Tuesday, October 4, 2011

three dimensions, and consider the shape of a DNA helix

Only the first two base-pairs are shown, but then we show all parts of the sugar–phosphate chains. These chains wrap as spirals around an imaginary cylindrical surface of radius 9Å, and each sugar ring is represented by a dot. a side view of the cylinder for just one of the two sugar–phosphate chains. Here the phosphates, P0, P1, P2, etc. – counting from the top – are drawn as open circles, and the same lengths of 6.0Å, 3.3Å, and 5Å that were found for our skew-ladder characterize the path of these phosphates through space. Finally, a top view along the vertical axis of the DNAcylinder. Again, for the sake of sim-plicity, only one chain is shown, and the phosphates along it arelabeled P0, P1,…, P10. Each successive phosphate in this view lies 3.3Å further away from us than the one before. The chain is shown with a break between P10 and P0, because P11 lies directly behind P0 in
this view: it is 11 3.3Å 36Åfurther away from us, when we look down into the plane of the paper.
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Bioelectronic DNA detection involves forming an electronic circuit mediated by nucleic acid hybridization and it serves as the basis for a DNA detection system called eSensor™ [1-4]. This system uses low-density DNA chips containing electrodes coated with DNA capture probes. Target DNA present in the sample hybridizes specifically both to capture probes and ferrocene labeled signal probes in solution thereby generating an electric current. Currente Sensor DNA chips contain as many as 36 electrodes for simultaneous detection of multiple pathogens from a single sample.

Many pathogens cause both acute and chronic disease at relatively low copy number and may be difficult or impossible to propagate in culture. Thus, most pathogen detection systems rely on nucleic acid amplification by using polymerase chain reaction (PCR). One highly effective amplification strategy targets conserved sequences among the family of organisms of interest. Such broad-range PCR strategies have been used to identify and characterize several known and previously uncharacterized bacteria [5,6] and viruses [7,8]. In order to maximize the utility of these effective pathogen nucleic acid amplification systems, amplification needs to be coupled with rapid, sensitive, and specific detection. Bioelectronic DNA detection by use of the eSensor chip might fulfill this need.

Human papillomaviruses (HPV) serve as an ideal model system for determining the efficiency and feasibility of eSensor DNA detection technology since there are at least 30 distinct genital HPV types that can be effectively amplified with broad-range consensus PCR primers. We designed two eSensor chips, each containing 14 probes specific for the conserved L1 region of the HPV genome. We evaluated clinical cervical cytology samples known to contain one or more HPV types. The eSensor DNA detection platform successfully detected the correct HPV type in most of these clinical samples, demonstrating that the system provides a rapid, sensitive, specific, and economical approach for multiple-pathogen detection and identification from a single sample.Background We used human papillomaviruses (HPV) as a model system to evaluate the utility of a nucleic acid, hybridization-based bioelectronic DNA detection platform (eSensor) in identifying multiple pathogens.