1. Atomic Force Microscopy Samrat Dutta, Ph.D. Samrat.Dutta@nau.edu
Experience, interest: Surface chemistry, microscopy, integrate, biomolecule/biocelluar interaction,solution surface interface, talk about AFM

2. Outline AFM background
AFM modes and techniques (imaging, force spectroscopy)
Surface treatments and functionalization
Potential applications
Mode and techniques: Multiple modes, talk about imaging and force spectroscopy mode, audience might be interested.
Surface treatment: Integral part of microscopy, surface chemistry technique.
Potential application: W.L Gore. and associate interests.

3. AFM Basic Working Principle
AFM: AFM working qualitatively explain by assuming an example of blind person walking on street, blind person walks with a stick and adjust his walking path by sensing obstackles.
AFM: Similarly, AFM tip raster scan a surface with a cantilever with a sharp tip at its end, adjust its movement in X,Y,Z upon encountering features on surface, deflects laser reflected from the cantilever to the photo-sensor, this deflection is recorded and gives information of surface.
Key features: of AFM at NAU
Scan range:
100 µm lateral (~5nm res)
12 µm vertical (Å res)
Force Resolution: 18 pN
Physiological environments
Key features

4. AFM Imaging Force Applications
Actin paracrystals
Force
Tapping (Topography): Biological samples
Tapping (Topography, phase): Material characterization
Contact (Force): Hard surfaces, Molecular interactions, mechanical properties
Applications
Contact mode: AFM tip physically applies force on surface represented by repulsive region in the lennard-jones curve. Interaction with feature changes force, producing image. Not suitable bio-sample.
Tapping mode: Raster scans by tapping the surface represented by attractive region in Lennard-jones curve. Feature dampens oscillation producing image.

5. Imaging modalities Topography Phase Chemical mapping
Unfixed rat brain: mechanical heterogeneity, surfacesciencewestern.com
Topography
Phase
Chemical mapping
AFM can also be used to measure other characteristics of surface while scanning in imaging mode.
Chemical mapping of PTCDA molecule: Arrow showing Hydrogen bonds, ACS.org

6. AFM molecular force spectroscopy
On surface
Above surface
Retracted
Force
Rupture force
AFM can also be operated in force spectroscopy mode: where it can measure forces of interaction between two molecules.
In this mode: AFM cantilever is constrained to move only in Z-direction w.r.t to the surface, causing any molecular bond formed between the molecule attach to the AFM-tip and the molecule attached surface, when AFM tip is on the surface, to rupture when the AFM tip is retracted back.
We calculate the dissociation rate between antiplatellte aggregation ligand: alpha2B beta 3.
Tip sample separation
Example result:
Ligand (cHarGD): αIIbβ3 interaction energy landscape
cHarGD:αIIbβ3: toff ~ seconds; cHarGD ≡ eptifibatide

7. AFM Lateral Force Spectroscopy
Fiber mechanics
W. Liu. Science 2006

8. AFM Indentation Spectroscopy
Example Result: Soft matter and cell-mechanics

9. AFM cell force spectroscopy
Example: Cell-substrate interactions

10. Surface chemistry and functionalization
Type
Advantage
Disadvantage
Application
Amino (APS, APTES)
Simple protocol
Non-specificity
DNA, protein, and ligand attachment on surface
Thiol
Specific conjugation
Disulfide bond formation, de-protonation needed
Lipid
Mimic membranous systems
Multi-step protocol
F-actin polymerization
PEG
Surface passivation,
finger-print of interaction
Diverse molecular weight

11. Potential applications
Polymer and material characterization
Chemical profiling of substrates
Mechanical testing of polymers
Dynamics of molecular interactions
Cell mechanics
Cell-substrate interaction