13 research outputs found
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 oligoÂ(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 polyÂ(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 oligoÂ(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
Noncationic Rigid and Anisotropic Coiled-Coil Proteins Exhibit Cell-Penetration Activity
Numerous cationic peptides that penetrate
cells have been studied
intensively as drug delivery system carriers for cellular delivery.
However, cationic molecules tend to be cytotoxic and cause inflammation,
and their stability in the blood is usually low. We have previously
demonstrated that a rigid and fibrous cationic coiled-coil protein
exhibited cell-penetrating ability superior to that of previously
reported cell-penetrating peptides. Making use of structural properties,
here we describe the cell-penetrating activity of a rigid and fibrous
coiled-coil protein with a noncationic surface. A fibrous coiled-coil
protein of p<i>I</i> 6.5 penetrated 100% of the cells tested
in vitro at a concentration of 500 nM, which is comparable to that
of previously reported cell-penetrating peptides. We also investigated
the effect of cell-strain dependency and short-term cytotoxicity
Hydrophilic Double-Network Polymers that Sustain High Mechanical Modulus under 80% Humidity
The effects of water on the mechanical properties of
synthetic
hydrophilic polymers with double-network (DN) structures were studied
under different relative humidities (RH). It was found that they could
sustain nearly the same high Young’s modulus as dry DN polymers
in the RH range 10–80% (water content 3–17 wt %), that
is, more than 10<sup>2</sup> MPa. However, when the RH exceeds 80%,
DN polymers abruptly absorb large amounts of water (water content
90 wt %) and transform to a highly water-swollen “gel state”
with a decrease in the Young’s modulus of 3 orders of magnitude.
Spectroscopic analyses revealed that water molecules below RH 80%
are strongly bound to hydrophilic moieties with highly restricted
mobility; water under such states improves rather than reduces mechanical
properties by behaving as a plasticizer. DN polymers capable of sustaining
high mechanical properties, even under RH 80%, have potential uses
as hydrophilic materials
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 oligoÂ(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 CH<sub>2</sub>Cl<sub>2</sub>. 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