Biomedical Engineering Reference
In-Depth Information
creating.a.mouse.OR.functionalized.chemical.sensor.chip.using.FET.technology.that.was.
able.to.sense.eugenol.vapor.at.a.concentration.of.1.ppm.(Goldsmith.et.al..2011)..It.is.thought.
that.the.conformational.change.induced.in.ORs.upon.ligand.binding.results.in.an.“active”.
state,.which.is.relected.by.a.shift.from.a.neutral.acid.form.to.a.negatively.charged.base.
form.of.receptor.cysteine.residues,.hence.inluencing.the.current-voltage.characteristic.of.
the.CNT.(Kim.et.al..2009,.Yoon.et.al..2009).
10.5.2 Surface Plasmon resonance
SPR.has.signiicantly.improved.our.ability.to.quantitate.interactions.of.molecules.in.real.
time,. providing. important. information. about. binding. afinity. and. kinetics.. It. is. based.
on.the.generation.of.electron.charge.density.waves.(plasmons).at.the.solid.(usually.gold).
and. liquid. interface,. following. evanescent. wave. generation. by. polarized. light.. Binding.
of. molecules. to. the. solid. surface. changes. the. wavelength. of. the. plasmon.. This. can. be.
detected. using. total. internal. relection. mode. (Kretschmann. coniguration),. where. the.
relected.light.intensity.at.a.given.angle.is.reduced.due.to.the.plasmon.wave..Binding.of.
molecules.to.the.sensor.surface.is.determined.by.a.shift.in.this.angle.(Maynard.et.al..2009,.
Chung.et.al..2011)..This.has.been.an.invaluable.tool.for.biological.research,.as.well.as.the.
pharmaceutical.industry.for.drug.design.and.discovery..It.provides.a.cell-free.system.that.
allows.for.the.characterization.of.individual.proteins.functionalized.on.the.SPR.platform..
Several.well-established.commercial.tools.are.available.that.take.advantage.of.SPR,.such.
as. the. Biacore. system. (GE. Health).. Most. commonly,. recombinantly. expressed,. tagged.
proteins. are. immobilized. onto. the. SPR. surface. using. tag-speciic. antibodies.. This. has.
shown. to. be. useful. for. ligand. analysis. of. chemokine. receptors. and. may. therefore. work.
for. certain. GPCRs. that. do. not. require. the. hydrophobic. environment. of. the. lipid. bilayer.
for. stability. and. conformation. (Navratilova. et. al.. 2006).. The. challenge. in. the. membrane.
receptor.and.ion.channel.ields.is.the.incorporation.of.the.lipid.bilayer.on.the.SPR.surface.
and.retaining.the.resonance.shifts.following.binding.of.analyte.to.receptor..While.SPR.has.
shown.promise.in.OR.biosensor.applications,.questions.remain.as.to.its.sensitivity.toward.
small. molecules,. including. a. number. of. volatile/odorant. compounds. (Vidic. et. al.. 2006,.
2007,.Kaiser.et.al..2008,.Cook.et.al..2009).(Table.10.1,.Figure.10.3)..In.an.attempt.to.circumvent.
this.problem,.Vidic.et.al..coexpressed.the.heterotrimeric.G-protein.complex.(αolf,.β.and.γ).
in.combination.with.human.OR1740.in.yeast.cells.and.immobilized.nanosome.membrane.
fractions.onto.a.dextran-coated.Biacore.sensor.chip,.with.the.ligand.binding.side.facing.the.
dextran-coated.gold.surface.(Vidic.et.al..2006)..Ligand.binding.could.thus.be.monitored.as.
a.consequence.of.the.Gαolf.unit.dissociating.from.the.complex,.resulting.in.a.large.SPR.
response.(Figure.10.3)..GTPγS.was.included.in.the.experiment.to.allow.Gαolf.activation..
When.the.investigators.included.an.antibody.on.the.sensor.surface.to.capture.the.OR.with.
a. myc. tag,. the. response. to. the. odorants. improved. 10-fold,. presumably. due. to. enhanced.
protein.immobilization.(Vidic.et.al..2007).
There. is. large. interest. in. scaling. down. the. SPR. platform. for. biosensor. applications.
(Maynard.et.al..2009,.Chung.et.al..2011)..The.goal.of.this.active.research.area.is.to.develop.
SPR.micro-.and.nanoscale.sensors.with.enhanced.sensitivity,.leading.to.single.molecule.
detection.(Anker.et.al..2008).
10.5.3 Acoustic Wave Sensors
Quartz. crystal. microbalance. (QCM). and. surface. acoustic. wave. (SAW). sensor. platforms.
take. advantage. of. the. acoustic. wave. generation. of. piezoelectric. materials.. The. QCM.
