High-efficiency Near-infrared Fluorescent Nanoparticles For Bioimaging

Fluorescent nanoparticles(FNPs) have recently attracted increasing attention in the biomedical field because of their unique optical properties, easy fabrication and outstanding performance in imaging. Compared with conventional molecular probes including small organic dyes and fluorescent proteins, FNPs based on aggregation-induced emission(AIE) fluorogens have shown significant advantages in tunable emission and brightness, good biocompatibility, superb photo- and physical stability, potential biodegradability and facile surface functionalization. Fluorescent nanoparticles based on fluorophores with intense emission in the far-red /near-infrared(FR/NIR)(650 –900 nm) region have attracted much interest due to their low photodamage, deep tissue penetration and minimal auto-fluorescence from biological substrates in this wavelength range. However, there are only limited reports on red AIE fluorescent nanoparticles, and the AIE fluorophores with intense emission in the far-red /near-infrared(FR/NIR)(650 –900 nm) region are also limited. Against this background, we designed and synthesised some new FR/NIR AIE or AEE molecules. Thanks to the bright emission in the aggregation for the AIE properties of these molecules, we have prepared some ultra bright nanoparticles with FR/NIR emission. And the nanoparticles could be applied effectively in bioimaging.1. Bright Fluorescent Magnetic Polymer Nanoparticles For Near-infrared Cell ImagingHere, we present a strategy to fabricate fluorescent magnetic polymer nanoparticles Fe3O4/DPPBPA@F-127 with bright near-infrared fluorescence, strong magnetism and superparamagnetism, by using oleic acid coated magnetic Fe3O4(OA-Fe3O4) and an aggregation enhanced emission(AEE) molecule(2Z, 2’Z)-3, 3’-(2, 5-di(piperidin-1-yl)-1, 4-phenylene) bis(2-phenylacrylonitrile)(DPPBPA) as the core, and biocompatible polymer Pluronic F-127 as the encapsulation matrix. The DPPBPA molecule shows strong red emission(Ф=78%) peaked at 654 nm in solid state. During the nanoparticle formation, OA-Fe3O4 and DPPBPA tended to entangled with the hydrophobic domains of Pluronic F-127 to afford the hydrophobic interiors, while the hydrophilic domains of Pluronic F-127 extended into the aqueous phase, which makes the nanoparticles stable in the aqueous suspension. The nanoparticles can stain in cytoplasm with a strong red fluorescent signal, and pose little toxicity to living cells.2. Bright Near-infrared Fluorescent Nanoparticles Based on FRET Effect for BioimagingWe demonstrate a generally applicable protocol to encapsulate hydrophobic AIE fluorophores into the biocompatible Pluronic F-127 NPs for cellular imaging and efficiently enhance the red AEE fluorophore emission through fluorescence resonance energy transfer(FRET). An AEE molecule 2-(4-bromophenyl)-3-(4-(4-(diphenylamino) styryl) phenyl) fumaronitrile(TPABDFN) with near-infrared emission(704nm) was synthesized and selected as the FRET acceptor.(2-p-tolylethene-1,1,2-triyl)tribenzene(TPE-Me) a blue-emitting AIE molecule, was selected as a FRET donor. By encapsulating both TPE-Me donor and TPABDFN acceptor simultaneously within the NPs, a significant FRET effect is induced, which contributes to the notable increase of acceptor emission. In addition, the obtained TPE-Me/TPABDFN co-loaded F127 NPs show a large Stokes shift of 275 nm, which can be used to avoid the interference between excitation and emission light, as well as shift the emission spectrum away from the sample auto-fluorescence to result in high detection sensitivity. Using the Pluronic F127 as the encapsulation matrix, the FRET NPs show bright fluorescence signals and low cytotoxicity. These results indicate that the FRET NPs can serve as efficient fluorescent probes for biological imaging.3. Ultra Bright Fluorescent Nanoparticles for Two-Photon BioimagingWe report the design and synthesis of two aggregation enhanced emission(AEE) fluorescent molecule TPABDFN and 2TPABDFN. With the near-infrared emission(691nm and 702 nm, respectively), the fluorescence quantum yield of TPABDFN and 2TPABDFN are 5.9% and 19.1%. The Stokes shift of TPABDFN and 2TPABDFN both reach to about 200 nm, which is beneficial for the bio-application. PSMA,PIMA and Pluronic F-127 were used to encapsulate different amounts of TPABDFN and 2TPABDFN to prepare fluorescent nanoparticles. Thanks to the excellent properties of the polymers, the nanoparticles show uniform size, spherical morphology and good water dispersibility. The effect of spatial confinement and interactions between these AIE dyes and the hydrophobic core of polymeric micelles on their photophy-sical properties were systematically investigated using micelles formed from three amphiphilic block copolymers. In addition, by using PSMA as the co-encapsulation matrix, the obtained eccentrically loaded NPs show eccentric increase of fluorescence quantum yield(19.6% and 34.0%, respectively). And on the contrary, the other two kinds of polymers were not have this kind of phenomenon. The ulbra bright NPs have been successfully applied for cellular imaging of A549 cancer cells. For the large amounts of carboxyl in the surface of the NPs, many kinds of functional groups could be modified on the partiles. So that, we believe that the ulbra bright NPs will have good application prospect in biological field.