(Alociljaand Radke,2003).Up to now medicalapplications(infection control,
etc.) havehad the largestmarketsegment.
For the determinationof fruit,vegetable, meatand fish freshness, biosensors
havebeendevelopedfor differentbiogenic amines(histamine,hypoxanthine,
xanthine)basedon specificoxidaseenzymesin combinationwithamperometric
transducers (Draisciet al., 1998)withdetection ranges from 10 ˇ^7 to 10ˇ^3 mol/L.
For rapiddetectionof bacterialcontamination in food,commercialbiosensors
basedon immunochemical assays and DNA hybridisationsin combinationwith
differenttransducer principles havebeenmanufactured.Theuse of analyte-
specific sensors makes it possible to discriminate between differentmicro-
organisms.Several commercialsystems existon the market for detectionof
specific bacteria in foods. Biacore AB delivers biosensor systems for the
detectionof foodpathogens(e.g.SalmonellaandE. coli) basedon immobilised
antibodies in combinationwithSPRtechnology. Gene-Trak Systems(USA)
delivers diagnostic products basedon DNA assays for the rapiddetection of
foodborne pathogensin food.It delivers probes withspecificityfor respectively
Listeria,Salmonella,E. coli,CampylobacterandStaphylococcus aureus.
ThecompanyApplied Biosystems (USA) offersystemsbased on DNA
hybridisationin combinationwith fluorescence detectionfor pathogendetection.
The Taqman’Detection Systemsallowquick determinationof the presenceof
pathogenicbacteria(e.g.E. coliand Salmonella) and fungiand for further
identification of genus and species, the MicroSeq’ system is used. The
MicroSeq’systemis basedon comparison of the genesequencefrom an
unknown sample with genesfromknownstrains.Withthesepathogen detection
biosensorsbacterialcellscan be detected downto 200±10^3 cells/mlfrom10±20
minutes up to 2 hours. However, it shouldbe emphasisedthat it is the sample
clean-upand extraction step of the sample matrixthat representsthe time-
consuming step in theseanalysesand this mayvaryfrom20 minutes to several
hours.
Therefore,thesetechniquesare in principle basedon on-line analysis.They
are availableas portabledevices,automated analysers and laboratoryinstru-
ments. Veryfew biosensorsare usedon-line, but in combination withflow-
injection systems theycouldin principlebe applied on-line(Tothill and Magan,
2003).
19.3.3 Labon a chip
In 1990Manzet al.proposedthe conceptof a miniaturised'totalanalysis system (-TAS),a hybridcombiningthe advantages of a sophisticatedanalysis system (pre-treatment,separation and detection)withthe sizeof a chemical sensor (Fig. 19.6).Sinceall thesestepsare performedin an integratedmicro system the morepopular termlab on a chip' was created. The construction of
automatedsmall-sized controlinstrumentsrequiresthe combination of classical
analyticalchemistry withmicro-fabrication technologyas wellas knowledgeof
biochemistryand biotechnology.
300 Handbookof hygiene controlin the foodindustry