6 research outputs found
Photothermal Control of Membrane Permeability of Microcapsules for On-Demand Release
We
report the use of a simple microfluidic device for producing microcapsules
with reversible membrane permeability that can be remotely controlled
by application of near-infrared (NIR) light. Water-in-oil-in-water
(W/O/W) double-emulsion drops were prepared to serve as templates
for the production of mechanically stable microcapsules with a core–shell
structure and highly uniform size distribution. A biocompatible ethyl
cellulose shell was formed, containing densely packed thermoresponsive
polyÂ(<i>N</i>-isopropylacrylamide) (pNIPAAm) particles in
which gold nanorods were embedded. Irradiation with a NIR laser resulted
in heating of the hydrogel particles due to the photothermal effect
of the gold nanorods, which absorb at that wavelength. This localized
heating resulted in shrinkage of the particles and formation of macrogaps
between them and the matrix of the membrane. Large encapsulated molecules
could then pass through these gaps into the surrounding fluid. As
the phase transition behavior of pNIPAAm is highly reversible, this
light-triggered permeability could be repeatedly switched on and off
by removing the laser irradiation for sufficient time to allow the
gold nanorods to cool. This reversible and remote control of permeability
enabled the programmed release of encapsulants, with the time and
period of the open valve state able to be controlled by adjusting
the laser exposure. This system thus has the potential for spatiotemporal
release of encapsulated drugs
Monolithic Photonic Crystals Created by Partial Coalescence of Core–Shell Particles
Colloidal crystals
and their derivatives have been intensively
studied and developed during the past two decades due to their unique
photonic band gap properties. However, complex fabrication procedures
and low mechanical stability severely limit their practical uses.
Here, we report stable photonic structures created by using colloidal
building blocks composed of an inorganic core and an organic shell.
The core–shell particles are convectively assembled into an
opal structure, which is then subjected to thermal annealing. During
the heat treatment, the inorganic cores, which are insensitive to
heat, retain their regular arrangement in a face-centered cubic lattice,
while the organic shells are partially fused with their neighbors;
this forms a monolithic structure with high mechanical stability.
The interparticle distance and therefore stop band position are precisely
controlled by the annealing time; the distance decreases and the stop
band blue shifts during the annealing. The composite films can be
further treated to give a high contrast in the refractive index. The
inorganic cores are selectively removed from the composite by wet
etching, thereby providing an organic film containing regular arrays
of air cavities. The high refractive index contrast of the porous
structure gives rise to pronounced structural colors and high reflectivity
at the stop band position
Colloidal Photonic Crystals toward Structural Color Palettes for Security Materials
Self-assembly of monodisperse colloidal
particles into regular
lattices has provided relatively simple and economical methods to
prepare photonic crystals. The photonic stop band of colloidal crystals
appears as opalescent structural colors, which are potentially useful
for display devices, colorimetric sensors, and optical filters. However,
colloidal crystals have low durability, and an undesired scattering
of light makes the structures white and translucent. Moreover, micropatterning
of colloidal crystals usually requires complex molding procedures,
thereby limiting their practical applications. To overcome such shortcomings,
we develop a pragmatic and amenable method to prepare colloidal photonic
crystals with high optical transparency and physical rigidity using
photocurable colloidal suspensions. The colloidal particles dispersed
in a photocurable medium crystallized during capillary force-induced
infiltration into a slab, and subsequent photopolymerization of the
medium permanently solidifies the structures. Furthermore, conventional
photolithography enables micropatterning of the crystal structures.
The low index contrast between particles and matrix results in high
transparency of the resultant composite structures and narrow reflection
peaks, thereby enabling structural color mixing through the overlapping
of distinct layers of the colloidal crystals. Multiple narrow peaks
in the spectrum provide high selectivity in optical identification,
thereby being potentially useful for security materials
Durable Plasmonic Cap Arrays on Flexible Substrate with Real-Time Optical Tunability for High-Fidelity SERS Devices
Active tunable plasmonic cap arrays
were fabricated on a flexible
stretchable substrate using a combination of colloidal lithography,
lift-up soft lithography, and subsequent electrostatic assembly of
gold nanoparticles. The arrangement of the plasmonic caps could be
tuned under external strain to deform the substrate in reversible.
Real-time variation in the arrangement could be used to tune the optical
properties and the electromagnetic field enhancement, thereby a proving
a promising mechanism for optimizing the SERS sensitivity
Shape Control of Ag Nanostructures for Practical SERS Substrates
Large-area, highly ordered, Ag-nanostructured arrays
with various geometrical features were prepared for use as surface-enhanced
Raman scattering (SERS)-active substrates by the self-assembly of
inorganic particles on an SU-8 surface, followed by particle embedding
and Ag vapor deposition. By adjusting the embedding time of the inorganic
particles, the size of the Ag nanogap between the geometrically separated
hole arrays and bowl-shaped arrays could be controlled in the range
of 60 nm to 190 nm. More importantly, the SU-8 surface was covered
with hexagonally ordered nanopillars, which were formed as a result
of isotropic dry etching of the interstices, leading to triangular-shaped
Ag plates on nanopillar arrays after Ag vapor deposition. The size
and sharpness of the triangular Ag nanoplates and nanoscale roughness
of the bottom surface were adjusted by controlling the etching time.
The potential of the various Ag nanostructures for use as practical
SERS substrates was verified by the detection of a low concentration
of benzenethiol. Finite-difference time-domain (FDTD) methodology
was used to demonstrate the SERS-activities of these highly controllable
substrates by calculating the electric field intensity distribution
on the metallic nanostructures. These substrates, with high sensitivity
and simple shape-controllability, provide a practical SERS-based sensing
platform
Freestanding and Arrayed Nanoporous Microcylinders for Highly Active 3D SERS Substrate
Surface-enhanced Raman scattering (SERS) has been considered as
one of the most promising tools for molecular analysis. To develop
practical platforms, a variety of nanoparticles and two-dimensional
(2D) nanostructures have been prepared. However, low signal intensity
or slow binding kinetics in conventional approaches limits their applications.
To overcome these shortcomings, production and usage of three-dimensional
(3D) nanostructures remain an important yet unmet need. In this paper,
we report novel and effective SERS-active materials by fabricating
hierarchically structured SiO<sub>2</sub> microcylinders decorated
with gold nanoparticles. In order to fully develop 3D nanostructures,
while maintaining fast diffusion of analyte molecules, we used self-assembled
nanostructures of block-copolymers (BCPs) confined in the microholes
of an imprinting mold; the BCPs could provide a template for producing
3D nanostructure composed of nanofibers with sub-100 nm diameter through
their microphase separation, whereas the imprinting technique provided
cylindrical geometry for the local confinement of the BCPs. Microcylinders
with nanodomains were then transformed into microcylinders with 3D
nanopores via reactive-ion etching and, subsequently, their nanopores
were decorated by gold nanoparticles. The resultant 3D nanopores enable
a high loading of gold nanoparticles and formation of abundant hot
spots and microcylinders facilitate the fast diffusion of analyte
molecules through the nanopores, resulting in significant enhancement
of SERS intensity