1. Microfluidics: introduction

2. Why miniaturize ? because it is possible?
because it is improves performance ?
because it opens up new possibilities ?
"Courtesy Sandia National Laboratories, SUMMiTTM Technologies,

3. Start of an era: Gas chromatograph on silicon wafer (1979):
-injector
-separation channel
-thermal conductivity detector
Gas fluidics minor activity compared to liquid fluidics (which started in 1990)

4. Drug delivery 100 identical drug chambers
Drug release by electrical puncturing of a gold membrane

5. APCI-MS, Atmospheric Pressure Chemical Ionization Mass Spectrometry

6. Protein interaction chip
256-mixer
Radiolabeling synthesis reactor for PET
S. Quake

7. Is microfluidics different ?

8. Channels by embossing
Bonding a cover slip

9. Closed channels: bonding
One wafer holds channel; other is planar
Both wafers hold structures; need alignment
Misalignment !
Is channel cross section important ?

10. Laminar vs. turbulent flow

11. Reynolds number (Re) ratio of inertial to viscous forces Re = ρνD/η
ρ = density of fluid (kg/m3)
ν = linear velocity (m/s)
D = dimension of the system, diameter (m)
η = viscosity of the fluid (Pa*s = kg/m*s)
viscosity is the quantity that describes a fluid's resistance to flow
small Re means large viscous forces

12. Reynolds number Microchannel: ρ = 1 kg/l (= 1000 kg/m3)
v = 1mm/s (=10-3 m/s)
D = 100 µm diameter (=10-4 m)
η = kg/m*s
Re = 1000* * 10-4/ (all in SI units)
Re = 1
If Re < 2300, flow is laminar (microfluidics always)

13. “Swimming” at high Reynolds: streamlined shape; yet turbulence
Re = ρνD/η
= 1000 * 10 *10/
0.001 =

14. Swimming at low Reynolds: shape does not matter
Swimming movements of CR (Chlamydomonas Reinhardtii)
Cell size ca. 10 µm, flagella 12 µm
Flagella shown at different stages of the stroke (1-7 power stroke)
40-60 Hz frequency
µm/s speed (One stroke 2-4 µm, or 20-40% of CR size)

15. Slow mixing in laminar flow
v ~ 100 m/year
V ~ 1 µm/s
 Re ~ 100
In laminar flow the streamlines do not mix.
Mixing is predominantly by diffusion.

16. Sperm selection

17. Cell/bead sorter (1) sample flow in hydrodynamic focusing
fluorescence detection
electrokinetic actuation
separated streams

18. Cell/bead sorter (2)

19. Nanofabrication
Microfabrication

20. Microfabricated sizes
Linewidth µm typical
Channel depths µm typical
Gaps 10 nm and up, by bonding or sacrificial etching

21. Nanofluidics: molecular size equals channel size
Side view
Top view

22. Diffusion d = √2Dt distance travelled
Object Size Diffusion constant Distance in 1000 s
small ion r=0.1 nm D=2*103 µm2/s µm
small protein r=5 nm D=40 µm2/s 280 µm
virus r=100 nm D=2 µm2/s 63 µm
bacterium r=1 µm D=0.2 µm2/s 20 µm
mammalian cell r=10 µm D=0.02 µm2/s 6.3 µm
hemoglobin: D = 7*10-7 cm2/s = 70 µm2/s

23. Macroscopic vs. atomistic
Diffusion constants can be measured in macroscopic experiments
Theory developed by Einstein in 1905 established a connection between atomic size (RH= hydrodynamic radius) and diffusion constant
D = kT/ 6ηRH  RH= kT/ 6η D
where η =viscosity; kT = thermal energy
r small protein = 1.38*10-23 *300/6*3.14*1*10-3*40*10-12
r small protein = 5.5*10-9 m

24. Scaling: diffusion & detection
Cube volume 1 µL 1 nL pL 1 fL
Cube edge 1 mm 100 µm µm 1 µm
Diffusion time 500 s 5 s s 0.5 ms
#molecules (1 µM) 6* * *

25. Detection limits vs. volume
Sabeth Verpoorte, IMT Neuchatel

26. Chemical microfluidics
-separation systems (CE, LC, GC,...)
-detectors (microelectrodes, MS, photodiodes,...)
-droplet generators (ESI)
-ionization systems (corona, UV, ...)
-synthesis reactors
-gradient generators
-crystallization chips
-...

27. Physical microfluidics
cooling ICs and high power lasers
power-MEMS: combustion engines, fuel atomizers, fuel cells
fluidic optical switching
fluid sensors (rate, viscosity, shear, ...)
MAVs = Micro Air Vehicles
microrockets
fluidic logic

28. Electronic paper by electrowetting

29. Microfluidic benefits
Many functions can be integrated in a single device
Small volumes lead to fast reactions
Sensitivity is enhanced because of
high surface-to-volume ratios
Laminar flow easy to control