The Biosynthesis of Anisotropic Nanoparticles - Bionanotechnology: Global Prospects - page 186

Recently.Sanghi.and.Verma 40 .demonstrated.long-term.operation.with.an.immobilized.
fungus,. Coriolus versicolor ,.in.continuous.column.mode..The.immobilized.fungus.served.
a.dual.purpose.of.both.bioremediating.cadmium.and.extracellularly.synthesizing.stable.
CdS.nanoparticles.in.aqueous.conditions..The.fungus.immobilized.in.the.column.could.
remove.98%.cadmium.within.2.h..The.research.highlighted.the.potential.of.this.approach.
to.remediate.both.waste.streams.and.promotes.large-scale.growth.of.CdS.nanoparticles.

9.3 ControlofGrowthParameterstoManipulate
NanoparticleCharacteristics
Although.the.screening.results.are.very.promising.and.show.that.a.wide.variety.of.organ-
isms.have.the.ability.to.produce.a.range.of.nanoparticles.with.interesting.shapes,.it.is.real-
ized.that.for.most.applications,.nanoparticles.of.well-deined.size.and.shape.are.required..
In. addition,. for. a. biological. process. to. successfully. compete. with. chemical. nanoparticle.
synthesis,.very.strict.control.over.average.particle.size.in.a.speciic.size.range.and.uniform.
particle.morphology.is.required..The.cellular.mechanism.leading.to.the.reduction.of.the.
metal. ions. and. formation. of. nanoparticles. is. not. well. understood,. but. it. has. been. sug-
gested.that.proteins.and.enzymes.play.a.role.in.regulating.gold.crystal.morphology. 33,41
In.an.attempt.to.achieve.better.size.and.shape.control,.the.effect.of.a.number.of.growth.
parameters. on. gold. nanoparticle. synthesis. using. the. fungal. culture. V. luteoalbum . was.
investigated. 28 .It.was. demonstrated. that. the.rate. of.particle. formation,. and.therefore.the.
size. of. the. nanoparticles,. could,. to. an. extent,. be. manipulated. by. controlling. parameters.
such.as.pH.(Figure 9.3),.temperature,.gold.concentration,.and.exposure.time.to.gold.ions.
In. similar. studies,. the. effect. of. pH. on. the. shape. of. gold. nanoparticles. produced. in.
Rhodopseudomonas capsulata was.established.by.He.et.al. 11 .The.results.from.TEM.analyses.
shown.in.Figure 9.4.indicate.the.various.sizes.and.shapes.formed.with.pH.changes.rang-
ing.from.4.to.7.
Sanghi.and.Verma 42 .investigated.the.ability.of.the.fungus. Coriolus versicolor to.produce.
Ag.nanoparticles..The.resulting.nanoparticles.displayed.controllable.structural.and.optical.
properties,.depending.on.experimental.parameters.such.as.pH.and.reaction.temperature.
In. another. study,. Ahmad. et. al. 35 . showed. that. incubation. of. the. fungus. Trichothecium .
sp.. in. the. presence. of. gold. ions. under. stationary. conditions. resulted. in. the. forma-

pH 3 (Scale bar = 100 nm) pH 5 (Scale bar = 100 nm) pH 7 (Scale bar = 100 nm) pH 9 (Scale bar = 100 nm)

FIGURE 9.3
TEM.images.showing.the.effect.of.pH.on.gold.nanoparticle.morphology.in. V. luteoalbum ..(From.Gericke,.M.,.and.
Pinches,.A.,. Hydrometallurgy ,.83,.132,.2006..With.permission.)