The interactions between a small molecule and G-quadruplexes are visualised by fluorescence lifetime imaging microscopy

Guanine-rich oligonucleotides can fold into quadruple-stranded helical structures known as G-quadruplexes. Mounting experimental evidence has gathered suggesting that these non-canonical nucleic acid structures form in vivo and play essential biological roles. However, to date, there are no small-molecule optical probes to image G-quadruplexes in live cells. Herein, we report the design and development of a small fluorescent molecule, which can be used as an optical probe for G-quadruplexes. We demonstrate that the fluorescence lifetime of this new probe changes considerably upon interaction with different nucleic acid topologies. Specifically, longer fluorescence lifetimes are observed in vitro for G-quadruplexes than for double- and single-stranded nucleic acids. Cellular studies confirm that this molecule is cell permeable, has low cytotoxicity and localizes primarily in the cell nucleus. Furthermore, using fluorescence lifetime imaging microscopy, live-cell imaging suggests that the probe can be used to study the interaction of small molecules with G-quadruplexes in vivo

Direct imaging of changes in aerosol particle viscosity upon hydration and chemical aging

Organic aerosol particles (OA) play major roles in atmospheric chemistry, climate, and public health. Aerosol particle viscosity is highly important since it can determine the ability of chemical species such as oxidants, organics or water to diffuse into the particle bulk. Recent measurements indicate that OA may be present in highly viscous states, however, diffusion rates of small molecules such as water are not limited by these high viscosities. Direct observational evidence of kinetic barriers caused by high viscosity and low diffusivity in aerosol particles were not available until recently; and techniques that are able to dynamically quantify and track viscosity changes during atmospherically relevant processes are still unavailable for atmospheric aerosols. Here we report quantitative, real-time, online observations of microscopic viscosity changes in aerosol particles of atmospherically relevant composition, using fluorescence lifetime imaging (FLIM) of viscosity. We show that microviscosity in ozonated oleic acid droplets and secondary organic aerosol (SOA) particles formed by ozonolysis of myrcene increases substantially with decreasing humidity and atmospheric oxidative aging processes. Furthermore, we found unexpected heterogeneities of microviscosity inside individual aerosol particles. The results of this study enhance our understanding of organic aerosol processes on microscopic scales and may have important implications for the modeling of atmospheric aerosol growth, composition and interactions with trace gases and clouds.Engineering and Physical Sciences Research Council (Career Acceleration Fellowship (Grant ID: EP/I003983/1), Prize studentship), Natural Environment Research Council (Studentship NE/J500070/1), European Research Council (Grant ID: 279405), Max Planck Society, European Union project PEGASOS (Grant ID: 265148

Direct imaging of changes in aerosol particle viscosity upon hydration and chemical aging

Organic aerosol particles (OA) play major roles in atmospheric chemistry, climate, and public health. Aerosol particle viscosity is highly important since it can determine the ability of chemical species such as oxidants, organics or water to diffuse into the particle bulk. Recent measurements indicate that OA may be present in highly viscous states, however, diffusion rates of small molecules such as water are not limited by these high viscosities. Direct observational evidence of kinetic barriers caused by high viscosity and low diffusivity in aerosol particles were not available until recently; and techniques that are able to dynamically quantify and track viscosity changes during atmospherically relevant processes are still unavailable for atmospheric aerosols. Here we report quantitative, real-time, online observations of microscopic viscosity changes in aerosol particles of atmospherically relevant composition, using fluorescence lifetime imaging (FLIM) of viscosity. We show that microviscosity in ozonated oleic acid droplets and secondary organic aerosol (SOA) particles formed by ozonolysis of myrcene increases substantially with decreasing humidity and atmospheric oxidative aging processes. Furthermore, we found unexpected heterogeneities of microviscosity inside individual aerosol particles. The results of this study enhance our understanding of organic aerosol processes on microscopic scales and may have important implications for the modeling of atmospheric aerosol growth, composition and interactions with trace gases and clouds.Engineering and Physical Sciences Research Council (Career Acceleration Fellowship (Grant ID: EP/I003983/1), Prize studentship), Natural Environment Research Council (Studentship NE/J500070/1), European Research Council (Grant ID: 279405), Max Planck Society, European Union project PEGASOS (Grant ID: 265148

Tuning the sensitivity of fluorescent porphyrin dimers to viscosity and temperature

Conjugated porphyrin dimers have emerged as versatile viscosity‐sensitive fluorophores that are suitable for quantitative measurements of microscopic viscosity by ratiometric and fluorescence lifetime‐based methods, in a concentration‐independent manner. Here, we investigate the effect of extended conjugation in a porphyrin‐dimer structure on their ability to sense viscosity and temperature. We show that the sensitivity of the fluorescence lifetime to temperature is a unique property of only a few porphyrin dimers