Biomedical Engineering Reference
In-Depth Information
interaction,.the.low.rate.of.the.otherwise.fast.diffusing.molecules.became.easier.to.control;.
this.resulted.in.smaller.dot.sizes..These.experiments.were.repeated.using.the.55,000-pen.
array,. mentioned. previously,. to. prove. that. the. temperature-controlled. DPN. methodol-
ogy. can. be. used. to. pattern. controlled. nanometer-sized. molecules. in. a. high-throughput.
manner.
The. ability. to. pattern. speciic. biomolecules,. like. nucleic. acids,. proteins,. and. antibod-
ies. onto. a. microchip. is. especially. attractive. for. the. fabrication. of. biosensors.. The. DPN.
technique. has. been. utilized. for. the. selective. detection. of. DNA. (Nam. et. al.. 2002). and. to.
generate. an. antibody. nanoarray. for. detection. of. human. immunodeiciency. HIV-1. virus.
p24.antigen.(Lee.et.al..2004)..In.these.studies,.DPN.was.used.to.create.the.nucleic.acid.or.
antibody.nanoarrays.via.indirect-patterning.through. MHA.dots..The.MHA.dots.served.
as.templates.for.the.antibody.immobilization,.upon.which.the.antigen.was.preferentially.
bound.and.detected.
Direct-patterning. of. nanoparticles. and. biomolecules. has. also. been. achieved. using.
DPN.and.other.approaches,.albeit.in.a.low-throughput.manner..Using.a.technique.called.
ele.ctrochemical. DPN,. GaN. nanowire. heterostructures. have. been. generated. by. a. local.
electrochemical. reaction. between. the. nanowire. and. a. tip-applied. KOH. “ink”. (Maynor.
et. al.. 2004).. By. controlling. the. ambient. humidity,. reaction. voltage,. and. reaction. time,.
control.over.the.modiication.geometry.was.obtained..Using.a.similar.approach,.we.and.
others.have.demonstrated.how.applications.of.electric.potentials.to.the.AFM.probe.in.DPN.
can. enable. direct. deposition. of. proteins. from. the. probe. onto. a. substrate. (Figure. 16.4B).
(Nam. et. al.. 2002;. Agarwal. et. al.. 2003a).. In. another. report,. sub-50.nm. gold. patterns. have.
been.generated.on.insulating.surfaces.via.molecular.diffusion.of.gold.chloride.followed.by.
an.annealing.process.(Sung.et.al..2010)..Besides.standard.AFM.probes,.a.volcano-shaped.
probe.has.also.been.used.as.an.on-chip.reservoir.through.which.controlled.delivery.of.ink.
can.be.achieved.to.provide.high-resolution.direct-patterning.(Kim.et.al..2005)..Cantilevered.
nanopipettes.have.been.utilized.to.directly.print.proteins.in.ambient.environments.under.
standard.normal.force.AFM.control.without.the.need.for.external.electric.ields.and.liquid.
environments.(Taha.et.al..2003).
16.5.3 Nanografting
Nanografting. is. another. AFM-based. technique. capable. of. selectively. manipulating.
molecules.at.sub-100.nm.resolutions..This.earliest.version.of.this.approach.was.performed.
with. a. substrate. of. a. self-assembled. monolayer. (SAM). in. the. presence. of. a. solvent. that.
contained. a. second. type. of. small. molecule. (Xu. 1997).. The. AFM. probe. was. used. to. etch.
away. molecules. of. the. SAM. on. the. substrate. to. create. a. pattern. of. selectively. exposed.
regions.. The. etched-out. molecules. washed. away. into. the. solvent. and. the. exposed. areas.
were. then. illed. by. the. second. small. molecule. present. in. the. solvent.. The. same. AFM.
probe.was.then.used.to.image.the.newly.manipulated.surface.(see.Figure.16.4C)..Several.
progressions.of.the.nanografting.technique.have.occurred.since.then.(Liu.et.al..2008).
The. nanografting. technique. is. especially. attractive. for. bionanotechnology. applica-
tions.due.to.its.high.resolution.(sub-100.nm),.ability.to.operate.in.wet.environments,.and.
versatility. to. selectively. assemble. nanostructures. of. large. molecules. and. biomolecules..
Thus,. nanografting. has. resulted. in. many. applications. in. nanobiotechnology.. One. note-
worthy.achievement.includes.Chung.et.al.'s.two-step.nanografting.of.patterns.on.SAMs..
The. patterns. were. used. to. create. highly. organized. genetically. or. chemically. modiied.
virus.particles.(Chung.et.al..2008)..Yu.et.al..also.used.nanografting.to.demonstrate.how.
