Label-free and self-signal amplifying molecular DNA sensors based on bioconjugated polyelectrolytes

Hybrid bio/-synthetic sensory conjugated polyelectrolytes were developed to achieve selective label-free detection of target oligonucleotides with amplified fluorescence signal in solution. A completely water soluble and highly fluorescent conjugated poly(p-phenyleneethynylene) (PPE) was rationally designed and synthesized as a signal amplifying unit and chemically modified with carboxylic functional groups at the ends of the polymer chains to bioconjugate with amine functionalized single-stranded oligonucleotides as a receptor using carbodiimide chemistry. This approach allows the functional groups on the polymers to be effectively linked to DNA without any damage to the conjugated it-system of the polymers. DNA detection results using the PPE-DNA hybrid system confirmed large signal amplification by means of efficient Forster energy transfer from the energy harvesting PPE to the fluorescent dye attached to the complementary analyte DNA. To realize label-free detection, we also connected a DNA molecular beacon to the newly developed conjugated polymer as a self-signaling molecular switch. A DNA detection study by using the resulting PPE-DNA beacon and single strand analyte DNAs showed not only signal-amplification properties but also self-signaling properties.