sensors

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VIII. Microfluidic Platforms Compared Winter
2009

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Content

• Fluidics Applications
• Scaling in Fluidics
• Different Propulsion Options-Pumps
• Valves
• A CD as a Fluidic Platform
• Nanofluidics
• Challenges in Microfluidic Platforms

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Fluidics Applications
Memory devices today and tomorrow
Diagnostics/Molecular diagnostics today and
tomorrow
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Fluidics Applications

• Lab-on-a-chip
• One system to provide all of the possible
  required analyses for a given type of problem
• All processing steps are performed on the chip
• No user interaction required except for
  initialization
• High throughput screening (HTS) and diagnostics
  are two major applications for Lab-on-a-chip
• Partitioning of functions between disposable and
  instrument is very different for HTS and
  Molecular Diagnostics

Instrument Power Propulsion Heater
(PCR) Electronics Detection
Disposable Cassette Reagents Fluidics
PROPULSION
Mechanical pressure
Acoustic
Centrifugal
Electrokinetic
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Fluidics Applications

• Lab-on-a-chip
• Goals
• Portable
• Robust
• Easy to use
• Flexible
• Inexpensive
• Modular?

• Components
• Separation
• Mixing
• Reaction(s)
• Sample injection
• Sample preparation
• Detection
• Pumping
• Transport (channels)
• Reservoirs
• Flow control
• Intelligence and Memory
• Power
• Display

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Scaling in Fluidics

• Most sensing techniques scale poorly in the micro
  domain (-)
• Often large samples are required to get enough
  target species collected (-)
• Short analysis time dictates small devices ()
• Fast heating/cooling (e.g., for PCR) requires
  small samples ()
• All flow is laminar (little turbulent mixing) (-
  for mixing)
• Surface tension becomes significant (/-)
• No inertia effects (/-)
• Apparent viscosity increases (/-)
• Evaporation is very fast for small samples (-)
• Devices are almost always too large for Si to be
  a solution.

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Different Propulsion Options-Pumps

• Propulsion Mechanisms-Pumps
• Mechanical (pneumatic/hydraulic)--example shown
  on the right is the blister pouch
  (kodak/JohnsonJohnson)
• Electrokinetic
• Thermal (shape memory alloy, phase changes)
• Acoustic
• Centrifuge
• Electrohydrodynamic
• Magnetic
• Chemical (hydrogel, osmotic pressure, phase
  change)
• Electrochemical (create bubles through
  electrolysis)

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Different Propulsion Options-Pumps

• Everything that makes for a valve can make for a
  pumping mechanisms.

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Different Propulsion Options-Pumps
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Different Propulsion Options

• Mechanical (blister pouch for example)
• Scales as L3
• No fluid contact
• Generic
• Innovation in the blister pouch
• Solves liquid and vapor valving !!
• Difficult to further miniaturize
• Difficult to multiplex

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Different Propulsion Options

• Electrokinetic (electro-osmosis)
• Requires materials with surface charge
• Preferably permanent
• Glasses and many polymers have permanent negative
  surface charge
• Positive charges assemble on surface
• Applied charges pull
• assembled charges
• Charges at surfaces drag bulk material
• Plug flow

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Different Propulsion Options

• Electrokinetic (DC)
• High voltage source is not convenient
• Many parameters influence propulsion force
• Not generic
• Mixing difficult to implement
• Fluid contact
• Scales as L2
• First products (Caliper)
• May solve liquid valving but not for vapors !
• Better for high-throughput screening (HTS) and
  smaller samples

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Different Propulsion Options

• Centrifugal
• Compatible with a wide range of samples
• Mixing easy to implement
• Sample preparation easier
• Simple and inexpensive CD player for drive
• No fluid contact
• Established
• Generic
• Solves liquid valving elegantly
• Scales a bit better than l3
• Most functions demonstrated
• Cell work easier
• Better for diagnostics

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Different Propulsion Options

• Acoustic (Dick Whites flexural plate wave device
  for example)
• Scales as L2
• No fluidic contact
• R D phase
• Generic
• Doesnt solve valving yet
• ZnO technology still difficult to reproduce
• Easy to further miniaturize

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Valves

• Polymer valve (Dr. David Beebe) pH actuated.
• Principle goes well beyond just Si!

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Valves

• Passive valves (e.g. Chong Ahn) changes in
  diameter of channel and/more or less hydrophobic
  walls. They are based on surface tension/wetting
  angle changes.
• These type of valves can hold a liquid but not
  vapor! They are of no use in a biomedical
  application if used alone.

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Valves

• Thermo-Pneumatic Valve (Redwood Microsystems).
  Too complicated. Why use Si at all?

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Valves

• Magnetic valves example of a typical mechanical
  valve.
• Miniaturization of the familiar solenoid valve.
• Why use Si? Once the valve becomes of a certain
  size there is no reason to use Si !

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Valves

• Reversible polymer valve (bilayer system) (Dr. M.
  Madou).
• We started with Si but ended up implementing the
  valve in flex circuit material.

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Valves

• Electrochemical valves with a metal the valve
  can be used only once. For many applications this
  might be good enough (shelf-life!)
• The same concept may be applied in non -Si
  structures.
• Using a metal is almost a must for a vapor valve.

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Valves

• Thermally-Actuated Bi-Stable Valve
• Phase-change control fluid that is solid at room
  temperature
• Cycling process
• Heat to melt the control fluid
• Pump the control fluid into or out of flow
  channel
• Cool to re-solidify the control fluid
• No power is required to maintain the valve in
  either the open or closed state
• Valve is leak-tight against liquids or gases

Flow Channel
Phase-Change Control Fluid
Control Channel
Reservoir and pump
Heater/cooler
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Valves

• Phase-Change Pumping Mechanism
• Multiple Peltier heaters/coolers on control
  channel provide directional solidification of
  control fluid.
• Volume change associated with phase change is
  used to provide precise pumping of control fluid.
• Choice of solidification sequence selects either
  open or closed valve position.
• Cycling time is tens of milliseconds for
  10-micron-deep flow channels.

Closing Sequence
Opening Sequence
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Valves

• Single-Use Valve
• Two methods of using heat to open an
  initially-closed single-use valve
• Useful for long-term storage of reagents on
  single-use microfluidic platform
• Initially-open versions also possible

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Valves

• Preventing Loss of Control Fluid
• Phase-change control fluid may be lost if there
  is flow in the main flow channel while valve is
  cycling
• Closing second valve in series with bi-stable
  valve prevents flow while bi-stable valve is
  cycling

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A CD as a Fluidic Platform

• Why a CD as a Microfluidic Platform ?
• Microscope, smart centrifuge and plastic
  disposable with fluid storage capability
• Comparison with other microfluidic platforms
• Example Applications
• Most Recent Application Integrated Molecular
  Diagnostics (DNA Arrays on a CD)
• Lysis
• Lysis 1 multiplex
• Lysis 2 single circular
• Fast hybridization detection
• Optical
• This is where we are headed
• Conclusions

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A CD as a Fluidic Platform

• The optical disc drive is a sophisticated laser
  scanning microscope designed to characterize and
  identify micrometer sized features at a rate of
  about a Megahertz (H. Kido and J.Zoval).

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A CD as a Fluidic Platform

• The voltages from the photodetector are sent to a
  computer using a fast A/D converter.
• The image is then reconstitued using simple
  graphics software

VOLTAGE
(H. Kido and J.Zoval).
TIME
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A CD as a Fluidic Platform

• Examples of pictures taken using the CD player.
• Vision is another dimension CD fluidics can
  offer.

DNA array
Gnat wing
White blood cells
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A CD as a Fluidic Platform

• The optical disc drive is a smart centrifuge.

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A CD as a Fluidic Platform

• The Compact Disc (CD) is a biocompatible solid
  phase (plastic)
• It can substitute for standard consumables such
  as slides, micro-wells, centrifuge tubes.

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A CD as a Fluidic Platform

• List of Lab tasks feasible on a CD
• Mixing,
• Two-point calibration,
• Washing,
• Centrifuge,
• Sample splitting,
• Sample metering,
• Molecule separation,
• PCR,
• Fast Immuno-assays,
• Fast DNA- assays,
• Cell viability tests

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A CD as a Fluidic Platform

• Cell lysis on the CD instead of using a vortex
  ---to make further integration possible
• Motivation To extract DNA from cells in a CD
  platform
• The design below has a single lysis chamber only.

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A CD as a Fluidic Platform

• Type Chinese Hamster Ovary (CHO-K1)
• Size 10 µm
• Glass Beads 100 220 µm
• No. of Rotation Cycles 300 (5 min.)

DNA concentration measured using PicoGreen
Quantitation Kit
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A CD as a Fluidic Platform

• Multiplex design allows the integration of
  several cell lysis chambers with other analysis
  tasks on the same platform.
• As we saw before the cells can also be visualized
  before and after lysis using the CD optics.

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A CD as a Fluidic Platform

• Fast DNA Hybridization Detection
• Problem Time consuming hybridization caused by
  slow diffusion of DNA molecules in passive DNA
  array approaches
• How to speed up hybridization ?
• Electrophoretic
• Mixing
• Flow

Microspots with DNA Capture Probes
Target DNA Injection
Out
Flow-through Hybridization column
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A CD as a Fluidic Platform
Modeling of DNA transport in flow-through
hybridization column
Navier Stokes eq. Species transport equation
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A CD as a Fluidic Platform

• Hybridization in a constrained column using CD
  platform for sample and reagent propulsion

• The flow cell consists of a hybridization column
  1, hydration buffer chamber 2, sample chamber 3,
  and two rinse chambers 45.
• Fast hybridization steps
• Hydration
• Sample flow
• Two consecutive wash steps

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A CD as a Fluidic Platform

• The figure (a) on the left shows the results of
  hybridization on the CD.
• The figure compares a non-specific sequence ssDNA
  (i) with specific sequence ssDNA (ii)
  hybridization experiment.
• A spinning velocity of 450 RPM was used
  (corresponding to the flow rate ranging from 0.65
  uL/min to 1.3uL/min).

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A CD as a Fluidic Platform

• DNA Hybridization results

Specific flow hybridization
Arbitrary optical intensity units
Specific passive hybridization
Non specific
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A CD as a Fluidic Platform

• Final goal
• Sample to answer nucleic acid analysis test
• Multi unit CD combining
• Live/dead viability assay for cell quantization.
• Hybrization detection in which Cells are lysed,
  nucleic acids are purified and mixed with RNAase
  inhibitor, calibrants, and reporters. Fast
  hybridization using flow-through column

Live/dead viability unit
Fast Hybridization detection unit
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A CD as a Fluidic Platform

• Diagnostics as a powerful new application of a
  very mature and well established technology CD,
  DVD, etc.
• Sample to answer for molecular diagnostics in a
  hand-held is not about if but when
  --microfluidics will make it possible and the CD
  approach has the most features that fit the
  applications need.
• Dont throw away your reject CDs (AOL, Barry
  Manilow, the Bee Gees, etc....).They may have
  some use after all. Put blood on the tracks !

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Nanofluidics

• As lithography tools go beyond 1 µm new fluidic
  possibilities arise.
• With fluidic channels of the size of biological
  polymers we can start interacting with these
  species.
• Figure on the right (H. Craighead) demonstrates
  DNA separation using nanochannels (artificial
  hydrogel).

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Microfluidic Challenges

• Wet reagent storage and dry reagent
  reconstitution
• Tight liquid and vapor valves
• Integrated microvalves and micropumps
• Packaging
• Interconnects (optimize, reduce, eliminate)
• Filling / bubbles / dead volume
• Leakage
• Surface functionalization
• Microflow measurement and characterization
• Control algorithms, data processing, and
  communications
• Integrated, ultrasensitive detection
• Heterogenous material integration
• Sensitivity limited by sample volume (front end
  amplifiers/concentrators?)
• Low power
• Harness energy from host or ambient
• Low power pressure sources