Chemically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 100

4.3.2.5.4 Redox Polymers and Other Electrocatalytic Systems
Redox.polymers.are.macromolecules.containing.redox.centers,.which.support.the.electron.transfer.
by.electron.hopping..Similar.to.organic.and.organometallic.electrocatalysts,.the.interest.of.redox.
polymers.relies.on.their.ability.to.reduce.overpotential.in.the.detection.of.target.analytes.
In.fact,.there.are.two.major.reasons.why.redox.polymers.can.be.preferred.over.“molecular”.elec-
trocatalysts:.irst,.the.catalytic.center.is.covalently.bonded.to.a.macromolecule.that.is.expected.to.
result.in.more.durable.immobilization.when.incorporated.into.the.carbon.paste.matrix.(leaching.can.
occur.in.case.of.“molecular”.modiiers).and,.second,.the.polymer.can.act.as.a.stabilization.matrix.
for.biomolecules..Both.effects.contribute.to.improving.the.(bio)sensor.operational.stability.and.can.
also.contribute.to.enhancing.its.analytical.performance.
Actually,. the. electrocatalytic. properties. of. redox. polymers. have. been. especially. exploited. in.
bioelectrochemistry. [935].. The. redox. polymers. involved. in. the. preparation. of. CPE-based. bio-
sensors. are. the. following:. ferrocene-containing. polymers. (polyacrylamide-based. [782,785,1555],.
poly(vinyl-ferrocene). derivatives. [924,1748]. or. ferrocene-modiied. poly(ethylene. imine). [1749]),.
phenothiazine-based. polymers. [938,939,1473,1750-1753],. osmium. or. ruthenium. 2,2′-bipyridine.
chloro. poly(4-vinylpyridine). complexes. [648,649,940]. (or. related. compounds. as. osmium. phenan-
throlinedione. [1754]. or. poly[1-vinyl. imidazole. osmium. (4,4′-dimethyl-bipyridinium)]. [1755]),.
poly(xylylviologen).[1498,1756],.poly(ether.amine.quinones).[1757,1758].and.related.poly(quinone).
systems. [1759],. as. well. as. poly( N -vinylimidazole). [1760,1761].. Some. redox. polymers. used. for.
CPE. modiication. have. been. applied. to. the. direct. electrocatalytic. detection. of. neurotransmitters.
[135,1762,1763],.ascorbic.acid.[135,1763,1764],.or.nitrite.[648]..Siloxane.polymers.with.covalently.
attached.ferrocene.derivatives.have.also.been.reported.[856,922,1554]..Finally,.one.should.mention.
that. polymers. supporting. catalytic. centers. (as. ions. or. solid. particles). have. been. used. to. modify.
CPEs.for.electrocatalytic.purposes,.as.reported.for.nickel.in.various.polymers.or.redox.polymers.
[131,841,1765-1780].or.for.metal.oxides.in.neutral.resins.[1229,1241].
4.3.2.5.5 Conducting Polymers
Conducting.polymers.are.attractive.electrode.modiiers,.yet.mainly.used.as.ilms.coated.onto.solid.
electrode. surfaces,. because. they. ensure. good. electronic. conductivity.. These. materials,. adhering.
very.well.on.hydrophobic.carbon.pastes.and.produced.directly.at.the.surface.by.potential.cycling,.
have. found. important. applications. with. amperometric. biosensors,. because. they. enable. eficient.
enzyme. immobilization. while. ensuring. good. electronic. transduction. [1791-1794].. Few. examples.
are. available. for. these. conducting. polymers. associated. to. CPEs,. including. mainly. polypyrrole.
[584,1776,1795-1803]. and. polyaniline. derivatives. [129,130,1497,1804-1806],. with. applications. in.
the.ield.of.biosensors.[1497,1798,1800].or.for.direct.electrocatalytic.detection.of.biologically.rel-
evant. molecules. [129,130,1795,1797,1799,1802,1806].. The. resort. to. poly(1,8-diaminonaphthalene).
[1807].and.poly(phenylenediamine).[1516].was.also.reported.
4.3.3 o Ther p ossibiliTies and r eCenT a pproaChes To C heMiCal M odiFiCaTion
This.section.describes.modiiers.that.are.not.purely.organic.or.inorganic.(such.as.organic-inorganic.
hybrids),.novel.materials.(notably.those.arising.from.nanotechnology.and.(nano)materials.sciences),.
as.well.as.some.CPE.surface.treatments.intended.to.modify.the.electrode.properties.(electrolytic.
modiications,.metal-ilm-plated.electrodes).
4.3.3.1 Organic-Inorganic Hybrid Materials
These.materials,.largely.arising.from.the.new.technologies,.combine.the.mechanical.stability.of.a.
rigid.inorganic.structure.with.the.particular.reactivity.of.organic.functions.
They. are. usually. classiied. into. two. categories,. the. hybrids. of. class. I. characterized. by. weak.
interactions. between. the. organic. and. inorganic. counterparts. and. hybrids. of. class. II. exhibiting.