Fluorescence-labeled hydrophilic nanoparticles via single-chain folding
Introduction
Fluorescent labeling of biomolecules has become an obbligato tool in many biological studies like cell imaging, molecular interaction, and photodynamic therapy [1], [2]. There are different types of fluorescent labeling agents, mainly organic dyes or fluorescing nanoparticles. Fluorescing nanoparticles often show improved optical properties (such as enhanced photostability and larger Stokes shift than conventional organic fluorophores), better localized within a cell than a molecularly dissolved dye, as well as maximized sensitivity [1]. Such nanoparticles include inorganic semiconductor quantum dots(QDs) [3], dye-doped silica particles [4], and dye-loaded polymer nanoparticles [2], which have some disadvantages, like limited dye loading for dye-doped silica or dye-loaded polymer nanoparticles, and cytotoxicity for use of QDs [3]. Among the technologies developed to prepare polymer nanoparticles, one is the dispersion of preformed polymers, including microphase inversion [5], nanopreciptation [6], self-assembly of block copolymers into micelles followed by chemical crosslinking(20–200 nm) [7]; the other is the polymerization of monomers in dispersed medium, such as emulsion polymerization(50–200 nm), microemulsion technique (20–50 nm) [8], as well as the synthesis of discrete spherical macromolecules like dendrimers(1–10 nm) [9]. A strategy involving the collapse and intramolecular crosslinking of polymers to give single-chain nanoparticles(1–20 nm) has also been reported [10], [11]. However, to functionalize the polymer nanoparticles is still challenging. In the present study, fluorescence-labeled polymers are synthesized from azide functionalized polymers, propargyl ether functionalized anthracene, as well as benzoxazine monomers via click chemistry. These linear polymers can undergo intramolecular crosslinking to give single-chain nanoparticles with fluorescence.
Section snippets
Experimental
Propargyl bromide(~80 vol% in toluene) was from Aldrich Co. N-(4-hydroxyphenyl) acetamide, tetrabutylammonium bromide, 9-anthracene methanol, sodium hydride(60%), paraformaldehyde, copper(I) bromide, N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), phenol, 1,4-dioxane, and other chemicals were all analytical grade and from Shanghai Chemical Reagent Co. 3-(4-Ethoxyphenyl)-3,4-dihydro-2H-benzo[e] [1], [3] oxazine (P-APPE) and St/MMA/1-(azidomethyl)-4-vinylbenzene copolymer(PS-N3) were
Results and discussion
PS-N3, 2 reacted with P-APPE and P-AN in the presence of CuBr/PMDETA (Fig. 1), and styrenic copolymers containing pendent anthracene and benzoxazine were obtained. The extent of conversion of the side azido moieties is monitored by 1H NMR spectroscopy by observing the disappearance of the protons on methylene adjacent to azido groups (N3-CH2Ph) at 4.25 ppm and the appearance of the new methylene protons adjacent to triazole ring at 5.36 ppm (triazole-CH2Ph). Moreover, the band corresponding to –N3
Conclusion
In summary, styrenic copolymers with benzoxazine and anthracene groups can be synthesized from PS-N3, 3-(4-ethoxyphenyl)-3,4-dihydro-2H-benzo[e] [1], [3] oxazine, and 9-((prop-2-ynyloxy) methyl) anthracene via click chemistry. The fluorescence-labeled hydrophilic nanoparticles are prepared via single-chain folding and intramolecular crosslinking of the copolymers in ultradiluted solution. The dimension of the polymer nanoparticles can be controlled in 5–20 nm. The hydrophilic nanoparticles
Acknowledgments
The project is sponsored by National Natural Science Foundation of China (21144006), and Research Fund for the Doctoral Program of Higher Education (20120072110062).
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