Analytical Sciences

Dual Temperature- and pH-Responsive Fluorescence Molecular Probe for Cellular Imaging Utilizing a PNIPAAm-Fluorescein Copolymer

Hiroki KOBAYASHI,* Mayumi NISHIKAWA,* Chikako SAKAMOTO,* Tadashi NISHIO,* Hideko KANAZAWA,* and Teruo OKANO**

*Faculty of Pharmacy, Keio University, 1-5-30 Shibakoen, Minato, Tokyo 105-8512, Japan
**Institute of Advanced Biomedical Engineering and Science, Tokyo Women's Medical University, 8-1 Kawadacho, Shinjyuku, Tokyo 162-8666, Japan

The thermally controlling fluorescence intensity of a molecular probe for cellular imaging has been investigated. A reversible temperature-induced phase transition of N-isopropylacrylamide/fluorescein copolymers [poly(NIPAAm-co-FL)] was used as a molecular switch to control the fluorescence intensity of the imaging probe. The copolymer displayed environmentally sensitive fluorescence properties, in which the fluorescence intensity changed with the response to both the temperature and the pH. Utilizing these features, we monitored the thermal-aggregation process of BSA by the fluorescence resonance energy transfer (FRET) method. Additionally, the cellular uptake in RAW264.7 cells of poly(NIPAAm-co-FL) conjugated with lipid was studied using a confocal laser scanning microscope.

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