Nathan Stevens

A covalently linked phenanthridine–ruthenium(II) complex as a RNA probe

A phenanthridine derivative covalently linked to a ruthenium complex yields an imaging probe whose fluorescence intensity and lifetime change substantially in the presence of RNA.

FLEth RNA intercalating probe is a convenient reporter for small interfering RNAs.

Here we report that the phenanthridine derivative covalently linked to a fluorescein moiety (FLEth) can act as a fluorescence based probe for duplex short interfering RNA (siRNA) and that this probe can also be used to report on protein-RNA interactions. A fluorescence resonance energy transfer (FRET) signal that is observed at 600 nm occurs when FLEth is complexed with siRNA. At least 2 molecules of FLEth can bind to 21 nt duplex siRNA, and the dissociation constants for these interactions are reported. We find that FLEth can also report on the interaction of siRNAs with the Carnation Italian ringspot viral suppressor of RNA silencing p19. FLEth does not bind to the siRNA-p19 complex nor can p19 bind to the siRNA-FLEth complex; rather FLEth can report on the fraction of siRNA that is unbound. FLEth can also bind siRNA in delivery systems such as liposomes. Once the siRNA reaches the interior of Huh 7.5 cells, FLEth dissociates from the siRNA and is found in the nucleoli suggesting that FLEth cannot bind to siRNAs that are associated with the RNA silencing machinery.

Nonlinear optical switching properties of dye-doped inorganic/organic nanocomposite films

The sol–gel method has been employed in the fabrication of composite films consisting of nanometer size self-assembled organic mesostructures surrounded by a silica framework. The hydrophobic domains within the mesostructures make these films an excellent host matrix for the donor/acceptor energy transfer complexes. Time-resolved fluorescence and transient absorption studies revealed that these complexes exhibit ultrafast nonlinear optical responses as a result of the energy transfer process. The optical properties of these composite films may make them suitable for use as the photonic film in future all-optical switching devices.

COUMARIN DYE AS A FLUORESCENCE SENSOR FOR METHANOL VAPOR

The sol-gel method has been employed in the fabrication of mesoporous composite films consisting of a nonionic surfactant, Pluronic P123, as the organic component, and silica as the inorganic component. The hybrid nature of these films resulted in their having an internal structure consisting of nanometer size self-assembled organic mesostructures surrounded by a silica framework. These films served as the host matrix for the laser dye coumarin 481 (C481) and an energy transfer complex formed between C481 and J-aggregated meso-tetra(4-sulfonatophenyl)porphyrin (TSPP). Upon exposure to methanol vapor, a rapid and reversible decrease in fluorescence intensity occurs for films containing C481 alone as well as containing both C481 and TSPP. Steady-state and time-resolved spectroscopic studies suggest that the decrease in fluorescence intensity is primarily due to an excited state interaction between methanol and C481; while, additionally, morphological changes within the film appear to play a role for films containing both C481 and TSPP.