Search PubMed⌕ Search

Biomedical subjects

Alan J Heeger

Publications and source records attributed to Alan J Heeger.

24 records · Page 2Linked to original sources
PubMed2003

Templating organic semiconductors via self-assembly of polymer colloids.

A route for producing semiconducting polymer blends is demonstrated in which a doped pi-conjugated polymer is forced into a three-dimensionally continuous minor phase by the self-assembly of colloidal particles and block copolymers. The resulting cellular morphology can be viewed as a high-internal phase polymeric emulsion. Compared with traditional blending procedures, this process reduces the percolation threshold for electrical conductivity by a factor of 10, increases the conductivity by several orders of magnitude, and simultaneously improves thermal stability. Following this route, new applications can be envisaged for semiconducting polymer blends that require only minimal concentrations of doped pi-conjugated polymer.

Journal Article↗
PubMed2003

DNA hybridization detection with water-soluble conjugated polymers and chromophore-labeled single-stranded DNA.

A sensor is provided that detects single-stranded deoxyribonucleic acid (ssDNA) with a specific base sequence. The ssDNA sequence sensor comprises an aqueous solution containing a cationic water-soluble conjugated polymer [in this case, poly(9,9-bis(6'-N,N,N-trimethylammonium)-hexyl)-fluorene phenylene), 1] with a ssDNA labeled with a dye (in this case, fluorescein). The emission of light from the sensor solution with the wavelength characteristic of the probe oligonucleotide indicates the presence of ssDNA with a specific base sequence complementary to that of the probe ssDNA-fluorescein. Maximum energy transfer from 1 to the signaling chromophore occurs when the ratio of polymer chains to DNA strands is approximately 1:1. Energy transfer from 1 results in a fluorescein emission that is more intense than that observed by direct excitation of the chromophore. Furthermore, the decrease in energy transfer upon addition of electrolyte indicates that electrostatic forces dominate the interactions between 1 and DNA.

Bacillus anthracis↗
PubMed2002

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

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.

Base Sequence↗
PubMed2002

High-efficiency fluorescence quenching of conjugated polymers by proteins.

The fluorescence of the water-soluble anionic conjugated polymer, poly[lithium 5-methoxy-2-(4-sulfobutoxy)-1,4-phenylenevinylene] (MBL-PPV), is quenched in dilute aqueous solution by cytochrome c, a small, naturally occurring electron-transfer protein. The large value obtained for the Stern-Volmer constant (K(sv) = 3.2 x 10(8) at pH 7.4, and approximately 10(9) in acidic solutions) is attributed to a combination of two factors: (1) facile ET between the luminescent semiconducting polymer and the protein and (2) the Columb attraction between the oppositely charged polyelectrolytes. This system shows significant potential for biosensor applications.

Biosensing Techniques↗
PubMed2001

Biosensors from conjugated polyelectrolyte complexes.

A charge neutral complex (CNC) was formed in aqueous solution by combining an orange light emitting anionic conjugated polyelectrolyte and a saturated cationic polyelectrolyte at a 1:1 ratio (per repeat unit). Photoluminescence (PL) from the CNC can be quenched by both the negatively charged dinitrophenol (DNP) derivative, (DNP-BS(-)), and positively charged methyl viologen (MV(2+)). Use of the CNC minimizes nonspecific interactions (which modify the PL) between conjugated polyelectrolytes and biopolymers. Quenching of the PL from the CNC by the DNP derivative and specific unquenching on addition of anti-DNP antibody (anti-DNP IgG) were observed. Thus, biosensing of the anti-DNP IgG was demonstrated.

Animals↗