Cyclic diguanylate (c-di-GMP) is a bacterial second messenger important for physiologic adaptation and virulence. Class-I c-di-GMP riboswitches are phylogenetically widespread and thought to mediate pleiotropic genetic responses to the second messenger. Previous studies suggest that the RNA aptamer domain switches from an extended free state to a compact, c-di-GMP-bound conformation in which two helical stacks dock side-by-side. Single molecule fluorescence resonance energy transfer (smFRET) experiments reveal that the free RNA exists in four distinct populations that differ in dynamics in the extended and docked conformations. In the presence of c-di-GMP and Mg2+, a stably docked population (>30 min) becomes predominant. smFRET mutant analysis demonstrates that tertiary interactions distal to the c-di-GMP binding site strongly modulate the RNA population structure, even in the absence of c-di-GMP. These allosteric interactions accelerate ligand recognition by pre-organizing the RNA, favoring rapid c-di-GMP binding.

Hybrid organic–inorganic perovskites demonstrate desirable photophysical behaviors and promising applications from efficient photovoltaics to lasing, but the fundamental nature of excited state species is still under debate. We collected time-resolved photoluminescence of single-crystal nanoplates of methylammonium lead iodide perovskite (MAPbI3) with excitation over a range of fluences and repetition rates to provide a more complete photophysical picture. A fundamentally different way of simulating the photophysics is developed that relies on unnormalized decays, global analysis over a large array of conditions, and inclusion of steady-state behavior; these details are critical to capturing observed behaviors. These additional constraints require inclusion of spatially correlated pairs along with free carriers and traps, demonstrating the importance of our comprehensive analysis. Modeling geminate and nongeminate pathways shows that geminate processes are dominant at high carrier densities and early times and that geminate recombination is catalyzed by free holes. Our combination of data and simulation provides a detailed picture of perovskite photophysics across multiple excitation regimes that was not previously available.

Intrinsically disordered proteins, such as tau protein, adopt a variety of conformations in solution, complicating solution-phase structural studies. We employ an anti-Brownian electrokinetic (ABEL) trap to prolong measurements of single tau proteins in solution. Once trapped, we record the fluorescence anisotropy to investigate the diversity of conformations sampled by the single molecules. A distribution of anisotropy values obtained from trapped tau protein is conspicuously bimodal while those obtained by trapping a globular protein or individual fluorophores are not. Time-resolved fluorescence anisotropy measurements are used to provide an explanation of the bimodal distribution as originating from a shift in the compaction of the two different families of conformations.

Direct tracking of lithium ions with time and spatial resolution can provide an important diagnostic tool for understanding mechanisms in lithium ion batteries. A fluorescent indicator of lithium ions, 2-(2-hydroxyphenyl)naphthoxazole, was synthesized and used for real-time tracking of lithium ions via widefield fluorescence microscopy. The fluorophore can be excited with visible light and was shown to enable quantitative determination of the lithium ion diffusion constant in a microfluidic model system for a plasticized polymer electrolyte lithium battery. The use of widefield fluorescence microscopy for in situ tracking of lithium ions in batteries is discussed.

Intrinsically disordered proteins,such as tau protein, adopt av ariety of conformations in solution, complicating solution-phase structural studies.W ee mployed an anti-Brownian electrokinetic (ABEL) trap to prolong measurements of single tau proteins in solution. Once trapped, we recorded the fluorescence anisotropyt oi nvestigate the diversity of conformations sampled by the single molecules.Adistribution of anisotropyv alues obtained from trapped tau protein is conspicuously bimodal while those obtained by trapping ag lobular protein or individual fluorophores are not. Timeresolved fluorescence anisotropym easurements were used to providea ne xplanation of the bimodal distribution as originating from as hift in the compaction of the two different families of conformations.

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Neuronal mRNA trajectories exhibit a diverse range of behaviors along tracks including cytosolic diffusion and retrograde/anterograde transport. From our analysis, we obtain detailed distributions of transport rates and diffusivities along individual mRNA trajectories, as well as the lifetimes of each state of motion. We find that the rate of anterograde transport is greater than that of retrograde transport, indicating a possible role of forwards-backwards transport of the mRNA particles in distributing these molecules throughout the cell. To illustrate the broad applicability of our approach, we also use it to classify the heterogeneous oscillatory motion of sister kinetochores during HeLa cell division. While our results are consistent with sliding window averages commonly employed to analyze kinetochore dynamics, the Bayesian HMM infers local switching and pausing dynamics that are uniquely resolved by singleparticle-based analysis.