Transcript Microfluidics

BITS Embryo
Chemical Engineering Lecture
Microfluidics – A Primer
Ketan “Kittu” Bhatt
(97 A1)
Post Doc, Material Science & Engineering
University of Illinois at Urbana-Champaign
Ph. D., Chemical & Biomolecular Engineering
North Carolina State University
Outline
• What are microfluidics & lab-on-a-chip systems?
• Why microfluidics?
• Some concepts
• Applications
Wikipedia: (www.wikipedia.org)
• Microfluidics deals with the behavior, precise control and
manipulation of microliter and nanoliter volumes of fluids
• Lab on Chip - Devices that integrate (multiple) laboratory
functions on a single chip of only millimeters to a few square
centimeters in size that are capable of handling extremely small
fluid volumes down to less than picoliters
mFluidics & Lab-on-chip systems
Advantages:
- Low cost
- High throughput
- Faster analysis
- Compact design
- Ease-of-use
- Reduced sample & reagent
consumption
- Extensive parallel architectures
- Reliability
Entirely new techniques might become available
opening up possibilities for new experiments and
innovations not possible by traditional methods
Photolithography: Fabrication of mfluidic channels
Photoresist
Glass
UV Light
Mask
Glass is coated with a layer of
photoresist
The channel pattern is transferred via a
mask and radiation source eg. UV light
The exposed photoresist is removed
An appropriate etchant, eg. HF/NH4F,
is used to etch the channel pattern
After the remaining photoresist surface
have been removed, the top plate can
be attached eg. by thermal bonding
Soft lithography: Stamp Fabrication
Schematics of the procedure
for fabricating PDMS stamps
from a master having relief
structures on its surface
Press on a surface, connect tubing
(Slide courtesy: Orlin Velev)
Xia & Whitesides, Annu. Rev. Mater. Sci. 28, 153 (1998)
Liquid transport: Pressure driven Laminar flow
Re 
LVavg 
m
L = Length scale, Diameter
Vavg = Average fluid velocity
 = Density
m = viscosity
Typical values:
Channel width, L = 1 mm
Average fluid velocity = 1 mm/s
Density = 1000 kg/m3
Viscosity = 0.001Ns/m2
Re = 1
(strc.herts.ac.uk/mm/)
Liquid transport: Electroosmotic pumping
The counterions next to
the wall move with the
field: plug flow
(Slide courtesy: Orlin Velev)
mFluidics: What principles are used to
make liquids and particles move?
Comparison of fluid- and particle-propulsion methods in microfluidics
Huang et al., Anal. Bioanal. Chem. 372, 49 (2002)
(Slide courtesy: Orlin Velev)
Microfluidic chips & devices: examples
Uses include:
Separations
Chemical analysis
Chemical sensing
Microscale synthesis
Combinatorial synthesis
Drug screening
Genetic fingerprinting
Genetic research
Cell screening
Clinical diagnostics
Materials research
Catalysis research
Microfabrication
Photonics
Electronics
(Slide courtesy: Orlin Velev)
DNA Arrays
DNA pairing basics
(Slide courtesy: Orlin Velev)
DNA array chips – Basic principles
 Human genome contains ~ 30000 genes which encode more than 90000
RNA species and basic proteins. The possible mutations increase this
number multiple fold.
 Many genes work in combination with others, so understanding and using
their function requires characterization of multiple genes.
 Massively parallel detection and analysis is required.
 The amount of reagents and samples is small and they are very expensive
so it all needs to be done on a miniature scale.
Fluorophore
Immobilized fragments
(Slide courtesy: Orlin Velev)
Hybridization
Match
DNA array chips – Basics
Basics of what’s on
the surface of a DNA
chip
(Slide courtesy: Orlin Velev)
Bioarrays: Future of bioresearch and medicine
Thousands of genes
checked on chip
Clinical diagnostics
Genetic fingerprinting
Drug screening
Genetic research
Cell research
(Slide courtesy: Orlin Velev)
Droplet – Based Microfluidics
Dielectrophoretic chips with suspended
microdroplets: Principle of operation
Liquid – liquid chip system without walls or channels
Velev, Prevo and Bhatt, Nature 426, 515 (2003)
Droplet equilibrium positions
High
intensity
regions
Droplet-chip geometry to scale.
Finite element electrostatic calculations using conformal triangles (Femlab)
Controlled parallel transport of
multiple droplets
300 V, 300 Hz
- 500 V DC
gold nanoparticles
2% white polystyrene latex
2% pink fluorescent latex
0.2% white latex
0.2% white polystyrene latex
0.2% pink fluorescent latex
On-chip microdroplet engineering
Mixing
Reaction
Synthesis
of supraparticles
Separation
at the top
Separation
at the bottom
Microbioassays
Mixing of droplets of aqueous suspension
and encapsulation inside oil droplet
latex in water 
gold

nanoparticles
dodecane 
 Foil /Water   Dodecane/Water   Foil / Dodecane
Chemical reactions and precipitations
3 CaCl2 + 2 K2HPO4  Ca3(PO4)2 + 4 KCl + 2 HCl
FeSO4 + 2 NaOH  Fe(OH)2 + Na2SO4
Simultaneous “eyeballs” syntheses in
multiple on-chip droplet microreactors
Massive parallelization possible
Gold – latex anisotropic assemblies
1 min
7 min
11 min
18 min
50 min
Time
Acknowledgements
Orlin Velev
Jennifer Lewis
BITS Embryo Team
Nitish Korula
Velev Group members
Lewis Group members
Contact information
[email protected]