Janus Gold Nanoparticles Research Articles

An imine-based approach to prepare amine-functionalized Janus gold nanoparticles.

An imine-based approach was developed to prepare Janus gold nanoparticles (Janus AuNPs) having amine functionality on one patch of the surface and a polyethylene glycol unit on the other. This unique technique features covalent bonding as the force to immobilize AuNPs on the template, enabling direct modification of AuNPs in both water and organic solvents. Colloidal clusters were then obtained via electrostatic assembly of these Janus AuNPs with citrate stabilized AuNPs or AgNPs.

Amphiphilic Janus gold nanoparticles prepared by interface-directed self-assembly: synthesis and self-assembly.

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub-10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface-directed self-assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface-directed self-assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol-terminated polystyrene (PS-SH) was dissolved in toluene and citrate-stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS-SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid-liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom-transfer radical polymerization (ATRP) initiator. Poly[2-(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface-initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self-assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.

Comparison of the Interfacial Activity between Homogeneous and Janus Gold Nanoparticles by Pendant Drop Tensiometry

The interfacial activity of 3.5 nm homogeneous (HPs) and amphiphilic Janus gold nanoparticles (JPs) was characterized by pendant drop tensiometry for water/air and water/decane interfaces. This technique requires a smaller quantity of nanoparticles than the traditional Langmuir balance technique. The direct deposition at the interface of the nanoparticles dispersed in a spreading solvent also requires smaller quantities of sample than does adsorption from the bulk. From the growing and shrinking of the pendant drops, the interfacial activity of the nanoparticles can be evaluated and compared within a wide range of area per particle. In this work, the JPs exhibited a higher interfacial activity than did the HPs in all cases. A hard disk model fits the piecewise compression isotherm of the HPs, yet this model underestimates the interactions between the JPs adsorbed at the interface.

High-Resolution Scanning Tunneling Microscopy Characterization of Mixed Monolayer Protected Gold Nanoparticles

Gold nanoparticles protected by a binary mixture of thiolate molecules have a ligand shell that can spontaneously separate into nanoscale domains. Complex morphologies arise in such ligand shells, including striped, patchy, and Janus domains. Characterization of these morphologies remains a challenge. Scanning tunneling microscopy (STM) imaging has been one of the key approaches to determine these structures, yet the imaging of nanoparticles' surfaces faces difficulty stemming from steep surface curvature, complex molecular structures, and the possibility of imaging artifacts in the same size range. Images obtained to date have lacked molecular resolution, and only domains have been resolved. There is a clear need for images that resolve the molecular arrangement that leads to domain formation on the ligand shell of these particles. Herein we report an advance in the STM imaging of gold nanoparticles, revealing some of the molecules that constitute the domains in striped and Janus gold nanoparticles. We analyze the images to determine molecular arrangements on parts of the particles, highlight molecular "defects" present in the ligand shell, show persistence of the features across subsequent images, and observe the transition from quasi-molecular to domain resolution. The ability to resolve single molecules in the ligand shell of nanoparticles could lead to a more comprehensive understanding of the role of the ligand structure in determining the properties of mixed-monolayer-protected gold nanoparticles.

Synthesis and Characterization of Janus Gold Nanoparticles

When gold nanoparticles are coated with binary mixtures of dislike ligand molecules, separation in the ligand shell occurs; if the particles are smaller than a threshold size the separation is solely enthalpy driven leading to the spontaneous formation of Janus particles.

Janus gold nanoparticle with bicompartment polymer brushes templated by polymer single crystals

Janus particles have attracted increasing attention from the communities of materials science, chemistry, physics and biology. While large size Janus particles are readily achieved, synthesizing Janus nanoparticles (JNP) with diameters smaller than ∼20 nm remains a challenging task. In this article, we report a systematic study on growing polymer brushes on polymer-single-crystal-immobilized 6 and 15 nm diameter gold nanoparticles (AuNPs) using atom transfer radical polymerization. JNPs with bicompartment polymer brushes, such as poly(ethylene oxide) (PEO)/poly(methyl methacrylate), PEO/poly(tert-butyl acrylate), and PEO/poly(acrylic acid), were synthesized. The grafting densities can be carefully controlled. The Janus feature of these particles was confirmed using both platinum nanoparticle decoration and UV/Vis spectroscopy analysis. The surface plasmon resonance absorbance of Janus particles exhibited a blue shift compared with that of symmetric AuNPs with either homopolymer or mixed polymer brushes. This work demonstrated that using polymer single crystal as the templates, small size (<20 nm diameter) JNPs having bicompartment polymer brushes can be readily obtained. The ability to tune grafting density and molecular weight of polymer brushes can lead to controlled particle amphiphilicity.

Disk micelles from amphiphilic Janus gold nanoparticles

Janus gold nanoparticles are synthesised via a simple preparation method and behave as amphiphiles self-assembling in water into disk-shaped micelles.