Polymerizable Fluorescein Derivatives: Synthesis of Fluorescent Particles and Their Cellular Uptake

Fluorescent Copolymers for Bacterial Bioimaging and Viability Detection

Novel fluorescent labels with high photostability and high biocompatibility are required for microbiological imaging and detection. Here, we present a green fluorescent polymer chain (GFPC), designed to be nontoxic and water-soluble, for multicolor bioimaging and real-time bacterial viability determination. The copolymer is synthesized using a straightforward one-pot reversible addition-fragmentation chain-transfer (RAFT) polymerization technique. We show that GFPC does not influence bacterial growth and is stable for several hours in a complex growth medium and in the presence of bacteria. GFPC allows the labeling of the bacterial cytoplasm for multicolor bacterial bioimaging applications. It can be used in combination with propidium iodide (PI) to develop a rapid and reliable protocol to distinguish and quantify, in real time, by flow cytometry, live and dead bacteria.

Novel fluorescein polymer-based nanoparticles: facile and controllable one-pot synthesis, assembly, and immobilization of biomolecules for application in a highly sensitive biosensor

A key aspect of biochip and biosensor preparation is optimization of the optical or electrochemical techniques that combine high sensitivity and specificity. Among them, optical techniques such as the use of fluorescent polymeric nanoparticles have resulted in dramatic progress in the field of diagnostics due to their range of advantages. We herein report a facile approach for the development of novel fluorescein polymeric nanoparticles (FPNPs) with immobilization of specific biomolecules for application in a highly sensitive optical biosensor. A series of three amphiphilic fluorescein polymers (poly(FMA-r-NAS-r-MA)), comprising hydrophobic fluorescein O-methacrylate (FMA), hydrophilic N-acryloxysuccinimide (NAS), and methacrylic acid (MA) monomers were synthesized through radical polymerization. In an aqueous environment, these fluorescein polymers self-assembled into spherical shaped nanoparticles with a well-defined particle size, narrow particle size distribution, and enhanced fluorescence properties. The bio-immobilization properties of the FPNPs were also tunable by control of the activated N-hydroxysuccinimide ester group in the polymer series. Furthermore, the fluorescence sensitivity of bovine serum albumin detection by the FPNPs indicates that the limit of detection and sensitivity were improved compared to conventional fluorescence dye-labelled proteins. These novel FPNPs therefore represent a suitable technology for disease diagnosis and biomarker detection to ultimately improve the sensitivity of existing analytical methodologies in a facile and cost-effective manner.

We report a facile approach for the development of novel fluorescein polymeric nanoparticles (FPNPs) with immobilization of specific biomolecules for application in a highly sensitive optical biosensor.

Emission-Color Control in Polymer Films by Memorized Fluorescence Solvatochromism in a New Class of Totally Organic Fluorescent Nanogel Particles

In this work, a new class of totally organic fluorescent nanogel particles and their exceptionally specific behaviors based on their unique structures are introduced, which draws a sharp line from conventional fluorophore-doped and fluorophore-branched-type particles. The nanogel particles, the diameter of which could be controlled by adjusting reaction conditions, such as the solvent system, were spontaneously fabricated with a spherical shape by direct polymerization of non-heterocyclic aromatic compounds, such as 2,6-dihydroxyanthracene, 2,6-dihydroxynaphthalene, and 9,9-bis(4-hydroxyphenyl)fluorene with triazinane as the cross-linker. A fluorophoric moiety formed from a polymer main chain was realized in the particle, and consequently, the resultant content of the fluorophoric moiety was around 70-80 wt % per particle. The uniqueness and versatility of the particles can be emphasized by their good compatibility with various solvents due to their amphiphilic and ampholytic swelling properties, but also by their remarkable fluorescent solvatochromism in the dispersion state. Furthermore, these behaviors were preserved even in their polymer composite system. This study also demonstrates that various fluorescent polymer films can be fabricated with emission color control due to memorization of the solvatochromism phenomenon of the dispersed fluorescent nanoparticles.

Surface Charge-Dependent Cellular Uptake of Polystyrene Nanoparticles

The evaluation of the role of physicochemical properties in the toxicity of nanoparticles is important for the understanding of toxicity mechanisms and for controlling the behavior of nanoparticles. The surface charge of nanoparticles is suggested as one of the key parameters which decide their biological impact. In this study, we synthesized fluorophore-conjugated polystyrene nanoparticles (F-PLNPs), with seven different types of surface functional groups that were all based on an identical core, to evaluate the role of surface charge in the cellular uptake of nanoparticles. Phagocytic differentiated THP-1 cells or non-phagocytic A549 cells were incubated with F-PLNP for 4 h, and their cellular uptake was quantified by fluorescence intensity and confocal microscopy. The amount of internalized F-PLNPs showed a good positive correlation with the zeta potential of F-PLNPs in both cell lines (Pearson’s r = 0.7021 and 0.7852 for zeta potential vs. cellular uptake in THP-1 cells and nonphagocytic A549 cells, respectively). This result implies that surface charge is the major parameter determining cellular uptake efficiency, although other factors such as aggregation/agglomeration, protein corona formation, and compositional elements can also influence the cellular uptake partly or indirectly.

Intrinsically fluorescent and highly functionalized polymer nanoparticles as probes for the detection of zinc and pyrophosphate ions in rabbit serum samples

Intrinsically fluorescent polymer nanoparticles (F-PNPs) were synthetized from 2-hydroxy-5-methylisophthalaldehyde and melamine by solvothermal method. F-PNPs can emit strong yellow green fluorescence at 542 nm without the conjugation to any external fluorescent agent and surface modification. Owing to the abundant amino and hydroxyl groups on their surface, the F-PNPs possess multiple binding sites, good biocompatibility and excellent water-solubility. Addition of Zn²⁺ to the F-PNPs solution resulted in a blue shift (Δλ=40 nm) with obvious enhancement in the fluorescence intensity at 502 nm; while there was negligible change in the presence of other metal ions. The subsequent treatment with pyrophosphate (PPi) can cause fluorescence recovery of F-PNPs by pulling the Zn²⁺ out of the coordination cavity of F-PNPs-Zn²⁺ nanocomposites. No interference was observed from other anions and nucleotides, making the F-PNPs-Zn²⁺ ensembles highly sensitive and selective nanoprobes for PPi. The detection limit is 2.75 × 10^-8 M/L and 7.63 × 10^-8 M/L for Zn²⁺ and PPi, respectively. The proposed nanoprobes were then used for detecting the recovery of Zn²⁺ and PPi in rabbit serum samples, which were found to be 99.4-104.2% and 98.6-104.7%, respectively. The present strategy for the fabrication of nanoparticles may offer a new sight for the preparation of polymer nanostructures. The F-FNPs based probes can provide an accurate method for the detection of Zn²⁺ and PPi in serum samples.

Incorporation of Coumarin-Based Fluorescent Monomers into Co-Oligomeric Molecules

With the purpose of modifying organic fluorescent dyes based on the coumarin scaffold, and developing and evaluating a route to its incorporation into a polymeric backbone, a study was conducted on the co-polymerization of 3-vinylcoumarins with styrene and methyl acrylate using 2,2-azobis(isobutyronitrile) (AIBN) as the radical initiator. The structural and photophysical characterization proved the incorporation of the coumarin monomers into the polymeric chain and further showed a decrease in the fluorescence quantum yields in the co-oligomers.

Synthesis and optimization of a reactive oxygen species responsive cellular delivery system

Reactive oxygen species responsive delivery systems for the detection of peroxides in live macrophages have been designed. The oxidative cleavage of a boronic ester to a phenol triggered by hydrogen peroxide followed by self-immolation of a ROS-sensitive cleavable linkervia1,6-elimination allowed the disturbance of the fluorescence resonance energy transfer turning on the near-infrared fluorescence.

Controlled core-to-core photo-polymerisation – fabrication of an optical fibre-based pH sensor

The fabrication of fluorescence-based pH sensors, embedded into etched pits of an optical fibre via highly controllable and spatially selective photo-polymerisation is described and the sensors validated.

Fluorescent Polymer Nanoparticles Based on Dyes: Seeking Brighter Tools for Bioimaging

Speed, resolution and sensitivity of today's fluorescence bioimaging can be drastically improved by fluorescent nanoparticles (NPs) that are many-fold brighter than organic dyes and fluorescent proteins. While the field is currently dominated by inorganic NPs, notably quantum dots (QDs), fluorescent polymer NPs encapsulating large quantities of dyes (dye-loaded NPs) have emerged recently as an attractive alternative. These new nanomaterials, inspired from the fields of polymeric drug delivery vehicles and advanced fluorophores, can combine superior brightness with biodegradability and low toxicity. Here, we describe the strategies for synthesis of dye-loaded polymer NPs by emulsion polymerization and assembly of pre-formed polymers. Superior brightness requires strong dye loading without aggregation-caused quenching (ACQ). Only recently several strategies of dye design were proposed to overcome ACQ in polymer NPs: aggregation induced emission (AIE), dye modification with bulky side groups and use of bulky hydrophobic counterions. The resulting NPs now surpass the brightness of QDs by ≈10-fold for a comparable size, and have started reaching the level of the brightest conjugated polymer NPs. Other properties, notably photostability, color, blinking, as well as particle size and surface chemistry are also systematically analyzed. Finally, major and emerging applications of dye-loaded NPs for in vitro and in vivo imaging are reviewed.

Soft fluorescent nanomaterials for biological and biomedical imaging

Soft fluorescent nanomaterials have attracted recent attention as imaging agents for biological applications, because they provide the advantages of good biocompatibility, high brightness, and easy biofunctionalization. Here, we provide a survey of recent developments in fluorescent soft nano-sized biological imaging agents. Various soft fluorescent nanoparticles (NPs) (including dye-doped polymer NPs, semiconducting polymer NPs, small-molecule organic NPs, nanogels, micelles, vesicles, and biomaterial-based NPs) are summarized from the perspectives of preparation methods, structure, optical properties, and surface functionalization. Based on both optical and functional properties of the nano-sized imaging agents, their applications are then reviewed in terms of in vitro imaging, in vivo imaging, and cellular-process imaging, by means of specific or nonspecific targeting.

Surface charge determines the lung inflammogenicity: A study with polystyrene nanoparticles

Surface functionalization is a routine process to improve the behavior of nanoparticles (NPs), but the induced surface properties, such as surface charge, can produce differential toxicity profiles. Here, we synthesized a library of covalently functionalized fluorescent polymeric NPs (F-PLNPs) to evaluate the role of surface charge on the acute inflammation and the localization in the lung. Guanidinium-, acetylated-, zwitterionic-, hydroxylated-, PEGylated-, carboxylated- and sulfated-F-PLNPs were synthesized from aminated-F-PLNP. The primary particle sizes were identical, but the hydrodynamic sizes ranged from 210 to 345 nm. Following surface functionalization, the F-PLNPs showed diverse zeta potentials from -41.2 to 31.0 mV, and each F-PLNP showed a single, narrow peak. Pharyngeal aspiration with these eight types of F-PLNPs into rats produced diverse acute lung inflammation, with zeta potentials of the F-PLNPs showing excellent correlation with acute pulmonary inflammation parameters including the percentage of polymorphonuclear leukocytes (R(2) = 0.90, p < 0.0001) and the levels of interleukin-1β (R(2) = 0.83, p < 0.0001) and of cytokine-induced neutrophil chemoattractant-3 (R(2) = 0.86, p < 0.0001). These results imply that surface charge is a key factor influencing lung inflammation by functionalized polymeric NPs, which further confirms and extends the surface charge paradigm that we reported for pristine metal oxide NPs. This demonstrates that the surface charge paradigm is a valuable tool to predict the toxicity of NPs.

Enzymatic multi-functionalization of microparticles under aqueous neutral conditions

Enzymatic multi-functionalization of microparticles under aqueous neutral conditions using tyrosinase.

Chiral, fluorescent microparticles constructed by optically active helical substituted polyacetylene: preparation and enantioselective recognition ability

Novel chiral fluorescent microparticles derived from helical substituted polyacetylene were prepared. The microparticles showed enantioselective recognition ability in both heterogeneous and homogeneous systems.

Fluorescent cross-linked polystyrene perylenebisimide/oligo(p-phenylenevinylene) microbeads with controlled particle size, tunable colors, and high solid state emission

A series fo cross-linked fluorescent polystyrene (PS) microbeads with narrow size distribution and intense solid state emission was developed. Fluorophores based on perylene bisimide (PBI) and oligo(p-phenylenevinylene) (OPV) designed as acrylic cross-linkers were introduced into the polymerization recipe in a two-stage dispersion polymerization, carried out in ethanol in the presence of poly(vinylpyrrolidone) (PVP) as stabilizer. The structural design permitted introduction of up to 10(-5) moles of the fluorophores into the polymerization medium without fouling of the dispersion. The particle size measured using dynamic light scattering (DLS) indicated that they were nearly monodisperse with size in the range 2-3 μm depending on the amount of fluorophore incorporated. Fluorescence microscope images of ethanol dispersion of the sample exhibited intense orange red emission for PS-PBI-X series and green emission for PS-OPV-X series. A PS incorporated with both OPVX and PBIX exhibited dual emission upon exciting at the OPV wavelength of 350 nm and PBI wavelength of 490 nm, respectively. The low incorporation of fluorophore resulted in almost complete absence of aggregation induced reduction in fluorescence as well as red-shifted aggregate emission. The solid state emission quantum yield measured using integrating-sphere setup indicated a very high quantum yield of ϕpowder = 0.71 for PS-OPV-X and ϕpowder = 0.25 for PS-PBI-X series. The cross-linked PS microbeads incorporating both OPV and PBI chromophores had a ϕpowder = 0.33 for PBI emission and ϕpowder = 0.20 for OPV emission. This strategy of introducing fluorophore as cross-linkers into the PS backbone is very versatile and amenable to simultaneous addition of different suitably designed fluorophores emitting at different wavelengths.