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Analytical > Microfluidics > Flashcards

Microfluidics Flashcards

1
Q

Microfluidics advantages

A

compact

faster and more efficient

multifunctional

mass production

less materials

safer handling

disposable

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2
Q

Microfluidics Disadvantages

A

complex

things work differently at smaller scales

harder to detect

no defined standards

things don’t scale linearly

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3
Q

Reynolds Number

A

measures if laminar or turbulent

> 4000 turbulent

< 2000 laminar

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4
Q

Transport mechanisms

A
  1. diffusion

entropy driven molecular movement

  1. convection/direction

controlled by a force

bulk fluid motion

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5
Q

Peclets Number

A

Measure if diffusion or directed dominates

> 1: convection dominates

< 1: diffusion dominates

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6
Q

Directed Convection Transport kinds

A
  1. Hydrodynamic

parabolic flow profile

  1. Electroosmotic Flow

uniform flow profile

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7
Q

Flow Rate

A

proportional to pressure difference/drop

smaller dimensions = slower flow

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8
Q

How to mix in microchannel

A
  1. Diffusion

increase length

  1. Flow focussing

flow directed in to continuous flow

  1. Microstructures in microchannel

creates secondary flows that mix

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9
Q

Materials

A

Silicon and Glass

Elastomers and plastics

hydrogels

paper

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10
Q

Silicon/glass advantages

A

organic solvents

metal depositing

high thermo conductivity

stable electroosmotic flow

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11
Q

silicon/glass disadvantages

A

expensive

dangerous fabrication

difficult to bond layers

can’t do valves

not gas permaeble

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12
Q

Elastomers Plastics advantages

A

Inexpensive

easy fabrication

non toxic

high resolution

reversibly or irreversibly bonded

multilayer

can make valves

gas permeable

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13
Q

elastomers plastics disadvantages

A

no organic solvents

interact with analytes limiting quantification

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14
Q

Hydrogel benefits

A

3D networks of hydrophilic polymer

highly porous

permeability

good for cell culture

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15
Q

Paper pros

A

highly porous

easy to fabricate

wiking of ligands

no pump/power needed

low cost

filters particles

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16
Q

paper cons

A

not transparent

poor detection sensitivity

evaporation from open channels

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17
Q

Fabrication Methods

A

Photolithography

chemical Etching

Physical etching

deposition

replication/moulds

3D printing

micromilling

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18
Q

Photoresist kinds

A

positive:

regions exposed become soluble

negative:

regions not exposed become soluble

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19
Q

Etching details

A

subtractive process

wet etching with chemicals

dry etching with plasma

isotropic - spherical front, undercuts mask

ansiotropic - directed, straight edges

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20
Q

Physical etching pros and cons

A

pros

faster

no clean room

cons

surface roughness

lower accuracy

21
Q

physical etching methods

A

powder blasting

electron discharge machining

laser abalation

22
Q

Replication Techniques

A

create high precision mold

  1. micro moulding

apply pdms to mould and bake

  1. injection moulding

inject molten plastic in mould

  1. hot embossing

master pressed into soft plastic

23
Q

Bonding layers

A

silicon to silicon - fusion bonding

silicon to glass - anodic bonding

pdms - reversible by contact, irreversible by oxygen plasma

24
Q

3D printing

A

layer by layer fabrication

fast prototyping

from 3D model

25
Q

micromilling

A

subtractive process

rapid prototyping

26
Q

Paper fabrication methods

A
  1. photolithography
  2. paper cutting
  3. wax printing
  4. oragami 3D structures
  5. hydrogel driven
27
Q

paper photolithography process

A
  1. soak in resist
  2. prebake
  3. mask
  4. expose to UV
  5. post bake
  6. wash away resist
  7. plasma oxidise residual

hydrophobic polymer creates channels

28
Q

Paper cutting

A

cut out channels

arrange and set between two layers of plastic

29
Q

wax printing

A

draw hydrophobic wax channels on paper

30
Q

Hydrogel driven devices

A

release fluid with stimulus e.g. temp

hence can control fluid flow

31
Q

Digital Droplet based devices

A

generate and manipulate drops of fluids in immiscible continuous phase

32
Q

digital droplet advantages

A

high control over droplet size, frequency with uniform

higher surface area to volume means faster transfer and reaction times

each droplet can be individually transported, mixed, reacted and analysed

allows for parallel processing

high through put

much greater control/uniformity than traditional agitation

33
Q

Droplet formation factors

A

flow rate

flow angle

controls size and frequency

34
Q

Droplet formation methods

A
  1. T junction
  2. flow/shear focussing
  3. Dielectrophoresis (DEP)
  4. Electrowetting (EWOD)
  5. Pneumatic valve pump
35
Q

Concentrating Sample

A
  1. Electrophoretic
    - stacking
    - isotachophoresis
    - isoelectric focussing
    - temperature gradient focussing
  2. support based
    - solid phase extraction
36
Q

why microfluidics good for biology

A
  • channels and chambers are same size as cells
  • study cell interactions in controlled environment
  • single cell handling
  • real time observations
  • continuous flow systems
  • can sort cells e.g. DEP
37
Q

biological applications

A
  1. mimick biological functions/organs

create microstructures for trapping cells and reducing shear stress

  1. bioreactor

chemical processes using arranged cells

  1. cell cultivation

trap cells in microstructures

  1. cell assays

create chemical gradients

  1. 3D hydrogel cell cultivation

contains water and forms 3D structures

38
Q

Digital Droplet applications

A

cell encapsulation

mixing

drug delivery

39
Q

T junction

A

cell size depends on flow rates and channel size

40
Q

flow shear focussing

A

increasing dispersed phase flow creates smaller droplets at higher frequency

41
Q

DEP details

A

polarisable fluid at higher dielectric permittivity

apply nnon-uniform elecric field generating droplets

magnitude of voltage and frequency determines size

42
Q

electrowetting details

A

electric field reduces interfacial energy/contact angle

causes wetting of surface

when voltage turned off surface becomes hydrophobic again creating droplets

size dependent on field strength, frequency and channel size

higher frequency produces smaller droplets

43
Q

Flow rate minimisation

A

rate decreases as fluidic resistance higher in microchannels

same time but lower reagent consumption

44
Q

Analytical Applications

A

Isotachophoresis preconcentration

solid phase extraction

purification of DNA for pcr analysis

isoelectric focussing

45
Q

Biological Applications

A

Replicating biological functions e.g. lung on a chip

Bioreactor

Cell cultures

46
Q

PDMS soft lithography process

A
  1. coat silicon wafer with photoresist
  2. soft bake
  3. apply photo mask
  4. expose to uv
  5. post bake
  6. develop photoresist
  7. apply pdms over mould and bake to cure
  8. remove PDMS layer
  9. permanenly seal by oxygen plasma
47
Q

Why Biological

A

Microchannels match cell size

study cell-cell/cell-matrix

trap cells in microstructures

can form complex cell structures/environments

gradients

sort cells

real time obserations

48
Q

shear stress minimisation

A

microstructures reduce shear stress

improves cell growth and survivability

Analytical (7 decks)

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