Biomedical Engineering Reference
In-Depth Information
envision.that.this.technique.could.be.used.for.a.variety.of.capture.mechanisms.in.which.
receptor.dimerization.is.necessary.for.ligand.afinity.
In. a. non-membrane-based. approach. to. afinity. separations,. Luchini. and. colleagues.
developed.“smart”.hydrogel.particles.of.
N
-isopropylacrylamide.(NIPAm).with.an.afinity.
bait. to. (1). sequester. the. low. molecular. weight. fraction. of. serum. proteins,. peptides,. and.
metabolites.using.size-based.separation;.(2).remove.and.concentrate.the.target.molecules.
from. solution. based. on. afinity. or. charge. interaction;. and. (3). protect. captured. proteins.
from.enzymatic.degradation.by.inhibiting.interactions.between.proteases.and.the.target.
molecules.(Luchini.et.al..2008).
15.3.2.3 Microluidic Applications to Bioseparations
Microluidics.or.“lab.on.a.chip”.technology,.in.which.very.small.amounts.of.luids.(10
−9
.to.
10
−18
.L).are.manipulated,.using.channels.with.dimensions.of.tens.to.hundreds.of.microm-
eters,.has.been.the.subject.of.a.number.of.recent.reviews.(including.a.multi-article.review.
section.in.
Nature
.in.2006.[Daw.and.Finkelstein.2006])..While.microluidics.is,.in.general,.
not. scalable,. a. variety. of. physiochemical. interactions. can. be. elucidated. using. microlu-
idics. which. can. then. be. translated. into. larger. systems.. In. addition,. microluidics. lends.
itself. well. to. the. separations. necessary. for. proteomic. analyses,. possibly. replacing. tradi-
tional.chromatographic.separations..Microluidic.separations.of.biological.molecules.can.
be. broadly. divided. into. two. categories,. electrophoretic. separations,. in. which. molecules.
migrate. under. electrical. potential,. and. hydrodynamic. separations,. in. which. molecules.
migrate.under.hydrodynamic.low.conditions.
Electrophoretic. separations. are. more. common. and. have. been. reviewed. recently. (Wu.
et.al..2008;.Chen.and.Fan.2009;.Kenyon.et.al..2011);.hence,.only.relatively.novel.advances.
will. be. discussed. here.. Makamba. et. al.. (2008). covalently. reacted. SWNTs. with. hydrogel.
materials. (acryloyl-PEG-
N
-hydroxysuccinimidyl. ester). and. then. photopolymerized. the.
SWNT-PEG-acrylate.with.acrylamide.and.the.cross-linker.ethylene.glycol.dimethacrylate.
(EDMA).in.microchannels..Using.both.hydrodynamic.low.and.electrokinetic.low,.they.
demonstrated. increased. mechanical. strength. in. the. presence. of. the. SWNTs.. They. also.
observed. improved. resolution. in. protein. separations. with. substantial. peak. sharpening.
in. the. presence. of. the. SWNTs.. To. address. the. low. concentrations. and. small. number. of.
molecules.of.a.particular.analyte.present,.Shen.et.al..(2010).developed.a.microluidic.device.
for.protein.preconcentration.based.on.the.electrokinetic.trapping.principle..Their.precon-
centrator.used.a.narrow.Naion.(a.highly.ion-permselective.membrane.normally.used.in.
proton.exchange.membrane.fuel.cells).strip.integrated.into.a.molded.PDMS.microluidic.
structure. using. a. specially. designed. guiding. channel.. Their. device. was. able. to. achieve.
concentration.factors.of.10
4
.within.a.few.minutes.
While. there. have. been. numerous. advances. in. the. use. of. microluidics. for. the. separa-
tion.of.biomolecules.(Mery.et.al..2008;.Bynum.et.al..2009;.Huh.et.al..2010),.the.discussion.
here. will. focus. on. microluidic. devices. that. incorporate. nanoscale. materials. to. improve.
the. separations.. Karwa. et. al.. (2005). and. Hu. et. al.. (2011). both. employed. silica. in. PDMS.
microchannels.for.solid.phase.extraction.(SPE).of.biomolecules..Karwa.et.al..immobilized.
nano.and.micro.silica.and.micron.size.octadecylsilica.(ODS).to.the.walls.of.PDMS.chan-
nels.using.sol-gel.chemistry..Crude.cell.lysates.from.
E. coli
.were.applied.to.the.SPE.devices.
to.extract.the.DNA..Both.devices.packed.with.micro.silica.and.nano.silica.showed.high.
extraction.eficiency.(>70%).with.slightly.higher.eficiency.from.the.micro.silica,.although.
the. nano. silica. showed. higher. capacity. as. might. be. expected.. They. attributed. the. lower.
eficiency.of.the.nano.silica.to.poor.recovery.rather.than.poor.trapping.eficiency..They.also.
