Chemically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 87

Many. examples. are. available. for. such. metal. oxide. or. metal. phosphate. thin. ilms. grafted. on. sil-
ica.gel.and.incorporated.into.CPEs,.including.titanium.dioxide,.TiO 2 .[852,923,1178-1186],.zirco-
nium. dioxide,. ZrO 2 . [1187-1190],. niobium. oxide,. Nb 2 O 5 . [535,1190-1203],. antimony. oxide,. Sb 2 O 3 .
[1204-1206],.tin.oxide,.SnO 2 .[1207-1209],.alumina,.Al 2 O 3 .[1210,1211],.as.well.as.titanium.phos-
phate. [87,534,1184,1212,1213],. tin. phosphate. [1207-1209],. or. zirconium. phosphate. [1214-1216]..
Generation.of.acid.sites.is.possible.in.aqueous.solution.on.the.surface.of.SiO 2 .or.M x O y .
Many.of.the.oxides.have.an.amphoteric.character,.so.they.can.adsorb.negatively.charged.spe-
cies. at. solution. pH. below. the. point. of. zero. charge. (“pzc”). and. positively. charged. species. above.
pzc.. This. has. been. especially. exploited. to. immobilize. various. organic. or. organometallic. medi-
ators,. such. as. Meldola's. blue. [87,1185,1194,1197,1200,1205,1209,1212,1217],. Methylene. blue.
[1178,1184,1190,1200,1205],. Methylene. green. [1196],. toluidine. blue. [1182,1195,1204,1205],. fer-
rocene. derivatives. [535,923],. metal. phthalocyanines. [1179,1180,1183],. and. metal. porphyrins.
[534,1191,1192,1206,1207,1208].among.others.[852,1186-1189,1199,1211]..The.corresponding.modi-
ied.electrodes.were.thereby.especially.applied.in.electrocatalytically.acting.biosensors.
4.3.1.3.2 Other Metal Oxides
Not. only. silica. but. also. other. metal. oxides. have. been. widely. used. to. modify. CPEs. because. of.
their. attractive. properties. such. as. catalysis,. host/support. for. further. modiication,. or. source. of.
metallic. deposits.. Ruthenium. oxides. (mainly. RuO 2 ). [1218-1224],. copper. oxides. (Cu 2 O,. CuO).
[77,556,699,703,401,1225-1229],. and. to. a. less. extent. cobalt. and. nickel. oxides. [1230,1231]. have.
been. exploited. for. their. catalytic. behavior,. mainly. with. respect. to. the. determination. of. carbohy-
drates. [77,1218,1221,1222,1225,1226],. amino. acids. [401,556,1223,1230],. or. hydrogen. peroxide.
[1224,1227,1230]..CPEs.modiied.with.manganese.oxides.(mainly.MnO 2 ).were.applied.either.to.the.
catalytic.detection.of.hydrogen.peroxide.[326,1232-1235].or.in.potentiometric.indication.during.the.
determination.of.alkali.metal.ions.[742,1236-1240].
Other.examples.of.metal.oxides.in.CPEs.are.PbO 2 .[556,1241],.Fe 2 O 3 .or.Fe 3 O 4 .[1001,1242],.Al 2 O 3 .
[1243,1244],. ZrO 2 . [1245],. La III -doped. TiO 2 . [1246],. and. some. others. [556,1247].. In. particular,.
Labuda.et.al..have.provided.a.comparison.between.performance.observed.at.CPEs.modiied.with.
various.metal.oxides.[556]..Perovskite-based.oxides.[1248-1250].and.ceramic.powders.[1251-1253].
have.also.been.reported.as.CPE.modiiers.
Finally,.HgO.[617].and.Bi 2 O 3 .[103,265,623].are.also.worth.mentioning.as.they.were.used.as.a.
potential.reservoir.for.the.formation.of.mercury.and.bismuth.ilms.on.CPE.surfaces.
4.3.1.4 Other Inorganic Modiiers
4.3.1.4.1 Metal Elements
Since.the.discovery.of.metal-dispersed.carbon.paste.electrodes.by.Wang.et.al..in.1992.[838],.a.huge.
amount.of.work.has.been.performed.in.this.ield.[94]..The.main.motivation.relies.on.the.ability.of.
small.metallic.particles.to.induce.catalytic.behaviors.by.lowering.overpotentials.(see.Figure.4.8)..
This.is.especially.attractive.for.improving.the.selectivity.of.amperometric.biosensors.by.shifting.the.
operational.potentials.to.lower.values.[1254,1255],.that.is,.where.interferent.species.are.no.longer.
likely.to.affect.the.transduction.of.the.biocatalytic.process.[1254].
At. irst,. metalized. graphite. particles. were. used. as. the. carbon. source. for. CPE. preparation.
for. which. various. metals. (Ru. [838,1256-1258],. Pt. [838,1259],. Pd. [838],. Rh. [647,1260-1262],.
Ir.[1263-1265],.and.even.bimetallic.Ru-Pt.[1266]).have.proven.to.be.eficient.electrocatalysts.
for. hydrogen. peroxide. and. NADH. detection,. which. have. generated. a. novel. family. of. highly.
eficient.irst-generation.biosensors.[1267]..Later.on,.metal.microparticles.or.NPs.were.directly.
.dispersed.in.conventional.carbon.paste.matrices,.and.their.catalytic.properties.were.exploited.
as.such.(direct.detections).or.associated.to.redox.proteins.in.biosensing.devices..Examples.are.
available.for.various.(usually.noble).metallic.particles,.such.as.Pd.[635,839,940,971,1268,1269],.