Developing a Singlet Oxygen Responsive Molecular Beacon Based on a Binuclear Ruthenium (II) Polypyridyl Complex

As a developed fluorescent reporter, molecular beacons have been applied to various situations for biological detection via fluorescence quenching/restoration. Photodynamic molecular beacons generate singlet oxygen in response to stimuli. A simple DNA molecular beacon conjugated with two Ruthenium compound was demonstrated to have 3-fold fluorescence increase. In order to develop a new photodynamic molecular beacon detection mechanism, a new singlet-oxygen sensing beacon was synthesized based on a novel binuclear Ruthenium compound linked with a singlet oxygen labile carbon-carbon double bond. Synthesis was confirmed by NMR, mass spectroscopy and absorption spectroscopy. An approximate 5∼6 fold quenching was observed compared to monomericic Ruthenium complex in aqueous but not in methanol. Singlet oxygen generated from another longer wavelength photosensitizer (methylene blue) was able to restore ∼4-fold emission in the binuclear Ruthenium complex.