An endoplasmic reticulum-targeting fluorescent probe for the imaging of hypochlorous acid in living cells and zebrafishes

Dicyanoisophorone-based near-infrared fluorescent probe with large Stokes shift for the monitoring and bioimaging of hypochlorite

Hypochlorite (ClO-), as one of reactive oxygen species (ROS), is closely linked to various illnesses and is essential for the proper functioning of immune system. Hence, monitoring and assessing ClO- levels in organisms are extremely important for the clinical diagnosis of ClO--related disorders. In this study, a novel ClO--selective fluorescent probe, DCP-ClO, was synthesized with dicyanoisophorone-xanthene unit as parent fluorophore, which displayed excellent selectivity towards ClO-, near-infrared emission (755 nm), large Stokes shift (100 nm), real-time response to ClO-, high sensitivity (LOD = 3.95 × 10-8 M), and low cytotoxicity. The recognition mechanism of DCP-ClO towards ClO- was confirmed to be a typical ICT process by HPLC-MS, HR-MS, 1H NMR and theoretical calculations. Meanwhile, DCP-ClO demonstrated remarkable efficacy in monitoring ClO- levels in water samples and eye-catching ability in imaging endogenous/exogenous ClO- in living organisms, which verified its potential as a powerful tool for the recognition of ClO- in complex biological systems.

A dual-responsive fluorescent probe based on cyanine and naphthalimide units for detecting HClO and H2S in living cells

Hypochlorous acid (HClO) and hydrogen sulfide (H2S) play very important roles in both physiological and pathological processes, however, the methods for simultaneously detecting HClO and H2S were rarely reported. Here, a dual-responsive fluorescent probe (CyNa-N3) based on cyanine and naphthalimide dyes was synthesized and investigated. The fluorescence probe showed better sensitivity, high selectivity response to HClO and H2S by red emission and green emission bands, and the limits of detection were 0.17 µM and 0.15 µM respectively. MS (Mass Spectrum) and 1H NMR (Nuclear Magnetic Resonance) confirmed the sensing mechanism of CyNa-N3 detected HClO and H2S, the calculation of density functional theory (DFT) further explained the internal mechanism of spectral change of CyNa-N3. Moreover, CyNa-N3 was successfully applied to image HClO and H2S in living cells, which is beneficial for more efficient application in biological imaging.

A novel AIRE-based fluorescent ratiometric probe with endoplasmic reticulum-targeting ability for detection of hypochlorite and bioimaging

Hypochlorite (ClO^-) plays an important role in the human immune defense system, but high concentrations of ClO^- in the endoplasmic reticulum (ER) damage cellular proteins, causing ER stress, cell death, and various diseases. Herein, we developed a simple hydrazone probe (1) featuring aggregation-induced ratiometric emission, which would quickly (within 20 s) and sensitively (detection limit of 15.4 μM) respond to ClO^- in an almost pure aqueous solution via a fluorescent ratiometric output. Furthermore, the probe was employed to track the level of ClO^- in the ER of HeLa cells and zebrafish.

Theoretical study on a series of naphthalimide-contained two-photon fluorescent hypochlorite probe targeting endoplasmic reticulum: response mechanism and receptor effect

The development of detecting hypochlorous acid (HClO) in living endoplasmic reticulum has attracted much attention in the fields of biology, medicine, and pharmacy. In the present work, the one-photon absorption (OPA), one-photon emission (OPE), and two-photon absorption (TPA) properties of a series newly synthesized chemosensors with naphthalimide as the fluorophore were systematically investigated using time-dependent density functional theory in combination with response theory. Special emphasis is placed on evolution of the probes' optical properties in the presence of HClO. These compounds show drastic changes in their photoabsorption and photoemission properties when they react with HClO, indicating them to be excellent candidates as fluorescent chemosensors. To further understand the mechanisms of the two probes, we have employed the hole and electron analysis to investigate the charge transfer process for the photoemission of the molecules. The receptor effect is found to play a dominant role in the sensing performance of these probes. Specifically, two-photon absorption properties of the molecules are calculated. We have found that all probes show significant two-photon responses in the near-infrared light region. And the maximum two-photon absorption cross section of probe 2 is greatly enhanced with the presence of HClO, indicating that probe 2 can act as a potential two-photon excited fluorescent HClO probe. The theoretical investigations would be helpful to build the structure-property relationships for the naphthalimide-contained probes, providing information on the design of efficient two-photon fluorescent sensors that can be used for biological imaging of HClO in endoplasmic reticulum.

A HBDI-Based Fluorescent Probe for Labeling Endoplasmic Reticulum in Living Cells

The endoplasmic reticulum (ER) is an important organelle in eukaryotic cells and is closely involved in the synthesis and processing of proteins, as well as the storage, regulation, and release of calcium. A series of signaling pathways within the ER play a crucial part in the pathogenesis of various diseases, including cancer. Thus, it is necessary to design ER-targeting probes to monitor these signaling pathways. Additionally, precision medicine also requires new ER-targeting group to facilitate the delivery of drug cargoes to the ER. However, only a limited number of ER-targeting groups have been used for the design of fluorescent probes for ER imaging in living cells, as well as the development of ER-targeted drug delivery systems. Herein, a new ER-targeting fluorescent probe (BDI-ER) was designed and prepared. BDI-ER contains the hydrophilic fluorophore, derived from the core structure of GFP, and two hydrophobic octadecane chains. The amphipathic nature of BDI-ER facilitates localization in the ER. Live cell imaging demonstrated selective localization of BDI-ER towards ER compared to other organelles. Additionally, co-localization imaging in various cell lines indicate that BDI-ER is effective at targeting the ER.

Recent progress in small-molecule fluorescent probes for endoplasmic reticulum imaging in biological systems

Endoplasmic reticulum (ER) is an indispensable organelle in eukaryotic cells involved in protein synthesis and processing, as well as calcium storage and release. Therefore, maintaining the quality of ER is of great importance for cellular homeostasis. Aberrant fluctuations of bioactive species in the ER will result in homeostasis disequilibrium and further cause ER stress, which has evolved to contribute to the pathogenesis of various diseases. Therefore, the real-time monitoring of various bioactive species in the ER is of high priority to ascertain the mysterious roles of ER, which will contribute to unveiling the corresponding mechanism of organism disturbances. Recently, fluorescence imaging has emerged as a robust technique for the direct visualization of molecular events due to its outstanding sensitivity, high temporal-spatial resolution and noninvasive nature. In this review, we comprehensively summarize the recent progress in design strategies, bioimaging applications, potential directions and challenges of ER-targetable small-molecular fluorescent probes.

A redox reversible endoplasmic reticulum-targeted fluorescent probe for revealing the redox status of living cells

The endoplasmic reticulum (ER) is one of the most important organelles in cells and is involved in protein synthesis, folding and orderly transport. Redox balance is the key to its normal function. In this work, we designed and synthesized an endoplasmic reticulum-targeted fluorescent probe N-Se with selenomorpholine as the redox reversible detection moiety. N-Se could selectively respond to ClO^- within only 8 s with a LOD of 28.8 nM. Furthermore, such a response is reversible in the regulation of GSH. Confocal fluorescence imaging confirmed the excellent endoplasmic reticulum targeting ability of N-Se. Thus, it could real-time monitor the dynamic changes of the redox status in the endoplasmic reticulum through the variation of the fluorescence intensity.

Optical Characteristics and Applications of AIE Racemic C6-Unsubstituted Tetrahydropyrimidines

Racemic C6-unsubstituted tetrahydropyrimidines (THPs) are the products of an efficient five-component reaction that we developed. THPs show strong AIE characteristics, that is, completely no fluorescence in different solvents but strong emission with fluorescence quantum yields (Φ F) up to 100% upon aggregation. However, the Φ F values of their pure enantiomers are lower than 46%. Unlike common AIE compounds with crowded aryl rotors on a π-bond or on an aryl ring, THPs have three completely non-crowded aryl rotors on a non-aromatic chiral central ring (tetrahydropyrimidine). In this mini review, we first discuss the AIE characteristics of THPs and the influences of molecular structures on their molecular packing modes and optical properties, and then present their applications and forecast the development of other racemic AIE compounds.

Research on endoplasmic reticulum-targeting fluorescent probes and endoplasmic reticulum stress-mediated nanoanticancer strategies: A review

Subcellular localization of organelles can achieve accurate drug delivery and maximize drug efficacy. As the largest organelle in eukaryotic cells, the endoplasmic reticulum (ER) plays an important role in protein synthesis, folding, and posttranslational modification; lipid biosynthesis; and calcium homeostasis. Observing the changes in various metal ions, active substances, and the microenvironment in the ER is crucial for diagnosing and treating many diseases, including cancer. Excessive endoplasmic reticulum stress (ERS) can have a killing effect on malignant cells and can mediate cell apoptosis, proper modulation of ERS can provide new perspectives for the treatment of many diseases, including cancer. Therefore, the ER is used as a new anticancer target in cancer treatment. This review discusses ER-targeting fluorescent probes and ERS-mediated nanoanticancer strategies.

The development of an endoplasmic reticulum-targeting fluorescent probe for the imaging of 1,4-dithiothreitol (DTT) in living cells

1,4-Dithiothreitol (DTT) is a robust reducing agent that contributes significantly to the folding process of proteins and maintaining endoplasmic reticulum (ER) homeostasis. Abnormally high levels of DTT can lead to severe endoplasmic reticulum stress (ERS), which induces cell death. In addition, DTT can also hinder cell growth and enhance reactive oxygen species (ROS) production in the ER. Herein, an effective turn-on ER-targeting fluorescent probe, ER-DTT, was designed to image DTT for the first time. The probe ER-DTT was based upon naphthalimide as a fluorophore, p-toluenesulfonamide as an exceptional unit for ER-targeting, and sulfoxide as a response site for imaging DTT based on an intramolecular charge transfer (ICT) mechanism. Optical-response experiments showed that the probe ER-DTT had good selectivity and sensitivity for DTT. Furthermore, confocal microscopy indicated that ER-DTT was suitable for selectively targeting ER in living cells and could be implemented to recognize cellular DTT.

An endoplasmic reticulum-targeting and ratiometric fluorescent probe for hypochlorous acid in living cells based on a 1,8-naphthalimide derivative

A novel reticulum-targeting and ratiometric fluorescent probe for determining hypochlorous acid has been developed.