1. 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

2. Flow Cytometry Capability Applications
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

3. Basics of Flow Cytometry
Injector
Tip
Fluorescence
signals
Focused laser
beam
Sheath
fluid
Hydrodynamic Focusing
Purdue University
Cytometry Laboratories
Focus cells in suspension by sheath fluid
Illuminate cells in the focused suspension stream
Analyze cells by detecting scattered and fluorescence light

4. Motivation for a MEMS Microcytometer
Conventional
Micro (Goals)
User Interface
Complex
Operated by skilled personnel
Easier to operate
Size etc.
Large, heavy
 A reservoir is required for the sheath flow medium, and need to be kept free of dust and bacteria
Small, portable
 Large components unnecessary
 Eliminate the use of gallons of sheath liquid
Price
Expensive
Inexpensive

5. Principle of Dielectrophoresis

6. Principle of Dielectrophoresis
Positive dielectrophoresis

7. Principle of Dielectrophoresis

8. Principle of Dielectrophoresis
Negative dielectrophoresis

9. Principle of Dielectrophoresis

10. Dielectrophoretic Particle Focusing
DEP forces can be used to focus, trap or repel particles, enabling particle fractionation and separation
Fringing fields at electrode edges provide DEP levitation forces in direction normal to the electrode plane

11. 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

12. Electrode Fabrication
Top View of the Bottom Electrodes
Bus bars to provide AC electric field of 90 phase difference, i.e. 0, 90,180, 270.
Bus Bar
Channel
Side View
Electrode

13. Electrode Fabrication (Cont’d)
Deposit inter-metal dielectrics, etch holes 2 1
Deposit gold electrodes
Si Substrate 3
Deposit and pattern gold layer
and insulation layer
Fabricate similar electrodes on a glass wafer 4
Glass substrate
Same phase of the electric field

14. Electrode Fabrication (Cont’d)5
Deposit SU-8, pattern a channel
SU-8 channel
Bonding process to complete the channel
Side View 6
Glass
SU-8 Si

15. Optical Detector Fabrication
Fiber coupled to a blue LED A
Glass wafer
TiO2/SiO2 multilayer interference filter
SU8
Au/Ti contact pads
P-Si
p-n diode A
Channel
A-A Side View
Flow in
Flow out

16. Acknowledgement BME Seed Grant
Graduate Student: Choongho Yu, UT Austin