Preparation Of Novel Polymer Dots With High Fluorescence Quantum Yield And Bioimaging Application

Bioimaging technology is one of the research hotspot of the areas in biotechnologyand biomedicine at present. Fluorescence imaging is a technique which can be easilyused for practical application with high effective and sensitivity. In recent years, withthe development of fluorescence imaging, it has become a crucial tool for directvisualization of physiological and pathological processes observation and clinicalimaging studies. To date, more and more fluorescent with aggregation-inducedemission (AIE) or aggregation enhanced emission (AEE) characteristics weresynthesized. Polymer nano materials, which based on AIE or AEE fluorescent exhibitexcellent result in biological imaging, have attracted great attention.Against this background, we prepared some novel polymer dots with highlyefficiency by using AIE or AEE molecules and the target cell imaging ability of thesepolymer dots were explored.1. Bright fluorescence polymer dots based on DSA for Hela cell imagingHere we prepared two fluorescence polymer dots by encapsulating AEEfluorescent9,10-divinyl anthracene (DSA) with amphiphilic polymer. By using twodifferent polymer, we obtained two polymer dots (PSMA dots and PIMA dots) withdifferent encapsulation matrix (PSMA and PIMA). These two kinds of polymer dotsboth have uniform particle size distribution, spherical appearance and small particlesize (about23nm). Comparison of these two kinds of dots, The PSMA dots havehigher fluorescence quantum yield. When the mass ratio of PSMA: DSA was1:1,PSMA dots reached the highest fluorescence quantum yield (about27.3%).Catalyzed by EDC/NHS, folic acid was conjugated to the surface of the PSMA dots(1:1) and FA-dots obtained. FA-dots possess good optical properties, stability andbiocompatibility. Due to the folate group from the surface of FA-dots, the FA-dotscould mark the cells where the folate receptor was over-expressing. Our in vitro cellexperiment, FA-dots were endocytosed into Hela cells and realized the cell imaging with specific.2. Highly efficient near-infrared polymer dots based on novel AEEfluorogen for specific cancer cell imagingWe report a new near-infrared emissive molecule (2Z,2’Z)-3,3’-(2,5-di(piperidin-1-yl)-1,4-phenylene)bis(2-phenylacrylonitrile)(DPPBPA) with very large stokesshift and high solid fluorescence quantum efficiency (Φ=78%). Near-infraredpolymer dots with a high fluorescence quantum efficiency were prepared by using anamphiphilic polymer poly(styrene-co-maleic anhydride)(PSMA) as theco-encapsulation matrix and AEE molecule DPPBPA as the high near-infraredemission core. DPPBPA dots are uniform spheres with small size of about20nm andshow large Stokes shift of306nm and strong emission in the near-infrared region.The fluorescence quantum efficiency (Φ) of DPPBPA dots dispersed in water canreach20%. Streptavidin was chosen as the biomolecule covalently linked into theDPPBPA dots to form streptavidin-dots (SA-dots) which can effectively label cellsby the biotin-streptavidin interaction. The SA-dots were applied to in vitro cellularimaging. The SA-dots can effectively and specifically label target cell without anynonspecific binding.3. Fluorescence amphiphilic polymer dots based on PCL-b-PEG fortargeted cell imagingHerein, new AIE Pdots for targeting HeLa cells were developed. Thesemonodispersed AIE Pdots can be easily prepared through a self-assembly process byusing AIE conjugated amphiphilic copolymers which contain an AIE fluorophore,9,10-bis(4-hydroxystyryl)anthracene (DSA), hydrophobic poly(з-caprolactone)segments, hydrophilic poly(ethylene glycol) segments and folate groups. Thepoly(з-caprolactone), a biodegradable material with good biocompatibility, was usedas the hydrophobic segment, and the biocompatible material poly(ethylene glycol)was used as the hydrophilic segment and folate groups acted as specifically targetedgroups. The AIE Pdots have good chemical stability and colloidal stability, whichindicates that no dye leakage phenomenon was found due to the stable chemical bondbetween DSA and PCL-b-PEG. These AIE Pdots possess strong emission and highsolid state fluorescence quantum efficiency. The biocompatibility and cell uptakebehavior of the folic acid modified AIE Pdots were further investigated using two cell lines (HeLa cells and3T3-L1cells), which indicated that the folic acid modifiedAIE Pdots pose little toxicity to living cells and can be applied for targeted HeLaintracellular imaging.