Biomedical Engineering Reference
In-Depth Information
hydrophobized. silver. nanoparticles. with. hydrophobized. chloroaurate. ions.. On. treat-
ing. aqueous. silver. sulfate. and. chloroauric. acid. solutions. with.
Emblica oficinalis
. fruit.
extract,.they.observed.a.rapid.reduction.of.the.silver.and.chloroaurate.ions,.leading.to.
the.formation.of.highly.stable.silver.and.gold.nanoparticles.in.solution..Transmission.
electron. microscopy. analysis. of. the. silver. and. gold. nanoparticles. indicated. that. they.
ranged.in.size.from.10.to.20.nm.and.15.to.25.nm,.respectively..Ag.and.Au.nanoparticles.
thus.synthesized.were.then.phase.transferred.into.an.organic.solution.using.a.cationic.
surfactant,.octadecylamine..A.transmetallation.reaction.between.hydrophobized.silver.
nanoparticles.and.hydrophobized.chloroaurate.ions.in.chloroform.resulted.in.the.for-
mation.of.gold.nanoparticles.
Despite.progress.in.the.biological.synthesis.of.nanomaterials,.the.molecular.mechanism.
of.synthesis.of.bionanomaterials.remains.largely.unknown..Parikh.et.al..reported.the.extra-
cellular.synthesis.of.crystalline.silver.nanoparticles.(AgNPs).by.bacterial.
Morganella
sp.,.and.
showed.evidence.of.the.synthesis.mechanism.
46
.The.AgNPs.created.were.20.±.5.nm.in.diam-
eter.and.were.highly.stable.at.room.temperature..The.kinetics.of.their.formation.was.inves-
tigated..The.formation.of.particles.was.linked.to.three.gene.homologues,.
silE
,.
silP
,.and.
silS
,.
identiied.in.silver-resistant.
Morganella
sp..The.genes.showed.99%.sequence.similarity.with.
the.previously.reported.gene,.
silE
,.which.encodes.a.periplasmic.silver-binding.protein.
In. 2003. Sastry. et. al.
47
. reviewed. the. progress. and. concepts. for. biological. synthesis. of.
nanomaterials..While.they.proposed.the.possibility.of.using.plants.and.microorganisms.
to.create.new.nanomaterials,.the.study.they.discussed.employed.fungi.and.two.species.of.
bacterial.actinomycetes.(
Verticillium
sp..and.
Thermomono sporia
)..They.could.demonstrate.
direct. nanoparticle. formation. from. metallic. ions. by. these. microorganisms.. The. authors.
discussed.and.highlighted.some.of.the.challenges.in.this.emerging.ield.
The. extension. of. nanoparticle. biosynthesis. to. plant. systems. has. also. been. reported.
recently. by. Sathishkumar. and. co-workers.
48
. Silver. (Ag). nanoparticles. can. be. prepared.
from.silver.precursors.using.the.bark.extract.of.
Cinnamon zeylanicum
,.the.small.evergreen.
tree. that. is. the. source. of. the. common. spice.. Water-soluble. organics. present. in. the. plant.
materials.were.mainly.responsible.for.the.reduction.of.silver.ions.to.nano-silver.particles..
TEM.and.x-ray.diffraction.were.used.to.prove.the.presence.of.nanocrystalline.Ag.particles..
Bark.extract.produced.more.Ag.nanoparticles.than.the.powder,.which.is.attributed.to.the.
large.availability.of.the.reducing.agents.in.the.extract.
26.7 QuantumDotsandSolarCells
26.7.1 Quantum Dots
In. 2009,. Lin. et. al.. reported. the. effects. of. quantum. dots. on. algal. photosynthesis.
49
. Using.
Chlamydomonas
sp.. (algae. that. have. chloroplasts. and. a. cell. wall),. the. authors. examined.
the.effects.of.quantum.dots.on.the.microorganisms'.growth.and.photosynthesis.behavior..
Microscopy. examination. showed. strong. interaction. of. CdSe/Zn/Se. quantum. dots. with.
the.cell.wall..There.was.no.evidence.of.uptake,.but.they.did.observe.a.decrease.in.the.luo-
rescence.intensity.of.bound.quantum.dots..This.decrease.was.attributed.to.ineficient.light.
absorption.in.the.multilayer-bound.quantum.dots,.and.not.due.to.luorescence.resonance.
energy.transfer.(FRET).quenching.from.the.algal.chlorophylls..Decreased.photosynthesis.
was.observed.and.attributed.to.a.physiochemical.phenomenon.causing.disruption.of.gas.
low.and.nutrient.uptake.by.bound.nanoparticles..This.inhibited.photosynthetic.activity.
