Dye-sensitized solar cells have provided a model to inexpensively harness solar energy, but the underlying physics that limit their efficiency are still not well understood. Researchers in the Fecko Group, published in the Journal of Physical Chemistry C, probe electron injection in sensitized nanocrystalline TiO2 films using time-correlated single photon counting (TCSPC) to measure time-dependent chromophore photoluminescence quenching.
The time-dependent emission exhibits kinetics that become faster and more dispersive with increasing ionic concentrations in both water and acetonitrile. The scientists quantify these trends by fitting the data using several kinetic models. Even more notably, they show that the residual emission under conditions that favor efficient electron injection exhibits a power-law decay in time. They attribute this highly dispersive kinetic behavior to electron injection from the dye into localized acceptor states of the TiO2 nanoparticle film, which exhibits a distribution of injection rate constants that depend on the energetic distribution of sub-band-gap trap states.
Single-molecule fluorescence imaging of DNA-binding proteins has enabled detailed investigations of their interactions. However, the intercalating dyes used to visually locate DNA molecules have the undesirable effect of photochemically damaging the DNA through radical intermediaries. Unfortunately, this damage occurs as single-strand breaks (SSBs), which are visually undetectable but can heavily influence protein behavior. Researchers in the Fecko Group, as published in Analytical Biochemistry, have investigated the formation of SSBs on DNA molecules by the dye YOYO-1 using complementary single-molecule imaging and gel electrophoresis-based damage assays.
The single-molecule assay imaged hydrodynamically elongated lambda DNA, enabling the real-time detection of double-strand breaks (DSBs). The gel assay, which used supercoiled plasmid DNA, was sensitive to both SSBs and DSBs. This enabled the quantification of SSBs that precede DSB formation. Using the parameters determined from the gel damage assay, the researchers applied a model of stochastic DNA damage to the time-resolved DNA breakage data, extracting the rates of single-strand breakage at two dye staining ratios and measuring the damage reduction from the radical scavengers ascorbic acid and β-mercaptoethanol. These results enable the estimation of the number of SSBs that occur during imaging and are scalable over a wide range of laser intensities used in fluorescence microscopy.