Preparation and encapsulation of highly fluorescent conjugated polymer nanoparticles

Multicolor conjugated polymer dots for biological fluorescence imaging

Highly fluorescent conjugated polymer dots were developed for demanding applications such as fluorescence imaging in live cells. These nanoparticles exhibit small particle diameters, extraordinary fluorescence brightness, and excellent photostability. Single particle fluorescence imaging and kinetic studies indicate much higher emission rates (approximately 10(8) s(-1)) and little or no blinking of the nanoparticles as compared to typical results for single dye molecules and quantum dots. Analysis of single particle photobleaching trajectories reveals excellent photostabilityas many as 10(9) or more photons emitted per nanoparticle prior to irreversible photobleaching. The superior figures of merit of these new fluorescent probes, together with the demonstration of cellular imaging, indicate their enormous potential for demanding fluorescence-based imaging and sensing applications such as high speed super-resolution single molecule/particle tracking and highly sensitive assays.

Twisted perylene dyes enable highly fluorescent and photostable nanoparticles

Polymeric fluorescent nanoparticles with covalently embedded perylene fluorophores were developed by facile synthesis strategy and their advanced features of extremely high fluorescence intensity, non-photoblinking and excellent photostability were experimentally confirmed at the single nanoparticle level.

Quantum efficiency enhancement in film by making nanoparticles of polyfluorene

We report on conjugated polymer nanoparticles of polyfluorene that were formed to exhibit higher fluorescence quantum efficiency in film (68%) and reduce undesired emission peak wavelength shifts in film (by 20 nm), compared to the solid-state polymer thin film made directly out of the same polymer solution without forming nanoparticles. Using the facile reprecipitation method, solutions of poly[9,9-dihexyl-9H-fluorene] in THF were added at different volume ratios to obtain different size distributions of nanoparticle dispersions in water. This allowed us to control the sizedependent optical emission of our polyfluorene nanoparticles. Such organic nanoparticles hold great promise for use as efficient emitters in optoelectronic device applications.

Ultrafast excited-state dynamics of nanoscale near-infrared emissive polymersomes

Formed through cooperative self-assembly of amphiphilic diblock copolymers and electronically conjugated porphyrinic near-infrared (NIR) fluorophores (NIRFs), NIR-emissive polymersomes (50 nm to 50 microm diameter polymer vesicles) define a family of organic-based, soft-matter structures that are ideally suited for deep-tissue optical imaging and sensitive diagnostic applications. Here, we describe magic angle and polarized pump-probe spectroscopic experiments that: (i) probe polymersome structure and NIRF organization and (ii) connect emitter structural properties and NIRF loading with vesicle emissive output at the nanoscale. Within polymersome membrane environments, long polymer chains constrain ethyne-bridged oligo(porphinato)zinc(II) based supermolecular fluorophore (PZn n ) conformeric populations and disperse these PZn n species within the hydrophobic bilayer. Ultrafast excited-state transient absorption and anisotropy dynamical studies of NIR-emissive polymersomes, in which the PZn n fluorophore loading per nanoscale vesicle is varied between 0.1-10 mol %, enable the exploration of concentration-dependent mechanisms for nonradiative excited-state decay. These experiments correlate fluorophore structure with its gross spatial arrangement within specific nanodomains of these nanoparticles and reveal how compartmentalization of fluorophores within reduced effective dispersion volumes impacts bulk photophysical properties. As these factors play key roles in determining the energy transfer dynamics between dispersed fluorophores, this work underscores that strategies that modulate fluorophore and polymer structure to optimize dispersion volume in bilayered nanoscale vesicular environments will further enhance the emissive properties of these sensitive nanoscale probes.

Swelling-controlled polymer phase and fluorescence properties of polyfluorene nanoparticles

Highly fluorescent nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) with distinct phases were prepared, and their photophysical properties were studied by steady state and time-resolved fluorescence spectroscopy. An aqueous suspension of PFO nanoparticles prepared by a reprecipitation method was observed to exhibit spectroscopic characteristics consistent with the glassy phase of the polymer. We demonstrate that controlled addition of organic solvent leads to partial transformation of the disordered polymer chains into the planarized conformation (beta-phase), with the fractions of each component phase dependent on the amount of solvent added. Fluorescence spectroscopy of the PFO nanoparticles containing beta-phase indicates efficient energy transfer from the glassy-phase regions of the nanoparticles to the beta-phase regions. Salient features of the nanoparticles containing beta-phase include narrow, red-shifted fluorescence and increased fluorescence quantum yield as compared to the glassy-phase nanoparticles. Fluorescence lifetime measurements indicate that the increased quantum yield of the beta-phase PFO originates from a decrease in the nonradiative decay rate, with little change in the radiative rate. This decrease is likely due to exciton trapping by the beta-phase, which leads to a reduction in the energy transfer efficiency to quencher species present within the nanoparticle.

Energy Transfer in a Nanoscale Multichromophoric System: Fluorescent Dye-Doped Conjugated Polymer Nanoparticles

We report on the fluorescence properties and the combined effects of energy diffusion and energy transfer in polyfluorene nanoparticles doped with a variety of fluorescent dyes. As the doping host, polyfluorene possesses extraordinary "light harvesting" ability, resulting in higher per-particle brightness as compared to dye-loaded silica nanoparticles of similar dimensions. Both the steady-state fluorescence spectra and time-resolved fluorescence measurements indicate highly efficient energy transfer from the host polymer to the acceptor dye molecules. A model that takes into account the combined effects of energy diffusion, Förster transfer, and particle size was developed. Comparisons of experimental data to the model results elucidate the importance of particle size and energy diffusion within the polymer in determining the optical properties of the doped conjugated polymer nanoparticles. Fluorescence quantum yields of ~40% and peak extinction coefficients of 1.5 × 10(9) M(-1)cm(-1) were determined for aqueous suspensions of ~30 nm diameter polymer nanoparticles doped with perylene or coumarin 6 (2 wt %). Photobleaching experiments indicate that energy transfer phenomena strongly influence the photostability of these dye-doped nanoparticles. Significant features of these nanoparticles include the high brightness, highly red-shifted emission spectrum, and excellent photostability, which are promising for biological labeling and sensing applications. In addition, the nanoparticles are a useful model system for studying energy transfer in dense, nanostructured, multichromophoric systems.

Energy Transfer in a Nanoscale Multichromophoric System: Fluorescent Dye-Doped Conjugated Polymer Nanoparticles

We report on the fluorescence properties and the combined effects of energy diffusion and energy transfer in polyfluorene nanoparticles doped with a variety of fluorescent dyes. As the doping host, polyfluorene possesses extraordinary "light harvesting" ability, resulting in higher per-particle brightness as compared to dye-loaded silica nanoparticles of similar dimensions. Both the steady-state fluorescence spectra and time-resolved fluorescence measurements indicate highly efficient energy transfer from the host polymer to the acceptor dye molecules. A model that takes into account the combined effects of energy diffusion, Förster transfer, and particle size was developed. Comparisons of experimental data to the model results elucidate the importance of particle size and energy diffusion within the polymer in determining the optical properties of the doped conjugated polymer nanoparticles. Fluorescence quantum yields of ~40% and peak extinction coefficients of 1.5 × 10(9) M(-1)cm(-1) were determined for aqueous suspensions of ~30 nm diameter polymer nanoparticles doped with perylene or coumarin 6 (2 wt %). Photobleaching experiments indicate that energy transfer phenomena strongly influence the photostability of these dye-doped nanoparticles. Significant features of these nanoparticles include the high brightness, highly red-shifted emission spectrum, and excellent photostability, which are promising for biological labeling and sensing applications. In addition, the nanoparticles are a useful model system for studying energy transfer in dense, nanostructured, multichromophoric systems.

The erratic emission of pyrene on gold nanoparticles

Gold nanoparticles functionalized with chromophores are known to present unpredictable fluorescence as a function of their structure. Odd-even effects, based on the number of methylene units of the chain to which the fluorophore is attached, and the nature of the anchoring group on the gold surface have, in the past, been suggested to be responsible for the behavior. Here we investigate the fluorescence processes of two newly synthesized pyrene derivatives bound to gold nanoparticles. Two structurally identical ligands, differing only in the nature of the anchoring group (a thiolate in one case and an amine in the other), were newly synthetized and attached to the gold nanoparticles. The same changes in the fluorescence properties, namely, a red spectral shift with a moderate increase of the quantum yield and a shortening of the excited-state lifetime, are observed in the two cases and ascribed to the proximity of the gold core. By comparison with the results reported for other pyrene derivatives, it has been possible to draw the conclusions that (i) the nature of the binding group does not affect the fluorescence properties of the fluorophores attached to the nanoparticle surface and (ii) much stronger fluorescence is observed in the case of pyrene separated from the gold by short alkyl chain. The unusual behavior is explained in simple terms of competing chain-chain and chromophore-chromophore interactions and by means of proper energy diagrams.

Energy transfer mediated fluorescence from blended conjugated polymer nanoparticles

Nanoparticles consisting of a derivative of the blue-emitting conjugated polymer polyfluorene doped with green-, yellow-, and red-emitting conjugated polymers were prepared by a reprecipitation method. The nanoparticles can be described as a system of densely packed chromophores that exhibit efficient energy transfer from the host to the dopant polymers. Fluorescence quenching analysis of the host polymer as a function of the dopant concentration indicates that one energy acceptor molecule can effectively quench 90% of the fluorescence of a nanoparticle consisting of 100-200 host conjugated polymer molecules. A nanoparticle energy transfer model was developed that successfully describes the quenching behavior of a small number of highly efficient energy acceptors per nanoparticle. The fluorescence brightness of the blended polymer nanoparticles was determined to be much higher than that of inorganic quantum dots and dye-loaded silica particles of similar dimensions. The combination of high fluorescence brightness and tunable fluorescence of these blended nanoparticles is promising for ultrasensitive fluorescence-based assays.

Carving Out Niches for Nanostructures: Implementation and Interplay of Building Blocks, Methods, and Tools

The number and diversity of techniques to create well-defined polymeric architectures has set the foundation to reinvent macromolecular chemistry’s tenor. This development offers the chance to build refined structures with multifaceted, cross-disciplinary applications. We discuss a few advances in the design and development of selected nanoobjects with far-reaching potential. Herein, well-defined building blocks and introduced methods to establish three-dimensional architectures will be presented. Sequential attachment strategies and tools taken from biological chemistries achieve new levels of specificity.