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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. (65 cards)

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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
Advantage of optical lever detection
sensitive - 0.1nm resolution
26
Disadvantage of optical lever detection
bulky external optical equipment with two alignments
27
Piezoresistive Readout
embed piezoresistive material on cantilever | as cantilever deflects - change resistance - electronic readout
28
Advantages of piezo
Miniaturised | simple readout
29
Disadvantages of piezo
resolution not as good ~1nm
30
Static mode considerations (5)
- 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
Dynamic mode/resonant mode: resonance | F0= (1/2pi) x (squareroot spring constant/mass)
tendency of a mechanical system to oscillate with greater amplitude at a certain frequency depends on geometry (mass) +spring constant
32
Dynamic mode mechanism
Apply voltage to piezoelectric actuator to drive to resonance (external or deposited onto cantilever)
33
Add mass to the cantilever
reduce resonant frequency | minimal detectable mass added proportionate to total mass
34
Advantage of dynamic mode
very low LOD
35
Disadvantage of dynamic mode
``` viscous damping (liquid) dissipated to fluid as thermal energy solution - carry out within cantilever long analysis time ```
36
Biointerface
Border between aqueous environment and physical devices - addition of recognition molecules
37
DNA/RNA apatamers
single stranded, form secondary structures
38
peptide apatamers
artificial antibodies
39
recognition molecules should
have affinity/ dissociation constant in nM to pM | streptavidin and biotin 10x-15
40
SAMs
Self assembling monolayers | basis of bio-interface assembly
41
SAMs - gold thiol chemistry
``` Sulphur Base (thiol (SH)) - spontaneous covalent bond with gold aliphatic Carbohydrate chain - hydrophobic - pack densely Headgroup - add functionality - cross link further molecules ```
42
SAMs - silicon base
(alkyl)silane molecule forms covalent bond also
43
Head Groups (5)
``` Amino - NH2 Carboxy - COOH Aldehyde - CHO Thiol - SH Hydroxyl - OH ```
44
Physisorption mechanism and groups
Charged Group (NH3+, COO-)
45
Chemisorption mechanism and groups
Cross-linking (ALL)
46
Physisorption Advantages (2)
simple cheap fast | non-covalent bonding improved using tags
47
Physisorption Negatives (3)
random orientation changes to pH etc cause leaching Physical contact could unfold protein
48
Physisiorption solution
tag head group and target molecule with biotin and use streptavidin (tetramer) to bind the two
49
Chemisorption Advantages (3)
Covalent bonding stable over time (amide bond) Specific cross-linking fairly simple Small physical contact with interface - no unfolding
50
Chemisorption Disadvantage
Orientation is random
51
Oriented Chemisorption
suitable for receptors, protein aptamers , synthesised DNA/RNA if adding cysteine (mutagenesis), must be no other cysteines - could have receptors pointing away
52
Antibody chemisorption
bind constant region via carbohydrate group etc | could biotinylate
53
Blocking layers
eliminate non-specific binding of proteins - bio-inert e.g. bovine serum albumin polyethylene glycol - block physisorption
54
Blocking layer mechanism
densely form hydrogen bonds with water - create thick layer - molecules flow over
55
Efficient Sensing Surface/bio-interface (4)
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
Clean gold with
Hydrogen peroxide and sulphuric acid
57
Require smooth surface
SAMs not line up
58
Site specific immobilisation
soft lithography - microcontact printing microcapillaries microspotter dip pen nanolithography
59
Microcontact printing
create master stamp by inking with cells/proteins on cast PDMS soft nature protects ink and substrate
60
Microcontact considerations
PDMS modified make it hyrdrophilic for biomolecules swelling in aqueous solvents - poor marking stamp may degrade requires skilled operator MEMS mechanically sensitive
61
Microcontact printing positives
simple direct write | submicron resolution
62
Functionalise microcantilevers with
microcapillaries microspotters simple write, but poor resolution
63
Dip pen nanolithography
AFM tip - 0.1nm molecular ink thioalkane 15nm protein in liquid ink 250nm
64
Dip pen positives
high resolution direct write potential for registration - exact positions
65
Dip pen negative
expensive slow processing limited parallelisation capabilites

Biotechnology (7 decks)

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