Gold Nanoparticles in Biomedicine - Bionanotechnology: Global Prospects - page 54

3.1 Introduction
Gold. nanoparticles. (AuNPs). were. irst. recognized. in. the. form. of. colloidal. gold.. Dating.
back.to.the.fourth.and.ifth.centuries.B.C.,.colloidal.gold.was.used.in.glass.and.ceramic.
staining,.as.exempliied.by.the.Lycurgus.Cup,.the.color.of.which.is.ruby.red.upon.trans-
mission.of.light.and.green.upon.relectance.of.light. 1 .Drinking.colloidal.gold.was.thought.
to.have.healing.powers.and.was.recorded.as.such.in.several.documents.historically..It.was.
Michael.Faraday,.in.1857,.who.is.said.to.have.irst.reported.the.synthesis.of.red.colloidal.
gold.by.the.reduction.of.chloroaurate.(AuCl 4 - ).and.explored.its.optical.properties. 1
Indeed,.it.is.the.unique.optical.properties.of.AuNPs.that.make.them.such.attractive.tools.
in.biomedicine,.in.addition.to.their.inertness,.biocompatibility,.and.high.surface-to-volume.
ratio.. At. the. nanoscale,. AuNPs. exhibit. properties. that. are. very. different. from. gold. in. its.
bulk.form,.and.surface.properties.become.more.pronounced..In.this.chapter,.we.discuss.the.
properties.of.AuNPs,.their.synthesis.by.chemical.and.biological.methods,.and.their.appli-
cations.in.biomedicine..Assessments.of.cytotoxicity.and.biodistribution,.as.well.as.future.
prospects.and.challenges.of.AuNPs.in.biomedical.applications,.are.also.discussed.herein.
3.2 GoldNanostructures
AuNPs. can. be. made. in. a. variety. of. shapes. that. have. an. effect. on. their. optical. features.
(Figure 3.1).. The. oldest. and. most. popular. gold. nanoparticles. are. the. gold. nanospheres,.
which.range.in.size.from.0.8.to.250.nm. 2 .Also.spherical.in.shape.are.the.gold.nanoshells,.
which. are. composed. of. a. dielectric. core. enclosed. in. a. thin. gold. shell,. where. the. core. is.
usually. made. of. silica. or. gold. sulide. 3. The. dielectric. core. helps. shift. the. plasmon. reso-
nance. into. the. NIR. region:. an. optical. property. which. is. further. discussed. in. the. next.
FIGURE 3.1
Most.commonly.used.gold.nanostructures.in.biomedical.applications.