3 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-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
Synthesis of Janus-Like Gold Nanoparticles with Hydrophilic/Hydrophobic Faces by Surface Ligand Exchange and Their Self-Assemblies in Water
This
study aims at the synthesis of Janus gold nanoparticles (Janus
GNPs) with hydrophilic/hydrophobic faces by a simple ligand exchange
reaction in an homogeneous system and at the elucidation of the self-assembled
structures of the Janus GNPs in water. As hydrophilic surface ligands,
we synthesized hexaethylene glycol (E6)-terminated thiolate ligands
with C3, C7, or C11 alkyl chains, referred to as E6<b>C3</b>, E6<b>C7</b>, and E6<b>C11</b>, respectively. As a hydrophobic
ligand, a butyl-headed thiolate ligand C4-E6<b>C11</b>, in which
a C4 alkyl was introduced on the E6<b>C11</b> terminus, was
synthesized. The degree of segregation between the two ligands on
the GNPs (5 nm in diameter) was examined by matrix-assisted laser
desorption/ionization time-of fright mass spectrometry (MALDI-TOF
MS) analysis. We found that the choice of immobilization methods,
one-step or two-step addition of the two ligands to the GNP solution,
crucially affects the degree of segregation. The two-step addition
of a hydrophilic ligand (E6<b>C3</b>) followed by a hydrophobic
ligand (C4-E6<b>C11</b>) produced a large degree of segregation
on the GNPs, providing Janus-like GNPs. When dispersed in water, these
Janus-like GNPs formed assemblies of ∼160 nm in diameter, whereas
Domain GNPs, in which the two ligands formed partial domains on the
surface, were precipitated even when the molar ratio of the hydrophilic
ligand and the hydrophobic ligand on the surface of the NPs was almost
1:1. The assembled structure of the Janus-like GNPs in water was directly
observed by pulsed coherent X-ray solution scattering using an X-ray
free-electron laser, revealing irregular spherical structures with
uneven surfaces