Biomedical Engineering Reference
In-Depth Information
proteins.and.lipid.membranes.used.in.biosensors.can.withstand.these.parameters.for.
the. required. life. of. the. sensor. in. the. ield.. A. life. of. a. sensor. may. allude. to. sensing.
over.a.continuous.period.of.time.or.repeated.sensing.cycles.(reusable.sensor)..In.either.
scenario,. reproducible. measurements. in. terms. of. sensitivity. and. selectivity. should. be.
achieved.over.this.time.frame.
Solutions.to.this.may.include.synthetic.lipid.bilayers.and.the.use.of.bio-engineered.ORs.
with.high.stability,.taking.into.consideration.our.knowledge.of.ligand-binding.domains.
and.important.structure-function.properties.of.native.ORs.(Cook.et.al..2008)..This.could.
also.lead.to.engineering.of.OR.hybrids.with.higher.ligand.afinity.than.the.native.receptors..
Alternatively,.researchers.have.designed.biosensors.linked.to.peptides.that.are.based.on.
sequences. of. potential. ligand-binding. regions. of. ORs. (Wu. and. Lo. 2000,. Lin. et. al.. 2001,.
Wu.et.al..2001,.Mascini.et.al..2005,.Sankaran.et.al..2011)..For.example,.Sankaram.et.al..have.
used.a.bioinformatics.approach.to.determine.the.optimal.peptide.sequence.for.sensing.the.
alcohol.odorants.from.food.spoiling.bacteria..In.experimental.validation,.immobilization.
of. the. peptide. on. QCM. resulted. in. a. lower. detection. limit. of. 2-3.ppm. for. heptanol. and.
3-5.ppm.for.pentanol.(Sankaran.et.al..2011).
Other. issues. that. are. common. to. biosensor. development. are. the. reproducibility. of.
immobilization.of.molecules.onto.surfaces..In.the.case.of.ORs,.the.number.and.orientation.
of.functional.OR.proteins.per.sensor.will.need.to.be.optimized.and.standardized,.which.
still. remains. challenging.. Furthermore,. analyte. application. to. the. sensor. platform. is.
relatively. simple. in. a. laboratory. setting. where. low. rate,. analyte. concentration,. and.
vehicle. solution/gas. can. be. carefully. controlled.. For. biological. characterization. studies,.
this.allows.for.very.accurate.kinetic.data.acquisition..However,.in.“ield”.settings,.careful.
device.design.consideration.is.needed.to.ensure.access.of.volatiles.to.chip.surfaces..Our.
nose.has.effectively.achieved.this.purpose..Interestingly,.unique.low.characteristics.of.the.
nasal.cavity.architecture.appear.to.signiicantly.inluence.odor.recognition.by.receptors.in.
the.nasal.epithelium.(Stitzel.et.al..2003)..Further,.since.our.nasal.mucosa.aids.in.odorant.
trapping,.use.of.an.artiicial.mucosal.coating,.as.well.as.structurally.changing.the.sensor.
surface. to. incorporate. channels,. improved. odorant. sensing. on. a. physical. sensor. array.
(Covington.et.al..2007)..The.feasibility.of.such.modiications.in.combination.with.OR-based.
biosensors.remains.to.be.determined..Lastly,.the.cost.of.manufacturing.biosensors.is.still.
relatively.high.compared.to.inorganic.devices,.largely.due.to.the.caveats.mentioned.earlier.
Continuing. research. will. focus. on. enhancing. sensitivity. of. OR-ligand. binding. and.
effective.sensing.of.this.event..Cell-free.olfactory.receptor.sensing.has.thus.far.primarily.
focused. on. measuring. the. ligand. receptor. interaction.. However,. in. the. future. we. may.
be.able.to.take.advantage.of.other.readouts.that.could.enhance.sensitivity.of.sensing.via.
GPCRs.. These. may. include. the. incorporation. of. the. G-proteins. in. the. sensor. platform.
and.measuring.dissociation.event.of.these.from.the.GPCR.following.ligand.binding..It.is.
known.that.GPCRs.exhibit.the.highest.ligand.afinity.when.found.in.their.ternary.complex.
(i.e.,.coupled.to.the.heterotrimeric.G-protein.complex).(Gether.and.Kobilka.1998,.Schneider.
and.Seifert.2010)..To.enable.higher.sensitivity.ligand.binding,.biosensor.design.may.have.
to.incorporate.the.G-protein.heterotrimeric.complex.(Vidic.et.al..2006)..The.challenge.is.to.
incorporate.a.multiprotein.complex.into.a.cell-free.lipid.bilayer,.keeping.in.mind.correct.
orientation,. protein. expression. and. puriication. of. each. component,. complex. assembly,.
immobilization.onto.a.sensor.platform,.and.stability.
To.extend.biosensor.research.using.biological.sensory.systems,.future.work.may.focus.
on. the. use. of. proteins. such. as. the. taste. receptors. T2R. (GPCR;. bitter. taste. receptor). and.
transient. receptor. potential. ion. channels. TRP-M. (melastatin). and. TRP-V. (vanilloid),.
vomeral.receptors.(V1R,.V2R;.pheromone.receptors).and.the.formyl.peptide.receptor-like.
