6 research outputs found
Large-Scale Single Particle and Cell Trapping based on Rotating Electric Field Induced-Charge Electroosmosis
We
propose a simple, inexpensive microfluidic chip for large-scale
trapping of single particles and cells based on induced-charge electroosmosis
in a rotating electric field (ROT-ICEO). A central floating electrode
array, was placed in the center of the gap between four driving electrodes
with a quadrature configuration and used to immobilize single particles
or cells. Cells were trapped on the electrode array by the interaction
between ROT-ICEO flow and buoyancy flow. We experimentally optimized
the efficiency of trapping single particles by investigating important
parameters like particle or cell density and electric potential. Experimental
and numerical results showed good agreement. The operation of the
chip was verified by trapping single polystyrene (PS) microspheres
with diameters of 5 and 20 μm and single yeast cells. The highest
single particle occupancy of 73% was obtained using a floating electrode
array with a diameter of 20 μm with an amplitude voltage of
5 V and frequency of 10 kHz for PS microbeads with a 5-μm diameter
and density of 800 particles/μL. The ROT-ICEO flow could hold
cells against fluid flows with a rate of less than 0.45 μL/min.
This novel, simple, robust method to trap single cells has enormous
potential in genetic and metabolic engineering
Continuously Electrotriggered Core Coalescence of Double-Emulsion Drops for Microreactions
Microfluidically
generated double emulsions are promising templates for microreactions,
which protect the reaction from external disturbance and enable in
vitro analyses with large-scale samples. Controlled combination of
their inner droplets in a continuous manner is an essential requirement
toward truly applications. Here, we first generate dual-cored double-emulsion
drops with different inner encapsulants using a capillary microfluidic
device; next, we transfer the emulsion drops into another electrode-integrated
polydimethylsiloxane microfluidic device and utilize external AC electric
field to continuously trigger the coalescence of inner cores inside
these emulsion drops in continuous flow. Hundreds of thousands of
monodisperse microreactions with nanoliter-scale reagents can be conducted
using this approach. The performance of core coalescence is investigated
as a function of flow rate, applied electrical signal, and core conductivity.
The coalescence efficiency can reach up to 95%. We demonstrate the
utility of this technology for accommodating microreactions by analyzing
an enzyme catalyzed reaction and by fabricating cell-laden hydrogel
particles. The presented method can be readily used for the controlled
triggering of microreactions with high flexibility for a wide range
of applications, especially for continuous chemical or cell assays
A Simplified Microfluidic Device for Particle Separation with Two Consecutive Steps: Induced Charge Electro-osmotic Prefocusing and Dielectrophoretic Separation
Continuous
dielectrophoretic separation is recognized as a powerful
technique for a large number of applications including early stage
cancer diagnosis, water quality analysis, and stem-cell-based therapy.
Generally, the prefocusing of a particle mixture into a stream is
an essential process to ensure all particles are subjected to the
same electric field geometry in the separation region. However, accomplishing
this focusing process either requires hydrodynamic squeezing, which
requires an encumbering peripheral system and a complicated operation
to drive and control the fluid motion, or depends on dielectrophoretic
forces, which are highly sensitive to the dielectric characterization
of particles. An alternative focusing technique, induced charge electro-osmosis
(ICEO), has been demonstrated to be effective in focusing an incoming
mixture into a particle stream as well as nonselective regarding the
particles of interest. Encouraged by these aspects, we propose a hybrid
method for microparticle separation based on a delicate combination
of ICEO focusing and dielectrophoretic deflection. This method involves
two steps: focusing the mixture into a thin particle stream via ICEO
vortex flow and separating the particles of differing dielectic properties
through dielectrophoresis. To demonstrate the feasibility of the method
proposed, we designed and fabricated a microfluidic chip and separated
a mixture consisting of yeast cells and silica particles with an efficiency
exceeding 96%. This method has good potential for flexible integration
into other microfluidic chips in the future
Visualization 4: High efficiency fabrication of complex microtube arrays by scanning focused femtosecond laser Bessel beam for trapping/releasing biological cells
Release of captured breast cancer cells. By aspirating with syringe, cells were released slowly from microtubes into cell culture. Originally published in Optics Express on 03 April 2017 (oe-25-7-8144
Visualization 3: High efficiency fabrication of complex microtube arrays by scanning focused femtosecond laser Bessel beam for trapping/releasing biological cells
The simulated process of NIH 3T3 capture. Cells were sucked into microtubes with extrusion deformation firstly, then, moved with fairly high speed in the first part and decelerated when close to the outlet of microtubes. Originally published in Optics Express on 03 April 2017 (oe-25-7-8144
Visualization 1: High efficiency fabrication of complex microtube arrays by scanning focused femtosecond laser Bessel beam for trapping/releasing biological cells
The simulated progress of microparticle capture. The results show that the fluid speed in the microtubes is related to the distance between fluid and the aspirating needle and increases dramatically when it is close to the aspirating needle. Originally published in Optics Express on 03 April 2017 (oe-25-7-8144