title: A ratiometric fluorescent metal ion indicator based on dansyl labeled poly(N-isopropylacrylamide) responds to a quenching metal ion.
abstract: The fluorescence emission of poly(N-isopropylacrylamide) (PNIPAM) covalently tagged with a 5-(dimethylamino)naphthalene-1-sulfonyl (dansyl) fluorophore and an iminodiacetic acid (IDA) chelator changes with temperature and with Cu(II) complexation. Increasing the temperature above the lower critical solution temperature (LCST) causes the polymer to collapse from a coil to a compact globule. This changes the environment experienced by the fluorophore causing a shift in maximum emission wavelength from 546 to 508 nm and an increase in the ratio of emission intensity at 508 nm to emission intensity at 546 nm from 0.70 to almost 1.40. Metal ions can be sensed by working at a temperature where the uncomplexed polymer is in an expanded state due to the charges on the ligand. Complexation with a metal ion such as Cu(II) neutralizes the charges on the ligand causing the polymer to collapse. At 35 °C, the emission intensity maximum shifted from 535 to 510 nm as Cu(II) concentration was increased and the intensity ratio increased from 0.84 to 1.28. By decoupling complexation from fluorescence, we have prepared a ratiometric fluorescent indicator for a metal ion that normally quenches fluorescence. The affinity for Cu(II) was found to be thermally tunable. The log apparent formation constants for the indicator-Cu(II) complex were estimated as the half way point in the intensity ratio vs. pCu curve. The values were determined to be 4.3 at 35 °C and 3.2 at 34 °C respectively.
authors: Department of Chemistry, University of New Hampshire, Durham, NH 03824, USA.
authors: Jie
authors: J
authors: Du
authors: Shaojun
authors: S
authors: Yao
authors: W Rudolf
authors: WR
authors: Seitz
authors: Nicholas E
authors: NE
authors: Bencivenga
authors: Justin O
authors: JO
authors: Massing
authors: Roy P
authors: RP
authors: Planalp
authors: Randy K
authors: RK
authors: Jackson
authors: Daniel P
authors: DP
authors: Kennedy
authors: Shawn C
authors: SC
authors: Burdette
mesh_terms: D000178:Acrylamides / Q000737:chemistry; D000180:Acrylic Resins; D003300:Copper / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes; D015590:Fluorophotometry / Q000379:methods*; D008024:Ligands; D011108:Polymers / Q000737:chemistry
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D005456:Fluorescent Dyes; D008024:Ligands; D011108:Polymers; C052970:poly-N-isopropylacrylamide; D003300:Copper