Biomedical Engineering Reference
In-Depth Information
16.2 Introduction to AFM
The.atomic.force.microscope.(AFM).is.more.than.just.a.“microscope”;.it.is.a.versatile.tool.
capable. of. not. only. imaging. but. also. force. measurements,. patterning,. and. manipula-
tion.of.samples..These.capabilities.are.tied.together.by.one.common.thread:.they.can.be.
achieved.at.the.nanoscale.level..AFM.is,.therefore,.regarded.as.an.indispensable.tool.for.
nanobiotechnology.
The.AFM.consists.of.a.lexible.cantilever.that.scans.a.sample.in.the.lateral.(X-Y).directions.
and/or.the.vertical.(Z).direction.(Figure.16.1)..The.cantilever.is.typically.composed.of.silicon.
or.silicon.nitride,.and.may.or.may.not.have.a.sharp.probe.attached.to.its.end..The.probe.or.
the.cantilever.tip.interacts.with.the.sample,.and.the.X-Y.and.Z.delections.of.the.cantilever.
are.recorded.as.a.function.of.the.angle.at.which.a.laser.beam.relects.off.the.backside.of.the.
cantilever.into.a.photodiode.detector..The.electronics.and.feedback.signals.from.the.AFM.
controller. enable. construction. of. an. AFM. image. or. force. map,. as. well. as. permit. precise.
positioning.of.the.nanoscale.AFM.probe.for.nanomanipulation.applications.
There.are.two.common.“modes”.in.which.the.AFM.cantilever.can.be.made.to.interact.
with.the.sample,.namely,.static.mode.and.dynamic.mode..In.static.mode,.commonly.called.
Photodiode
Z
Cantilever
movement
Y
X
Bu
er solution
ambient temperature
Tip
Cell
Figure 16.1
(See companion CD for color igure.)
.Schematic.representation.of.AFM..A.cantilever.with.a.sharp.tip.scans.
over. the. sample. surface. in. not. only. the. X-. and. Y-directions. but. also. the. Z-direction.. A. laser. delects. off. the.
backside.of.the.tip.and.into.a.photodiode..Any.change.in.the.tip's.delection.due.to.interactions.with.the.sample.
surface.is.depicted.by.a.change.in.the.laser's.path.into.the.photodiode..The.sample.can.be.in.a.buffer.solution.(as.
indicated).or.in.air..(Reprinted.from.
Trends Cell Biol.,
.21(8),.Müller,.D.J..and.Dufrêne,.Y.F.,.Atomic.force.micros-
copy:.A.nanoscopic.window.on.the.cell.surface,.461-469,.Copyright.2011,.Elsevier.)
