Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 205

clay. [1069]. or. magnetic. particles. [3039]. can. be. monitored. with. methylene. blue.. Ru(II)-bipyridyl.
improves.the.oxidation.of.guanine.moieties.in.DNA.[1604].
Oligonucleotides.are.detectable.via.Cu(I)-complexes.[591],.via.accumulation.and.direct.oxida-
tion.[3040],.via.preferential.inclusion.of.oligonucleotides.in.electropolymerized.polypyrrole.ilms.
and.discrimination.from.ssDNA.and.dsDNA.[3041],.or.via.handling.with.magnetic.particles.[299]..
Heated.electrodes.improve.the.accumulation.process.[90].
DNA.dendrimers.are.highly.branched.DNA.molecules.where.subregions.of.more.than.two.strands.
form.double.helical.structures,.thus.interconnecting.the.different.strands;.they.adsorb.strongly.to.
CPE.and.show.very.low.detection.limits.[3042].
Peptide.nucleic.acids.(PNA),.introduced.in.1992.by.Egholm,.Burchardt,.Nielsen,.and.Berg.[3262],.
are.completely.synthetic.ssDNA.mimicries.with.a.peptide.backbone.(rather.than.ribose-phosphate):.
H-(NH-CH 2 -CH 2 -NR-CH 2 -CO) n -lys-NH 2 .where.“R”.means.-CO-CH 2 -.Base.with.Base.as.a.
common.nucleic.base.[3263]..PNAs.can.hybridize.with.ssDNA..PNA.can.be.accumulated.at.car-
bon.paste.electrodes.and.determined.with.stripping.analysis,.for.example,.potentiometric.stripping.
analysis,.similar.to.DNA.[1988]..In.fact,.not.only.DNA.but.also.RNA.can.be.adsorptively.precon-
centrated. and. determined. by. means. of. ESA. with. either. voltammetric. or. (chrono)potentiometric.
detection.[91].
Many.investigations.deal.with.DNA-modiied.carbon.paste.electrodes.in.order.to.exploit.them.for.
accumulation.of.analytes.or.to.uncover.interactions.between.target.compounds.and.the.nucleic.acid.
[85,289,292,293,376,390,430,608,1424,1463,1464,1467,1480,1602,1625,1921,2422,2451,2535,2538,.
2541,2546,2549,2553,2565,2580,2582,2595,2596,2611,2622,2869,3043-3074].. Many. substances.
intercalate. with. DNA,. that. is,. they. penetrate. into. the. DNA. helical. structure.. Interactions. can. be.
monitored.by.changes.in.the.guanidine.signal.(increase.or.decrease).or.by.a.stripping.behavior.of.
an.electroactive.analyte..By.immobilizing.DNA.it.is.easy.to.perform.damage.and.protection.stud-
ies.[292,293,2764,2422,3051,3066,3067].or.to.discover.new.electroactive.intercalating.compounds.
which.can.advantageously.be.employed.as.reporter.molecules.for.hybridization.[289,1463,1464,146
7,1625,2565,3069].
One.very.promising.ield.for.many.future.applications.are.hybridization.and.sequencing.sensors.
[289,298,378,388,421,766,953-955,1004,1005,1465,1466,1603,1638,1801,3075-3120,3269].. Usually.
a. single-stranded. DNA. or. oligonucleotide. is. adsorbed. on. the. electrode. surface;. on. exposition. to.
the.sample.solution,.hybridization.occurs.if.complementary.ssDNA.is.present..Hybridization.can.
be.monitored.with.hybridization.indicators,.also.called.reporter.molecules..They.are.electroactive.
substances.which.have.either.a.higher.afinity.to.the.free.bases.or.which.show.a.dominating.inter-
calating.effect.with.the.double.helix..In.the.former.case.a.signal.decrease.compared.to.the.ssDNA-
modiied.electrode.will.be.observed,.in.the.latter.an.increase.
An. interesting. approach. is. the. replacement. of. electroactive. guanine. by. electroactive. inosine.
(hypoxanthine.as.a.base).in.the.single.strands,.which.still.can.pair.with.adenine,.cytosine,.and.ura-
cil;.the.signal.comes.from.guanine.from.the.complementary.strand.in.the.hybrid.[3084,3087,3088]..
ssDNA-modiied.biosensors.have.been.used.to.determine.HIV.virus.[3093,3106],.hepatitis.B.virus.
[289,3103-3105],.caulilower.mosaic.virus.[954,1005,1025],.alatoxigenic. Aspergillus .spp..[3075],.
Cryptosporidium .[3083,3084],. Mycobacterium tuberculosum .[3094],. Microcystis .spp..[3095],.and.
Salmonella .[3115].and.also.to.reveal.genetic.diseases.and.mutations,.such.as.cystic.ibrosis.(muco-
viscidosis).[1638],.factor.V.Leiden-mutation.(hypercoagulability.of.the.blood).[3087],.achondropla-
sia.(a.form.of.dwarism.with.normal.torso.and.short.limbs).[3088],.point-mutations.in.genes.[3089],.
and.genetically.modiied.food.[298,954,1004,3098,3099,3107,3108,3110,3112-3114,3116,3117];.even.
single.base.mismatches.can.be.detected.[3120].
8.4.10 p urines , p yridines , and p yriMidines
Purine.and.pyrimidine.bases.which.are.important.for.nucleic.acids.have.already.been.considered.in.
previous.section..Table.8.24.gives.an.overview.of.other.“-ines,”.that.is,.pyridines.and.pyrimidines.