DNA hybridization; electrochemical biosensor; enzyme-linked assay; trinucleotide repeat expansion; neurodegenerative diseases; osmium

Molecular diagnostics of inherited neurodegenerative disorders such as fragile X syndrome, myotonic dystrophy or Friedreich ataxia (FRDA) is based on analysis of the length of trinucleotide repetitive sequences in certain loci of genoimc DNA. The current methods employ PCR and electrophoretic determination of the amplified DNA fragment size. We have recently shown that length of a triplet repetitive DNA sequence can be determined using a double-surface electrochemical technique involving multiple hybridizaton of the expanded triplet repeat with short labeled reporter probe (spanning several trinucleotides). Here we propose a single-surface sensor employing an analogous principle. Target DNA (tDNA) is adsorbed onto surface of a carbon (pyrolytic graphite or screen-printed) electrode. Biotin-labeled reporter probe (RP) is hybridized with the immobilized tDNA followed by binding of streptavidin-alkaline phosphatase (ALP) Conjugate.