Lecture 18: Microfluidic MEMS, Applicationsmech466/MECH466-Lecture-18.pdf · 2016-07-11 · PDMS...

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MECH 466Microelectromechanical Systems

University of VictoriaDept. of Mechanical Engineering

Lecture 18:Microfluidic MEMS,

Applications

© N. Dechev, University of Victoria

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Microfluidic Electrokinetic Flow

Basic Microfluidic Components

Applications of Microfluidics

Overview


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The science of using electric fields to move fluids, or to use fluids to generate electric fields.

There are two main electrokinetic phenomena that can be utilized:

(a) Electro-osmotic effect (EO)

(b) Electrophoresis and Dielectrophoresis

These methods utilize electric fields to move fluids, and are primarily used in microfluidics.

Electrokinetics


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An electrochemical reaction will occur at liquid/solid interfaces, when an electrolyte solution is present, causing an electric polarization of the channel wall.

For the glass surfaces used in microfluidics, the electrolytes will cause deprotonation of the wall surface, producing a negatively charged wall. Where deprotonation is the removal of a proton (H+) from a molecule.


Fluid Transport by Electro-osmotic Flow

- - - - - - - - - - -

- - - - - - - - - - -

Here, water molecules absorbed by theglass wall will be subject to deprotonation,resulting in a negative charge distributionon the surface of the glass.

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The charged wall will attract ions from the bulk liquid, and they will form an ion layer called a ‘electric double layer’ on the wall surface.

If an electric field is applied parallel to the wall, these ions adjacent to the wall will move in response to the E-field, and will ‘drag’ the surrounding fluid. This fluid flow is called ‘electro-kinetic flow’.


Fluid Transport by Electro-osmotic Flow

- - - - - - - - - - -

- - - - - - - - - - -

+ + + + + + + + +

+ + + + + + + + +

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Here, the electric field is used to act upon the particles within the fluid, for the purposes of separation, transportation and characterization.

The force exerted on a ‘particle’ due to the electric field can be defined as:

Fluid Transport by Electrophoresis


Where: Q - Charge P - Polarization E - Electric Field

+ -

+ -

+

_

_

+

+

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Fluid Transport by Electrophoresis


[Image from Chang Liu]

Electrophoresis force is defined as:

Dielectrophoresis force is defined:

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Size-based separation of biological macromolecules such as DNA restriction fragments and proteins.

Capillary Gel Electrophoresis


http://www.ceandcec.com/http://ntri.tamuk.edu/ce/ce.html

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Microfluid channels and chambersfor transporting and storing fluid

Microfluid pumpsfor moving fluid

Microfluid valvesfor isolation of fluid

Mixersstructures to prompt mixing at the micro scale

Electrodes (metal)for provide potential or current, or to detect signals

Sensorsflow parameter sensors and chemical parameter sensors

Basic Microfluidic Components


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Fabrication of Micro-Channels


Micro-Channels are often fabricated in Glass or Pyrex Substrates using Isotropic Wet Etching Processes.

Fabrication Process Sequence for creating Micro-Channels in a Glass Substrate[Image from Chang Liu]

Mask Glass

Isotropic Etch

Remove Mask

Bond Overlying Layer of Glass to Create Channel

(a) Glass

GlassGlass

Chrome Mask

(b)

(c)

(d)

(e)

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Micro-Channels fabricated using Silicon Substrate, and subsequent wafer to wafer bonding.

Step (a): Create pattern in silicon bulk using isotropic, anisotropic or DRIE etch process.Step (b): Conformal growth of layer (i.e. silicon nitride) to create channel wall.Step (c): Bond original wafer to main wafer using anodic bonding.Step (d): Selectively etch away original silicon material, without removing Silicon Nitride channels, to create structure shown.

[Images from Chang Liu]

(a)

(c) (d)

(b)

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Micro-Channels fabricated into Silicon Substrate, and sealed with oxide growth.

[Images from Chang Liu]

(a) Deep Reactive Ion Etching (b) Passivation of Sidewalls (c) Isotropic Etching (d) Channel Sealing

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Pumping of microfluids can be done in a number of ways, including:

Pressure driven flowfluid flow caused by pressure differential

Electrokinetic flowfluid flow caused by movement of charged particles or molecules

Surface acoustic wave

Capillary force driving

Micro-Pumps


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Recall two conventional technologies for pumping fluids:

Review of Macro-Scale Pumps


Centrifugal Water Pump [www.wfdasia.com/]

Peristaltic Pump

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To create flow in the micro-channel, a conventional macro-scaled pump pressurizes the fluid, and is connected to the chip via flexible tubes.

Pressure Drive Flow in Microchannels


[labs.pharmacology.ucla.edu/tsenglab]

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Micro-Pump using a pair of one-way valves. Pump membrane is actuated using an external magnetic field.

Micro-Pump with One-Way-Valves

© N. Dechev, University of Victoria[Image from Chang Liu]

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Piezoelectric-Actuator driven flow

Surface Acoustic Wave Driven Flow


[Ogawa J., Kanno I., Kotera H., Wasa K., Suzuki T., “Development of liquid pumping devices using vibrating microchannel walls”, Sensors and Actuators A, 152, pp 211–218, (2009). ]

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Increase interfacial area to reduce diffusion length- sinusoidal, square-wave, or zigzag channels - divide and conquer approach- lamination-splitting

Micro-Mixers


Lamination splitting mixerLIGA micro mixerLamination Splitting Mixer

[J. Branebjerg, et al., IEEE MEMS, 1996, p. 442] LIGA Micro-Mixer [W. Erhfeld, et al., Ind. Eng. Chem. Res., 1999, 38, p. 1077]

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Micro-Magnetic Stir Bar


Tip to channel clearance= 10 microns b) Mixer c) Pump

offset

Parylene

Inputs

Output

Parylene channel

Flow

a) perspectiveview

Photoresist

Parylene

Copper seed layer

Permalloy (10 microns)

Stirrer bar formation

Hub and chamberformation

Fabrication Process to create the Micro-Magnetic Stir Bar in a Channel [Chang Liu]

Micro-Magnetic Stir Bar in a Channel [Chang Liu]

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Micro-Magnetic Stir Bar


T=0s

In

Out

T=2s T=3s

Two Micro-Channels Mixing. Note: Micro-Magnetic Stir Bar is Off. [Chang Liu]

Micro-Pumping Using a Micro-Magnetic Stir Bar Time = 0. [Chang Liu]

Micro-Pumping Using a Micro-Magnetic Stir Bar Time = 2 sec. [Chang Liu]

Micro-Pumping Using a Micro-Magnetic Stir Bar Time = 3 sec. [Chang Liu]

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Case Study 13.2: Electrophoresis in Microchannels

Case Study 13.4: PDMS Microfluid Channels

Case Study 13.6: PDMS Pneumatic Valves

Micro-Fluidic Applications:


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(a) A buffer injection is done to fill in the entire channel

(b) Analyte injection using electrokinetic flow

(c) Sample introduction and analyte electrophoretic separation

Optical detection is done near the waste port.

Case Study 13.2: Electrophoresis in Microchannels


[Image from Chang Liu]

(a) (b) (c)

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PDMS (polydimethysiloxane) is part of the ‘silicone’ group of plastics.

They produce a ‘thermoset’ plastic, that is transparent and flexible.

Additionally, PDMS is porous, allowing liquids and gasses to slowly diffuse through the material.

Microchannels are made using micro-molds

Case Study 13.4: PDMS Microfluid Channels


Fig. 13.13 PDMS Molding[Image from Chang Liu]

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Soft membrane micro-valves actuated by air pressure



Fig. 13.15 PDMS Microvalve Fabrication[Image from Chang Liu]!"#$"%

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Fig. 13.16 Fabrication of peristalic pump[Image from Chang Liu]

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Fluid VLSI [Image from Chang Liu]

Microscopic Images of PUMP[Image from Chang Liu]

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Lecture 18: Microfluidic MEMS, Applicationsmech466/MECH466-Lecture-18.pdf · 2016-07-11 · PDMS...

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