Class 7 Microfluidic Platforms Compared, Winter 2011

Content

Fluidics Applications Scaling in Fluidics A CD as a Fluidic Platform Nanofluidics Challenges in Microfluidic Platforms

Memory devices today and tomorrow

Diagnostics/Molecular diagnostics today and tomorrow

Raw sample

Cell Separation

bacteria,

cancer cell,

WBC, et al

DNA

RNA

protein

Hybridization

Electrophoresis

SequencingCell Lysis, Purification

Amplification

Sample Preparation

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

Mechanical pressure Acoustic Centrifugal Electrokinetic

PROPULSION

InstrumentPowerPropulsionHeater (PCR)ElectronicsDetection

Disposable CassetteReagentsFluidics

Fluidics Applications

Lab-on-a-chip:– Goals

» Portable» Robust» Easy to use» Flexible» Inexpensive» Modular?

Fluidics Applications

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

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.

Propulsion Mechanisms-Pumps:– Mechanical

(pneumatic/hydraulic)--example shown on the right is the blister pouch (kodak/Johnson&Johnson)

– Electrokinetic– Thermal (shape memory alloy,

phase changes)– Acoustic– Centrifuge– Electrohydrodynamic– Magnetic – Chemical (hydrogel, osmotic

pressure, phase change)– Electrochemical (create bubles

through electrolysis)

Different Propulsion Options-Pumps

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

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 pullassembled charges– Charges at surfaces drag

bulk material– Plug flow

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

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

Different Propulsion Options

Acoustic (Dick White’s flexural plate wave device for example)

– Scales as L2

– No fluidic contact

– R & D phase

– Generic

– Doesn’t solve valving yet

– ZnO technology still difficult to reproduce

– Easy to further miniaturize

Different Propulsion Options

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

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).

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

TIME(H. Kido and J.Zoval).

A CD as a Fluidic Platform

Gnat wing

White blood cells

DNA array

Examples of pictures taken using the CD player.

Vision is another dimension CD fluidics can offer.

A CD as a Fluidic Platform

The optical disc drive is a smart centrifuge.

r

R1

R2

Center

ΔPc =ρω2(R2 −R1)R2 +R1

2=ρω2ΔR⋅R

ΔPs =γcosθ ⋅C

A

fb ≥(γcosθ ⋅C

π2ρ⋅R⋅ΔR⋅4A)

12 =(

γcosθπ2ρ ⋅R⋅ΔR⋅dH

)12

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.

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

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.

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

E.coli Lysis

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.

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 withDNA Capture Probes

Flow-through Hybridization column

Target DNA Injection

Out

A CD as a Fluidic Platform

Navier Stokes eq.:

Species transport equation:

Modeling of DNA transport in flow-through hybridization column

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 4&5. Fast hybridization steps:

HydrationSample flow Two consecutive wash steps

A CD as a Fluidic Platform

(i) (ii)

(a) (b)

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).

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

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 application’s need.

Don’t throw away your reject CD’s (AOL, Barry Manilow, the Bee Gees, etc....).They may have some use after all. Put blood on the tracks !

Raw sample

Cell Separation

bacteria,

cancer cell,

WBC, et al

DNA

RNA

protein

Hybridization

Electrophoresis

SequencingCell Lysis, Purification

Amplification

Sample Preparation

A CD as a Fluidic Platform

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).

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