A highly sensitive strand specific DNA assay, which consists of a peptide nucleic acid (PNA) probe, a cationic conjugated polymer (PFVP), and self-assembled polystyrene beads in microwell arrays on silicon chip, is reported. PFVP, as an efficient signal amplifier and signal reporter, has been specially designed and synthesized to be compatible with commercial confocal microscopes for sensing on solid substrates. The assay operates on the net increase in negative charge at the PNA surface that occurs upon single-stranded DNA hybridization, which subsequently allows complex formation with the positively charged PFVP to favor energy transfer between the polymer and Cy5-labeled target. With maximized surface contact provided by bead arrays and signal amplification provided by PFVP, this assay allows detection of ∼300 copies of Cy5-labeled DNA using a commercial confocal microscope. In addition, the same strategy is also extended for label-free DNA detection with a detection sensitivity of 150 attomole. Excellent discrimination against single nucleotide polymorphism (SNP) is also demonstrated for both Cy5-labeled and label-free target detection. This study indicates that cationic conjugated polymers have great potential to be incorporated into the widely used microarray technology for simplified process with improved detection sensitivity.
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