Biomedical Engineering Reference
In-Depth Information
The.exact.mechanism.leading.to.the.formation.of.silver.nanoparticles.is.yet.to.be.elu-
cidated,. but. it. is. speculated. that. the. nanoparticle. formation. might. result. from. speciic.
mechanisms. of. resistance.
16
. Furthermore,. Joerger. and. colleagues
17
. have. shown. that. bio-
composites. of. nanocrystalline. silver. and. the. bacteria,. when. thermally. treated,. yield. a.
carbonaceous.material.with.interesting.optical.properties.for.potential.application.in.func-
tional.thin-ilm.coatings.
17
Even.bacteria.normally.not.exposed.to.metal.ions.could.be.used.to.synthesize.nanopar-
ticles..Nair.and.Pradeep
18
.demonstrated.the.ability.of.
Lactobacillus
(present.in.buttermilk).
to. produce. large. amounts. of. gold. and. silver. nanoparticles. within. the. cells.. In. addition,.
the.formation.of.alloy.nanoparticles.of.silver.and.gold.could.be.shown.after.exposure.of.
the.organisms.to.mixtures.of.silver.and.gold..Similarly,.Jha.and.colleagues
19
.and.Jha.and.
Prasad
20
.demonstrated.the.use.of.
Lactobacillus
.sp..to.produce.TiO
2
.(8-35.nm).and.BaTiO
3
.
(20-80.nm).particles.
In.addition.to.gold.and.silver.nanoparticles,.attention.has.also.been.focused.on.the.devel-
opment.of.methods.for.the.synthesis.of.semiconductors,.so-called.quantum.dots,.such.as.
CdS,.ZnS,.and.PbS..Holmes.and.co-workers
21
.demonstrated.that.exposure.of.
Klebsiella aero-
genes
to.Cd
2+
.ions.resulted.in.the.formation.of.CdS.nanoparticles.in.the.nanometer.range.
(20-200.nm).
Although.much.less.is.known.about.the.bioreduction.of.PGMs,.the.sulfate-reducing.bac-
terium.
Desulfovibrio desulfuricans
.has.been.shown.to.produce.palladium.nanoparticles.in.
the.presence.of.an.electron.donor.
22
.Similarly,.
Shwanella algae
.produced.platinum.nanopar-
ticles,.around.5.nm.in.diameter,.located.in.the.periplasm.when.exposed.to.PtCl
6
2-
.in.the.
presence.of.lactate.as.electron.donor.
23
One. of. the. most. intriguing. examples. of. biologically. controlled. mineralization. is. the.
formation. of. magnetic. nanocrystals. in. magnetosomes. within. magnetotactic. bacteria..
Magnetosomes.consist.of.magnetic.iron.mineral.particles.enclosed.within.membrane.ves-
icles..In.most.cases.the.magnetosomes.are.organized.in.a.chain.or.chains.(Figure 9.1),.and.
in. many. cases. the. iron. mineral. particles. consist. of. magnetite. (Fe
3
O
4
). or. greigite. (Fe
3
S
4
).
characterized.by.narrow.size.distributions.and.uniform.morphology.
24
9.2.2 The Use of Yeast in Nanoparticle Synthesis
Yeasts. have. been. successfully. explored. for. the. production. of. mainly. cadmium. nano-
particles.. Dameron. and. co-workers
25
. were. the. irst. to. demonstrate. that. yeasts. such. as.
Schizosaccharomyces pombe
and.
Candida glabrata
were. capable. of. intracellular. production.
of. CdS. nanoparticles. when. challenged. with. cadmium. salt. in. solution.. These. cadmium.
sulide. nanocrystals. can. potentially. be. used. in. quantum. semiconductor. crystallites.
25,26
.
Conditions.have.also.been.standardized.for.the.synthesis.of.silver.nanoparticles.using.a.
silver-tolerant.yeast.strain.MKY3.
27
.More.recently,.the.yeast.strain.
Pichia jadinii
has.been.
identiied.for.its.ability.to.produce.gold.nanoparticles,.which.included.spheres,.triangles,.
and.hexagons,
28
.and.Agnihotri.et.al.
29
.demonstrated.the.use.of.
Yarrowia lipolytica
.for.the.
synthesis.of.gold.nanoparticles.
9.2.3 Nanoparticle Formation by Actinomycetes
Sastry.et.al.
30
.and.Ahmad.et.al.
31
.described.the.extracellular.formation.of.gold.nanoparti-
cles.by.the.extremophilic.actinomycete.
Thermomonospora
.when.exposed.to.gold.ions..Gold.
