Time resolved in cellulo studies on luminescent metal complex-based cell probes

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In Sheffield, the Thomas group have developed a series of metal complexes that can be used as cellular optical imaging probes for confocal microscopy. These probes work through luminescence, so their cell location can only be imaged when they are emissive. At the same time, in Jena, the Dietzek group have developed an entirely new, and currently unique, microscope technology: Transient Absorption Microscopy. This time resolved technique allows the photoexcited states of molecules to be probed within cells. In this six week study, probes developed in the Thomas lab will be investigated in Jena using TAM. This work has a number of aims. First, since the probes have distinctive photo-absorption profiles, their localization across a cell can be "mapped" even if they are not luminescent in that part of the cell. One of the complexes to be studied "turns on" its luminescence only when bound to nuclear DNA. The high-resolution maps will allow us to investigate where else in the cell the probe localization. In cell free studies, the emission from a second probe is "switched off" when it binds to DNA. This effect has been seen before and it is due to the DNA quenching the probe emission through a light activated electron transfer from the DNA to the metal complex. This kind of process is also known to occur when DNA is damaged by exposure to sunlight and is a cause of aging and even cancer genesis. In unpublished work involving cells, it is clear that the probe is taken up by cells and shows emission from several intracell locations, but there is no luminescence from DNA within the nucleus. It is possible that the probe does not get into the nucleus at all, but it seems likely that the effect is due to DNA quenching within cells. The experiments in Germany will resolve thus issue and potentially provide the first opportunity to investigate within cells an important photochemical process involving DNA.