A solvent-assisted ESIPT fluorescent dye for F-/Ag+ sensing and high-resolution imaging of the cilia in live cells

Design and Synthesis of ESIPT-Based Imidazole Derivatives for Cell Imaging

Excited-state intramolecular proton transfer (ESIPT)-based fluorescent molecules offer several exciting applications and are utilized most frequently as a cell imaging agent. Because of this, four distinct imidazole derivatives with ESIPT emission have been synthesized, and their fluorescence characteristics have been assessed in a variety of settings. Measurements using fluorescence spectroscopy have shown a promising candidate for cell staining, and potential candidate was specifically investigated for cell imaging uses in HT-29, MDA-MB-231, and HaCaT. Cytotoxicity of candidate molecule (1d) was analyzed using HT-29 and HaCaT cell lines, and at a dosage of 160 μM, HT-29 and HaCaT cell lines showed no signs of important cell toxicity. When spectroscopically measured, compound 1d showed no fluorescence ability in phosphate-buffered saline (PBS) solution. However, after 8 h of incubation in several cell lines, excellent fluorescence characteristics were seen in the green and red filters.

A visible BODIPY-based sensor for 'Naked-Eye' recognition of Ag+ and its application on test paper strips

In this study, a novel, highly sensitive fluorescent sensor (E)-2-((2-(benzo[d] thiazol-2-yl) quinolin-8-yl) oxy)-N'-(4-(5, 5-difluoro-1, 3, 7, 9-tetramethyl-5H-4λ4, 5λ4-dipyrrolo [1, 2-c:2', 1'-f] [1, 3, 2] diazaborinin-10-yl) benzylidene) acetohydrazide (TQB) was developed for dual mode of Ag+ detection (colorimetric/fluorescence), and its structural and spectral properties were characterized by 1H NMR, ESI-MS, X-ray, ultraviolet and fluorescence photometry. It is found that TQB could specifically and efficiently identify Ag+ among many other metal ions in CH3OH/H2O (7:3 v/v, pH = 7.23) buffer. The maximum absorption wavelength of TQB is red-shifted while its fluorescence is quenched with a quenching rate of 88.7%. The energy difference between TQB and TQB-Ag+ complex was calculated by DFT, and the applicability of TQB was verified by paper strip test. In addition, TQB has been successfully applied to the determination of Ag+ in real water samples with good reversibility and recoveries.

ESIPT-based probes for cations, anions and neutral species: recent progress, multidisciplinary applications and future perspectives

Fluorescent and colourimetric probes for small analytes (cations, anions and neutral molecules) have drawn significant attention in recent years. These probes interact with analytes and induce spectral change due to the variations in the photo-physical properties of the fluorophore/chromophore used. Among several photo-physical mechanisms, ESIPT (excited state intramolecular proton transfer) based probes are more advantageous due to their photo-physical properties viz. solvent polarity effect, large spectral shift with multi-channel fluorescence, high quantum yield etc. In recent years, ESIPT-based probes have shown several promising applications, especially monitoring small analytes in biological samples, smartphone app-assisted heavy metal detection in environmental samples, inkless writing, anti-counterfeiting applications etc. Therefore, this review is dedicated to recently reported ESIPT-based probes for small analytes. We have highlighted the organic units responsible for the ESIPT mechanism, their photo-physical parameters, selectivity and sensitivity properties and recent advances in their applications.

Protein-activated and FRET enhanced excited-state intermolecular proton transfer fluorescent probes for high-resolution imaging of cilia and tunneling nanotubes in live cells

Excited-state intermolecular proton transfer (inter-ESPT) fluorescent probes responsive to specific bioactive molecules should be greatly promising for protein sensing, DNA mutation simulating and cellular process regulating. However, the inter-ESPT molecules are recessive ESPT fluorophores, which need the assistance of other molecules with both hydrogen-bond accepting and donating abilities to turn on the tautomeric fluorescence. Valid design strategies to create powerful inter-ESPT fluorescent probes are poorly developed, particularly for proteins as targets. We recently reported a unique supramolecular strategy to trigger the inter-ESPT process based on the probe-protein recognition by H-bonding and to image protein-based subcellular structures in live cells. Herein, we found that our inter-ESPT probes (inter-ESPT-01) bearing a 2-amino-3-cyanopyridine scaffold can anchor proteins and light up the "invisible" ESPT state, so as to image the proteins or the protein-based subcellular organelles. More importantly, the inter-ESPT emission of inter-ESPT-01 can be significantly enhanced by the FRET process between amino and imino tautomers, endowing the inter-ESPT-01 probes with super-bright tautomeric fluorescence. The expressed proteins Ecallantide and MarTX were selected as the models to light up the inter-ESPT fluorescence of the probes and revealed that the inter-ESPT process can be triggered by the specific probe-protein recognition events. In the use of the super-bright inter-ESPT fluorescence, not only the proteins, but also the protein-based cilia and tunneling nanotubes (TNTs) can be specifically visualized in living cancer cells. Furthermore, such recognition-driven strategy allows us to construct a unique inter-ESPT probe to track and image specific endogenous proteins in live cells, highlighting the potential of inter-ESPT fluorogens as novel intelligent biomaterials.