Hydrophilic Gold Nanoparticles Adaptable for Hydrophobic Solvents

Surface ligand molecules enabling gold nanoparticles to disperse in both polar and nonpolar solvents through changes in conformation are presented. Gold nanoparticles coated with alkyl-head-capped PEG derivatives were initially well dispersed in water through exposure of the PEG residue (bent form). When chloroform was added to the aqueous solution of gold nanoparticles, the gold nanoparticles were transferred from an aqueous to a chloroform phase through exposure of the alkyl-head residue (straight form). The conformational change (bent to straight form) of immobilized ligands in response to the polarity of the solvents was supported by NMR analyses and water contact angles

pH-Responsive Coassembly of Oligo(ethylene glycol)-Coated Gold Nanoparticles with External Anionic Polymers via Hydrogen Bonding

Stimuli-responsive assembly of gold nanoparticles (AuNPs) with precise control of the plasmonic properties, assembly size, and stimuli responsivity has shown potential benefits with regard to biosensing devices and drug-delivery systems. Here we present a new pH-responsive coassembly system of oligo­(ethylene glycol) (OEG)-coated AuNPs with anionic polymers as an external mediator via hydrogen bonding in water. Hydrogen-bond-driven coassemblies of OEG-AuNPs with poly­(acrylic acid) (PAA) were confirmed by the monitoring of plasmonic peaks and hydrodynamic diameters. In this system, the protonation of anionic polymers on change in pH triggered the formation of hydrogen bond between the OEG-AuNPs and polymers, providing sensitive pH responsivity. The plasmonic properties and assembly size are affected by both the ratio of PAA to AuNPs and the molecular weight of PAAs. In addition, the attachment of hydrophobic groups to the surface ligand or anionic polymer changed the responsive pH range. These results demonstrated that the coassembly with an external mediator via hydrogen bonding provides a stimuli-responsive assembly system with tunable plasmonic properties, assembly size, and stimuli responsivity

Sub-100 nm Gold Nanoparticle Vesicles as a Drug Delivery Carrier enabling Rapid Drug Release upon Light Irradiation

Previously, we reported gold nanoparticles coated with semifluorinated ligands self-assembled into gold nanoparticle vesicles (AuNVs) with a sub-100 nm diameter in tetrahydrofuran (THF). Although this size is potentially useful for in vivo use, the biomedical applications of AuNVs were limited, as the vesicular structure collapsed in water. In this paper, we demonstrate that the AuNVs can be dispersed in water by cross-linking each gold nanoparticle with thiol-terminated PEG so that the cross-linked vesicles can work as a drug delivery carrier enabling light-triggered release. Rhodamine dyes or anticancer drugs were encapsulated within the cross-linked vesicles by heating to 62.5 °C. At this temperature, the gaps between nanoparticles open, as confirmed by a blue shift in the plasmon peak and the more efficient encapsulation than that observed at room temperature. The cross-linked AuNVs released encapsulated drugs upon short-term laser irradiation (5 min, 532 nm) by again opening the nanogaps between each nanoparticle in the vesicle. On the contrary, when heating the solution to 70 °C, the release speed of encapsulated dyes was much lower (more than 2 h) than that triggered by laser irradiation, indicating that cross-linked AuNVs are highly responsive to light. The vesicles were efficiently internalized into cells compared to discrete gold nanoparticles and released anticancer drugs upon laser irradiation in cells. These results indicate that cross-linked AuNVs, sub-100 nm in size, could be a new type of light-responsive drug delivery carrier applicable to the biomedical field

Thermoresponsive Assembly of Gold Nanoparticles Coated with Oligo(Ethylene Glycol) Ligands with an Alkyl Head

This paper presents the thermoresponsive assembly behaviors of gold nanoparticles (AuNPs; 3, 5, and 10 nm in diameter) that are coated with a self-assembled monolayer of oligo­(ethylene glycol) (OEG) ligands terminated with alkyl heads. AuNPs (5 nm in diameter) coated with OEG ligands without an alkyl head did not assemble within a temperature range from 20 to 70 °C. However, AuNPs coated with ethyl, iso-propyl, and propyl-headed OEG AuNPs afforded assembly at temperatures of 56, 33, and 19 °C, respectively, indicating that the assembly temperature can be tuned over a wide range by slight changes in the hydrophobicity of the alkyl head. Almost no hysteresis during the heating/cooling cycles was observed for the assembly/disassembly process. The diameter of the AuNPs also affected the assembly temperature, with increases in the diameter of the AuNP affording a lower assembly temperature. The ligand with the shorter alkyl tail length provided the lower assembly temperature of AuNPs than the ligand with longer tail

Gold Nanoparticles Coated with Semi-Fluorinated Oligo(ethylene glycol) Produce Sub-100 nm Nanoparticle Vesicles without Templates

Gold nanoparticles (NPs) with diameters of 5, 10, and 20 nm coated with semifluorinated oligo­(ethylene glycol) ligands were formed into sub-100 nm hollow NP assemblies (NP vesicles) in THF without the use of a template. The NP vesicles maintained their structure even after the solvent was changed from THF to other solvents such as butanol or CH₂Cl₂. NMR analyses indicated that the fluorinated ligands are bundled on the NPs and that the solvophobic feature of the fluorinated bundles is the driving force for NP assembly. The formed NP vesicles were surface-enhanced Raman scattering-active capsules

Reverse Size Dependences of the Cellular Uptake of Triangular and Spherical Gold Nanoparticles

Gold nanoparticles (GNPs) show promise as both drug and imaging carriers with applications in both diagnosis and therapy. For the safe and effective use of such gold nanomaterials in the biomedical field, it is crucial to understand how the size and shape of the nanomaterials affect their biological features, such as in vitro cellular uptake speed and accumulation as well as cytotoxicity. Herein, we focus on triangular gold nanoparticles (TNPs) of four different sizes (side length 46, 55, 72, and 94 nm; thickness 30 nm) and compare the cellular internalization efficiency with those of spherical nanoparticles (SNPs) of various diameters (22, 39, and 66 nm). Both surfaces were coated with anionic thiol ligands. Inductively coupled plasma–emission spectrometry (ICP-ES) data demonstrated that TNPs with longer sides showed higher levels of uptake into RAW264.7 and HeLa cells. On the other hand, in the case of SNPs, those with smaller diameters showed higher levels of uptake in both cells. Our results support the notion of a reverse size dependence of TNPs and SNPs in terms of cellular uptake. For HeLa cells, in particular, 20-fold more efficient internalization was observed for TNPs with longer sides (72 nm side length) compared to SNPs (66 nm) with a similar surface area. These results highlight the importance of the shape of nanomaterials on their interactions with cells and provide a useful guideline for the use of TNPs

pH-Dependent Network Formation of Quantum Dots and Fluorescent Quenching by Au Nanoparticle Embedding

A simple approach to the creation of colloidal assemblies is in high demand for the development of functional devices. Here, we present the preparation of CdTe-QD (quantum dot) networks in as little as 1 day simply by pH modification without the use of oxidants. The QD network was tractable in water and casting from a droplet produced a porous networked film on both hydrophobic and hydrophilic solid substrates. Further, we found that citrate-protected gold nanoparticles (AuNPs, <i>d</i> = 5 nm) could be incorporated into the QD networks to afford a QD/Au composite network, and that the fluorescence from the QDs was largely decreased by the addition of a small proportion of AuNPs (QD:AuNP = 99.4:0.6), probably due to the efficient charge transfer through the network. These data indicate that our method is suitable for application to the creation of metal/QD hybrid materials that can be integrated into wet-based processes

DNA Brush-Directed Vertical Alignment of Extensive Gold Nanorod Arrays with Controlled Density

Control over the orientation of metal nanorods is important for both fundamental and applied research. We show that gold nanorods (GNRs) can be aligned in a single direction by adsorbing positively charged GNRs onto a double-strand DNA-grafted substrate through electrostatic interaction. The ordered structure can be optimized by controlling the density of the positive charges on the surface of the GNRs. We found, in agreement with the results of theoretical simulation, that the resultant structure exhibits plasmonic properties that are dependent on the GNR orientation relative to the direction of an oscillating electric field. Our approach provides new insights into the polymer-assisted self-assembly of rod-shaped nanoparticles utilizing electrostatic interactions

Stabilities of WT Vp1 and C80A and C247A mutant Vp1s expressed in HeLa cells.

<p>(A) HeLa cells transfected with an empty plasmid (Mock) or plasmid encoding WT, C80A, or C247A Vp1 were pulse-labeled for 5 min and then either harvested immediately (lanes 1 to 3) or chased for 12 h (lanes 4 to 6) or 24 h (lanes 7 to 10). The anti-Vp1 immunocomplexes (IP) prepared from the lysates were analyzed by SDS-PAGE and autoradiography. (B) The intensities of the bands in <i>A</i> were quantified with an image analyzer and plotted as relative values compared to those obtained at 0 h of chase. Data are the means ± S.D. of values from three independent experiments. The solid line, dotted line, and broken line represent WT, C80A, and C247A samples, respectively.</p

Structural difference around C80 between JCV Vp1 and SV40 Vp1.

<p>Vp1 structures of JCV and SV40 are shown in green and red, respectively. The different residues within 4 Å of C80 of the Vp1s are shown as stick models. An arrow indicates C80 in JCV Vp1 and C87 in SV40 Vp1.</p