Biomedical Engineering Reference
In-Depth Information
TABLe 15.2
Enzymatic.Loading.of.the.Various.
CNT-AMG.Conjugates
Loading (μg of
Enzyme/mg of CNT)
Physical adsorption
SWNTs
564
MWNTs
621
Covalent immobilization
SWNTs
290
MWNTs
274
Periodate-oxidized immobilization
SWNTs
105
MWNTs
142
Source:
.
Image. reproduced. from. Cang-Rong,.
J.T.. and. Pastorin,. G.,. The. inluence. of.
carbon. nanotubes. on. enzyme. activity.
and.structure:.Investigation.of.different.
immobilization. procedures. through.
enzyme.kinetics.and.circular.dichroism.
studies,.
Nanotechnology
,.20(25),.255102,.
2009.. Copyright. (2009). with. permis-
sion.from.IOP.Publishing.
nanotubes. (via. carbodiimide. chemistry),. as. well. as. on. amino-functionalized. nanotubes.
(via.periodate-oxidized.AMG)..Typical.enzyme.loadings.for.the.different.immobilization.
methods.are.shown.in.Table.15.2..Physical.adsorption.was.superior.for.both.SWNTs.and.
MWNTs,.followed.by.the.standard.covalent.immobilization.using.carbodiimide.chemistry.
and.inally.periodate-oxidation..In.all.cases,.higher.loadings.were.observed.using.MWNTs..
These.loadings.are.similar.to.reports.for.immobilization.of.SBP,.alpha-chymotrypsin,.and.
Subtilisin.Carlsberg.to.MWNTs.(Karajanagi.et.al..2004;.Asuri.et.al..2006b),.but.signiicantly.
lower.than.the.∼1.mg.enzyme/mg.SWNT.described.earlier..When.they.assayed.the.kinetic.
activity. of. the. immobilized. enzymes. using. starch. as. a. substrate,. for. the. adsorbed. and.
carbodiimide-conjugated.samples,.the.V
max
.of.all.samples.was.similar.and.about.50%.of.
the.free.enzyme.in.solution..However,.the.K
m
,.which.represents.the.afinity.of.the.enzyme.
for.its.substrate.was.increased.in.all.of.the.samples,.more.so.in.the.samples.attached.to.the.
MWNTs. and. in. the. covalently. coupled. samples.. As. a. result,. the. catalytic. eficiency. was.
decreased.in.all.of.the.immobilized.samples..For.the.periodate-immobilized.samples,.no.
activity.was.found..Finally,.using.CD.spectroscopy,.they.analyzed.the.maintenance.of.the.
secondary. structure. after. immobilization.. The. physically. adsorbed. samples. maintained.
∼40%.of.their.native.structure,.whereas.the.covalently.bound.samples.maintained.∼20%.of.
the.native.structure..Hence,.there.was.a.strong.correlation.between.the.catalytic.eficiency.
and.the.maintenance.of.structural.integrity,.as.might.be.expected.
In. contrast. to. the. curved. structures. of. nanotubes. and. fullerenes,. Zhang. et. al.. (2010b).
recently.immobilized.horseradish.peroxidase.(HRP).and.lysozyme.to.graphene.oxide,.and.
characterized.the.enzyme-nanomaterial.conjugate.using.atomic.force.microscopy.(AFM),.
followed. by. enzyme. activity. assays.. Graphene. oxide. (GO). provides. some. advantages.
over.nanotubes.and.fullerenes.for.enzyme.immobilization.in.that.the.presence.of.oxygen.
