Cantilevers Flashcards
What is a cantilever?
A beam that is fixed at only one end
How do we produce a cantilever?
Microfabrication
What is a BioMEMS?
MEMS device functionalism with a biological recognition element. Allow for recognition of target analyte (mechanical) and conversation into a discernible reading (electrical form)
What are some of the current diagnostic techniques? What are the key adv/disadv of each?
ELISA - slow (24 hours) /low LOD
LFA - quick/high LOD
SPR - quick/low LOD, EXPENSIVE
What are the key properties we want to achieve for a diagnostic test?
Low LOD Quick Array technology (multiple biomarkers to increase sensitivity) Cheap at large volume Label free
When was the AFM created?
1986
When was the first micro cantilever for BioMEMS created?
1996
What determines the properties of a micro cantilever?
Geometry K=WT3/4L3
Flexible - Low spring constant (measure of stiffness) - long narrow, thin - used for diagnostic purposes
Rigid - High spring constant - short, narrow, wide - used for dermal drug delivery
What are the two modes of detection for a cantilever?
Static Mode of Detection (Surface Stress)
Dynamic Mode of Detection (Resonance Mode)
How does the static mode of detection work?
When biomolecules bind, there is an increase in surface stress
If analyte binds, and the surface molecules contract, there is an increase in tensile surface stress - the cantilever moves up (e.g. ssDNA and dsDNA)
If analyte bind and the surface molecules expand, there is an increase in compressive surface stress - cantilever moves down
What forces can generate surface stress?
Electrostatic repulsion/attraction
Confirmational change
How do we inactivate a cantilever?
Silane chemistry
How do we activate a cantilever?
Thiol Chemistry
How do we detect the deflection in static mode?
Optical Beam - Gold covered cantilever deflects laser beam - detected by photodiode - compare to reference cantilever - sensitive (high resolution 0.1nm), bulky external equiptment
PR readout - doped silicon is a semi conductor and as a result deflection results in change in resistance - no bulky external equipment, but lowe resolution (1nm)
What considerations must we consider when performing the static mode of detection?
Can we conducted in an aqueous environment (RT)
Must develop protocol before implementation (unpredictable deflection)
pH dependent (deprotination of surface molecules - inrecase in negative charge - electrostatic repulsion - increase in compressive surface stress - down)
Temp sensitive
What is the dynamic mode of deflection?
Resonance mode - drive cantilever in resonance - addition of analyte (changes mass) and results in different frequency for resonance - measure against reference
How do we drive a cantilever into resonance?
PZ material (e.g. PZT) - actuator mode
What determines the resonance frequency of a cantilever?
Geometry (mass) and spring constant (K)
What are the pros/cons of dynamic mode?
Much lower LOD - fg/ml pg/ml
Must be conducted in a vacuum - viscous damping - can be overcome by using microfluidic channel within cantilever - very difficult
