Transcript Separation of Carbon Nanotube by Dielectrophoresis

A MEMS Micro Flow-cytometer Based on
Dielectric Particle Focusing and Integrated
Optical and Impedance Detection
Peter R.C. Gascoyne
Department of Molecular Pathology
MD Anderson Cancer Center
Li Shi
Department of Mechanical Engineering
The University of Texas at Austin
Flow Cytometry

Capability
Measures physical and chemical properties of single
cells or other biological particles as they flow in fluid
stream past a light source
 Analyze 105 cells per second


Applications
Analysis of blood cells, bacteria, nuclei, chromosomes
 Detection of cancer cells – labeling of surface markers
 Measurement of particle size, shape, granularity, etc.
 Sort cells

Basics of Flow Cytometry
Hydrodynamic
Focusing
Injector
Tip
Sheath
fluid
Fluorescence
signals
Focused laser
beam
Purdue University
Cytometry Laboratories
1. Focus cells in suspension by sheath fluid
2. Illuminate cells in the focused suspension stream
3. Analyze cells by detecting scattered and fluorescence light
Motivation for a MEMS Microcytometer
Conventional
User
Complex
Interface
Operated by skilled
personnel
Size etc. Large, heavy
Price
Micro (Goals)
Easier to operate
Small, portable
 A reservoir is required for
the sheath flow medium,
and need to be kept free of
dust and bacteria
 Large components
unnecessary
 Eliminate the use
of gallons of sheath
liquid
Expensive
Inexpensive
Principle of Dielectrophoresis
FDEP ( f )  2m r Re( f CM )E
3
f CM
 

  2
*
p
*
p
*
m
*
m

   j
2f
*
2
rms
Principle of Dielectrophoresis
Positive dielectrophoresis
E
FDEP

m1

Principle of Dielectrophoresis
Principle of Dielectrophoresis
Negative dielectrophoresis
E
FDEP

m2

Principle of Dielectrophoresis
Dielectrophoretic Particle Focusing
DEP forces can be
used to focus, trap
or repel particles,
enabling particle
fractionation and
separation
flow
Fringing fields at
electrode edges
provide DEP
levitation forces in
direction normal to
the electrode plane
Design of
the DEP
focusing
channel
Use negative DEP
to focus cells in
the central region
of the stream
Integrate
fluorescent and
impedance
detectors into flow
channel
Electrode Fabrication
Top View of the Bottom Electrodes
Bus
Bar
Channel
Bus bars to provide AC electric
field of 90 phase difference, i.e.
0, 90,180, 270.
Side View
Electrode
Electrode Fabrication (Cont’d)
1
Deposit gold electrodes
2
Deposit inter-metal
dielectrics, etch holes
Si Substrate
3
Deposit and pattern gold layer
4
and insulation layer
Fabricate similar electrodes
on a glass wafer
Glass substrate
Same phase of the electric field
Electrode Fabrication (Cont’d)
5
Deposit SU-8, pattern a channel
SU-8 channel
6
Bonding process to
complete the channel
Side View
Glass
SU-8
Si
Optical Detector Fabrication
Fiber coupled
to a blue LED
A
Glass wafer
Au/Ti
contact pads
SU8
P-Si
TiO2/SiO2
multilayer
interference
filter
p-n diode A Channel
A-A Side View
Flow in
Flow out
Acknowledgement
 BME
Seed Grant
 Graduate
Student: Choongho Yu, UT Austin