Chitosan-encapsulated ZnS : M (M: Fe3+ or Mn2+) quantum dots for fluorescent labelling of sulphate-reducing bacteria

Abstract

Chitosan-encapsulated Mn2+andFe^{3+}−dopedZnScolloidalquantumdots(QDs)weresynthesizedusingchemicalprecipitationmethod.Thoughtherearemanyreportsonbio−imagingapplicationsofZnSQDs,thepresentstudyfocussedonthenewtypeofmicrobial−inducedcorrosivebacteriaknownassulphate−reducingbacteria,Thiobacillusnovellus.Sulphate−reducingbacteriacanobtainenergybyoxidizingorganiccompoundswhilereducingsulphatestohydrogensulphide.Thiscancreateaprobleminengineeringindustries.Whenmetalsareexposedtosulphatecontainingwater,waterandmetalinteractsandcreatesalayerofmolecularhydrogenonthemetalsurface.Sulphate−reducingbacteriathenoxidizethehydrogenwhilecreatinghydrogensulphide,whichcontributestocorrosionforinstance,inpipelinesofoilandgasindustries.Inthisstudy,detectionandlabellingofsulphate−reducingbacteriaisdemonstratedusingfluorescentQDs.ChitosancappedZnSQDsweresynthesizedusingdopantsatdifferentdopingconcentrations.UV–Visspectroscopy,XRDandFTIRcharacterizationsweredonetoidentifytheopticalbandgapenergy,crystalplanesanddeterminethepresenceofcappingagent,respectively.Themorphologyandtheaverageparticlesizeof3.5\pm 0.2$ nm were analysed using TEM which substantiated UV–Vis and XRD results. Photoluminescence spectroscopy detected the bacteria attachment to the QDs by showing significant blue shift in bacteria conjugated ZnS QDs. Fluorescence microscopy confirmed the fluorescent labelling of QDs to Thiobacillus novellus bacteria cells making them ideal for bio-labelling applications.