Severalvolatileorganiccompounds(VOCs)arereleasedfromhumanbreathorskin.Likechemical
substances inbloodorurine,someofthesevaporscanprovidevaluableinformationregardingthestate
of thehumanbody.Ahighlysensitiveacetonebiochemicalgassensor(bio-sniffer)wasdevelopedand
used tomeasureexhaledbreathacetoneconcentration,andassesslipidmetabolismbasedonbreath
acetone analysis.A fiber-opticbiochemicalgassensingsystemwasconstructedbyattachinga flow-cell
with nicotinamideadeninedinucleotide(NADH)-dependentsecondaryalcoholdehydrogenase(S-ADH)
immobilized membraneontoa fiber-opticNADHmeasurementsystem.TheNADHmeasurementsystem
utilizes anultraviolet-lightemittingdiodewithpeakemissionof335nmasanexcitationlightsource.
NADHisconsumedbytheenzymaticreactionofS-ADH,andtheconsumptionisproportionaltothe
concentration ofacetonevapor.PhosphatebufferwhichcontainedNADHwascirculatedintothe flow-
cell torinseproductsandtheexcessivesubstratesfromtheoptode.Thechangeof fluorescent emitted
from NADHisanalyzedbythePMT.Hence, fluorescence intensitydecreasedastheacetoneconcentration
increased. Therelationshipbetween fluorescence intensityandacetoneconcentrationwasidentified
from 20ppbto5300ppb.Thisintervalincludedtheconcentrationofacetonevaporinthebreathof
healthypeopleandthosesufferingfromdisordersofcarbohydratemetabolism.Finally,theacetonebio-
sniffer wasusedtomeasurebreathacetoneduringanexercisestresstestonanergometerafteraperiod
of fasting.Theconcentrationofacetoneinbreathwasshowntosignificantly increaseafterexercise.This
biosensor allowsrapid,highlysensitiveandselectivemeasurementoflipidmetabolism