Hydroporphyrin-Doped Near-Infrared-Emitting Polymer Dots for Cellular Fluorescence Imaging.

Near-infrared (NIR) fluorescent semiconductor polymer dots (Pdots) have shown great potential for fluorescence imaging due to their exceptional chemical and photophysical properties. This paper describes the synthesis of NIR-emitting Pdots with great control and tunability of emission peak wavelength. The Pdots were prepared by doping poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-(2,1',3)-thiadiazole)] (PFBT), a semiconducting polymer commonly used as a host polymer in luminescent Pdots, with a series of chlorins and bacteriochlorins with varying functional groups.

Interplay of electrostatic repulsion and surface grafting density on surface-mediated DNA hybridization.

Single-molecule Förster Resonance Energy Transfer was used to observe the adsorption of fluorescently-labeled "target" DNA oligonucleotides and their association and hybridization with complementary DNA "probes" tethered to the surface as a function of surface grafting density. Ionic strength was varied systematically to disentangle the potentially competing effects of probe accessibility and electrostatic repulsion. At high ionic strength, when the Debye length was ~1 nm, the adsorption of target DNA was not significantly inhibited by the presence of tethered probe DNA, even at high grafting density, and the fraction of adsorbed target strands undergoing hybridization increased systematically with grafting density, leading to a dramatic increase in the net hybridization rate at high grafting density.

Influence of Oligonucleotide Grafting Density on Surface-Mediated DNA Transport and Hybridization.

Adsorption of soluble DNA to surfaces decorated with complementary DNA plays an important role in many bionanotechnology applications, and previous studies have reported complex dependencies of the surface density of immobilized DNA on hybridization. While these effects have been speculatively ascribed to steric or electrostatic effects, the influence of surface-mediated molecular transport (i.e.

Surface-Mediated DNA Hybridization: Effects of DNA Conformation, Surface Chemistry, and Electrostatics.

Single-molecule Förster Resonance Energy Transfer (FRET) was used to study the dynamic association of mobile donor-labeled ssDNA oligonucleotides ("target") with covalently immobilized complementary acceptor-labeled ssDNA oligonucleotides ("probe"). While probe-target association events were resolved for all experiments, such FRET events were far more likely to occur in systems with complementarity and on hydrophobic, as compared to hydrophilic, surfaces. The distribution of donor-acceptor association-time intervals did not exhibit simple first-order kinetics, and when decomposed into a superposition of first-order processes, only a small fraction of events corresponded to a long-lived state that was presumed to represent true DNA hybridization, while the majority of association events were transient, representing nonspecific associations or partial hybridization.