An ɑ-ketoamide-based fluorescent probe via aggregation induced emission for ONOO- detection in vivo.

Fluorescent rotors with aggregation-induced emission (AIE) and organelle-targeting properties have attracted great attention for sensing subcellular viscosity changes, which could help understand the relationships of abnormal fluctuations with many associated diseases. Despite the numerous efforts spent, it remains rare and urgent to explore the dual-organelle targeting probes and their structural relationships with viscosity-responsive and AIE properties. Therefore, in this work, we reported four meso-five-membered heterocycle-substituted BODIPY-based fluorescent probes, explored their viscosity-responsive and AIE properties, and further investigated their subcellular localization and viscosity-sensing applications in living cells. Interestingly, the meso-thiazole probe 1 showed both good viscosity-responsive and AIE (in pure water) properties and could successfully target both mitochondria and lysosomes, further imaging cellular viscosity changes by treating lipopolysaccharide and nystatin, attributing to the free rotation and potential dual-organelle targeting ability of the meso-thiazole group. The meso-benzothiophene probe 3 with a saturated sulfur only showed good viscosity-responsive properties in living cells with the aggregation-caused quenching effect and no subcellular localization. The meso-imidazole probe 2 showed the AIE phenomenon without an obvious viscosity-responsive property with a C═N bond, while the meso-benzopyrrole probe 4 displayed fluorescence quenching in polar solvents. Therefore, for the first time, we investigated the structure-property relationships of four meso-five-membered heterocycle-substituted BODIPY-based fluorescent rotors with viscosity-responsive and AIE properties, and among these, 1 with a C═N bond and a saturated sulfur on the meso-thiazole, potentially contributing to their corresponding AIE and viscosity-responsive properties, served as a sensitive AIE fluorescent rotor for imaging dual-organelle viscosity in both mitochondria and lysosomes.

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish

Herein, BSA-tetraphenylethene derivative conjugates with aggregation-induced emission (AIE) properties were constructed and used as fluorescent probes for label-free detection of protease and α1-antitrypsin. Conjugated AIE probes were formed based on the electrostatic induced assembly between an ammonium cation of quaternized tetraphenylethene salt and carboxyl anion groups of BSA. While water soluble quaternized tetraphenylethene salt showed very low fluorescence in its well-dispersed state, obvious enhancement in the fluorescence of the aggregated tetraphenylethene derivative on the BSA templates was achieved due to the abnormal aggregation-induced emission properties of tetraphenylethene. These BSA-tetraphenylethene derivative conjugates enabled label-free detection of protease. In the presence of trypsin, the BSA templates were enzymatically hydrolyzed and the conjugates decomposed. Therefore the quaternized tetraphenylethene molecules became increasingly isolated from each other. Accordingly, the aggregation to dispersing state change of tetraphenylethene derivative resulted in an obvious decrease in the fluorescence of the conjugates probes and enabled the sensitive and selective detection of trypsin. Furthermore, upon addition of α1-antitrypsin, the enzymatic activity of trypsin was inhibited and the fluorescence was consequently preserved. Sensitive detection of α1-antitrypsin was thus realised. The protein-tetraphenylethene derivative conjugates with aggregation-induced emission properties therefore show great promise for the monitoring of biological processes and cancer diagnostics with simplicity, high sensitivity, and rapid response.

Lipid-related cancers cause a large number of deaths worldwide. Therefore, development of highly efficient Lipid droplets (LDs) fluorescent imaging probes will be beneficial to our understanding of lipid-related cancers by allowing us to track the metabolic process of LDs. In this work, a LDs-specific NIR (λmax = 698 nm) probe, namely BY1, was rationally designed and synthesized via a one-step reaction by integrating triphenylamine (electron–donor group) unit into the structure of rofecoxib. This integration strategy enabled the target BY1 to form a strong Donor–Acceptor (D-A) system and endowed BY1 with obvious aggregation-induced emission (AIE) effect. Meanwhile, BY1 also showed observable solvent effect and reversible mechanochromatic luminescent property, which could be interpreted clearly via density functional theory (DFT) calculations, differential scanning calorimetry (DSC), powder X-ray diffraction (XPRD), and single crystal X-ray data analysis. More importantly, BY1 exhibited highly specific fluorescent imaging ability (Pearson’s correlation = 0.97) towards lipid droplets in living HeLa cells with low cytotoxicity. These results demonstrated that BY1 is a new promising fluorescent probe for lipid droplets imaging, and it might be beneficial to facilitate biological research of lipid-related cancers.

Fluorescence bioimaging is considered an indispensable technique in biological research due to its high sensitivity, excellent spatial and temporal resolution, non-invasiveness, rapid and real-time responsiveness, as well as its ease of accessibility. Among these, fluorescence probes play a pivotal role in fluorescence imaging technology thanks to their strong specificity, high sensitivity, rapid response, and straightforward implementation. Aggregation-Induced Emission (AIE) molecules exhibit a unique phenomenon: they emit weak or no fluorescence when dissolved in a solution but become highly luminescent under aggregated/clustering conditions. Leveraging this, fluorescent probes with AIE characteristics often demonstrate fluorescence activation under conditions of spontaneous aggregation or binding with analytes, showcasing high sensitivity and exceptional signal-to-noise ratios. Consequently, fluorescence probes based on the distinctive optical properties of AIE hold immense potential for applications in fluorescence bioimaging. This paper primarily investigates the synthesis properties and applications in biosensing of a series of novel organic fluorescence probes with aggregation-induced emission (AIE) characteristics. By synthesizing a range of compounds with AIE properties and experimentally determining their photophysical properties and molecular structures, the study explores the potential applications of these compounds in DNA recognition, protein detection, small molecule recognition, cellular pH detection, and bioimaging.

Fluorescence bioimaging is considered an indispensable technique in biological research due to its high sensitivity, excellent spatial and temporal resolution, non-invasiveness, rapid and real-time responsiveness, as well as its ease of accessibility. Among these, fluorescence probes play a pivotal role in fluorescence imaging technology thanks to their strong specificity, high sensitivity, rapid response, and straightforward implementation. Aggregation-Induced Emission (AIE) molecules exhibit a unique phenomenon: they emit weak or no fluorescence when dissolved in a solution but become highly luminescent under aggregated/clustering conditions. Leveraging this, fluorescent probes with AIE characteristics often demonstrate fluorescence activation under conditions of spontaneous aggregation or binding with analytes, showcasing high sensitivity and exceptional signal-to-noise ratios. Consequently, fluorescence probes based on the distinctive optical properties of AIE hold immense potential for applications in fluorescence bioimaging. This paper primarily investigates the synthesis properties and applications in biosensing of a series of novel organic fluorescence probes with aggregation-induced emission (AIE) characteristics. By synthesizing a range of compounds with AIE properties and experimentally determining their photophysical properties and molecular structures, the study explores the potential applications of these compounds in DNA recognition, protein detection, small molecule recognition, cellular pH detection, and bioimaging.

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

Aggregation-induced emission (AIE)-type small-molecular fluorescent rotors have attracted wide interest due to their inherent excellent properties in bioimaging viscosity, which can potentially reveal the relationships between microviscosity and related diseases. Although many fluorescent probes have been designed, easy-to-prepare and multifunctional AIE rotors remain a hot topic and less reported. Herein, four easy-to-prepare and water-soluble meso-pyrimidine/pyridine BODIPY-based multifunctional fluorescent probes were rationally designed to investigate the effects of the number and position of nitrogen in six-membered-N-heterocycles on viscosity, AIE, and viscosity imaging. Luckily, the meso-o-pyrimidine-based probe 1 displayed significant fluorescence enhancements at 525 nm with gradually increasing viscosity from water to glycerol, which also showed obvious AIE property in an acetonitrile/water mixture due to two nitrogen at the ortho positions of pyrimidine. Meso-o-pyridine-based 2 exhibited no viscosity-enhanced emissions, but obvious AIE enhancements appeared. Comparatively, the meso-m-pyridine-based probe 3 showed no viscosity- and aggregation-induced emission enhancements, while the meso-p-pyridine-based one 4 displayed obvious viscosity response without AIE character. Furthermore, 1 and 4 were applied to cellular imaging, which displayed lysosomal and mitochondrial localizations in HeLa cells, respectively, and successfully monitored viscosity variations induced by the addition of lipopolysaccharide (LPS) or monensin. In summary, four meso-pyrimidine and meso-pyridine-BODIPY multifunctional fluorescent rotors have been prepared using easy synthesis, in which meso-o-pyrimidine and meso-o-pyridine ones showed improved AIE properties in water, and meso-o-pyrimidine and meso-p-pyridine ones showed good subcellular localization and viscosity changes in HeLa cells. This work can provide an easy-to-prepare and useful strategy for multifunctional fluorescent probes with enhanced AIE property for imaging viscosity and other applications.

The application of fluorescent probes is limited due to the small Stokes shifts and aggregation-caused quenching (ACQ) effect when accumulated in cells. Herein, a novel colorimetric and turn-on fluorescent probe based on salicylaldehyde azine with both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) properties for Cys/Hcy is proposed to solve these issues. This probe showed a large Stokes shift (148 nm), low cytotoxicity as well as outstanding photostability upon recognition and the response mechanism was confirmed by fluorescence spectroscopy, High performance liquid chromatography (HPLC), thin layer chromotography (TLC), and transmission electron microscope (TEM). In addition to being used for cell imaging, a simple and user-friendly portable kit based on this probe was proposed as a new tool for the on-site inspection of more than ten microsamples simultaneously, which could effectively prevent the occurrence of false positives and visual errors.

Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species

A novel aggregation-induced dual emission probe for in situ light-up detection of endogenous alkaline phosphatase

A benzothiazole-based near-infrared fluorescent probe for sensing SO2 derivatives and viscosity in HeLa cells

Fluorescence probes with strong near-infrared (NIR) emission and water solubility are considered useful visualization tools for localization marking as well as investigating cell migration and tran...

In this paper, we present three ratiometric near-infrared fluorescent probes (A-C) for accurate, ratiometric detection of intracellular pH changes in live cells. Probe A consists of a tetraphenylethene (TPE) donor and near-infrared hemicyanine acceptor in a through-bond energy transfer (TBET) strategy, while probes B and C are composed of TPE and hemicyanine moieties through single and double sp2 carbon-carbon bond connections in a π-conjugation modulation strategy. The specific targeting of the probes to lysosomes in live cells was achieved by introducing morpholine residues to the hemicyanine moieties to form closed spirolactam ring structures. Probe A shows aggregation-induced emission (AIE) property at neutral or basic pH, while probes B and C lack AIE properties. At basic or neutral pH, the probes only show fluorescence of TPE moieties with closed spirolactam forms of hemicyanine moieties, and effectively avoid blind fluorescence imaging spots, an issue which typical intensity-based pH fluorescent probes encounter. Three probes show ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with TPE fluorescence decreases and hemicyanine fluorescence increases, because acidic pH makes the spirolactam rings open to enhance π-conjugation of hemicyanine moieties. However, probe A shows much more sensitive ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with remarkable ratio increase of TPE fluorescence to hemicyanine fluorescence up to 238-fold than probes B and C because of its high efficiency of energy transfer from TPE donor to the hemicyanine acceptor in the TBET strategy. The probe offers dual Stokes shifts with a large pseudo-Stokes shift of 361 nm and well-defined dual emissions, and allows for colocalization of the imaging readouts of visible and near-infrared fluorescence channels to achieve more precisely double-checked ratiometric fluorescence imaging. These platforms could be employed to develop a variety of novel ratiometric fluorescent probes for accurate detection of different analytes in applications of chemical and biological sensing, imaging, and diagnostics by introducing appropriate sensing ligands to hemicyanine moieties to form on-off spirolactam switches.

ConspectusThis Account describes a range of strategies for the development of fluorescent probes for detecting reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive (redox-active) sulfur species (RSS). Many ROS/RNS have been implicated in pathological processes such as Alzheimer’s disease, cancer, diabetes mellitus, cardiovascular disease, and aging, while many RSS play important roles in maintaining redox homeostasis, serving as antioxidants and acting as free radical scavengers. Fluorescence-based systems have emerged as one of the best ways to monitor the concentrations and locations of these often very short lived species. Because of the high levels of sensitivity and in particular their ability to be used for temporal and spatial sampling for in vivo imaging applications. As a direct result, there has been a huge surge in the development of fluorescent probes for sensitive and selective detection of ROS, RNS, and RSS within cellular environments. However, cellular environments are extremely complex, often with more than one species involved in a given biochemical process. As a result, there has been a rise in the development of dual-responsive fluorescent probes (AND-logic probes) that can monitor the presence of more than one species in a biological environment. Our aim with this Account is to introduce the fluorescent probes that we have developed for in vitro and in vivo measurement of ROS, RNS, and RSS. Fluorescence-based sensing mechanisms used in the construction of the probes include photoinduced electron transfer, intramolecular charge transfer, excited-state intramolecular proton transfer (ESIPT), and fluorescence resonance energy transfer. In particular, probes for hydrogen peroxide, hypochlorous acid, superoxide, peroxynitrite, glutathione, cysteine, homocysteine, and hydrogen sulfide are discussed. In addition, we describe the development of AND-logic-based systems capable of detecting two species, such as peroxynitrite and glutathione. One of the most interesting advances contained in this Account is our extension of indicator displacement assays (IDAs) to reaction-based indicator displacement assays (RIAs). In an IDA system, an indicator is allowed to bind reversibly to a receptor. Then a competitive analyte is introduced into the system, resulting in displacement of the indicator from the host, which in turn modulates the optical signal. With an RIA-based system, the indicator is cleaved from a preformed receptor–indicator complex rather than being displaced by the analyte. Nevertheless, without a doubt the most significant result contained in this Account is the use of an ESIPT-based probe for the simultaneous sensing of fibrous proteins/peptides AND environmental ROS/RNS.