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Bioengineering
AC Electrokinetics  
Micro and Nano PIV  
Microchannel Flow Physics  
Micromixer 
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Bioengineering |
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Shear stress distributions near biological cells - Matthew Pommer
The purpose of my research is to study shear stress distributions near biological cells.
I am currently investigating the correlation between Poly-L-Lysine concentrations
and micro-flow induced shear stress intensity near erythrocyte cell lyse conditions using micro-PIV.
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AC Electrokinetics
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Tunable Laser Cavity Sensor (TLCS) - Marin Sigurdson
A Tunable Laser Cavity Sensor (TLCS) is being developed for on-chip molecular diagnostics.
Two semiconductor Distributed Bragg Reflector (DBR) lasers, a sensor-laser and a reference-laser,
are used to detect minute changes in refractive index resulting from specific antigen-antibody
binding on the wall of an adjoining microchannel.
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Dielectrophoresis - a force on particles in a
non-uniform electric field arising from differences in dielectric properties between the particles
and the suspending fluid - is incorporated in the system to concentrate antigen in the binding region
of the microchannel, thereby increasing detector sensitivity. This system directly measures changes in
index of refraction due to the binding chemistry, and therefore does not require mixing of conjugate
antibodies or fluorescent molecules during sample preparation as is common for biosensors.
In addition,
the system is fully integrated and does not require any external optics. By fabricating a one-dimensional
array of laser sensors on a single chip, the TLCS is readily scaleable to measuring tens of assays
simultaneously.
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Electrothermally induced flows in microchannels - Gaurav Soni
I am working on the numerical simulation and experimentation of electrothermally induced flows in microchannels.
We are trying to develop novel AC electrokinetic pumps using electrothermal flow. These pumps will utilize very
small AC voltages (5-10 V) and will be free from problem of electrolysis.
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I am also interested in
microfabrication and enjoy working in cleanrooms. I have fabricated some microfluidic devices for my research. I plan to test these devices with micro PIV (particle image velocimetry) techniques.
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AC electrically driven micropumps - Gavin Wu
We have developed micropumps for microfluidics that use AC electric fields
to drive aqueous fluid motion through micro channels. These pumps operate at
relatively low voltages (~5–10Vrms), and high frequencies (~100kHz). They have
several distinct advantages over the DC electrokinetic pumps. The low voltages
make the pumps well suited for a wide variety of biosensor and “Lab-on-a-Chip”
applications (e.g. PCR chip for DNA amplification). The high frequencies minimize electrolysis,
so that bubbles do not form on the electrode surfaces, and do not contaminate the working fluid.
The pumps can also be used as active valves or precision micro-dispensers.
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Micro and Nano PIV|
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Nanoscale PIV and Electronic DNA (E-DNA) sensor - Patrick Freudenthal
We propose to develop and pursue commercialization of a Particle Image Velocimetry
(PIV) system specifically designed to investigate the fluid mechanics of near-wall
phenomena, such as slip flow and boundary layer regions in micro/nanofluidic
devices. The research will focus on measuring fluid flows near a micro/nanofluidic
device wall with an out-of-plane resolution of 100 nm, and with a temporal
resolution of 1 ms. The instrument will measure velocity in nanochannels down
to 100 nm.
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The overall system design will be given high importance in balancing cost and
functionality. For example, by using diode lasers, and streamlining the imaging
optics, the cost of the instrument should be reduced by approximately ~$30,000 –
$40,000. This will increase market acceptance, thereby allowing micro/nano-PIV
to be a mainstream desktop instrument used by a large number of micro/nano device
research laboratories and companies.
Technical Objectives
 Evanescent Illumination
Evanescent fields have been shown to be an effective means of illuminating
seed particles within ~200 nm of a planar surface for PIV. The proposed research
will extend the capability of evanescent technology to achieve higher spatial and
temporal resolutions by using quantum dots or small clusters of quantum dots as
flow tracing particles. An evanescent field will be created through total internal
reflection (TIR) of a laser light beam within a glass waveguide, such as a cover
slip. The field will energize the seed particles and cause them to fluoresce.
Inexpensive Light Source
A variety of optical diagnostic techniques will be used to determine suitable
light sources and methods for coupling light into a waveguide thereby creating
an evanescent field. We will test low power (1 to 25mW), inexpensive (under $1000)
laser sources operating at various wavelengths. For example, a laser diode emitting
violet light at a wavelength of 433 nm may be ideal for illuminating quantum dots.
This could reduce the cost of traditional micro-PIV systems, which typically use a
$35,000 pulsed chemical laser light source.
Quantum Dots as Seed Particles
We will use Quantum dots (QDs) as seed particles. QDs are nanometer-sized (10-30 nm)
semiconductor crystals (CdSe-nanocrystals), which produce a strong fluorescent
emission when excited by light in the blue and UV spectrum. QDs may be ideally
suited for nano-PIV. Their small size (~10 – 30 nm) allows them to be transported
through ~100 nm channels. Although QDs are available with photoluminescence (PL)
quantum efficiencies of as high as 50%, matching that of the best organic
lumophores. Individual QDs may be too small to be useful as seed particles due
to their low individual light output. Brownian motion of the QDs is greater than
for larger particles and may make them difficult to image when suspended in a fluid.
These problems may be mitigated by joining a few QDs together, making a brighter
slightly larger particle.
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Microchannel Flow Physics |
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Reducing friction losses in micro/nano channel flows - Kathy Liu
The research is focus on finding efficient ways to reduce
the friction losses in nano/micro channel flows. A simple
one-dimensional theoretical model has shown that, by adding
air gap in the micro/nano channels, the flow rate of water can
be increased to as 5.86 times as that in normal flat channel.
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The theoretical results were compared to numerical simulations,
which were carried out using the structured multi-block flow solver
CFD-ACE+. The free surface problem in those simulations was solved
with the Volume-Of-Fluid (VOF) method. Two flow patterns are studied:
parallel flow and transverse flow.
The numerical results show that
increasing water flow rate by adding air gap in nano/micro channels
is practicable. The flow rate can be increased more efficient by coating
the channels with hydrophobic materials and forming a slip boundary
condition on their solid surfaces.
Also, we are trying to make the
nano/micro channel super-hydrophobic by coating particles in side the
channel to trap air. Therefore the efficiency of air gap can be studied
further by pressure drop verses flow rate experiments.
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Surface Boundary Conditions - Dr. Derek Tretheway
Since the surface to volume
ratio in enclosed flow devices scales as L-1, the small length scale
associated with micro-devices dictates the importance of boundary
conditions. Several researchers have suggested that the well-accepted
no-slip boundary condition may not be suitable for hydrophilic flows
over hydrophobic boundaries at the micro- and nano-scale.
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However,
these conclusions are reached from indirect measurements of pressure
drop in channels, and normal forces on nano-scale film squeezing devices.
Unfortunately, there are no direct velocity measurements of slip at
the micro-scale. Currently we are addressing the controversy of slip
at hydrophilic-hydrophobic interfaces by applying micron-resolution
Particle Image Velocimetry (m-PIV) (a technique developed in the microfluidics
lab) to measure the flow of water through 30 x 300 micron channels
that have a clean surface (hydrophilic) and channels that are coated
with hydrophobic OTS (octadecyltrichlorosilane).
Preliminary results
indicate that the no-slip boundary condition is not necessarily valid
for hydrophilic liquids flowing over hydrophobic boundaries. Thus,
modeling fluid flow at the micro-scale with the assumption of no-slip
may or may not be valid, but will depend on the interactions between
the fluid and the surface properties of the wall.
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The current mixer is
a silicon-etcheddevice with a glass cover slip anodically bonded on top
to hermetically seal the chip. The main channel is 200 microns wide, 100
microns deep and 1300 microns long.
Experiments are performed with either
the first, the two first or all three side channels activated. The flow is
pressure driven in the side channels using a specially developed
oscillating syringe pump and is controlled using a software/hardware
Labview. The working fluids injected in the main channel consist of a
fluorescent aqueous solution and deonized water. The time evolution of
the flow is observed using an epi-fluorescent microscope and a YAG laser.
The flow is characterized by micro-PIV measurements and visualizations.
Mixing is quantified using the Mixing Variance Coefficient function. We
achieve a good mixing of the two fluids when the three side channels are
activated within 0.1 second.
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Numerical simulation of mixing in a microchannel - Caroline Cardonne
I am performing 3D numerical simulations in order to understand and optimize the mixing at the
microscale in an active micromixer. I am using the CFD software Fluent
for the computation and Gambit to create the geometry.
The micromixer I am working on is composed of one main channel, where the fluids to be mixed are injected,
and of three
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pairs of side channels. The mixing is achieved in the laminar flow by perturbing the main flow with transverse oscillating flows imparted in the secondary
side channels. This stretches and folds the layers in the flow stream causing chaotic advection, thereby increasing mixing.
The main channel is 200 microns wide, 100 microns
deep and 1350 microns long. Simulations were performed with either the first or all three side channels activated. The mixing is quantified using the Mixing Variance Coefficient function.
We achieve a good mixing of the two fluids whith the three side channels activated within 0.1 second.
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