Kirchhoff-Institut für Physik

Molekulare Biophysik (F15)

Gerrit L. Heuvelman

Atomic Force Microscope

Scanning Probe Microscopy

STM: scanning tunneling microscope

AFM: atomic force microscope

MFM: magnetic force microscope

SNOM: scanning near-field optical microscope

yx

tunneling of electrons between probe and surface

measuring of the force on the probe

AFM with magnetical probe

probe is a fiber; tunneling of fotonen

STM: scanning tunneling microscope

nA

R

piezo-element

e-e-

e-

e-e-

e-

e-

e-

e-

< 1nm

tunneling of electrons through air between probe

and surface

only conducting material

probe

x-y stage

STM: scanning tunneling microscope

nA

Icontrol

Itip

∆I

R

∆I -> ∆Vtransfer

piezo-element (changes length at different voltages)

AFM: atomic force microscope

AFM probe scans over the surface (in contact)

e.g. living cells, chromatin fibers

laser photodiode

piezo-element

probe

SFM: scanning force microscope

QuickTime™ and aGIF decompressor

are needed to see this picture.

MFM: magnetic force microscope

AFM with magnetic probe

e.g. hard disc, tape

magnetic tip

laser photodiode

piezo-element

SNOM: scanning near-field optical microscope

fiber tunneling of photons between probe and surface

shows the amount of light that is

absorbed/transmitted for different colors

sample

lens

detector

filter

e.g. fluorescent molecules

metal-coated fiber

tip

Atomic Force Microscope

cantilever tip

laser

cantileverpiezo

y

z

x

photodiode

tipholder

motor control

SPM tip

sample

piezo translat

or

laser beam

mirror

photodiode

samplex,y,z piezo translator

fluid in fluid out

fluid cell

O-ring

Atomic Force Microscope

in air and in buffer solutions

path of AFM tip

AFM tip

superhelical DNA plasmid

DNA double helix

Mg2

+

negatively charged mica surface

Mg2

+

Mg2+Mg2+Mg2+Mg2+

movement of the AFM tip along the sample

AFM image of a 6.8 kb superhelical plasmid

AFM tip

AFM image of a nucleosome on a 614 base pair DNA

2 µm x 2 µm overview scan

zoom of mononucleosome complexes

Kepert, F., Fejes Tóth, K., Caudron, M., Mücke, N., Langowski, J. & Rippe, K., manuscript in preparation

AFM image of a nucleosome on a 614 base pair DNA

2 µm x 2 µm overview scan

zoom of mononucleosome complexes

Kepert, F., Fejes Tóth, K., Caudron, M., Mücke, N., Langowski, J. & Rippe, K., manuscript in preparation

0

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0

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DNA entry-exit angle

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DNA entry-exit angle

DNA entry-exit angle of nucleosomes

movement of a 600 bp DNA fragment by AFM

different levels of chromatin packing

A

C

D

E

F

B

300 nm

700 nm11 nm

30 nm

2 nm

1400 nm

2 nm

11 nm

30 nm

300 nm

700 nm

1400 nm

chromatin structure400 nm x 400 nm

chromatin structure400 nm x 400 nm

chromatin structure

spectrin

C-terminal

Helix C

N-terminal

Helix B

Helix A

molecule that contributes to the mechanical properties,

especially the elasticity of the cells

measurement of its mechanical stability provides information

about the physiological function

stretching spectrin with an AFM

distance

force

1 2 3

surface

cantilever tip

4 repeated spectrin domain

1. adhesion force between cantilever tip and surface

2. dissociation from the folded state to the intermediate unfolded state

3. dissociation from the intermediate to the total unfolding state

0.15

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0.05

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0.10

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0.00

unfolding force (pN)

pro

babili

ty

stretching spectrin with an AFMfo

rce (

pN

)

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0

4020

608010

0

distance (nm)

-20