Listeria monocytogenes is aseriouscauseofhumanfoodborneinfectionsworldwide,whichneeds
spending billionsofdollarsforinspectionofbacterialcontaminationinfoodeveryyear.Therefore,there
is anurgentneedforrapid,in-field andcosteffectivedetectiontechniques.Inthisstudy,rapid,low-cost
and simplecolorimetricassaywasdevelopedusingmagneticnanoparticlesforthedetectionoflisteria
bacteria. TheproteasefromthelisteriabacteriawasdetectedusingD-aminoacidsubstrate.D-aminoacid
substratewaslinkedtothecarboxylicacidonthemagneticnanoparticlesusingEDC/NHSchemistry.The
cysteineresidueattheC-terminalofthesubstratewasusedfortheself-assembledmonolayerformation
on thegoldsensorsurface,whichinturntheblackmagneticnanobeadswillmaskthegoldencolor.The
color willchangefromblacktogoldencoloruponthecleavageofthespecific peptidesequencebythe
Listeria protease.Thesensorwastestedwithserialdilutionsof Listeria bacteria. Itwasfoundthatthe
appearance ofthegoldsurfaceareaisproportionaltothebacterialconcentrationsinCFU/ml.Thelowest
detection limitofthedevelopedsensorforListeriawasfoundtobe2.17102 colonyformingunit/ml
(CFU/ml). Thespecificity ofthebiosensorwastestedagainstfourdifferentfoodborneassociatedbacteria
(Escherichiacoli, Salmonella, Shigella flexnerii and Staphylococcusaureus). Finally,thesensorwastested
with artificially spikedwholemilkandgroundmeatspikedwith listeria.