DNA detection using water-soluble conjugated polymers and peptide nucleic acid probes

Abstract

The light-harvesting properties of cationic conjugated polymers are used to sensitize the emission of a dye on a specific peptide nucleic acid (PNA) sequence for the purpose of homogeneous, "real-time" DNA detection. Signal transduction is controlled by hybridization of the neutral PNA probe and the negative DNA target. Electrostatic interactions bring the hybrid complex and cationic polymer within distances required for Förster energy transfer. Conjugated polymer excitation provides fluorescein emission >25 times higher than that obtained by exciting the dye, allowing detection of target DNA at concentrations of 10 pM with a standard fluorometer. A simple and highly sensitive assay with optical amplification that uses the improved hybridization behavior of PNA/DNA complexes is thus demonstrated.

Scheme 1.

Schematic representation for the use of a water-soluble CP with a specific PNA-C* optical reporter probe to detect a complementary ssDNA sequence.

Scheme 2.

Molecular structure of 1 and the PNA-C* and DNA sequences.

Fig 1.

Absorption [(a) green and (c) orange] and emission [(b) blue and (d) red] spectra of polymer 1 and single-stranded PNA probe 2, respectively. Fluorescence was measured by exciting at 380 and 480 nm, for 1 and 2, respectively.

Fig 2.

Emission spectra of PNA-C* in the presence of complementary [(a) red] and noncomplementary [(b) black] DNA by excitation of polymer 1. Conditions are in water at pH = 5.5. The spectra are normalized with respect to the emission of polymer 1.

Scheme 3.

Molecular structure of 4.

Fig 3.

Emission spectra of PNA-C* in the presence of complementary [(a) red] and noncomplementary [(b) black] DNA by excitation of 4. Conditions are in water and pH = 5.5. The spectra are normalized with respect to the emission of 4.