Voltammetric determination of the Alzheimer's disease-related ApoE 4 gene from unamplified genomic DNA extracts by ferrocene-capped gold nanoparticles

A sensitive method is described for detection of the apoE 4 gene detection which is important for early diagnosis of Alzheimer's disease. It is based on signal amplification by using ferrocene(Fc) capped gold nanoparticlesmodified withstreptavidin. The immobilized oligonucleotide probe captures complementary apoE 4 gene. This is followed by the specific recognition of theGCGC sequences which are hydrolyzedby the restriction enzyme HhaI. Cleavage only occurs at the complementary apoE 4 duplex, while mismatches prevent enzymatic cleavage. Thus, the apoE 4 sequence can be discriminated against other apoE sequences. Benefitting from amplified signal by Fc-capped nanoparticle/streptavidin and the recognition of HhaI, the detection limit is as low as 0.1 pM of the ApoE 4 gene. Four genomic DNA samples extracted from blood were analyzed for the presence of the apoE 4 gene. The approach presented here will provide viable proof-of-principle for an enzyme-assisted electrochemical assay for the apoE 4 gene in genomic DNAs.