Biomedical Engineering Reference
In-Depth Information
Odorant
Ca
2+
Na
2+
Cl
-
OR
-
-
-
AC
+
+ +
αolf
β
Ca
2+
Na
2+
Cl
-
αolf
γ
ATP
cAMP
GTP
GDP
Figure 10.1
(See companion CD for color igure.)
. Activation. of. the. G-protein. coupled. olfactory. receptor. by. odorant.
ligands..Odorants.enter.the.nasal.cavity.and.bind.to.speciic.olfactory.receptors.(OR).localized.to.cilia.of.olfac-
tory.neuron.dendrites..Conformational.changes.in.the.receptor.and.heterotrimeric.G-protein.complex.result.in.
GTP/GDP.exchange,.Gα.protein.activation,.translocation.of.Gα.to.adenylate.cyclase.(AC),.and.AC.activation..
Cyclic.AMP.(cAMP).levels.increase,.activating.cation.channels,.resulting.in.calcium.(Ca
2+
).and.sodium.(Na
2+
),.
opening.of.chloride.(Cl
−
).channels.and.Cl
−
.eflux..The.resultant.membrane.depolarization.cumulates.in.action.
potential.propagation.and.electrical.signals.being.transmitted.to.the.olfactory.bulb.and.cortex.
ORs.are.able.to.sense.odorants.based.on.their.structural.characteristics,.including.func-
tional.groups.and.carbon.chain.length..In.addition,.different.ORs.are.able.to.respond.to.
varying.degrees.of.odorant.concentrations..An.odorant.is.able.to.be.sensed.by.a.number.of.
different.ORs,.adding.another.layer.of.complexity.to.our.sophisticated.sense.of.smell..ORs.
have.been.identiied.for.odorants.such.as.citronellal,.esters,.ketones,.helional,.and.bour-
geonal..Table.10.1.gives.examples.of.vertebrate.and.insect.ORs.and.their.preferred.ligands,.
focusing. on. ORs. that. have. been. functionalized. onto. biosensors.. For. more. information.
on. ORs. with. known. ligands,. the. reader. is. referred. to. a. number. of. review. articles. and.
references.within.(Malnic.et.al..2004,.Lagerström.and.Schiöth.2008,.Touhara.and.Vosshall.
2009)..Interestingly,.there.is.a.huge.push.for.“de-orphaning”.of.ORs,.as.the.ligands.for.a.
large.proportion.of.receptors.still.remain.to.be.identiied..Biosensors.coupled.to.orphan.
ORs.will.likely.aid.in.our.characterization.of.these.receptors.and.the.identiication.of.their.
speciic.ligands.(Glatz.and.Bailey-Hill.2011).
10.3.3 Or Biosensor Applications
The.electronic.nose.(e-nose).was.irst.introduced.in.1982.by.Persaud.and.Dodd.(Persaud.and.
Dodd.1982)..E-noses.are.based.on.interaction.of.volatiles.with.various.surface.chemistries.
and. the. consequential. signal. being. transduced. to. a. sensor,. such. as. a. semiconductor,.
piezoelectric,. or. optical. sensor. (Pearce. et. al.. 2006).. This. technology. has. been. applied. to.
sensing.of.chemicals.and.volatiles.in.a.number.of.real-life.applications,.such.as.the.food.
and. fragrance. industries,. detection. of. toxins,. environmental. monitoring,. and. medical.
diagnostics.(Pearce.et.al..2006)..Speciic.examples.include.the.use.of.biosensors.for.breath.
analysis.to.detect.alcohol,.or.disease-related.volatiles,.such.as.acetone.(enhanced.in.diabetes),.
gas.and.explosive.sensing,.and.detection.of.volatiles.from.food-spoiling.microorganisms..
While. much. progress. has. been. made. in. e-nose. development,. this. technology. still. lacks.
