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1、DNA表面密度的計(jì)算[1]ThesurfacedensityofDNA,morespecificallythenumberofnucleotidephosphateresidues,iscalculatedfromtheamountofcationicredoxmarkermeasuredattheelectrodesurface.Thesaturatedamountofcharge-compensatingredoxmarkerintheDNAmonolayer,determinedusingchronocoulometry,isdirectlyproportiona
2、ltothenumberofphosphateresiduesandtherebythesurfacedensityofDNA.Thismethodpermitsquantitativedeterminationofbothsingle-anddouble-strandedDNAatelectrodes.Surfacedensitiesofsingle-strandedDNAwerepreciselyvariedintherangeof(1-10)*1012molecules/cm2,asdeterminedbytheelectrochemicalmethod,usin
3、gmixedmonolayers.Wemeasuredthehybridizationefficiencyofimmobilizedsingle-strandedDNAtocomplementarystrandsasafunctionoftheimmobilizedDNAsurfacedensityandfoundthatitexhibitsamaximumwithincreasingsurfacedensity.WehavequantifiedthesurfacedensityofDNAbytakingadvantageoftheelectrostaticattrac
4、tionofspecificredoxcationswiththenucleotidephosphatebackbone.TherearetwotypesofinteractionsforsmallredoxmoleculeswithDNA:electrostaticattractionandintercalation.Redoxcationsexchangefornativecounterionsassociatedwiththenucleotidephosphateresiduesoftheprobe.Theamountofredoxmarker“electrost
5、aticallytrapped”attheDNA-modifiedelectrodeisthendeterminedusingchronocoulometry.Atsaturationcoverageoftheredoxmarker,thesurfacedensityoftheprobeiscalculatedassumingcompletechargecompensationoftheDNAphosphateresiduesbyredoxcations.Astrongappealofthisapproachisthatthismeasurement,unlikemea
6、surementsusingothernoncovalentlabels,isinsensitivetoboththebasecompositionandthechainorder(single-strandedvsduplex).Themeasuredredoxmarkerisdirectlyproportionaltothenumberofphosphategroupspresentatthesurface.Anattractiveaspectofchronocoulometry(計(jì)時(shí)庫(kù)倫分析法)isthatthedoublelayerchargeandthecha
7、rgeduetoreactionofspeciesadsorbedontheelectrodesurfacecanbedifferentiatedfromthechargeduetoreactionofredoxmoleculesthatdiffusetotheelectrodesurface.MCH的作用：liftstheDNAfromthesurfacetoaconformationwhereeachprobeisimmobilizedsolelythroughthethiolate.[1]固定DNA及MCH的方法[2]：atwo-s
