Chemically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 103

4.3.3.2.2 Nanoparticles
The.second.category.of.“nano”.additives.to.CPEs.concerns.the.nanoparticles.(NPs).for.which.the.
physicochemical.properties.can.differ.from.those.of.the.bulk.materials..It.was.mentioned.in.Section.
4.3.1.4.that.metal.particles.can.be.advantageously.exploited.in.electrocatalysis.and.biosensors.(due.
to.their.ability.to.lower.usually.observed.overpotentials).and.some.of.them.were.indeed.NPs.(i.e.,.
Au.[485,567,774,946,950,958,959,1277-1280],.Cu.[960-964,1280,1281],.Pd.[969,971],.Pt.[970],.or.
Fe.[976]..Note.that.AuNPs.are.also.attractive.for.immobilization.of.thiol-containing.groups.(e.g.,.
cysteamine.[1877,1878])..In.addition.to.them,.several.other.NPs.have.attracted.the.attention.of.elec-
troanalysts,.mainly.because.of.their.electrocatalytic.properties..This.is.the.case.of.various.metal.
oxides.or.hydroxides,.the.most.used.in.connection.with.CPEs.being.TiO 2 .because.of.its.intrinsic.
catalytic.properties.[499,992,995,996,1879].or.as.support.for.mediators.[920,991,993,997,1880].
Other. metal. oxides. include. nano. Fe 2 O 3 . [1001],. Fe 3 O 4 . [980],. CoO. [1881],. SiO 2 . [419],. ZrO 2 .
[998],.and.CdO.[1003]..CPEs.containing.dysprosium.or.dysprosium.oxide.nanowires.[1882-1887].
and. Cu(OH) 2 . nanowires. [1888]. have. been. applied. to. electrocatalytic. sensing. of. drugs.. The.
CdS. nanorods. [1889],. CdSe. quantum. dots. [953],. and. neodymium(III). hexacyanoferrate(II).
NPs. [1008]. have. been. exploited. in. biosensors,. while. cobalt. and. iron. phthalocyanine. NPs. in.
CPEs. exhibited. electrocatalytic. behavior. in. some. organics. [932-934].. A. last. category. is. that.
of. core-shell. iron. oxide-based. NPs. (MgFe 2 O 4 /SiO 2 . and. MgFe 2 O 4 /SiO 2 . [302,990],. Fe 3 O 4 /SiO 2 .
[988,979],.Fe 3 O 4 /Au.[986],.and.Fe 2 O 3 /Co.hexacyano-ferrate.[983]),.which.were.mostly.used.in.
CPE.biosensors.
4.3.3.3 Surface Treatments and Alterations
Qualitatively.new.properties.can.be.brought.to.the.CPE.surface.by.its.“total”.modiication.by.means.
of.electrolytic.deposition.of.some.metals.in.the.form.of.a.thin.layer..(Momentarily.popular. litho-
graphic sputtering .[263,264].or. screen printing .[323].of.such.layers.could.also.be.applicable,.but.
for. extraordinarily. resistant. solid-like. CPEs. only,. whereas. common. types. of. incompact,. liquid-
containing,.and.temperature-sensitive.carbon.pastes.cannot.be.used.)
4.3.3.3.1 Metallic-Film-Plated Carbon Paste Electrodes (MeF-CPEs)
Carbon. pastes. covered. with. preplated. metal. ilms. have. gained. considerable. attention. for. several.
reasons:.(I).this.can.increase.much.the.cathodic.polarization.of.the.electrode,.as.hydrogen.evolution.
occurs.at.much.lower.potentials.on,.for.example,.mercury.or.bismuth.surfaces.than.on.carbon.ones;.
(II).avoiding.the.use.of.bulk.metallic.electrodes.is.often.cost-effective.(i.e.,.with.respect.to.noble.
metals).and.might.be.safer.(e.g.,.in.comparison.to.mercury.drop);.they.can.be.applied.to.electro-
chemical.stripping.analysis..The.so-called. metallic ilm carbon paste electrodes .can.be.basically.
prepared.by. in situ .electrolytic.deposition.from.a.solution.containing.the.metal.ion.precursors.or.
in nascenti .by.reducing.solid.precursors.embedded.in.the.paste.[103,265,268,269,617]..The.second.
method.offers.the.advantage.of.operating.in.conditions.of.reagent-free.sensors.for.which.successive.
experiments.can.be.easily.performed.by.mechanical.polishing.of.the.electrode.surface.and.subse-
quent. metal. ilm. deposition. between. each. measurement. without. the. need. for. an. external. plating.
solution..(Remember.that.morphological.transformations.can.occur.in.various.successive.phases.of.
the.ilm.formation,.when.metal.ilms.obtained. in situ .can.suffer.from.nonuniformity.due.to.local.
nucleation.(see,.e.g.,.Section.6.5.and.Figure.6.11).
Following.the.worldwide.success.and.use.of. mercury ilm electrodes .[1890],.the.story.of.metallic-
ilm-plated. CPEs. has. started. with. mercury-ilm-plated. carbon. paste. electrodes. (MF-CPEs;. [257-
259,624]),.but.the.main.boom.of.MeF-CPEs.is.undoubtedly.connected.with.the.rediscovery.of.bismuth.
ilm. electrodes. (BiFEs;. [102,262-264,268]),. when. the. BiF-CPEs. [255,626]. were. the. irst. conigura-
tion.to.employ.a.support.really.concurrent.to.the.glassy.carbon.disc.(see.also.Section.2.2.1)..Besides.
these. mercury-. [257-259,623,624,1891,1892]. and. bismuth-. [265,626,637,669,671]. plated. CPEs,. the.
family.of.related.electrodes.gathers.also.gold.[108,1893],.antimony.[1894],.palladium.[621],.and.lead.