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Target DNA fragments at 10 fM concentration (approximately 6 X 10s molecules) were detected against a DNA background simulating the noncomplementary genomic DNA present in real samples using a simple, PCR- free, optics-free approach based on electromechanical signal transduction. The development of a rapid, sensitive, and cost-effective nucleic add detection platform is highly desired for a range of diverse applications. We previously described a potentially low-cost device for sequence-specific nudeic add detection based on conductance change measurement of a pore blocked by electrophoretically mobilized bead-(peptide nudeic add probe) conjugates upon hybridization with target nudeic acid. Here, we demonstrate the operation of our device with longer DNA targets, and we describe the resulting improvement in the limit of detection (LOD). We investigated the detection of DNA oligomers of 110, 235, 419, and 1613 nucleotides at 1 pM to 1 fM and found that the LOD decreased as DNA length increased, with 419 and 1613 nudeotide oligomers detectable down to 10 fM. In addition, no false positive responses were obtained with noncomplementary, control DNA fragments of similar length. The 1613-base DNA oligomer is similar in size to 16S rRNA, which suggests that our device may be useful for detection of pathogenic bacteria at clinically relevant concentrations based on recognition of species-specific 16S rRNA sequences. [ABSTRACT FROM AUTHOR]