Chemistry Reference
In-Depth Information
Pinhole
Hydrophilic
interaction
van der Waals
interaction
Liquid
(A)
Electrode surface
(B)
FIGURE 4.1
Self-assembled. monolayers. (A). and. Langmuir-Blodgett. ilms. (B).. A. scheme.. (Redrawn. and.
rearranged.from.Arrieta,.A..et.al.,.
Sens. Actuat. B
,.B95,.357,.2003.)
formed.on.silica.[551,769-772].or.dextrin.substrates,.which.are.used.as.modiiers.for.carbon.pastes.
[773]..SAMs.on.gold.may.be.used.for.potentiometric.sensors.[774].
Polylayers
..These.structures.consist.of.many.layers.of.the.modiier.and.can.be.homogeneous.or.het-
erogeneous.in.nature..In.the.latter.case,.modiiers.are.embedded.in.a.polymeric.three-dimensional.
network.. Such. layers. may. be. produced. by. electrodeposition,. such. as. electropolymerized. organic.
polymers.(see.Figure.4.2),.by.application.of.solutions.after.evaporation.of.the.solvent.(typically.poly-
meric.solutions),.or.by.direct.application.of.a.(usually.polymeric).membrane..The.deposited.layer.
may.interact.with.the.target.analyte.directly,.serving.as.anchoring.backbone.or.trap.for.the.actual.
modiier,.or.may.act.via.its.size-exclusion.characteristics.
Typical.examples.for.polymeric.membranes.are.dialysis.membranes,.commonly.used.for.immobili-
zation.of.biological.entities.at.the.electrode.surface.[156,288,775-788],.Naion
®
,.and.other.ion.exchang-
ers.[789-791],.redox.polymers.[783-794],.or.conductive.organic.polymers.[795-798]..Membranes.can.
be.applied.directly.as.sheets.to.cover.the.electrode.surface.or.may.be.generated.by.casting.a.solution.of.
the.corresponding.polymer.on.the.electrode.surface.and.evaporation.of.the.solvent.
Another.possibility.is.in-place.polymerization.from.monomers.either.by.electrolysis.or.by.other.
common.polymerization.processes..A.special.form.of.the.latter.is.
cross-linking
,.frequently.applied.
H
N
S
n
n
(A)
(B)
N
N
n
(C)
FIGURE 4.2
Some.electrolytically.generated.polymers:.polypyrrole.(A),.polythiophene.(B),.and.polyaniline.(C).
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