Phase Transfer Of Gold Nanoparticles Research Articles

Ionic Liquid-Responsive Phase Transfer of Gold Nanoparticles: Anionic Metathesis.

In this work, a fresh approach has been proposed for the efficient transfer of gold nanoparticles (AuNPs) from an aqueous to organic phase by the metathesis reaction or anion exchange reaction. Here, we synthesized ionic liquid 1-butyl 3-hexadecyl imidazolium bromide [C4C16Im]Br-stabilized AuNPs which exhibit excellent stability in solution. Transfer of Au@[C4C16Im]Br from an aqueous to organic phase was investigated by the metathesis reaction with different hydrophobic ionic liquid-forming salts such as LiNTf2, LiClO4, and KPF6. The anionic exchange process in ionic liquids at the AuNP surface to make hydrophilic to hydrophobic AuNPs is demonstrated. It was found that hydrophobic ionic liquids provide the most effective transfer of AuNPs from the aqueous to organic phase. Interestingly, we have noticed no change in color, size, and shape of AuNPs for more than a month, indicating more efficient transfer of AuNPs in organic solvents, which remained stable for over a month. The ionic liquids with anions NTf2-, ClO4-, and PF6- make the AuNP surface hydrophobic, indicating their good dispersibility in nonpolar solvents. Finally, these AuNPs exhibit excellent sensitivity toward the refractive index of organic solvents, which is correlated with the surface plasmon resonance (SPR) λSPR bands.

Self-assembly and redox induced phase transfer of gold nanoparticles at a water-propylene carbonate interface.

Citrate-stabilized gold nanoparticles were found to spontaneously self-assemble into a lustrous film at a bare water-propylene carbonate interface after vigorous shaking, due to the extremely low interfacial tension. The presence of an electron donor, tetrathiafulvalene, in the oil phase, led to the extraction of particles into the organic phase.

Fully Reversible Quantitative Phase Transfer of Gold Nanoparticles Using Bifunctional PNIPAM Ligands.

Ligand exchange with end-functionalized polymers is often applied to render nanoparticles with enhanced colloidal stability, to change the solubility in various environments, and/or to introduce new functionalities. Here we show that exchange of citrate molecules with α-trithiocarbonate-ω-carboxyl-terminated poly(N-isopropylacrylamide) can successfully stabilize spherical gold particles of different diameters ranging from 15 to 53 nm. This is verified by transmission electron microscopy, dynamic light scattering, and extinction spectroscopy. We show that the polymer-decorated nanoparticles respond to temperature and pH allowing access to control interparticle interactions. In a range of pH slightly below the pKa of the terminal carboxyl groups, phase transfer of the particles from water to chloroform can be mediated by increasing the dispersion temperature above the lower critical solution temperature of poly(N-isopropylacrylamide). Upon cooling, fully reversible phase transfer to the water phase is observed. Extinction spectroscopy reveals phase transfer efficiencies close to 100% for every system under investigation.

Conjugates of gold nanoparticles and poly(ethylene glycol): Formation in hydrosol, direct transfer to organic medium, and stability of organosols

A onestage method has been developed for phase transfer of gold nanoparticles (NPs) with a diameter of 17.2 ± 0.5 nm from a hydrosol to an organic medium (chloroform). The method is based on the high affinity of thiolated poly(ethylene glycol) (TPEG) for nonpolar solvents and the capability of its molecules for chemisorption on a gold NP surface with the formation of a dense monolayer. Results of thermo-gravimetric analysis have been used to determine the maximum packing density (≈0.85 nm−2) of TPEG molecules on the surface of Au NPs with the aforementioned diameter. It has been shown that TPEG can play the roles of both an NP stabilizer and a phase transfer agent. Therewith, the degree of NP transfer from water to chloroform is ≈90%. The stability to aggregation of the obtained organosols has been found to increase with the chemisorption value of PEG molecules. It has been demonstrated that these organosols can be used to form two-dimensional ensembles of gold NPs on planar substrates.

Multidentate ionic surfactant mediated extraction and dispersion of gold nanoparticles in organic solvents.

Resorcinarenes with three different quaternary ammonium headgroups were synthesized and evaluated for their ability to stabilize gold nanoparticles in organic and aqueous medium. Aqueous dispersions of citrate stabilized gold nanoparticles of dimensions up to 29 nm could be extracted into organic solvents by resorcinarenes functionalized with tetrapyridinium tetrabromide (1), tetratrimethylammonium tetrabromide (2), and tetratributylammonium tetrabromide (3). Such nanoparticles were characterized by TEM, EDS, UV-vis, and IR. Their long-term dispersion stability varied significantly and depended on the nature of the resorcinarene headgroup, and in particular nanoparticles extracted by resorcinarene 1 were stable for several weeks. Nanoparticles passivated by resorcinarenes 1 and 2 were also stable in the presence of thiourea for several hours in both aqueous and organic medium. This is notable as thiourea is known to result in the instantaneous aggregation of citrate stabilized nanoparticles. Remarkably nanoparticles stabilized by resorcinarenes 1 and 2 could be precipitated and redispersed in chloroform without any visible aggregation. The critical parameters controlling the extraction of the nanoparticles into the organic phase have also been evaluated. The resorcinarene surfactant mediated facile phase transfer of gold nanoparticles described here can be readily applied for the stabilization of other citrate stabilized mono- and bimetallic nanoparticles, thus providing opportunities to disperse and stabilize relatively larger nanoparticles in organic solvents using ionic surfactants opening up new applications.

Effect of the alkyl chain length of secondary amines on the phase transfer of gold nanoparticles from water to toluene.

In the present paper we describe a phase transfer of aqueous synthesized gold nanoparticles (AuNPs) from water to toluene using secondary amines: dioctylamine, didodecylamine, and dioctadecylamine. The effect of the hydrocarbon chain length and amount of amines on the transfer efficiency were investigated in the case of nanoparticles (NPs) with three different sizes: 5, 9, and 13 nm. Aqueous colloids were precisely characterized before the transfer process using UV-vis spectroscopy, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Nanoparticles were next transferred to toluene and characterized using UV-vis and DLS techniques. It was found that dioctadecylamine provides the most effective transfer of nanoparticles. No time-dependent changes in the NP size were observed after 12 days, showing that the dioctadecylamine-stabilized nanoparticles dispersed in toluene were stable. This indicates that long hydrocarbon chains of dioctadecylamine exhibit sufficiently hydrophobic properties of nanoparticles and consequently their good dispersibility in nonpolar solvent.

Reversible phase transfer of nanoparticles based on photoswitchable host-guest chemistry.

An azobenzene-containing surfactant was synthesized for the phase transfer of α-cyclodextrin (α-CD)-capped gold nanoparticles between water and toluene phases by host–guest chemistry. With the use of the photoisomerization of azobenzene, the reversible phase transfer of gold nanoparticles was realized by irradiation with UV and visible light. Furthermore, the phase transfer scheme was applied for the quenching of a reaction catalyzed by gold nanoparticles, as well as the recovery and recycling of the gold nanoparticles from aqueous solutions. This work will have significant impact on materials transfer and recovery in catalysis and biotechnological applications.

Facile phase transfer of gold nanoparticles from aqueous solution to organic solvents with thiolated poly(ethylene glycol)

A simple approach for the efficient transfer of large gold nanoparticles from water to organic solvents using thiolated poly(ethylene glycol) as a phase transfer agent is presented.

Gold–Pluronic core–shell nanoparticles: synthesis, characterization and biological evaluation

This study presents the synthesis of gold–Pluronic core–shell nanoparticles by a two-step method and investigates their biological impact on cancer cells, specifically nanoparticle internalization and cytotoxicity. Uniform, 9–10-nm-sized, hydrophobic gold nanoparticles were synthesized in organic phase by reducing gold salt with oleylamine, after which oleylamine-protected gold nanoparticles were phase-transferred into aqueous medium using Pluronic F127 block copolymer, resulting in gold–Pluronic core–shell nanoparticles with a mean hydrodynamic diameter of ~35 nm. The formation and phase-transfer of gold nanoparticles were analyzed by UV–Vis absorption spectroscopy, transmission electron microscopy, and dynamic light scattering. The obtained gold–Pluronic core–shell nanoparticles proved to be highly stable in salted solution. Cytotoxicity tests showed no modification of cellular viability in the presence of properly purified particles. Furthermore, dark-field cellular imaging demonstrated that gold–Pluronic nanoparticles were able to be efficiently uptaken by cells, being internalized through nonspecific endocytosis. The high stability, proven biocompatibility, and imaging properties of gold–Pluronic core–shell nanoparticles hold promise for relevant intracellular applications, with such a design providing the feasibility to combine all multiple functionalities in one nanoparticle for simultaneous detection and imaging.

Comparative study of alkylthiols and alkylamines for the phase transfer of gold nanoparticles from an aqueous phase to n-hexane

An efficient ligand-assisted phase transfer method has been developed to transfer gold nanoparticles (Au-NPs, d: 5–25nm) from an aqueous solution to n-hexane. Four different ligands, namely 1-dodecanethiol (DDT), 1-octadecanethiol (ODT), dodecylamine (DDA), and octadecylamine (ODA) were investigated, and DDT was found to be the most efficient ligand. It appears that the molar ratio of DDT to Au-NPs is a critical factor affecting the transfer efficiency, and 270–310 is found to be the optimum range, under which the transfer efficiency is >96%. Moreover, the DDT-assisted phase transfer can preserve the shape and size of the Au-NPs, which was confirmed by UV–vis spectra and transmission electron microscopy (TEM). Additionally, the transferred Au-NPs still can be well dispersed in the n-hexane phase and remain stable for at least 2weeks. On the other hand, the ODT-, DDA-, and ODA-assisted phase transfer is fraught with problems either related to transfer efficiency or NPs aggregation. Overall, the DDT-assisted phase transfer of Au-NPs provides a rapid and efficient method to recover Au-NPs from an aqueous solution to n-hexane.

Versatile film formation and phase transfer of gold nanoparticles by changing the polarity of the media

A simple method to prepare gold particles of different sizes and polydispersities is presented. The diameter of the gold particles ranges from 5 to 50 nm. All systems were prepared in either ethylene glycol or mixtures of ethylene glycol:water without adding any external reducing agent in the presence of sodium docecyl sulfate as a stabilzer and afterward transferred into chloroform or accumulated at interface in the form of film. The absence of water in ethylene glycol is a prerequisite for successful 3-dimensional self-assembly film at the interface. The free standing film was very stable and could be easily transferred on solid support. The probability of the film formation at the interface decreased with the increase in the content of water in the mixture. It was observed that as the polarity of the media increases after a certain extent, Au particles neither get transferred nor accumulated at interface and remained in the form of emulsion. However, addition of NaOH leads to the transfer process. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be re-dispersed in different nonpolar solvents. The dispersed particles were stable for at least 45 days. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques.

Versatile Phase Transfer of Gold Nanoparticles from Aqueous Media to Different Organic Media

A novel, simple, and very efficient method to prepare hydrophobically modified gold particles is presented. Gold nanoparticles of different sizes and polydispersities were prepared. The diameter of the gold particles ranges from 5 to 37 nm. All systems were prepared in aqueous solution stabilized by citrate and afterwards transferred into an organic phase by using amphiphilic alkylamine ligands with different alkyl chain lengths. The chain length was varied between 8 and 18 alkyl groups. Depending on the particle size and the alkylamine, different transfer efficiencies were obtained. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be redispersed in different organic solvents. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) techniques. The effect of organic solvents with various refractive indices on the plasmon band position was investigated.

Phase transfer of gold nanoparticles from aqueous to organic solution containing resorcinarene

Citrate-capped gold nanoparticles (NPs) in aqueous solution were transferred directly into the organic solution mesitylene containing C-undecylcalix[4]-resorcinarene (C11-resorcinarene). C11-resorcinarene, which has long hydrophobic tails and phenolic hydroxyl groups, acted as both a phase-transfer and a capping agent. The C11-resorcinarene-capped gold particles could be isolated and dispersed in different organic solvents. Optical absorption spectra corresponding to surface plasmon resonance provided a broad band centered at 534 nm for C11-resorcinarene-capped gold NPs in mesitylene. High-resolution transmission electron micrograph images revealed that the average particle diameter of C11-resorcinarene-capped gold NPs is ∼12 nm.

Aqueous-organic phase transfer of gold nanoparticles and gold nanorods using an ionic liquid.

The water-immiscible ionic liquid, [C4MIM][PF6], is a solvent medium that allows complete transfer of gold nanoparticles from an aqueous phase into an organic phase. Both spherical and rod-shaped gold nanoparticles are efficiently transferred from an aqueous solution into the organic phase without requiring the use of thiols. The sizes and shapes of the gold nanoparticles were preserved during the phase-transfer process when a surfactant was added to the ionic liquid. This process offers a simple approach for obtaining solutions of differently sized and shaped gold nanoparticles in ionic liquids.

Size-Dependent Phase Transfer of Gold Nanoparticles from Water into Toluene by Tetraoctylammonium Cations: A Wholly Electrostatic Interaction

In this study, it is demonstrated that the tetraoctylammonium cation can be used directly as a phase-transfer reagent of negatively charged water-based gold nanoparticles. The transference is size-dependent and is based on a wholly electrostatic interaction.

Phase Transfer of Gold Nanoparticles across a Water/Oil Interface by Stoichiometric Ion-Pair Formation on Particle Surfaces

Abstract The transfer of surface-modified gold nanoparticles across a water/toluene interface was demonstrated. Stoichiometric ion-pair formation between carboxylate anions on particle surfaces and tetraoctylammonium cations brought about the phase transfer, and was revealed by transmission electron microscopy (TEM), IR, UV-vis absorption, and energy dispersive X-ray (EDX) spectroscopies. A surface structure of the transferred gold nanoparticles was also presented. During the nanoparticle transfer from water into an organic phase, an improvement in the dispersibility and a slight decrease in the average diameter were observed (3.6 → 2.9 nm) accompanied by a slight narrowing in the size distribution (standard deviation: 0.80 → 0.54 nm). The phenomena could lead to a new methodology for size and/or dispersibility selections.