Synthesis and Photostability of Unimolecular Submersible Nanomachines: Toward Single-Molecule Tracking in Solution

Self-Healing Dyes-Keeping the Promise?

Self-healing dyes have emerged as a new promising class of fluorescent labels. They consist of two units, a fluorescent dye and a photostabilizer. The latter heals whenever the fluorescent dye is in danger of taking a reaction pathway toward photobleaching. We describe the underlying concepts and summarize the developmental history and state-of-the-art, including latest applications in high-resolution microscopy, live-cell, and single-molecule imaging. We further discuss remaining limitations, which are (i) lower photostabilization of most self-healing dyes when compared to solution additives, (ii) limited mechanistic understanding on the influence of the biochemical environment and molecular oxygen on self-healing, and (iii) the lack of cheap and facile bioconjugation strategies. Finally, we provide ideas on how to further advance self-healing dyes, show new data on redox blinking caused by double-stranded DNA, and highlight forthcoming work on intramolecular photostabilization of fluorescent proteins.

Light-Activated Organic Molecular Motors and Their Applications

Molecular motors are at the heart of cellular machinery, and they are involved in converting chemical and light energy inputs into efficient mechanical work. From a synthetic perspective, the most advanced molecular motors are rotators that are activated by light wherein a molecular subcomponent rotates unidirectionally around an axis. The mechanical work produced by arrays of molecular motors can be used to induce a macroscopic effect. Light activation offers advantages over biological chemically activated molecular motors because one can direct precise spatiotemporal inputs while conducting reactions in the gas phase, in solution and in vacuum, while generating no chemical byproducts or waste. In this review, we describe the origins of the first light-activated rotary motors and their modes of function, the structural modifications that led to newer motor designs with optimized rotary properties at variable activation wavelengths. Presented are molecular motor attachments to surfaces, their insertion into supramolecular structures and photomodulating materials, their use in catalysis, and their action in biological environments to produce exciting new prospects for biomedicine.

Redefining the photo-stability of common fluorophores with triplet state quenchers: mechanistic insights and recent updates

Light microscopy can offer certain advantages over electron microscopy in terms of acquiring detailed insights into the biological/intra-cellular milieu. In recent years, with the development of new fluorescence imaging technologies, it has become extremely important to assess the role of designing appropriate fluorophores in acquiring desired biological information without encountering any untoward hitches. Over the years, external fluorophores have been prevalently used in fluorescence microscopy and single-molecule fluorescence microscopy-based studies. Photostable fluorogenic probes with high extinction coefficients and quantum yields, exhibiting minimum autofluorescence and photobleaching properties, are preferred in single-molecule microscopy as they can tolerate long-term laser exposure. Therefore, the development of triplet state quenchers and/or any other suitable new strategy to ensure the photo-stability of the fluorophores during long-term live cell imaging exercises is highly anticipated. In this feature article, various strategies for stabilizing fluorophores, including the mechanisms of TSQ-induced stabilization, have been thoroughly reviewed considering contemporary literature reports and applications.