title: Design of Environmentally Responsive Fluorescent Polymer Probes for Cellular Imaging.
abstract: We report the development of environmentally responsive fluorescent polymers. The reversible temperature-induced phase transition of copolymers composed of N-isopropylacrylamide and a fluorescent monomer based on the fluorescein (FL), coumarin (CO), rhodamine (RH), or dansyl (DA) skeleton was used as a molecular switch to control the fluorescence intensity. The poly(N-isopropylacrylamide) (PNIPAAm) chain showed an expanded coil conformation below the lower critical solution temperature (LCST) due to hydration, but it changed to a globular form above the LCST due to dehydration. Through the combination of a polarity-sensitive fluorophore with PNIPAAm, the synthetic fluorescent polymer displayed a response to external temperature, with the fluorescence strength dramatically changing close to the LCST. Additionally, the P(NIPAAm-co-FL) and P(NIPAAm-co-CO) polymers, containing fluorescein and coumarin groups, respectively, exhibited pH responsiveness. The environmental responsiveness of the reported polymers is derived directly from the PNIPAAm and fluorophore structures, thus allowing for the cellular uptake of the fluorescence copolymer by RAW264.7 cells to be temperature-controlled. Cellular uptake was suppressed below the LCST but enhanced above the LCST. Furthermore, the cellular uptake of both P(NIPAAm-co-CO) and P(NIPAAm-co-RH) conjugated with a fusogenic lipid, namely, l-α-phosphatidylethanolamine, dioleoyl (DOPE), was enhanced. Such lipid-conjugated fluorescence probes are expected to be useful as physiological indicators for intracellular imaging.
authors.affiliation: Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan.
authors.forename: Arisa
authors.initials: A
authors.lastname: Yamada
authors.affiliation: Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hiruta
authors.affiliation: Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.affiliation: Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Ayano
authors.affiliation: Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan.
authors.forename: Hideko
authors.initials: H
authors.lastname: Kanazawa
mesh_terms: D000178:Acrylamides / Q000737:chemistry; D000180:Acrylic Resins / Q000737:chemistry; D058948:Cell Tracking; D003374:Coumarins / Q000737:chemistry; D019793:Fluorescein / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057054:Molecular Imaging; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D012235:Rhodamines / Q000737:chemistry; D013696:Temperature
chemical_list: C496906:1-myristoyl-2-(12-((5-dimethylamino-1-naphthalenesulfonyl)amino)dodecanoyl)-sn-glycero-3-phosphocholine; D000178:Acrylamides; D000180:Acrylic Resins; D003374:Coumarins; D005456:Fluorescent Dyes; D010713:Phosphatidylcholines; D011108:Polymers; D012235:Rhodamines; C052970:poly-N-isopropylacrylamide; C030123:coumarin; C067295:N-isopropylacrylamide; D019793:Fluorescein