Biomedical Engineering Reference
In-Depth Information
AuNPs.are.relatively.simple,.inexpensive,.and.less.time-consuming..Assays.based.on.col-
orimetric. detection. can. be. used. in. laboratories. with. limited. infrastructure,. without. the.
need.for.sophisticated.instruments,.as.well.as.at.the.point.of.care.
Suspensions.of.AuNPs.are.relatively.stable.and.reliable.as.they.are.less.likely.to.produce.
false.negative.or.false.positive.results.caused.by.nonspeciic.aggregation.
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.In.turbidimetric.
assays,.AuNPs.increase.sensitivity.since.their.suspensions.do.not.signiicantly.scatter.vis-
ible.light,.thereby.reducing.any.background.signals.that.may.occur.
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Molecular. assays. include. colorimetric. techniques,. where. AuNPs. can. be. modiied. or.
unmodiied.. AuNPs. are. also. used. as. quenchers. in. Förster. resonance. energy. transfer.
(FRET)-based. assays.. Examples. of. other. assays. include. the. molecular. biobarcode. assay.
(BCA),.where.AuNPs.are.used.in.conjunction.with.magnetic.microparticles.for.the.detec-
tion.of.DNA.
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.This.method.has.been.extended.for.multiplexed.detection.of.DNA,.as.well.
as. by. designing. different. barcodes. to. suit. different. targets.
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. In. electrochemical. tech-
niques,. for. example,. biotinylated. AuNPs. and. magnetic. beads. coated. with. streptavidin.
are.used.in.a.process.that.leads.to.detection.of.target.DNA.
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.AuNPs.have.been.used.in.
molecular.diagnostics.for.nucleic.acid.detection,.as.well.as.in.immunoassays.to.detect.dif-
ferent.proteins..In.the.next.section,.we.will.expand.upon.molecular.techniques,.in.addition.
to.applications.in.immunoassays.
3.5.2.1 Nucleic Acid Assays
3.5.2.1.1 Modiied AuNPs' Colorimetric Method
3.5.2.1.1.1 Cross-Linking (Two Probe) Method
This.method.can.be.used.for.the.detection.of.
ssDNA.by.functionalization.of.two.sets.of.AuNPs,.each.with.a.different.oligonucleotide.
probe,.and.each.complementary.to.one.end.of.the.target.DNA.(Figure 3.7)..This.causes.them.
to.align.in.a.tail-to-tail.manner..Upon.hybridization.to.the.target,.the.close.proximity.of.the.
AuNPs.causes.them.to.aggregate,.shifting.the.solution.color.from.red.to.blue..By.spotting.
FIGURE 3.7
Modiied. cross-linking. colorimetric. detection. of. nucleic. acid. targets.. Two. sets. of. oligonucleotide. probes. are.
conjugated.to.the.AuNPs..If.the.added.DNA.is.complementary,.hybridization.occurs,.cross-linking.the.AuNPs.
together.in.a.tail-to-tail.fashion..This.brings.the.AuNPs.closer.to.one.another.and.aggregation.occurs,.turning.
the.solution.color.from.red.to.blue..If.the.added.DNA.is.noncomplementary,.no.hybridization.occurs,.the.AuNPs.
do.not.aggregate,.and.the.solution.color.remains.red.
