Photoactivation and saturated emission in blended conjugated polymer nanoparticles.

Blended poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT)/poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) conjugated polymer nanoparticles were prepared and characterized by conventional and single-particle fluorescence spectroscopy. The particles exhibit red emission and improved quantum efficiency resulting from highly efficient energy transfer from donor PFBT to acceptor MEH-PPV as well as suppression of MEH-PPV aggregation. Photobleaching results indicate better photostability in the blended sample compared to undoped MEH-PPV nanoparticles and photoactivation of donor emission, which could be useful for single-molecule localization-based super-resolution microscopy. Single blended nanoparticles exhibit bright fluorescence as well as saturation behavior at very low excitation intensities. These and other properties of the blended conjugated polymer nanoparticles could provide substantial improvements in resolution when employed in super-resolution microscopy.

Conjugated polymer nanoparticles incorporating antifade additives for improved brightness and photostability.

Conjugated polymer nanoparticles with incorporated antifade agents were prepared, and ensemble and single particle measurements showed that incorporation of antifade agents effectively improves the fluorescence quantum yield and photostability of the conjugated polymer nanoparticles, likely by a combination of triplet quenching and suppression of processes involved in photogeneration of hole polarons (cations), which act as fluorescence quenchers. The photostability of conjugated polymer nanoparticles and CdSe quantum dots was compared, at both the ensemble and single particle level. The results provide confirmation of the hypothesis that quenching by photogenerated hole polarons is a key factor limiting the fluorescence quantum yield and maximum emission rate in conjugated polymer nanoparticles. Additionally, the results indicate the involvement of oxygen in photogeneration of hole polarons. The results also provide insight into the origin of quenching processes that could limit the performance of conjugated polymer devices.

Bioconjugation of ultrabright semiconducting polymer dots for specific cellular targeting.

Semiconducting polymer dots (Pdots) represent a new class of ultrabright fluorescent probes for biological imaging. They exhibit several important characteristics for experimentally demanding in vitro and in vivo fluorescence studies, such as their high brightness, fast emission rate, excellent photostability, nonblinking, and nontoxic feature. However, controlling the surface chemistry and bioconjugation of Pdots has been a challenging problem that prevented their widespread applications in biological studies. Here, we report a facile yet powerful conjugation method that overcomes this challenge. Our strategy for Pdot functionalization is based on entrapping heterogeneous polymer chains into a single dot, driven by hydrophobic interactions during nanoparticle formation. A small amount of amphiphilic polymer bearing functional groups is co-condensed with the majority of semiconducting polymers to modify and functionalize the nanoparticle surface for subsequent covalent conjugation to biomolecules, such as streptavidin and immunoglobulin G (IgG). The Pdot bioconjugates can effectively and specifically label cellular targets, such as cell surface marker in human breast cancer cells, without any detectable nonspecific binding. Single-particle imaging, cellular imaging, and flow cytometry experiments indicate a much higher fluorescence brightness of Pdots compared to those of Alexa dye and quantum dot probes. The successful bioconjugation of these ultrabright nanoparticles presents a novel opportunity to apply versatile semiconducting polymers to various fluorescence measurements in modern biology and biomedicine.