a 2D structure. The first method by which 3D and 2D structures were distinguished was imaging them at different defocusing values. While for 2D structures all the four GNPs acquire Fresnel fringes at the same defocusing value, for 3D structures at least one particle is at a different plane with respect to the others, and so it acquires Fresnel fringes at a different defocusing value. The second method we show is imaging of the structures at different angles. While a single TEM image gives only a 2D projection of the structure, by combining information achieved from imaging at several tilting angles one may verify the structural construct.     

Preparation of functional spherical polysilsesquioxane/gold nanoparticle composites and their applications in DNA assay

Functional spherical solid and hollow particles of polysilsesquioxanes (PSQs) containing amine, thiol, and vinyl groups were prepared by polymerizing organotrialkoxysilanes (OTASs) containing corresponding chemical groups. Fluorescent PSQ particles were prepared by physically entrapping Rhodamine 6G, Coumarin 7, and Fluoresceine sodium salts. The intensity of fluorescent light increased initially with increasing amount of entrapped fluorophores and then leveled off or decreased slightly after reaching a maximum value. PSQ particles containing gold nanoparticles (GNPs), both inside and on the surface, were prepared by the in situ reduction of gold ions by the PSQ particles. When the reduction reaction was carried out for extended periods of time, the GNP that had formed inside the poly(3-mercaptopropyl)silsesquioxane (PMPSQ) and polyvinylsilsesequioxane (PVSQ) particles underwent interesting morphological changes. PSQ particles containing amine and thiol groups fixed the GNPs on the surface, which could be utilized further in binding amine-modified oligo-DNA strands. The aggregation of PSQ/GNP particles combined with complementary oligo-DNA strands was examined to demonstrate that these particles could be applied to DNA assays and isolation. The particles were characterized by scanning electron microscopy, transmission electron microscopy, solid state nuclear magnetic resonance spectroscopy, ultraviolet/visible spectroscopy, and fluorescence microscopy.     

Controllable synthesis of Ag nanorods using a porous anodic aluminum oxide template

This paper describes a new approach to the synthesis of Ag nanorods. A solvothermal method was used to make Ag nanoparticles inside anodic aluminum oxide (AAO) templates. The nanoparticles were then annealed at 300 °C to produce Ag nanorods. The size of AAO templates, which is focused on in this study, would determine the diameter of Ag nanorods. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this study, a nanorod growth mechanism is deduced, and understanding of the growth of nanorods inside AAO templates is furthered. This work demonstrates that it is possible to make crystalline nanorods that the size can be varied.     

Effects of temperature,pH, and ionic strength on the adsorption of nanoparticles at liquid–liquid interfaces

The effects of temperature, pH and sodium chloride (NaCl) concentration on the equilibrium and dynamic interfacial tension (IFT) of 4.4-nm gold nanoparticles capped with n-dodecanethiol at hydrocarbon–water interfaces was studied. The pendant drop technique was used to study the adsorption properties of these nanoparticles at the hexane–water and nonane–water interfaces. The physical size of the gold nanoparticles was determined by TEM image analysis. The interfacial properties of mixtures of these nanoparticles, having different sizes and capping agents, were then studied. The addition of NaCl was found to cause a decrease of the equilibrium and dynamic IFT greater than that which accompanies the adsorption of nanoparticles at the interface in the absence of NaCl. Although IFT values for acidic and neutral conditions were found to be similar, a noticeable decrease in the IFT was found for more basic conditions. Increasing the temperature of the system was found to cause an increase in both dynamic and equilibrium IFT values. These findings have implications for the self-assembly of functionalized gold nanoparticles at liquid–liquid interfaces.     

Size-dependent interaction of gold nanoparticles with transport protein: A spectroscopic study

Gold nanoparticles of different sizes have been synthesized using sodium citrate as a reducing agent for tetrachloroauric (III) acid. The formed gold nanoparticles have been characterized by the UV-visible and transmission electron microscopy (TEM) measurements. The different sized gold nanoparticles have been used to study the interaction with model transport protein, bovine serum albumin (BSA). Experimental results reveal that BSA molecules adsorbed on the metallic surfaces, suffer strong quenching of their fluorescence and the rate of quenching efficiency is different for different particle size. The analysis of the quenching results has been performed in terms of the Stern-Volmer equation. The mechanism of quenching of fluorescence has been explained. The extent of adsorption of BSA on the gold nanoparticles has been estimated.