Electronic transduction of DNA sensing processes on surfaces: Amplification of DNA detection and analysis of single-base mismatches by tagged liposomes

Tagged, negatively charged, liposomes are used to amplify DNA sensing proce sses. The analyses of the target DNA are transduced electrochemically by us ing Faradaic impedance spectroscopy, or by microgravimetric measurements wi th Au-quartz crystals. By one method, a probe oligonucleotide (1) is assemb led on Au-electrodes or Au-quartz crystals. The formation of the double-str anded assembly with the analyte DNA (2) is amplified by the association of the 3-oligonucleotide-functionalized liposomes to the sensing interface. Th e target DNA is analyzed by this method with a sensitivity limit that corre sponds to 1 x 10(-12) M. A second method to amplify the sensing of the anal yte involves the interaction of the 1-functionalized electrode or Au-quartz crystal with the target DNA sample (2) that is pretreated with the biotiny lated oligonucleotide (4). The formation of the three-component double-stra nded assembly between 1/2/4 is amplified by the association of avidin and b iotin-labeled liposomes to the sensing interfaces. By the secondary associa tion of avidin and biotin-tagged liposomes, a dendritic-type amplification of the analysis of the DNA is accomplished. The analyte DNA (2) is sensed b y this method with a sensitivity Limit corresponding to 1 x 10(-13) M. The biotin-tagged liposomes are also used to probe and amplify single-base mism atches in an analyte DNA. The 6-oligonucleotide-functionalized An-electrode or Au-quartz crystal was used to differentiate the single-base mismatch (G ) in the mutant (5) from the normal A-containing gene (5a). Polymerase-indu ced coupling of the biotinylated-C-base to the double-stranded assembly gen erated between 6 and 5 followed by the association of avidin and biotin-tag ged Liposomes is used to probe the single base mismatch. The functionalized liposomes provide a particulate building unit for the dendritic amplificat ion of DNA sensing.