Time-Resolved Fluorescence and Fluorescence Anisotropy of Fluorescein-Labeled Poly(N-isopropylacrylamide) Incorporated in Polymersomes

详细信息    查看全文

• 作者：Jung Seok Lee ; Rob B. M. Koehorst ; Herbert van Amerongen ; Jan Feijen
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：November 17, 2011
• 年：2011
• 卷：115
• 期：45
• 页码：13162-13167
• 全文大小：845K
• 年卷期：v.115,no.45(November 17, 2011)
• ISSN：1520-5207

文摘

The phase behavior of fluorescein isothiocyanate (FITC) labeled poly(N-isopropylacrylamide) (PNIPAAm) incorporated in polymersomes (Ps) was studied by monitoring the fluorescence lifetime (FL) and the time-resolved fluorescence anisotropy (TRFA) as a function of temperature at pH 7.4. Ps containing FITC-labeled PNIPAAm with a diameter less than 200 nm were prepared by injecting a THF solution of poly(ethylene glycol)-b-poly(d,l-lactide) (mPEG-PDLLA) and FITC tagged PNIPAAm (FITC-N) into phosphate buffered saline (PBS, pH 7.4). Solutions of free FITC (2 渭M) and FITC-N (2 渭M) in PBS were used as controls. The polarized fluorescence decay curves of FITC were fitted with one rotational correlation time (胃₁) and the corresponding amplitude (尾₁), while those for FITC-N were fitted with two rotational correlation times (胃_1,2) and their corresponding amplitudes (尾_1,2). Short rotational correlation times, 胃₁, correspond with the rotation of the FITC molecule itself, whereas 胃₂ corresponds to FITC-segmental rotation. FITC-N encapsulated in Ps (FITC-N/Ps) showed a decrease of the rotational motion upon increasing the temperature. The long rotational correlation time (胃₂) of FITC-N increased 3 fold, going from 15 to 40 掳C, reflecting a reduced rotational mobility. The residual anisotropy (尾_鈭?/i>) of FITC-N/Ps at pH 7.4 showed a gradual increase, going from 15 to 25 掳C followed by a gradual decrease at higher temperatures. These results are explained by a transition from coil to globule, a gradual increase of intermolecular aggregation, and possibly phase separation and hydrogel formation.