Electrochemical Investigation with Carbon Paste Electrodes and Sensors - Electroanalysis with Carbon Paste Electrodes - page 163

been.established.thanks.to.extensive.investigations.by.Blaha.et.al..(who.had.begun.in.the.late.1970s.
[595].regularly.publishing.up.to.the.early.2000s.[603]),.O'Neill.et.al..(starting.in.the.early.1980s.
[598].and.active.up.until.now.[2119]),.or.newly.by.Ly.et.al..[376,390,409].
Thus,.with.a.collection.of.contributions.from.other.authors.(see,.e.g.,.[611,1108,1717,2120-2125]),.
the.speciic.area.of. in vivo .applied.CPEs.has.already.spawned.around.100.papers,.a.major.part.of.
which.is.also.cited.herein—see.the.reference.list.and.the.entries.[48-50,152,376,377,390,396,409,430,.
593-606,611,1022-1028,1108,1629,1642,1662,1717,2116-2154]..Others.can.then.be.anticipated.in.the.
near.future.in.connection.with.the.dynamic.progress.of.new.carbon.pastes.and.brain.neuroscience.
7.3.2 b asiC C haraCTerizaTion oF in V iVo M easureMenTs
For. in vivo . measurements,. various. carbon. paste-based. mini-. or. microelectrodes. (CPm/μEs). are.
used,.with.the.surface.diameter.in.the.range.of.50-300.μm.[50,152,606],.which.is.also.the.case.of.a.
microtip.of.otherwise.nearly.half.a.meter.long.electrode.described.by.Wang.et.al..[600]..In.fact,.the.
variability.of.implantable.CPm/μEs.is.rather.in.construction.than.in.the.carbon.paste.composition.
Thus,. traditional. mixtures. of. graphite. powder. +. Nujol. have. largely. prevailed. (see,. e.g.,.
[152,600,606]. and. references. therein),. and. only. a. limited. series. of. reports. quote. other. mixtures,.
such.as.those.made.of.silicone.oil.[598,2143],.luorocarbon.oil.[611],.or.new.kinds.of.paste-like.com-
posites. from. carbon. nanotubes. [376,377,390,396,409].. With. respect. to. the. construction,. a. simple.
electrode.can.be.made.from.a.miniature.glass.capillary,.where.the.carbon.paste.is.additionally.ixed.
with.epoxy.resin.([50];.see.also.Section.2.3.6.and.Figure.2.13).
More.sophisticated.design.is.an.implantable.CPm/μE.(shown.on.a.schematic.picture.in.[605]).con-
structed.from.PTFE-coated.thin.wire..One.end.of.this.electrode.is.devised.with.soldered.gold.clip.
(for.connection.with.potentiostat),.whereas.the.other.hides.a.small.cavity.for.carbon.paste.obtained.by.
peripheral.cutting.of.the.plastic.sleeve.near.the.gold.contact,.followed.by.careful.pulling.of.the.insula-
tion.out.for.0.5.mm.over.the.wire.(from.silver.or.Ir-Pt.alloy)..The.carbon.paste.can.then.be.packed.into.
the.obtained.cavity.using.a.piece.of.the.same.wire,.again,.with.removed.insulation.at.one.end.
CPm/μEs. for. in vivo . measurements. could. be. operated. via. the. native. carbon. pastes. as. well. as.
various.chemically.and.biologically.modiied.variants..Native.(unmodiied).pastes.have.been.used.
as.such.[50,2126].or.treated.electrolytically.by.anodization.(see.[63,68].and.Section.3.2).as.well.as.
chemically.via.“surface.erosion”.[64,243].by.surfactants.and.lipids.(e.g.,.stearate.[1028,2121,2133]),.
or. even. by. the. measured. tissue. alone. [1027].. Yet. another. surface. modiication. was. the. case. of.
Naion. protective. layer. [1717],. whereas. the. most. typical. approach. for. carbon. pastes—the. bulk.
modiication—was. successfully. accomplished. with. natural. clay. (zeolite. [1108]),. some. enzymes.
[1450,2124,2125],.albumin.[2134],.or.a.piece.of.spinach.leaf.[2123].
Experimentation. with. implanted. electrodes. is. traditionally. connected. with. in vivo . voltammetry.
(IVV).[605,606]..Besides.voltammetric.measurements.with.a.potential.ramp.in.the.linear.sweep/scan.
(LSV;.e.g.,.[2135]),.staircase.(SCV;.[2143]),.and.differential.pulse.(DPV;.[597]).modes,.amperometry.
[2145].and.chronoamperometry.(CA;.[2124]).complete.the.techniques.of.choice.for. in vivo .applica-
tions.. Due. to. extremely. low. currents. to. be. measured. (in. the. nA. range. or. even. below. [2135]). with.
possible.signal.oscillations.and.baseline.drift,.less.favorable.signal-to-noise.ratio.due.to.higher.back-
ground.in.complex.matrices.of.biological.luids.and.tissues,.and.mainly.because.of.very.close.peak-
potential.characteristics.of.principal.compounds.of.interest.(e.g.,.catechols.vs..ascorbate,.DOPAC,.or.
uric.acid),.“current.vs..potential.applied”.(“ I i .vs.. E APP ”).measurements.are.often.combined.with.com-
puter.processing.of.the.resultant.signal(s).by.means.of.the.so-called.deconvolution.[2155,2156],.using.
mathematical.transformation.of.the.experimental.data.by.using.semidifferentiation.(or.semiderivation,.
respectively;.[2157-2159]).and,.eventually,.the.baseline.subtraction.(i.e.,.correction.or.even.total.elimi-
nation. of. undesirable. background. [1937].. For. other. information. on. these. techniques,. go. to. Section.
6.2.1.1)..In.IVV.assays.(e.g.,.[596,598,2121,2131]),.these.operations.enable.one.to.(i).evaluate.abnor-
mal. responses,. such. as. overlaps,. background-obscured. and. badly. developed. peaks,. and. otherwise.
deformed.signals).or.(ii).suppress.the.unwanted.background.or.residual.noise..On.the.other.hand,.there.