Covalently Platinated DNA Oligonucleotides as Ratiometric Dioxygen Sensors

In an attempt to broaden the scope of functional nucleic acids, phosphorescent platinum(II) complexes, resembling artificial metal-containing nucleobases, were attached covalently to DNA oligonucleotides via a deoxyribose moiety. The distance between the deoxyribose and the complex was varied by selecting three different linkers (propylene, ethylene, and methylene). Stable duplexes were obtained with any of the canonical nucleobases in the complementary position. When guanine was placed in this position, the most stable duplexes were obtained. No clear correlation was found between the identity of the linker and duplex stability. When two platinum(II) complexes were placed in adjacent positions within an oligonucleotide strand, photoluminescence spectra exhibited an additional broad low-energy band due to luminescence with excimeric character, indicating Pt···Pt interactions. The ratio of monomeric and excimeric emissions depends on the linker length and, interestingly, on the presence of dioxygen. Hence, a platinated oligonucleotide was developed into a ratiometric dioxygen sensor, capable of rapidly detecting dioxygen levels in volumes as small as 2 μL. The oligonucleotide proved to be nontoxic at relevant concentrations and could be transfected into cells, where it appeared to degrade so that further modification will be necessary to obtain an oligonucleotide-based ratiometric dioxygen sensor for intracellular measurements.