Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 200

surface.[1440,2850]..Other.organic.electron.acceptors.used.with.glucose.biosensors.were.methy-
lene.green.[244],.viologen.derivatives.[1498,1756],.1-( N , N -dimethylamine)-4-(4-morpholine).ben-
zene.[574,2857,2858],.Meldola.blue.[1482],.and.poly( o -.or. m -phenyl-enediamine.ilms.[1261,1780]..
GOD.bound.to.poly(ethylene.glycol).gives.access.to.direct.electron.transfer.[1781,1782,860,2853]..
HRP.detects.hydrogen.peroxide.which.oxidizes.the.enzyme.that.can.be.electrochemically.reduced.
directly. or. via. a. mediator,. tetramethylbenzidine. [321].. Fibrinogen. increases. the. sensitivity. of. a.
glucose.biosensor.with.direct.oxidation.of.H 2 O 2 .[2855,2856].
Glucose.can.be.also.oxidized.with.glucose.dehydrogenase.[385,935,938,1481,1601,1754,2850,2860,.
2862]..It.needs.a.co-factor,.NAD + ,.which.is.reduced.to.NADH.and.can.be.electrochemically.reoxi-
dized,.either.directly.or.via.mediators..Typical.representatives.are.Meldola.blue.[1481,2801,2859],.
phenazine.methosulfate.[2861],.toluidine.blue.O.[935,938,2860],.ruthenium.complexes.[1601],.and.
Os-polymers. [385,1754].. Glucose. biosensors. were. also. constructed. from. microorganisms. which.
serve.as.a.source.of.glucose.dehydrogenase:. Gluconobacter .sp..[1441,2863,2864],. Escherichia coli .
[288],. Lactobacillus fructivorans .[1443],.and. Aspergillus niger .[1521].
Occasionally.special.designs.with.carbon.paste.were.used.for.determining.glucose.+.other.car-
bohydrates..Carbon.paste.served.only.as.a.support.for.GOD,.where.the.released.hydrogen.peroxide.
was.detected.with.a.platinum.electrode.placed.downstream.[2865]..An.optical.iber.sensor.based.
on. luminescence. from. H 2 O 2 ,. enzymatically. released. by. GOD,. and. electrooxidized. luminol. was.
described.in.[2866]..Dual.electrodes.were.employed.for.the.simultaneous.determination.of.glucose.
and.other.sugars,.such.as.lactose.[2867].and.sucrose.[250]..For.the.lactose,.sensor.galactosidase.
was.used.additionally.to.GOD,.for.sucrose.GOD,.invertase.and.mutarotase;.catalase.was.placed.
between.the.electrodes.to.avoid.cross-talks.via.hydrogen.peroxide..In.both.cases,.another.electrode.
was.a.glucose.sensor.based.on.GOD;.the.disaccharide.concentration.was.evaluated.as.difference.
Pyranose.oxidase.can.metabolize.a.few.carbohydrate,.such.as.glucose,.xylose,.galactose,.and.is.the.
main.ingredient.of.a.pyranose.biosensor.[2868]..It.detects.hydrogen.peroxide.with.HRP.and.contains.
other.additives.as.supporters.and.stabilizers,.mutarotase.for.quick.formation.of.the.beta-anomer.of.
glucose,.polyethyleneimine.for.its.stabilizing.effect.on.the.oxidase,.and.streptomycin/dihydrostrep-
tomycin.for.its.positive.action.on.the.peroxidase..Hydrogen.peroxide.from.pyranose.oxidase.can.be.
detected. also. with. carbon. nanotubes. [400].. Sixteen. mono-. and. oligosaccharides. were. observed. to.
give.response.with.a.biosensor.containing.oligosaccharide.dehydrogenase.and.benzoquinones.[1439].
Pectins,.mainly.poly(galacturonic.acid).esteriied.with.methanol,.can.be.quantiied.via.the.alco-
holic.component.with.a.tissue-enzyme.hybrid.biosensor:.orange.peel.as.a.source.of.pectin.esterase.
on. top. of. an. alcohol. sensor. (alcohol. oxidase). will. release. methanol. which. is. monitored. by. the.
enzyme.electrode.[277].
8.4.6 C oenzyMes , e nzyMes , p roTeins , and r elaTed C oMpounds
Table.8.20.relects.extensive.investigations.with.carbon.paste.electrodes.on.proteins,.enzymes,.and.
coenzymes.
FAD,. lavin. mononucleotide. (FMN;. ribolavin-5′-phosphate),. and. ribolavin. were. adsorbed. on.
silica. gel. modiied. with. zirconium. oxide;. their. voltammetric. behavior. was. studied. with. cyclic.
voltammetry. [1188].. Lipoic. acid. can. be. catalytically. oxidized. with. Ni(II)-cyclohexyl. butyrate.
[1606].or,.like.other.thiols.and.disulides,.with.cobalt.phthalocyanine.[886].
Most.studies.were.performed.with.nicotine.adenine.dinucleotide.in.reduced.and.oxidized.forms.
(NADH,. NAD + ). as. well. as. on. its. phosphate. (NADPH,. NADP + ). with. a. phosphate. group. on. the.
2′-C.atom.of.the.ribose,.because.NAD + .is.a.very.frequent.co-factor.with.dehydrogenases.[64,119,.
124,203,368,395,439,453,472,535,654,656,782,875,876,938,1130,1189,1190,1193,1194,1195,1196,.
1199,1205,1212,1286,1287,1290-1293,1295,1296-1298,1299,1469,1473,1476,1503,1512,1779,1786,.
1904,2869-2890]..The.reduced.form.can.be.oxidized.at.plain.carbon.paste,.though.surfactants.[64],.
carbon.nanotubes.[124,395,2871],.carbon.nanoibers.alone.[203].or.with.Pd.nanoparticles.[2875],.and.
ordered. mesoporous. carbon. [119]. support. the. electron. transfer.. Poly(methyl. methacrylate). [2872].