Biomedical Engineering Reference
In-Depth Information
The.authors.proposed.that.a.network.of.hydrophobic.channels.exists.between.the.active.
site.and.the.molecular.surface.in.the.Ni-Fe.hydrogenase,.and.that.these.channels.serve.as.
a.passage.for.metal.ions..It.is.believed.that.at.conditions.suitable.for.platinum.nanoparticle.
formation,.the.H
2
PtCl
6
.platinum.salt.is.rapidly.reduced.by.a.passive.two-electron.transfer.
process.into.a.species.at.a.remote.site.on.the.molecular.surface.of.the.enzyme.(Figure 9.5D)..
The. Pt
2+
. migrates. to. the. active. region. through. the. network. of. channels. and. is. reduced,.
during. conditions. favorable. for. hydrogenase. activity,. by. a. second,. slower. two-electron.
reduction.into.Pt
0
.
Another. recent. example. is. the. work. performed. by. Jha. et. al.,
19
. who. suggested. that. the.
synthesis.of.TiO
2
.nanoparticles.produced.by.
Lactobacillus
.sp..and.
S. cerevisiae
might.have.
resulted. due. to. pH-sensitive. membrane-bound. oxido-reductases,. as. well. as. the. partial.
pressure.of.gaseous.hydrogen.of.the.culture.solution,.which.seemed.to.play.an.important.
role.in.the.process.
9.5 TheUseofTemplatesforNanoparticleSynthesis
Biological.materials.naturally.display.an.astonishing.variety.of.sophisticated.nanostruc-
tures. that. are. dificult. to. obtain. even. with. the. most. technologically. advanced. synthetic.
methodologies.. As.the.need.for.nano-engineered.materials. with. improved. performance.
characteristics.is.becoming.increasingly.important,.the.potential.of.biological.scaffolds.for.
the.fabrication.of.novel.types.of.nanostructures.is.being.actively.explored.and.recognized.
as.a.unique.approach.for.the.synthesis.and.organization.of.inorganic.nanostructures.into.
well-deined.architectures.
49
.These.synthesis.techniques.utilize.the.molecular.recognition.
properties. of. the. biological. molecules. to. nucleate. and. control. growth. of. the. nanoscale.
structure.
50
A.range.of.biotemplates.has.been.evaluated.and.described.in.the.literature,.and.a.few.
examples.are.presented.in.Figure 9.6..A.brief.overview.of.advances.in.the.use.of.protein-
mediated.biotemplating.and.trends.involved.in.its.applications.for.the.nanostructuring.of.
inorganic.material.is.discussed.here.
Certain.proteins,.such.as.ferritin.and.ferritin-like.protein.(FLP),.have.cavities.in.the.cen-
ter. (Figure 9.6A),. and. these. protein. cavities. can. be. used. as. templates. for. the. growth. of.
nanoparticles.
51
.Yoshimura
51
.showed.that.the.protein.shells.served.as.a.template.to.restrain.
particle.growth.and.as.a.coating.to.prevent.coagulation.between.nanoparticles,.enabling.
the. preparation. of. nanoparticles. with. uniform. size. and. shape.. Zhang. et. al.
52
. also. dem-
onstrated. that. gold. nanoparticles. could. form. on. the. surface. of. apoferritin,. and. in. turn.
become.stabilized.in.solution.by.the.protein.cage.
Crystalline.bacterial.cell.surface.layers.(S-layers).provide.an.outer.cell.envelope.in.many.
eubacteria.and.archaebacteria..These.layers.can.be.readily.isolated.and.reconstructed.in.
vitro.to.generate.a.two-dimensional.monomolecular.protein.array.with.a.pore.size.in.the.
2-6.nm.range.(Figure 9.6B).
7
.Reconstructed.S-layers.have,.for.example,.been.used.as.tem-
plates. for. the. in. situ. nucleation. of. ordered. two-dimensional. arrays. of. cadmium. sulide.
nanocrystals. and. gold. nanoparticles,. 5. nm. in. size,
54,55
. and. for. core-shell. quantum. dot.
arrays.
56
The.synthesis.of.nanowires,.25-30.nm.in.diameter,.templated.using.naturally.occurring.
nano-sized.tubes,.e.g.,.rhapidosomes
57
.and.microtubuli,
58,59
.has.been.reported.(Figure 9.6C)..
Improved.process.control.has.enabled.biotemplating.directed.to.the.formation.of.arrays.of.
metallic.silver.grains,.approximately.5.2.nm.in.size.
60
