Water-soluble Gold Nanoparticles Research Articles

Synthesis, characterization, DNA interaction and potential applications of gold nanoparticles functionalized with Acridine Orange fluorophores

Two new water-soluble gold nanoparticles (AO-TEG-Au and AO-PEG-Au NPs) are prepared and characterized. They are stabilized by thioalkylated oligoethylene glycols and functionalized with fluorescent Acridine Orange (AO) derivatives. Despite the different core sizes (11.8 and 3.9 nm respectively) and shell composition, they are both well dispersed and are stable in water, even if some self-aggregation is observed in the case of AO-TEG-Au NPs. However, AO-PEG-Au NPs show much lower emission efficiency with respect to AO-TEG-Au NPs. Spectrophotometric and spectrofluorometric experiments indicate that both types of nanoparticle are able to bind to calf thymus DNA, either by external binding or partial intercalation. Preliminary FACS flow cytometry tests seem to indicate that the AO-TEG-Au nanoparticle is able to cross the cell membrane where it is absorbed by Chinese hamster ovary (CHO) cells at the picomolar concentration level.

Synthesis and characterization of azidoalkyl-functionalized gold nanoparticles as scaffolds for “click”-chemistry derivatization

We demonstrate how water-soluble gold nanoparticles prepared by the citrate reduction method can be functionalized with 11-azidoundecane-1-thiol in a single-step procedure, which combines phase transfer and ligand exchange. The advantages of our method include high reproducibility, low cost of gold nanoparticle production, and rapid and clean ligand exchange, with minimal intermediate steps and none of the laborious efforts. The resulting azido-functionalized nanoparticles were characterized by 1H NMR and UV-visible spectroscopy, and visualized by transmission electron microscopy (TEM).

Simultaneously Controlled Directionality and Valency on a Water-Soluble Gold Nanoparticle Precursor for Aqueous-Phase Anisotropic Self-Assembly

The anisotropic interaction of gold nanoparticles (AuNP's) into a highly accurate, scalable complex structure not only would aid practical nanoscale assembly but also would increase their utility in many applications, including electronics, optics, and biosensing. Particularly for biological purposes, here we demonstrate an aqueous-phase serial solid-phase monofunctionalization approach to synthesize water-soluble AuNP linkers that contain distinctive single or double diametric functionalities in a site-specific way. Using a mild, rapid, effective single-phase 1:1 ligand replacement reaction between mixed-ligand-protected AuNP precursors and ligand-group-attached silica gels, we successfully synthesized (1) two types of monofunctionalized (monof-) carboxyl- or amino-AuNP's with enhanced yield and accuracy and (2) heterobifunctionalized (bif-) AuNP's with one carboxyl and one amine end group at a discrete angle (∼160°). The controlled coupling chemistry in aqueous solution allowed the covalent bond-directed assembly of intentionally designed 1D dimers with monof-AuNP's and 2D rings with heterobif-AuNP's, confirming the highly functional as well as directional selectivity of the functionalized NPs. This study thus represents an important step toward active control over the design and assembly of bottom-up nanostructures with increased complexity and biocompatibility.

Amphiphilic gold nanoparticles: Synthesis, characterization and adsorption to PEGylated polymer surfaces

The direct synthesis of water-soluble gold nanoparticles with a mixed shell of two different thiols, 1-mercaptoundec-11-yl-hexa(ethylene glycol) (EG6) and dodecanethiol (C12), and their characterization are reported. Data from IR spectroscopy and contact angle (CA) measurements as well as the solubility of the nanoparticles in water support that the composition of the shell is in the range of the thiol ratio used for synthesis (EG6:C12=72:28). Results of transmission electron microscopy and atomic force microscopy (AFM) for deposited particles as well as the UV–vis spectrum in solution are in line with a size of ≤10nm. Self-assembled monolayers (SAMs) as model surfaces were prepared from mixtures of EG6 and C12 on planar gold films. Polystyrene (PSt) spin-coated films on silicon wafers and on gold-coated surface plasmon resonance (SPR) sensor disks were used as substrates for surface functionalization via adsorption/self-assembly of a polystyrene poly(ethylene glycol) diblock copolymer (PSt-b-PEG) from aqueous solutions. CA and AFM results revealed pronounced differences of the hydrophilicity/hydrophobicity and topography of the surface as a function of PSt-b-PEG concentration used for the modification. The adsorption of myoglobin and the novel gold nanoparticles to the PSt-b-PEGylated surfaces was analyzed by SPR. A control of adsorbed amounts by the degree of surface PEGylation, i.e. a reduction by up to 55% for the highest degree of modification, could be confirmed for both kinds of colloids. Adsorption of the novel gold nanoparticles to the mixed SAM surfaces as analyzed by SPR showed an even stronger dependency of surface composition. All experiments demonstrate that amphiphilic, water-soluble gold-based nanoparticles can be used as model colloids for the investigation of interactions with polymer surfaces of varied structure and architecture, and that they could be further developed for analytical or biological applications.

Surface Effects in Water-Soluble Shell−Core Hybrid Gold Nanoparticles in Oligonucleotide Single Strand Recognition for Sequence-Specific Bioactivation

Highly monodisperse water-soluble shell-core hybrid gold nanoparticles were prepared by in situ reduction of gold salts in the presence of a bifunctional thiol, tiopronin. The resulting particles exhibited diameters of 20-60 nm, as characterized by scanning electron microscopy. The tiopronin coating was uniform, exposing a carboxylated monolayer surface that was further modified by coupling with an amino-maleimide linker. The polar heteroorganic shell rendered these materials water-soluble and, as a result, amenable to conditions for coupling with molecules of biological importance, for example, thiolated oligonucleotides. When brought into contact with a homogeneously dispersed oligonucleotide chain, the functionalized shell-core particle binds with a complementary oligonucleotide chain with high specificity. Binding could be qualitatively recognized by easily observed fluorescence differences. The largest particles (ca. 60 nm diameter) were unstable in buffered water, and further condensation ultimately led to aggregation and precipitation. In contrast, particles with diameters of 20-30 nm were stable in buffered water and were easily further functionalized with matched oligonucleotide double strands. This work thus constitutes a new route for the preparation of stable modified gold nanoparticles that can be easily further modified to deliver a metal core particle in aqueous media, as required for recognition, and manipulation, of specific biological sequences. Surface properties are key variables for these applications.

Synthetic antibacterial agent assisted synthesis of gold nanoparticles: Characterization and application studies

In this study, we report synthesis of water-soluble gold nanoparticles (Au-NPs), having an average diameter of ca. ∼20 nm, using ciprofloxacin (CF) as a reducing/stabilizing agent. The synthesized Au-NPs have been characterized by scanning electron microscopy (SEM), EDX, TEM, UV–visible spectroscopy (UV–vis), X-ray diffraction and cyclic voltammetry. TEM and SEM combined with EDX analysis confirmed that spherical-shaped Au-NPs were formed. UV–vis spectra of the Au-NPs showed two absorption bands corresponding to the capping agent ciprofloxacin and surface plasmon absorption bands at 274 and 527 nm, respectively. The synthesized Au-NPs are used to modify a glassy carbon electrode (GCE) and its electrochemical and electrocatalytic properties are investigated. The Au-NPs modified electrode showed excellent electrocatalytic activity towards the oxidation of methanol at +0.33 V in alkaline solution, which was not observed on the unmodified GCE. Further, electrocatalytic reduction of oxygen was also studied using the Au-NPs modified electrode at lower potential. Here, CF was used as a reducing agent for the preparation of Au-NPs dispersion. This Au-NPs dispersion is highly stable, and can be stored for more than three months in air at room temperature.

Protein Enhanced Near-Infrared Fluorescence of AuNPs and Its Application for Protein Determination

The 15∼25 nm water soluble and stable gold nanoparticles were synthesized and studied for their spectral properties and interactions with proteins. Results showed that 15 nm gold nanoparticles can emit near infrared fluorescence with an emission peak of 811.2 nm under the excitation of 538 nm. The study also showed that proteins can obviously enhance the near infrared fluorescence intensity of gold nanoparticles. Under the optimized conditions, there is a linear relationship between the fluorescence intensity enhancement of the system and the concentrations of the proteins, which can be used in a new method for the determination of trace proteins. The mechanisms of the interaction and the fluorescence enhancement of the nano-gold-protein system were also studied.

One-Phase Synthesis of Water-Soluble Gold Nanoparticles with Control over Size and Surface Functionalities

We report a simple and efficient synthetic method to prepare gold nanoparticles (AuNPs) in aqueous phase using HAuCl(4) and poly(ethylene glycol) (PEG) ligands appended with bidentate anchoring groups. Our approach provides narrow size distribution nanocrystals over the size range between 1.5 and 18 nm; this range is much wider than those achieved using other small molecules and polymer ligands. The NP size was simply controlled by varying the molar ratio of Au-to-PEG ligand precursors. Further passivation of the as-prepared AuNPs permitted in situ functionalization of the NP surface with the desired functional groups. The prepared AuNPs exhibit remarkable stability in the presence of high salt concentrations, over a wide range of pHs (2-13), and a strong resistance to competition from dithiothreitol (DTT). These results are a clear manifestation of the advantages offered by our synthetic approach to prepare biocompatible AuNPs, where modular, multifunctional ligands presenting strong anchoring groups and hydrophilic PEG chains are used.

Water-Soluble Palladium and Gold Nanoparticles Functionalized by a New Phosphine with Zwitterionic Liquid Based on Imidazolium Sulfonate Linked Ethylene Glycol Moiety

A new phosphine with zwitterionic liquid based on imidazolium sulfonate linked ethylene glycol moiety (1) as a protective ligand for metal nanoparticles has been prepared. Its phosphine 1-stabilized palladium and gold nanoparticles (1-Pd and 1-Au) were found to be soluble in water, and remarkably stable in high concentration of aqueous electrolyte and ionic liquid. 1-Pd nanoparticles behave as an efficient catalyst for the Suzuki cross-coupling reaction in an aqueous medium.

Size-Tunable Synthesis of Monodisperse Water-Soluble Gold Nanoparticles with High X-ray Attenuation

Size-Tunable Synthesis of Monodisperse Water-Soluble Gold Nanoparticles with High X-ray Attenuation

Minute synthesis of extremely stable gold nanoparticles

We describe a rapid environmentally friendly wet-chemical approach to synthesize extremelystable non-toxic, biocompatible, water-soluble monodispersed gold nanoparticles (AuNPs) inone step at room temperature. The particles have been successfully achieved in just a fewminutes by merely adding sodium hydroxide (NaOH) acting as an initiator for the reduction ofHAuCl4 in aqueous solution in the presence of polyvinylpyrrolidone (PVP) without the use of anyreducing agent. It is also proved to be highly efficient for the preparation of AuNPs withcontrollable sizes. The AuNPs show remarkable stability in water media with highconcentrations of salt, various buffer solutions and physiological conditions in biotechnologyand biomedicine. Moreover, the AuNPs are also non-toxic at high concentration (100 µM). Therefore, it provides great opportunities to use these AuNPs for biotechnology andbiomedicine. This new approach also involved several green chemistry concepts, such as theselection of environmentally benign reagents and solvents, without energy consumption,and less reaction time.

Synthesis of Thioethyl Pendant Ligand-Stabilized Colloidal Gold Nanoparticles

A general synthetic method capable of producing a kind of water-soluble gold nanoparticles possessing single-phase synthetic route, high concentration, small size under control, easy store, and excellent thermal, pH and salt stability, was demonstrated. The combined studies with transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and UV-visible spectra clearly show that the gold nanoparticles modified by thioethyl-pendant ligand exist.

Evaluating Aggregation of Gold Nanoparticles and Humic Substances Using Fluorescence Spectroscopy

The fate and transport of diagnostic gold nanoparticles in surface waters would significantly depend on their interactions with humic substances, which are ubiquitously found in natural aquatic systems. The current study employs UV-visible absorbance and fluorescence spectroscopy to investigate the interactions of commercial humic acid (HA) with gold nanoparticles having a core size of 5 nm and coated with two different stabilizers, beta-D-glucose and citrate. Humic substances (HS) are fluorescent in nature, providing a unique probe of nanometer-scale morphological changes for interactions between these natural polyelectrolytes and water-soluble gold nanoparticles. Quenching of fluorescence intensity was observed with beta-D-glucose-coated gold nanoparticles, whereas an enhancement effect was noticed with the citrate-coated particles when mixed with HA having concentrations of 2 and 8 ppm (surface waters typically may contain approximately 10 ppm HS). Examining the quenching and enhancement of fluorescence provides insight into the structural changes taking place at the coated gold nanoparticle-HA interface. The quenching behavior suggested ligand exchange due to nanometer-scale contact between the HA and beta-D-glucose-coated gold nanoparticles, whereas the enhancement effect with citrate particles would indicate overcoating, leading to increased transfer distances for fluorescence resonance energy transfer.

Lanthanide luminescent gold nanoparticles: pH-driven self-assembly formation between Eu(III)-cyclen conjugated AuNPs and sensitising β-diketonate antenna in water

The formation of a self-assembly between water soluble gold nanoparticles AuNP-1.Eu, functionalised with a heptadentate macrocyclic Eu(III) cyclen conjugate via an alkyl thiol spacer, and a naphthalene β-diketone antenna was investigated as a function of pH in water. In the study, the changes in the absorption spectra of the antenna and the gold surface plasmon resonance band, the fluorescence and the delayed Eu(III) emission of the self-assembly were all monitored. We demonstrate that the Eu(III) emission arising from the self-assembly formation on AuNP is significantly modulated as a function of pH, where within the physiological pH range, the emission is ‘switched on’ and that a direct connection can be made between theses changes and the quenching in the antenna as a function of pH.

Luminescent, water-soluble gold nanoparticles functionalised with 3MLCT emitting rhenium complexes

Rhenium complexes functionalised with thioester-terminated alkyl chains can be attached to gold nanoparticles to yield water-soluble, visibly luminescent Re-GNP hybrid conjugates.

Water-Soluble Gold Nanoparticles Protected by Fluorinated Amphiphilic Thiolates

The preparation and the properties of gold nanoparticles (Au NPs) protected by perfluorinated amphiphiles are described. The thiols were devised to form a perfluorinated region close to the gold surface and to have a hydrophilic portion in contact with the bulk solvent to impart solubility in water. The monolayer protected clusters were prepared, in an homogeneous phase using sodium thiolates because of the low nucleophilicity of the alpha-perfluorinated thiols, and fully characterized with (1)H, (19)F NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Au NPs with core diameters ranging from 1.6 to 2.9 nm, depending on the reaction conditions, were obtained. Water-soluble NPs (MPC-F8-PEGs) were obtained with the thiol HS-F8-PEG ending with a short poly(ethylene glycol) unit (PEG-OMe 550), whereas thiols with shorter PEG chains give rise to NPs insoluble in water. MPC-F8-PEGs undergo an exchange reaction with amphiphilic alkyl thiols. ESR investigations, using a hydrophobic radical probe, indicate that the MPC-F8-PEG monolayer shows a greater hydrophobicity compared to the analogous hydrogenated monolayer.

Simple one-step synthesis of water and organic media soluble gold nanoparticles with various shapes and sizes

Gold nanoparticles with an average diameter in the range 1–100 nm have been synthesized from hydrogen tetrachloroaureate (III) hydrate (HAuCl 4·3H 2O) in didodecyldimethyl ammonium bromide (DDAB) aqueous solutions at room temperature. The particle size could be controlled by the concentration of DDAB and HAuCl 4·3H 2O, and reaction temperature. An increase in DDAB concentration caused a change in the particle shape from spherical to triangular, rectangular or various shapes. Until critical concentration of DDAB, where the size of gold nanoparticles seemed to prevent particle growth from aggregation, and resulted in small particle size and narrow size distribution. And DDAB-coated nanoparticles can be dispersed well in both water and organic solvent with high colloidal stability.

ω-Thioacetylalkylphosphonium salts: Precursors for the preparation of phosphonium-functionalised gold nanoparticles

Two new ω-thioacetylalkylphosphonium salts that function as masked cationic alkanethiolate ligands for the stabilisation of gold nanoparticles have been prepared. Both (3-thioacetylpropyl)triphenylphosphonium bromide and (6-thioacetylhexyl)triphenylphosphonium bromide were shown to form water-soluble gold nanoparticles of ca. 5–10 nm in size that are stable for up to six months. The related (3-thioacetylpropyl)diphenylphosphine oxide was also prepared but did not act as a stabilising ligand in gold nanoparticle formation.

Fabrication of gold nanoparticles using luminol as a reductive and protective reagent

An easy and simple reaction is employed to synthesize ligand-protected gold nanoparticles. In this reaction, luminol is used as a reductive and protective reagent to prepare gold nanoparticles in aqueous solution. It includes two steps: chemiluminescence and formation of gold nanoparticles. The formation processes were monitored by resonance light scattering spectroscopy, and the results were observed by transmission electron microscopy and x-ray photoelectron spectroscopy. Highly stable gold nanoparticles about 110 ± 2 nm in size can be readily obtained. A new insight into the design of water-soluble ligand-protected gold nanoparticles for biomedical, analytical, and catalytic applications has been provided.

Monodisperse Protein Stabilized Gold Nanoparticles via a Simple Photochemical Process

Protein stabilized, water soluble gold nanoparticles are essential for biomedicines and biotechnology. Bovine Serum Albumin (BSA) is one of the most abundant proteins. It has a remarkable ability of binding and transporting materials across cell membrane that makes it ideal for drug delivery and very useful for pharmaceutical industry. Herein, we explored the direct synthesis of BSA stabilized gold nanoparticles via a simple photochemical process. BSA stabilized gold nanoparticles are synthesized in one step, using Irgacure (I-2959) as photoinitiator. UV radiation facilitates the easy one step synthesis of protein stabilized gold nanoparticles without any denaturation of the protein, during the process. Polyacrylamide Gel (PAGE) shows that there is no difference in the bands height and mobility of native BSA and UV irradiated BSA. PAGE results are further confirmed by fluorescence spectroscopy of native and UV irradiated BSA. BSA/PEG (polyethylene glycol) mixed monolayer stabilized gold nanoparticles have...