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Biotechnology > MEMS: Micro Electro Mechanical Systems > Flashcards

MEMS: Micro Electro Mechanical Systems Flashcards

http://www.zyvex.com/nanotech/feynman.html 1) Jurgen Fritz. Cantilever biosensors. Analyst, 2008, 133, 855-863. 2) Kyo Seon Hwang et. al. Micro and nanocantilever devices and systems for biomolecule detection. Annual Review of Analytical Chemistry, 2009, 2, 77-98.

1
Q

Microfabrication

A

used to manufacture integrated circuits and MEMS

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2
Q

Minaturise for

A

enhanced performance
scalable fabrication and quality
cheaper at larger volumes

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3
Q

Positives

A 
Force effects required for pzieoelectric effect as close together
High surface to volume ratio - good thermal dissipation
Quick Response
Lower Power Consumption
reduced footprint -array
dynamic range
electrical integration
minimally invasive
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4
Q

Negatives

A

High frictional forces
Manufacturing inaccuracy can be higher
strong surface effects- aggregate due to charges

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5
Q

Piezolelectric l

A

ceramic and crystalline display linear electromechanical response to stress or electric field

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6
Q

Piezoelectric used in MEMS

A

actuate mechanical movement

transduce mechanical response to discernible electrical response

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7
Q

Piezoresistive effect

A

semi-conductor material (doped silicon) undergoes mechanical stress which resistance properties
transduce mechanical event into an electrical response see change in resistance
temperature sensitive, compensate with Wheatstone bridge

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8
Q

Electrostatic effect

decreases with the square of the distance

A

actuation - attractive/repulsive force between moving and fixed plates as voltage applied between them
Sensing - capacitance (energy store) changes as distance between plates changes

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9
Q

Pressure sensors

A

blood pressure

intracranial/cerebro spinal fluid/intraocular/endoscopes for organs

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10
Q

BioMEMs

A

biological sensor - recognition element in contact with transducer —> electrical signal
MEMS functionalised with a recognition biomolecule that can pull down a specific target molecule and lead to a physical mechanical change that can be observed

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11
Q

Deliver drugs topically

A

microfabrication of microneedles - no pain, not long enough to reach nerve endings, also continuous extraction
shallow penetration - reduce infection
deliver where most effective, larger molecular

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12
Q

Ideal Bio-MEMS (3)

A

dynamic range
low limit of detection
quick analysis time

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13
Q

Advantages of Bio-MEMS

A

Could show excellent LOD due to scaling
Microfabrication - low cost mass production
Label free
Array format for multiplexing (different markers)

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14
Q

Cantilever

A

Beam anchored at one point

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15
Q

Microneedles cantilever

A

stiff to penetrate skin - short thick and wide

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16
Q

Diagnostic cantilever

A

flexible - long thin and narrow

transduction through mechanical deflection or or dynamic mechanical motion

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17
Q

Properties of microcantilever dependent on

A

geometry and material properties

stiffness Kspring = EWTcubed/4Lcubed

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18
Q

Static mode of detection/stress mode/deflection mode

A

mechanical compliance of cantilever increases with uniform reduction in size (smaller LOD) (when binding analyte) (surface stress not weight)

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19
Q

Static mode cantilever action

A

bend up or down

similar to bimetallic strip on heating (one metal expands more)

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20
Q

Static mode mechanism

A 
biomolecules bind - surface stress developed
electrostatic repulsion/attraction
conformational change
hydration change
steric interaction
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21
Q

Probe coating contracts relative to cantilever

A

creates tensile surface stress - bends up

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22
Q

Probe coating expands relative to cantilever

A

creates compressive surface stress - bends down

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23
Q

Recognition molecule bind one side

and not the other

A

Activate - thiol chemistry

Passivate - silane chemistry

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24
Q

Measure/Record microcantilever detection

A

beam deflection/optical lever detection - reflective gold

recorded on position-sensitive photodetector

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25
Q

Advantage of optical lever detection

A

sensitive - 0.1nm resolution

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26
Q

Disadvantage of optical lever detection

A

bulky external optical equipment with two alignments

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27
Q

Piezoresistive Readout

A

embed piezoresistive material on cantilever

as cantilever deflects - change resistance - electronic readout

28
Q

Advantages of piezo

A

Miniaturised

simple readout

29
Q

Disadvantages of piezo

A

resolution not as good ~1nm

30
Q

Static mode considerations (5)

A
  • in real time in aqueous environment
  • temperature sensitive
  • change buffer composition –> deflection
  • Differential reference sensors needed to remove unwanted background
  • unpredictable when protocol developed
31
Q

Dynamic mode/resonant mode: resonance

F0= (1/2pi) x (squareroot spring constant/mass)

A

tendency of a mechanical system to oscillate with greater amplitude at a certain frequency
depends on geometry (mass) +spring constant

32
Q

Dynamic mode mechanism

A

Apply voltage to piezoelectric actuator to drive to resonance
(external or deposited onto cantilever)

33
Q

Add mass to the cantilever

A

reduce resonant frequency

minimal detectable mass added proportionate to total mass

34
Q

Advantage of dynamic mode

A

very low LOD

35
Q

Disadvantage of dynamic mode

A 
viscous damping (liquid) dissipated to fluid as thermal energy
solution - carry out within cantilever 
long analysis time
36
Q

Biointerface

A

Border between aqueous environment and physical devices - addition of recognition molecules

37
Q

DNA/RNA apatamers

A

single stranded, form secondary structures

38
Q

peptide apatamers

A

artificial antibodies

39
Q

recognition molecules should

A

have affinity/ dissociation constant in nM to pM

streptavidin and biotin 10x-15

40
Q

SAMs

A

Self assembling monolayers

basis of bio-interface assembly

41
Q

SAMs - gold thiol chemistry

A 
Sulphur Base (thiol (SH)) - spontaneous covalent bond with gold
aliphatic Carbohydrate chain - hydrophobic - pack densely
Headgroup - add functionality - cross link further molecules
42
Q

SAMs - silicon base

A

(alkyl)silane molecule forms covalent bond also

43
Q

Head Groups (5)

A 
Amino - NH2
Carboxy - COOH
Aldehyde - CHO
Thiol - SH
Hydroxyl - OH
44
Q

Physisorption mechanism and groups

A

Charged Group (NH3+, COO-)

45
Q

Chemisorption mechanism and groups

A

Cross-linking (ALL)

46
Q

Physisorption Advantages (2)

A

simple cheap fast

non-covalent bonding improved using tags

47
Q

Physisorption Negatives (3)

A

random orientation
changes to pH etc cause leaching
Physical contact could unfold protein

48
Q

Physisiorption solution

A

tag head group and target molecule with biotin and use streptavidin (tetramer) to bind the two

49
Q

Chemisorption Advantages (3)

A

Covalent bonding stable over time (amide bond)
Specific cross-linking fairly simple
Small physical contact with interface - no unfolding

50
Q

Chemisorption Disadvantage

A

Orientation is random

51
Q

Oriented Chemisorption

A

suitable for receptors, protein aptamers , synthesised DNA/RNA
if adding cysteine (mutagenesis), must be no other cysteines - could have receptors pointing away

52
Q

Antibody chemisorption

A

bind constant region via carbohydrate group etc

could biotinylate

53
Q

Blocking layers

A

eliminate non-specific binding of proteins - bio-inert
e.g. bovine serum albumin
polyethylene glycol - block physisorption

54
Q

Blocking layer mechanism

A

densely form hydrogen bonds with water - create thick layer - molecules flow over

55
Q

Efficient Sensing Surface/bio-interface (4)

A

Optimal density recognition molecule
absence non-specific binding (not too many biotin etc.)
stability
excessive high density cross-linker - steric interference and reduced recognition molecule immobilisation

56
Q

Clean gold with

A

Hydrogen peroxide and sulphuric acid

57
Q

Require smooth surface

A

SAMs not line up

58
Q

Site specific immobilisation

A

soft lithography - microcontact printing
microcapillaries
microspotter
dip pen nanolithography

59
Q

Microcontact printing

A

create master stamp by inking with cells/proteins on cast PDMS
soft nature protects ink and substrate

60
Q

Microcontact considerations

A

PDMS modified make it hyrdrophilic for biomolecules
swelling in aqueous solvents - poor marking
stamp may degrade
requires skilled operator
MEMS mechanically sensitive

61
Q

Microcontact printing positives

A

simple direct write

submicron resolution

62
Q

Functionalise microcantilevers with

A

microcapillaries
microspotters
simple write, but poor resolution

63
Q

Dip pen nanolithography

A

AFM tip - 0.1nm
molecular ink thioalkane 15nm
protein in liquid ink 250nm

64
Q

Dip pen positives

A

high resolution
direct write
potential for registration - exact positions

65
Q

Dip pen negative

A

expensive
slow processing
limited parallelisation capabilites

Biotechnology (7 decks)

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