Fluorescence quenching ethylene glycol

Thymidine phosphate and cytidine phosphate do not phosphoresce in a rigid ethylene glycol-water glass at 77°K109 when directly excited, but thymidine which has lost its proton at Nx does have a triplet which phosphoresces with a decay time of 0.50 sec at high pH uridine also fluoresces with a similar decay time. The quenching of purine fluorescence and appearance of T" fluorescence in UV-irradiated DNA and poly dAT (as well as U" fluorescence in poly rAU) was attributed by Rahn et al.109 to proton transfer from thymine to adenine. This quenches adenine fluorescence and enhances thymine fluorescence. 

A representative example of indirect imaging with SWNTs labeled with fluorescent molecules was illuminated by Dai and coworkers.102 They solubilized as-produced SWNTs via sonication with fluorescein-modified poly (ethylene glycol) (Fluor-PEG, 114 PEG units). The absorption maximum of the nanotube-attached Fluor-PEG was red shifted 3 nm from that of free fluorescein, and the fluorescence intensity was quenched about 67% in phosphate buffer solution (pH 7.4). In the bioevaluation with BT474 breast cancer cells, substantial intracellular fluorescence was observed, suggesting cellular uptake of the Fluor-PEG-functionalized SWNTs.102... 

Ultra pH-sensitive (UPS) fluorescent nanoprobes with a 355-fold signal amplification in tumor relative to blood after systemic injection were recently established [40]. UPS probes possess an ultra pH-sensitive core copolymer (poly (ethylene glycol)-b-poly (2-(hexamethyleneimino) ethyl methacrylate) with micellar transitions within 0.25 pH units, fluorophores and cRGD for broad targeting of the tumor vasculature. The pH responsiveness is based on pH-dependent micellization of the core, micellization induced self-quenching of conjugated fluorophores (homoFRET), whereas micelle dissociation in acidic conditions resulted in an increased fluorescence signal. Systemic... 

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