Biomedical Engineering Reference
In-Depth Information
have.also.been.successful.(Martin.et.al..1998)..Nanostructures.of.various.materials,.sizes,.
and.shapes.have.been.horizontally.manipulated.at.ambient.air.(Junno.et.al..1995;.Hansen.
and.Bohr.1998;.Ju.Yun.et.al..2007).and.even.in.luid.environments.(Resch.et.al..2000)..Forces.
present.between.the.probe.and.particle.and/or.between.the.particle.and.substrate.are.of.
little. importance. here,. making. horizontal. manipulation. less. challenging. than. vertical.
manipulation.
Vertical.nanomanipulation.must.take.into.consideration.the.binding.afinities.between.
the.selected.probe.and/or.substrate.and.the.particle.of.choice..Extraction.or.placement.of.
larger.biomolecules.like.proteins.and.DNA,.therefore,.require.the.use.of.mechanical.forces.
as.in.AFM-based.nanografting.(Xu.et.al..1999).or.electric.forces.as.in.electrochemical.Dip-
pen.nanolithography.(DPN).(Agarwal.et.al..2003a),.nanopipetting.(Bruckbauer.et.al..2002,.
2007).and.dielectrophoretic.deposition.(Unal.et.al..2006)..Thus.far,.vertical.lifting.or.depo-
sition.of.nanoparticles.has.mainly.been.accomplished.using.higher.probe-sample.contact.
forces. in. dynamic. mode. (Decossas. et. al.. 2003). or. by. manipulating. each. particle. before.
lifting.(Prime.et.al..2005;.Wang.et.al..2007)..In.our.recent.work,.we.have.shown.how.the.
polarity.and.magnitude.of.an.electric.potential.applied.to.an.AFM.tip.can.be.modulated.
to. enable. selective. lifting. of. positively. or. negatively. charged. gold. nanoparticles. from. a.
surface.(Xu.et.al..2010)..Thus,.the.AFM.can.also.be.used.as.a.
nanobroom
.or.a.
nanocrane
.to.
remove.and/or.deposit.nanoparticles.at.desired.locations.
16.5.2 Dip-Pen Nanolithography
DPN. has. been. the. most. popular. AFM-based. technique. to. pattern. small. molecules. on. a.
solid.surface.(Piner.et.al..1999)..The.technique.resembles.an.old-style.quill.pen,.in.which.
an.AFM.cantilever.probe.is.used.as.a.nanosized.“pen”.for.“writing”.small.molecules.on.
a. “paper”. or. substrate.. The. AFM. probe. is. irst. dipped. into. an. “ink”. of. molecules. and.
capillary.forces.are.used.to.transfer.the.molecules.from.the.probe.(pen).onto.a.substrate.
(paper). in. a. well-controlled. manner. (see. Figure. 16.4A).. The. DPN. technique. has. evolved.
to.encompass.a.variety.of.different.ink.and.paper.combinations.(Ginger.et.al..2004),.and.
both.the.static.and.dynamic.modes.of.AFM.have.been.employed.(Agarwal.et.al..2003a)..
The. progression. of. DPN. for. bionanotechnology. applications. is. reviewed. in. this. citation.
(Ginger.et.al..2004).
Shortly.after.the.advent.of.DPN.technology,.it.was.clear.that.the.low.throughput.of.gen-
erating.patterns.with.a.single.AFM.probe.tip.was.a.major.nanofabrication.drawback..Since.
then,.attempts.have.been.made.to.create.large-scale.multicantilever.DPN.probes..Salaita.
et. al.. used. photolithographic. techniques. to. fabricate. a. 2D,. 55,000. AFM. probe. array. for.
massive.lithographic.patterning.(Salaita.et.al..2006)..This.array.spans.a.1.cm.×.1.cm.area.
and.does.not.require.independent.feedback.from.each.individual.tip..The.creation.of.the.
55,000-probe. array. increased. the. throughput. of. DPN. by. over. four. orders. of. magnitude,.
thus.making.it.a.compelling.technique.for.small.molecule.patterning.for.nanobiotechnol-
ogy.applications.
Humidity.and.ink.water.solubility.are.two.factors.that.can.limit.the.capabilities.of.DPN..
Sanedrin. et. al.. studied. the. effects. of. temperature. on. the. lithographic. patterning. of. low.
and. high. melting. point. alkanethiol. molecules,. as. well. as. gold. and. thiolated. molecules.
like. 16-mercaptohexadecanoic. acid. (MHA). and. 1-octadecanethiol. (ODT). (Sanedrin. et. al..
2010).. They. demonstrated. how. temperature. and. dwell. time. can. control. the. diffusion. of.
these. molecules. onto. a. substrate. to. obtain. well-calibrated. nanometer-. and. micrometer-
sized.features..By.decreasing.the.dwell.times.and.the.temperature.of.the.probe-substrate.
