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In the realm of cell research, membraneless organelles have become a subject of increasing interest. However, their ever‐changing and amorphous morphological characteristics have long presented a formidable challenge when it comes to studying their structure and function. In this paper, a fluorescent probe Nu‐AN is reported, which exhibits the remarkable capability to selectively bind to and visualize the nucleolus morphology, the largest membraneless organelle within the nucleus. Nu‐AN demonstrates a significant enhancement in fluorescence upon its selective binding to nucleolar RNA, due to the inhibited twisted intramolecular charge–transfer (TICT) and reduced hydrogen bonding with water. What sets Nu‐AN apart is its neutral charge and weak interaction with nucleolus RNA, enabling it to label the nucleolus selectively and reversibly. This not only reduces interference but also permits the replacement of photobleached probes with fresh ones outside the nucleolus, thereby preserving imaging photostability. By closely monitoring morphology‐specific changes in the nucleolus with this buffering fluorogenic probe, screenings for agents are conducted that induce nucleolar stress within living cells. [ABSTRACT FROM AUTHOR]

Long‐term super‐resolution imaging appears to be increasingly important for unraveling organelle dynamics at the nanoscale, but is challenging due to the need for highly photostable and environment‐sensitive fluorescent probes. Here, we report a self‐blinking fluorophore that achieved 12 nm spatial resolution and 20 ms time resolution under acidic lysosomal conditions. This fluorophore was successfully applied in super‐resolution imaging of lysosomal dynamics over 40 min. The pH dependence of the dye during blinking made the fluorophore sensitive to lysosomal pH. This probe enables simultaneous dynamic and pH recognition of all lysosomes in the entire cell at the single‐lysosome‐resolved level, which allowed us to resolve whole‐cell lysosome subpopulations based on lysosomal distribution, size, and luminal pH. We also observed a variety of lysosome movement trajectories and different types of interactions modes between lysosomes. [ABSTRACT FROM AUTHOR]

Although super‐resolution imaging offers an opportunity to visualize cellular structures and organelles at the nanoscale level, cellular heterogeneity and unpredictability still pose a significant challenge in the dynamic imaging of live cells. It is thus vital to develop better‐performing and more photostable probes for long‐term super‐resolution imaging. Herein, we report a probe, LD‐FG, for imaging lipid droplet (LD) dynamics using structured illumination microscopy (SIM). LD‐FG allows wash‐free imaging of LDs, owing to a hydrogen‐bond sensitive fluorogenic response. The replacement of photobleached LD‐FG by intact probe molecules outside the LDs ensures the long‐time stability of the fluorescence imaging. With this buffering fluorogenic probe, fast and unpredictable dynamic processes of LDs can be visualized. Using this probe, two LD coalescence modes were discovered. The dynamic imaging also allowed us to propose a new model of LD maturation during adipocyte differentiation, i.e. a fast LD coalescence followed by a slow ripening step. The excellent performance of LD‐FG makes the buffer strategy an effective method for designing fluorescent probes for cell dynamic imaging. [ABSTRACT FROM AUTHOR]

Subcellular pH plays a key role to modulate protein structures or specific active sites to impact diverse biological processes. The heterogeneity and high dynamics of intracellular pH require probes that can detect pH in the vicinity of the protein and have a wide pH response range. Here, we reported a protein proximity ligation fluorescent probe for super-resolution imaging of subcellular pH dynamics. Relying on SNAP-tag protein labeling technology, the pH-sensitive fluorophore BG-NDM based on photo-induced electron transfer mechanism was localized to the adjacent positions of the target protein in different subcellular organelles. The equilibrium between the non-fluorescent aggregate and the fluorogenic monomer enabled BG-NDM to have the ability of wash-free super-resolution imaging in live cells. And the wide pH response ranges from pH 6 to pH 12 made the probe have the ability of recognizing pH dynamics. The pH changes around functional proteins during mitophagy, cellular alkalosis and acidosis were revealed. Through long-term super-resolution imaging, we could further record the pH dynamics around mitochondrial proteins COX8A during mitochondrial contacts, fusion and fission at the resolution of a single mitochondria. [Display omitted] • Probe BG-NDM was used to super-resolution imaging of subcellular pH dynamics. • SNAP-tag labeling ensures that BG-NDM detects the pH near the protein of interest. • The aggregate/monomer equilibrium endowed BG-NDM wash-free imaging in living cells. • Mitochondrial pH dynamics was recorded with Long-term SIM imaging. [ABSTRACT FROM AUTHOR]

We reported fluorescent probes to image Zn2+ with plasma membrane-specific and Zn2+-specific fluorogenicities. The probes contained hydrophobic alkyl chains as membrane-anchored domains and hydrophilic zinc sensor ZTRS, and aggregated to display quenched fluorescence. Cells dissolved the aggregates and the liberated probes were dispersed on the outside of the cell plasma membrane. Aggregates that did not bind to the cell membrane still exhibited aggregation-induced fluorescence quenching after complexing with zinc ions, while probes anchored on the membrane surface exhibited a fluorescence-enhanced response upon recognition of zinc ions. [ABSTRACT FROM AUTHOR]

Charge transfer and separation are important processes governing numerous chemical reactions. Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry. Herein, we report the discovery of a new charge‐transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems, the donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 90° intramolecular rotation. TICS systems thus exhibit charge shuttling. TICSs exist in several chemical families of fluorophores (such as coumarin, BODIPY, and oxygen/carbon/silicon–rhodamine), and could be utilized to construct functional fluorescent probes (i.e. viscosity‐ or biomolecule‐sensing probes). The discovery of the TICS process expands the current perspectives of charge‐transfer processes and will inspire future applications. [ABSTRACT FROM AUTHOR]

We have, for the first time, reported a fluorescent probe (ZTRS–C18–Cd(ii) complex) which discriminated four types of surfactants. This recognition was realized depending on the transformation of ZTRS–Cd2+ binding patterns in different microenvironments formed in various types of surfactants. [ABSTRACT FROM AUTHOR]

SNAP-tag is one of most popular genetically encoded protein tags that can be labeled with fluorescent molecules for visualizing a protein of interest in live cells. Fluorogenic probes keep dark until they label protein tags, significantly improving the signal-to-noise ratio to image proteins without wash-out step. However, most of reported fluorogenic probes for SNAP-tag suffered from the low or mild labeling rate comparing with non-fluorogenic ones. In this paper, we reported a 4-amino-naphthliamide derived fluorogenic probe for SNAP-tag, which exhibited the fast record labeling rate among fluorogenic probes. Finally, we applied this probe to image proteins in mitochondria and nucleus in live cells without wash-out steps. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescent probes for hydrogen sulfide have received considerable attention because of the biological significance of H2S recognized recently. Two-photo microscopy offers advantages of increased penetration depth, localized excitation, and prolonged observation time. However, two-photon fluorescent probes for H2S are still rare. In this work, we introduced a dinitrophenyl ether group into the 4-position of 1,8-naphthalimide, which acts as the H2S reactive site, to efficiently yield compound NI–NHS as a two-photo fluorescent probe for H2S. The probe NI–NHS has a high selectivity for H2S over competitive anions and sulfide-containing analytes. This probe exhibits turn-on fluorescence detection of H2S in bovine serum and two-photon fluorescent imaging of H2S in living cells. [Copyright &y& Elsevier]

Abstract: Fluorescent probes for hydrogen sulfide have received considerable attention because of the biological significance of H2S recognized recently. However, near-infrared fluorescent probes for H2S are still rare. In this work, a new near-infrared fluorescent probe for H2S was developed based on the reduction reaction of azide with H2S to amine based on the fluorophore of dicyanomethylene-4H-chromene because of its long excitation and emission wavelength. The probe has a high selectivity for H2S over competitive anions and sulfide-containing analytes. Finally, the probe was applied to sense H2S in living cells. [Copyright &y& Elsevier]

The dye rhodamine, as the most popular scaffold to construct fluorescent labels and probes, has been explored extensively on its structure-fluorescence relationships. Particularly, the replacement of the oxygen atom in the 10th position with heteroatoms obtained various new rhodamines with improved photophysical properties, such as brightness, photostability, red-shifted emission and fluorogenicity. However, the applications of heteroatom-substituted rhodamines have been hindered by difficult synthetic routes. Herein, we explored the condensation strategy of diaryl ether analogues and o -tolualdehyde to synthesize various heteroatom-substituted rhodamines. We found that the electron property and steric effect in the rhodamine 10th position determined the synthetic yield. It's concluded that this condensation method was more suitable for the synthesis of heteroatom-substituted rhodamines with small or electron-donating groups like rhodamine, S-rhodamine and Si-rhodamine. We hope these results will benefit the design and synthesis of heteroatom-substituted rhodamines. Unlabelled Image • Heteroatom-substituted rhodamines through the condensation of diaryl ether analogues and o -tolualdehyde were synthesized. • Electron-donating moiety increased the nucleophilic ability of diaryl ether analogues and facilitated the reaction. • Rhodamines with strong electron-withdrawing moiety in the 10th position hindered the reaction and resulted poor yield. [ABSTRACT FROM AUTHOR]