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 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

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

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

Principle of Dielectrophoresis

Principle of Dielectrophoresis Positive dielectrophoresis

Principle of Dielectrophoresis

Principle of Dielectrophoresis Negative dielectrophoresis

Principle of Dielectrophoresis

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

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

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

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

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

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