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Hypochlorous acid (HOCl) is a crucial reactive oxygen species in biological systems, and its abnormal metabolism is associated with various diseases. Therefore, it is essential to accurately detect HOCl to understand its biological function and develop related therapeutic strategies for diseases. In this work, we developed a novel fluorescence probe, BCy-S , based on the twisted intramolecular charge transfer (TICT) mechanism for rapid and sensitive detection of HOCl in an aqueous solution. The probe exhibited a significant turn-on fluorescence response to HOCl, with high selectivity, rapid kinetics (less than 40 s), large Stokes shift (about 170 nm), and low detection limit (35.2 nM), based on the specific oxidation reaction of HOCl with sulfur atoms. Additionally, the outcomes of the bioimaging experiment showed that BCy-S was capable of real-time fluorescence visualization of HOCl in living HeLa cells and zebrafish. The development of BCy-S presents a new tool for investigating the physiological function of HOCl and its pathological role in diseases. [Display omitted] • A new TICT-based HOCl fluorescent probe has been designed and developed. • The probe exhibits an excellent sensitivity, large Stokes Shift and low detection limit to HOCl. • The probe could be applied for real-time fluorescence imaging of HOCl in live HeLa cells and zebrafish. [ABSTRACT FROM AUTHOR]

Monoamine oxidase A (MAO-A) is involved in various diseases such as heart failure (HF), prostate cancer (PCa), psychiatric disorders, etc. The precise sensing of MAO-A is important to elucidate its function in various biological processes, as well the diagnosis and treatment of related diseases. In this research, we created a brand-new fluorescence probe ANET for the specific detection of MAO-A. Propylamine moiety of ANET was specifically recognized for MAO-A and then the product EHBT was released. A well-calculated p K a value of 8.01 ± 0.02 was achieved for EHBT by pH-dependent spectra. The fluorescence at 700 nm of EHBT was observed at pH 8.0 due to the enhanced intramolecular charge transfer (ICT). The fluorescence intensity of EHBT at 559/700 nm was in a linear relationship with MAO-A concentration in the 0.375–1.50 μg/mL range. The detection limit was 19.8 ng/mL. It is well known that the environment of mitochondria is microalkaline (pH 8.0), however, other organelles are neutral or acidic. So the fluorescence at 700 nm of ANET could be notably turned on by MAO-A in mitochondria. In addition, ANET can selectively accumulate in the mitochondria through powerful electrostatic attractions. Finally, ANET was applied for specific imaging of MAO-A in mitochondria of SH-SY5Y, PC-3, and glucose-deprived (GD) H9c2 cells. [Display omitted] • A probe was developed for Monoamine Oxidases A (MAO-A) based on ICT. • ANET can selectively accumulate in the mitochondria through strong electrostatic interactions. • Since the p K a of EHBT matches the pH in mitochondria, fluorescence of EHBT can be specifically turned on at 700 nm. • ANET was capable of differentiating MAO-A overexpressing cells from other cells. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new N-oxide based and turn on fluorescent probe for Fe2+ was developed. • The probe possessed a high selectivity for Fe2+ among various biologically relevant species and fast rapid response. • Monitoring Fe2+ with TPM fluorescence imaging for the first time. Abstract Iron is an essential element for human body, involved in important biochemical processes in the body, especially in biological oxidation. Misregulation of iron levels in the cell is concerned with serious diseases. Here, a novel two photon and turn on NIR-fluorescent probe based ICT for detection of Fe2+ is first reported. The probe exhibited brilliant selectivity and excellent sensitivity (DL = 4.5 μM), rapid response (15 min) and "naked-eye colorimetric sensor" for monitoring of Fe2+. More importantly, the probe was successfully applied to real-time monitor Fe2+ in living cell through two-photon microscopy fluorescence imaging with excitation 680 nm. [ABSTRACT FROM AUTHOR]

Herein we report a new carbazole-benzo[e]indolium dye (CEBI) as a ratiometric fluorescent and chromogenic probe for sulfite (SO 3 2− ) detection based on intramolecular charge transfer (ICT) mechanism. Upon treatment with SO 3 2− , the probe CEBI displayed a remarkable fluorescence ratiometric response (∼560-fold fluorescenc enhancement) together with a color change from red to weak red and a large shift (135 nm) in emission wavelength. The experimentally observed changes in the spectral features of the probe upon addition of SO 3 2− were systematically studied using high resolution electrospray ionization mass spectrometry (HR-ESI–MS), proton nuclear magnetic resonance ( 1 H NMR), and time-dependent density functional theory (TDDFT) calculations. We found a linear relationship between the ratio of fluorescence intensities at 465 nm and 600 nm ( F 465 /F 600 ) and SO 3 2− concentration over the range of 0–40 μM with a detection limit of 0.025 μM. Moreover, the novel probe demonstrated fluorescence imaging of SO 3 2− in living cells and zebrafish, suggesting its potential in clinical diagnostics. [ABSTRACT FROM AUTHOR]

A supramolecular fluorescent probe based on double-cavity nor-seco -cucurbit[10]uril (ns -Q[10]) was constructed using the non-covalent host-guest interactions between ns -Q[10] and positively charged Astrazon Pink FG (APFG). The intramolecular charge transfer (ICT) effect induces the APFG@ ns -Q[10] probe to emit strong orange-red fluorescence. APFG@ ns -Q[10] exhibits desirable optical properties and low toxicity, and has been successfully applied to the imaging of HK2 and HeLa cells. When APFG@ ns -Q[10] interacts with ClO-, the C C double bond in APFG is oxidized and the molecule is cleaved, which leads to the fluorescence is quenched. The specificity and sensitivity of APFG@ ns -Q[10] to ClO- allows it to be used for the detection and tracking of ClO- in cells. APFG@ ns -Q[10] demonstrates good biocompatibility, which is an excellent foundation for its application in cell imaging. • A supramolecular fluorescent probe based on ns -Q[10])was constructed using the non-covalent host-guest interactions. • APFG@ ns -Q[10] exhibits desirable optical properties and low toxicity, and was applied to the cell imaging. • The specificity and sensitivity of APFG@ ns -Q[10] to ClO- allows it to be used for the detection of ClO- in cells. [ABSTRACT FROM AUTHOR]

We report a novel turn-on two-photon fluorescent probe ( TPNF ) for detecting formaldehyde based on aza-Cope rearrangement and intramolecular charge transfer (ICT). The probe, containing a 1,8-naphthalimide dye with a homoallylamino group, has was shown with high selectivity, sensitivity and low cytotoxicity and it was capable of detecting formaldehyde in live cells. Moreover, a time-dependent density functional theory (TD-DFT) calculation was performed to demonstrate the turn on mechanism of the probe via ICT effect. Finally, a zebrafish larvae imaging experiment reveals that TPNF displayed a significant signal change when treated with FA in vivo. These results indicated that TPNF is a promising tool in more biomedical researches. [ABSTRACT FROM AUTHOR]

Fluorescence imaging plays an increasingly important role in biomedicine field due to its superior sensitivity and selectivity along with dynamic, real-time, in situ monitoring the occurrence and development of biological events. Therefore, it is crucial to construct a near-infrared (NIR) fluorescent molecule with excellent optical properties. Herein a NIR robust out mitochondria-targeting dye NN has been designed, synthesized and characterized, whose fluorescence properties are easily adjusted by changing the substitution position of the nitro group at the benzene ring in this fluorescent dye. NN was a unique fluorescence-enhanced nitro dye with high fluorescence quantum yields∼0.17, a large Stokes shift∼120 nm and stable chemical structure. Encouraged by this, a novel fluorescent probe NN - Sec based on intramolecular charge transfer (ICT) was constructed by grafting NN with a selenocysteine (Sec) recognition group 2,4-dinitrobenzenesulfonyl (DNBS), and it exhibited a targeted ability with great sensitivity and selectivity. Subsequently, the probe was used for NIR imaging in living cells and mice, and deep imaging results further illustrate its potential application in biosystems. The successful design of NN and NN - Sec offer a valuable theoretical basis and technical support for investigating the occurrence and development of Sec-related diseases. • A novel NIR fluorescent dye NN bearing nitro was reported with an enhanced fluorescence quantum yields. • The recognition group 2,4-dinitrobenzenesulfonyl of Sec was grafted with dye NN to synthesize fluorescent probe NN-Sec. • ANN-Sec can detect Sec in live cells and mice by high sensitivity and selectivity, accompanied by bright NIR emission. [ABSTRACT FROM AUTHOR]