32 research outputs found
Rheotaxis of Bimetallic Micromotors Driven by Chemical–Acoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Rheotaxis of Bimetallic Micromotors Driven by Chemical–Acoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Rheotaxis of Bimetallic Micromotors Driven by Chemical–Acoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Rheotaxis of Bimetallic Micromotors Driven by Chemical–Acoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Three-Dimensional Hydrodynamic Focusing Method for Polyplex Synthesis
Successful intracellular delivery of nucleic acid therapeutics relies on multiaspect optimization, one of which is formulation. While there has been ample innovation on chemical design of polymeric gene carriers, the same cannot be said for physical processing of polymer–DNA nanocomplexes (polyplexes). Conventional synthesis of polyplexes by bulk mixing depends on the operators’ experience. The poorly controlled bulk mixing process may also lead to batch-to-batch variation and consequent irreproducibility. Here, we synthesize polyplexes by using a three-dimensional hydrodynamic focusing (3D-HF) technique in a single-layered, planar microfluidic device. Without any additional chemical treatment or postprocessing, the polyplexes prepared by the 3D-HF method show smaller size, slower aggregation rate, and higher transfection efficiency, while exhibiting reduced cytotoxicity compared to the ones synthesized by conventional bulk mixing. In addition, by introducing external acoustic perturbation, mixing can be further enhanced, leading to even smaller nanocomplexes. The 3D-HF method provides a simple and reproducible process for synthesizing high-quality polyplexes, addressing a critical barrier in the eventual translation of nucleic acid therapeutics
Shape-Controlled Synthesis of Hybrid Nanomaterials <i>via</i> Three-Dimensional Hydrodynamic Focusing
Shape-controlled synthesis of nanomaterials through a simple, continuous, and low-cost method is essential to nanomaterials research toward practical applications. Hydrodynamic focusing, with its advantages of simplicity, low-cost, and precise control over reaction conditions, has been used for nanomaterial synthesis. While most studies have focused on improving the uniformity and size control, few have addressed the potential of tuning the shape of the synthesized nanomaterials. Here we demonstrate a facile method to synthesize hybrid materials by three-dimensional hydrodynamic focusing (3D-HF). While keeping the flow rates of the reagents constant and changing only the flow rate of the buffer solution, the molar ratio of two reactants (<i>i.e.</i>, tetrathiafulvalene (TTF) and HAuCl<sub>4</sub>) within the reaction zone varies. The synthesized TTF–Au hybrid materials possess very different and predictable morphologies. The reaction conditions at different buffer flow rates are studied through computational simulation, and the formation mechanisms of different structures are discussed. This simple one-step method to achieve continuous shape-tunable synthesis highlights the potential of 3D-HF in nanomaterials research
Combining the Masking and Scaffolding Modalities of Colloidal Crystal Templates: Plasmonic Nanoparticle Arrays with Multiple Periodicities
Surface patterns with prescribed
structures and properties are
highly desirable for a variety of applications. Increasing the heterogeneity
of surface patterns is frequently required. This work opens a new
avenue toward creating nanoparticle arrays with multiple periodicities
by combining two generally separately applied modalities (i.e., scaffolding
and masking) of a monolayer colloidal crystal (MCC) template. Highly
ordered, loosely packed binary and ternary surface patterns are realized
by a single-step thermal treatment of a gold thin-film-coated MCC
and a nonclose-packed MCC template. Our approach enables control of
the parameters defining these nanoscale binary and ternary surface
patterns, such as particle size, shape, and composition, as well as
the interparticle spacing. This technique enables preparation of well-defined
binary and ternary surface patterns to achieve customized plasmonic
properties. Moreover, with their easy programmability and excellent
scalability, the binary and ternary surface patterns presented here
could have valuable applications in nanophotonics and biomedicine.
Specific examples include biosensing via surface-enhanced Raman scattering,
fabrication of plasmonic-enhanced solar cells, and water splitting
An Acoustofluidic Micromixer via Bubble Inception and Cavitation from Microchannel Sidewalls
During
the deep reactive ion etching process, the sidewalls of
a silicon mold feature rough wavy structures, which can be transferred
onto a polydimethylsiloxane (PDMS) microchannel through the soft lithography
technique. In this article, we utilized the wavy structures of PDMS
microchannel sidewalls to initiate and cavitate bubbles in the presence
of acoustic waves. Through bubble cavitation, this acoustofluidic
approach demonstrates fast, effective mixing in microfluidics. We
characterized its performance by using viscous fluids such as polyÂ(ethylene
glycol) (PEG). When two PEG solutions with a resultant viscosity 54.9
times higher than that of water were used, the mixing efficiency was
found to be 0.92, indicating excellent, homogeneous mixing. The acoustofluidic
micromixer presented here has the advantages of simple fabrication,
easy integration, and capability to mix high-viscosity fluids (Reynolds
number: ∼0.01) in less than 100 ms
Self-Powered Glucose-Responsive Micropumps
A self-powered polymeric micropump based on boronate chemistry is described. The pump is triggered by the presence of glucose in ambient conditions and induces convective fluid flows, with pumping velocity proportional to the glucose concentration. The pumping is due to buoyancy convection that originates from reaction-associated heat flux, as verified from experiments and finite difference modeling. As predicted, the fluid flow increases with increasing height of the chamber. In addition, pumping velocity is enhanced on replacing glucose with mannitol because of the enhanced exothermicity associated with the reaction of the latter
<i>In Situ</i> Fabrication of 3D Ag@ZnO Nanostructures for Microfluidic Surface-Enhanced Raman Scattering Systems
In this work, we develop an <i>in situ</i> method to grow highly controllable, sensitive, three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrates via an optothermal effect within microfluidic devices. Implementing this approach, we fabricate SERS substrates composed of Ag@ZnO structures at prescribed locations inside microfluidic channels, sites within which current fabrication of SERS structures has been arduous. Conveniently, properties of the 3D Ag@ZnO nanostructures such as length, packing density, and coverage can also be adjusted by tuning laser irradiation parameters. After exploring the fabrication of the 3D nanostructures, we demonstrate a SERS enhancement factor of up to ∼2 × 10<sup>6</sup> and investigate the optical properties of the 3D Ag@ZnO structures through finite-difference time-domain simulations. To illustrate the potential value of our technique, low concentrations of biomolecules in the liquid state are detected. Moreover, an integrated cell-trapping function of the 3D Ag@ZnO structures records the surface chemical fingerprint of a living cell. Overall, our optothermal-effect-based fabrication technique offers an effective combination of microfluidics with SERS, resolving problems associated with the fabrication of SERS substrates in microfluidic channels. With its advantages in functionality, simplicity, and sensitivity, the microfluidic-SERS platform presented should be valuable in many biological, biochemical, and biomedical applications