6 research outputs found
Catalytic Mesoporous Janus Nanomotors for Active Cargo Delivery
We report on the
synergy between catalytic propulsion and mesoporous
silica nanoparticles (MSNPs) for the design of Janus nanomotors as
active cargo delivery systems with sizes <100 nm (40, 65, and 90
nm). The Janus asymmetry of the nanomotors is given by electron beam
(e-beam) deposition of a very thin platinum (2 nm) layer on MSNPs.
The chemically powered Janus nanomotors present active diffusion at
low H<sub>2</sub>O<sub>2</sub> fuel concentration (i.e., <3 wt
%). Their apparent diffusion coefficient is enhanced up to 100% compared
to their Brownian motion. Due to their mesoporous architecture and
small dimensions, they can load cargo molecules in large quantity
and serve as active nanocarriers for directed cargo delivery on a
chip
Motion Control of Urea-Powered Biocompatible Hollow Microcapsules
The
quest for biocompatible microswimmers powered by compatible
fuel and with full motion control over their self-propulsion is a
long-standing challenge in the field of active matter and microrobotics.
Here, we present an active hybrid microcapsule motor based on Janus
hollow mesoporous silica microparticles powered by the biocatalytic
decomposition of urea at physiological concentrations. The directional
self-propelled motion lasts longer than 10 min with an average velocity
of up to 5 body lengths per second. Additionally, we control the velocity
of the micromotor by chemically inhibiting and reactivating the enzymatic
activity of urease. The incorporation of magnetic material within
the Janus structure provides remote magnetic control on the movement
direction. Furthermore, the mesoporous/hollow structure can load both
small molecules and larger particles up to hundreds of nanometers,
making the hybrid micromotor an active and controllable drug delivery
microsystem
Self-Propelling Nanomotors in the Presence of Strong Brownian Forces
Motility in living systems is due
to an array of complex molecular
nanomotors that are essential for the function and survival of cells.
These protein nanomotors operate not only despite of but also because
of stochastic forces. Artificial means of realizing motility rely
on local concentration or temperature gradients that are established
across a particle, resulting in slip velocities at the particle surface
and thus motion of the particle relative to the fluid. However, it
remains unclear if these artificial motors can function at the smallest
of scales, where Brownian motion dominates and no actively propelled
living organisms can be found. Recently, the first reports have appeared
suggesting that the swimming mechanisms of artificial structures may
also apply to enzymes that are catalytically active. Here we report
a scheme to realize artificial Janus nanoparticles (JNPs) with an
overall size that is comparable to that of some enzymes ā¼30
nm. Our JNPs can catalyze the decomposition of hydrogen peroxide to
water and oxygen and thus actively move by self-electrophoresis. Geometric
anisotropy of the PtāAu Janus nanoparticles permits the simultaneous
observation of their translational and rotational motion by dynamic
light scattering. While their dynamics is strongly influenced by Brownian
rotation, the artificial Janus nanomotors show bursts of linear ballistic
motion resulting in enhanced diffusion
Self-Propelling Nanomotors in the Presence of Strong Brownian Forces
Motility in living systems is due
to an array of complex molecular
nanomotors that are essential for the function and survival of cells.
These protein nanomotors operate not only despite of but also because
of stochastic forces. Artificial means of realizing motility rely
on local concentration or temperature gradients that are established
across a particle, resulting in slip velocities at the particle surface
and thus motion of the particle relative to the fluid. However, it
remains unclear if these artificial motors can function at the smallest
of scales, where Brownian motion dominates and no actively propelled
living organisms can be found. Recently, the first reports have appeared
suggesting that the swimming mechanisms of artificial structures may
also apply to enzymes that are catalytically active. Here we report
a scheme to realize artificial Janus nanoparticles (JNPs) with an
overall size that is comparable to that of some enzymes ā¼30
nm. Our JNPs can catalyze the decomposition of hydrogen peroxide to
water and oxygen and thus actively move by self-electrophoresis. Geometric
anisotropy of the PtāAu Janus nanoparticles permits the simultaneous
observation of their translational and rotational motion by dynamic
light scattering. While their dynamics is strongly influenced by Brownian
rotation, the artificial Janus nanomotors show bursts of linear ballistic
motion resulting in enhanced diffusion
High-Performance ZnO Nanowire Transistors with Aluminum Top-Gate Electrodes and Naturally Formed Hybrid Self-Assembled Monolayer/AlO<sub><i>x</i></sub> Gate Dielectric
A method for the formation of a low-temperature hybrid gate dielectric for high-performance, top-gate ZnO nanowire transistors is reported. The hybrid gate dielectric consists of a self-assembled monolayer (SAM) and an aluminum oxide layer. The thin aluminum oxide layer forms naturally and spontaneously when the aluminum gate electrode is deposited by thermal evaporation onto the SAM-covered ZnO nanowire, and its formation is facilitated by the poor surface wetting of the aluminum on the hydrophobic SAM. The hybrid gate dielectric shows excellent electrical insulation and can sustain voltages up to 6 V. ZnO nanowire transistors utilizing the hybrid gate dielectric feature a large transconductance of 50 Ī¼S and large on-state currents of up to 200 Ī¼A at gate-source voltages of 3 V. The large on-state current is sufficient to drive organic light-emitting diodes with an active area of 6.7 mm<sup>2</sup> to a brightness of 445 cd/m<sup>2</sup>. Inverters based on ZnO nanowire transistors and thin-film carbon load resistors operate with frequencies up to 30 MHz
Reversed Janus Micro/Nanomotors with Internal Chemical Engine
Self-motile
Janus colloids are important for enabling a wide variety
of microtechnology applications as well as for improving our understanding
of the mechanisms of motion of artificial micro- and nanoswimmers.
We present here micro/nanomotors which possess a reversed Janus structure
of an internal catalytic āchemical engineā. The catalytic
material (here platinum (Pt)) is embedded within the interior of the
mesoporous silica (mSiO<sub>2</sub>)-based hollow particles and triggers
the decomposition of H<sub>2</sub>O<sub>2</sub> when suspended in
an aqueous peroxide (H<sub>2</sub>O<sub>2</sub>) solution. The pores/gaps
at the noncatalytic (Pt) hemisphere allow the exchange of chemical
species in solution between the exterior and the interior of the particle.
By varying the diameter of the particles, we observed size-dependent
motile behavior in the form of enhanced diffusion for 500 nm particles,
and self-phoretic motion, toward the nonmetallic part, for 1.5 and
3 Ī¼m ones. The direction of motion was rationalized by a theoretical
model based on self-phoresis. For the 3 Ī¼m particles, a change
in the morphology of the porous part is observed, which is accompanied
by a change in the mechanism of propulsion <i>via</i> bubble
nucleation and ejection as well as a change in the direction of motion