| Localization in specific orgenelles of targeted cells is crucial for the proteins, peptides, nucleic acids, and other bioactive macromolecules to produce desired effect. Because the acidic and enzyme environment of endosome and lysosome can destroy the structure and bioactivity of biomacromolecules, the escape from endosome is one of the key factors in subcellular delivery of biomacromolecules. pH-sensitive polymers can be degraded in acidic conditions, while are stable in neutral and alkaline condition. Therefore, biomacromolecules encapsulated by pH-sensitive polymers can be successfully delivered into cytoplasm, because the acidic conditions of endosome and lysosome accelerate the polymer degradation and the increased osmotic pressure leads the rupture of endosome. Due to their unique photochemical properties, Quantum dots (QDs) have gained widespread interests in the field of biological and medical as a new type of fluorescent probes, while the biosafety and photostability of QDs need further improved. In present study, QDs were encapsulated into pH-sensitive polymeric nanospheres by nanoprecipitation method, and the luminescence properties, acid-labile characteristics and cytotoxicity were investigated. Further more, the phagocytic index of nanospheres into cells and the migration of nanospheres within cells had been evaulated based on the luminescence properties of QDs.Galactose modified acid-liable polymers of PGBELA, acetal groups containing acid-liable polymers of PBELA, and poly(DL-lactide)-poly(ethylene glycol) (PELA) were introduced as nanospher carriers for QDs by naopreciptation method. Scanning electron microscope (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) showed that QDs encapsulated nanosphers possessed uniformly spherical and smooth features with the average size of around 200 nm. The loading efficiency of QDs in nanospheres was measured by atom absorption spectroscope (AAS), and up to 50-60% of loading efficiency was detected. The results of fluorescence spectrophotometer (FL), Fourier tansformed infrared spectroscopy (FTIR), and X-ray diffraction (XRD) indicated that there had some interactions between the polymers and QDs and that the encapsulation processes did not influence the photoluminescence properties of QDs. The photostability has been significanly improved due to the protective effect of the polymer coatings.The fluorescence decay of QDs in nanospheres, the haemolysis of red blood cells, and the matrix polymer degrdation were evaluated by incubating the nanospheres in the media with pH values of 7.4,6.0, and 5.0. The fluorescene intensity of QD/PBELA and QD/PGBELA nanospheres were rapidly decreased under acid conditions. With the reduction of pH value, both the fluorescent decay and haemolysis effect were more obvious. In vitro degrdegradation experiment confirmed that PELA nanpspheres in neutral and acid conditions had the same degradation profiles with PBELA and PGBELA nanospheres in neutral buffers, but the mass loss and molecular weight reduction of PBELA and PGBELA nanospheres were significantly higher than PELA nanospheres in the acidic environment, due to their acid-liable properties.In vitro cell experiments indicated that polymer nanospheres without QDs encapsulated had no significant influence on cell viability, while QDs-loaded nanospheres exhibited cytotoxicity in a dose-dependent manner. The phagocytic percentage of MCF-7 and NIH 3T3 cells to these three kinds of nanospheres were about 40%, and there was no significant difference. However, the cellular uptake efficiency of HepG2 cells for PGBELA nanospheres was significant greater than others, which confirmed that PGBELA naospheres had better targeting effect for HepG2 cells. Compared with QD/PELA nanospheres residing in lysosome, PGBELA nanospheres escaped from lysosome to cytoplasm and much higher fluorescene intensity was detected, which further confirmed that PGBELA nanosphere had good acid-liable and hepatic targeting properties. |
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