A rhodamine-based fluorescent probe used to determine nitroxyl (HNO) in lysosomes

The reactive nitrogen species (RNS) in lysosomes play a major role during the regulation of lysosomal microenvironment. Nitroxyl (HNO) belongs to active nitrogen species (RNS) and is becoming a potential diagnostic and therapeutic biomarker. However, the complex synthesis routes of HNO in biosystem always hinder the exact determination of HNO in living cells. Here, a rhodamine-based fluorescent probe used to determine nitroxyl (HNO) in lysosomes was constructed and synthesized. 2-(Diphenylphosphino)benzoate was utilized as the sensing unit for HNO and morpholine was chose as the targeting group for lysosome. Before the addition of HNO, the probe displayed a spirolactone structure and almost no fluorescence was found. After the addition of HNO, the probe existed as a conjugated xanthene form and an intense green fluorescence was observed. The fluorescent probe possessed fast response (3 min) and high selectivity for HNO. Furthermore, fluorescence intensity of the probe linearly related with the HNO concentration in the range of 6.0 × 10-8 to 6.0 × 10-5 mol L-1. The detection limit was found to be 1.87 × 10-8 mol L-1 for HNO. Moreover, the probe could selectively targeted lysosome with excellent biocompatibility and had been effectually utilized to recognize exogenous HNO in A549 cells.

A Near-Infrared Fluorescent Probe for the Rapid Detection of Nitroxyl in Living Cells

Nitroxyl (HNO) plays an important role in various physiological activities. It has the potential to be used as a treatment for certain diseases such as alcohol poisoning, acute hypertension, and atherosclerosis. However, traditional methods for detecting HNO are challenging due to its rapid polymerization and elimination into N2O. Therefore, it is crucial to establish direct and effective HNO detection methods to comprehend these physiological processes better. In this study, a new near-infrared fluorescent probe called HXM-P based on the intramolecular charge transfer (ICT) mechanism was designed and synthesized. This probe employs 2-((6-hydroxy-2,3dihydro-1 H-xanthen-4-yl)methylene)malononitrile as a fluorophore and 2-(diphenylphosphine) benzoate as a recognition group. The results showed that probe HXM-P can detect HNO with high sensitivity (1.07 × 10- 8 M). A good linear correlation was observed between the fluorescence intensities at 640 nm and the concentrations of HNO in the range of 0-80 µM (R2 = 0.997). Moreover, probe HXM-P exhibited a rapid response rate (within 15 s) toward HNO, and the fluorescent intensity reached a plateau within 5 min, making it easier to track the highly reactive and short-lived HNO in living systems. Additionally, HXM-P was successfully employed for imaging HNO in HepG2 cells.

Specific Reactions of RSNO, HSNO, and HNO and Their Applications in the Design of Fluorescent Probes

Nitric oxide (NO)-derived species play essential roles in regulating cellular responses. Among these species, S-nitrosothiols (including RSNO and HSNO) and nitroxyl (HNO) are especially interesting. Owing to their high reactivity and short survival time, the detection of these molecules in biological settings can be challenging. In this regard, much effort has been invested in exploring novel reactions of RSNO/HSNO/HNO and applying these reactions to develop fluorescence probes. Herein, reported specific reactions of RSNO/HSNO/HNO are summarized and strategies used in the design of fluorescent probes are illustrated. The properties and potential problems of representative probes are also discussed.

An isophorone-fused near-infrared fluorescent probe with a large Stokes shift for imaging endogenous nitroxyl in living cells and zebrafish

Nitroxyl (HNO) plays an important role in multiple physiological and pathological processes, but the detailed generation mechanism of the endogenous HNO still remained to explore and perfect further. There is an urgent need to develop an excellent fluorescent probe for selective recognition and sensitive detection of HNO in biological systems. Near-infrared (NIR) fluorescent probes with a large Stokes shift are an ideal tool for bioimaging applications. Here, we have developed a NIR fluorescent probe with a large Stokes shift, namely, NIR-HNO, to monitor HNO in cells and zebrafish. NIR-HNO consists of an isophorone-fused NIR fluorescence reporter and a diphenylphosphinobenzoyl HNO-responsive unit. Based on an aza-ylide intramolecular ester aminolysis reaction, NIR-HNO showed a rapid selective NIR fluorescent turn-on response for HNO, high sensitivity (detection limit was 39.6 nM), and large Stokes shift (265 nm). The biological imaging results indicate that NIR-HNO is a good candidate for imaging of endogenous HNO in living systems.

Recent Advances in Fluorescent Probes for Detection of HOCl and HNO

It is known that reactive oxygen (ROS) and nitrogen (RNS) species play a diverse role in various biological processes, such as inflammation, signal transduction, and neurodegenerative injury, apart from causing various diseases caused by oxidative and nitrosative stresses, respectively, by ROS and RNS. Thus, it is very important to quantify the concentration level of ROS and RNS in live cells, tissues, and organisms. Various small-molecule-based fluorescent/chemodosimetric probes are reported to quantify and map the effective distribution of ROS/RNS under in vitro/in vivo conditions with a great spatial and temporal resolution. Such reagents are now appreciated as an excellent tool for aiding breakthroughs in modern redox biology. This mini-review is a brief, but all-inclusive, account of such molecular probes that have been developed recently.

Rhodol-based fluorescent probes for the detection of fluoride ion and its application in water, tea and live animal imaging

Herein, we presented two novel turn-on colorimetric and fluorescent probes based on a F^- triggered SiO bond cleavage reaction, which displayed several desired properties for the quantitative detection for F^-, such as high specificity, rapid response time (within 3 min) and naked-eye visualization. The fluorescence intensity at 574 nm (absorbance at 544 nm) of the solution was found to increase linearly with the concentration of F^- (0.00-30.0 μM) with the detection limit was estimated to be 0.47 μM/0.48 μM. Based on these excellent optical properties, the probes were employed to monitor F^- in real water samples and tea samples with satisfactory. Furthermore, it was successfully applied for fluorescent imaging of F^- in living nude mice, suggesting that it could be used as a powerful tool to predict and explore the biological functions of F^- in physiological and pathological processes.

A seminaphthorhodafluor-based near-infrared fluorescent probe for hydrazine and its bioimaging in living systems

Hydrazine (N₂H₄) has been classified as a potential carcinogen with its high toxicity, which can be readily absorbed through the skin or via breathing directly. Although some fluorescent probes have been developed for imaging of N₂H₄, very little can be used for imaging of N₂H₄ in vivo because of its short emission wavelength. In this study, a new colorimetric and near-infrared (NIR) fluorescent probe CF-1 based on a seminaphthorhodafluor dye was successfully designed and used for hydrazine determination. Upon reaction with N₂H₄, probe CF-1 showed obvious off-on NIR emission spectrum centered at 657 nm, as well as a distinct color change that can be distinguished by the naked eye. The results of fluorescence spectrum experiments indicated that probe CF-1 has high selectivity and low detection limitation (40.6 nM in the solution). Probe CF-1 has low cytotoxicity and was applied to imaging hydrazine in mitochondria of HeLa cells and in zebrafish.

Imaging of anti-inflammatory effects of HNO via a near-infrared fluorescent probe in cells and in rat gouty arthritis model

Nitroxyl (HNO) plays a crucial role in anti-inflammatory effects via the inhibition of inflammatory pathways, but the details of the endogenous generation of HNO still remain challenging owing to the complex biosynthetic pathways, in which the interaction between H₂S and NO simultaneously generates HNO and polysulfides (H₂S_n) in mitochondria. Moreover, nearly all the available fluorescent probes for HNO are utilized for imaging HNO in cells and tissues, instead of the in situ real-time detection of the simultaneous formation of HNO and H₂S_n in mitochondria and animals. Here, we have developed a mitochondria-targeting near-infrared fluorescent probe, namely, Mito-JN, to detect the generation of HNO in cells and a rat model. The probe consists of three moieties: Aza-BODIPY as a fluorescent signal transducer, a triphenylphosphonium cation as a mitochondria-targeting agent, and a diphenylphosphinobenzoyl group as an HNO-responsive unit. The response mechanism is based on an aza-ylide intramolecular ester aminolysis reaction with fluorescence emissions on. Mito-JN displays high selectivity and sensitivity for HNO over various other biologically relevant species. Mito-JN was successfully used for the detection of the endogenous generation of HNO, which is derived from the crosstalk between H₂S and NO in living cells. The additional generation of H₂S_n was also confirmed using our previous probe Cy-Mito. The anti-inflammatory effect of HNO was examined in a cell model of LPS-induced inflammation and a rat model of gouty arthritis. The results imply that our probe is a good candidate for the assessment of the protective effects of HNO in inflammatory processes.

Fluorescent probes for the detection of nitroxyl (HNO)

Nitroxyl (HNO), which according to the IUPAC recommended nomenclature should be named azanone, is the protonated one-electron reduction product of nitric oxide. Recently, it has gained a considerable attention due to the interesting pharmacological effects of its donors. Although there has been great progress in the understanding of HNO chemistry and chemical biology, it still remains the most elusive reactive nitrogen species, and its selective detection is a real challenge. The development of reliable methodologies for the direct detection of azanone is essential for the understanding of important signaling properties of this reactive intermediate and its pharmacological potential. Over the last decade, there has been considerable progress in the development of low-molecular-weight fluorogenic probes for the detection of HNO, and therefore, in this review, we have focused on the challenges and limitations of and perspectives on nitroxyl detection based on the use of such probes.

Reaction-Based Fluorescent Probes for the Imaging of Nitroxyl (HNO) in Biological Systems

Nitroxyl (HNO) has been identified as an important signaling molecule in biological systems and plays critical roles in many physiological processes. Fluorescence imaging could provide a robust approach to explore the biological formation of HNO and its physiological functions. Herein, we summarize the organic reaction types for constructing HNO probes and specifically focus on review of the recent advances in the development of the reaction-based HNO probes and their imaging applications in living systems.

A novel fibroblast activation protein-targeted near-infrared fluorescent off-on probe for cancer cell detection, in vitro and in vivo imaging

A new hemicyanine-based fibroblast activation protein-targeted near-infrared fluorescent probe is designed and it shows high selectivity and sensitivity to cancer cell detection, and in vitro and in vivo imaging. This probe is successfully applied in fluorescence detection of living cells (with a detection limit of 1500 cells per mL). It is believed that many new functions or distributions of FAP could be discovered by this new probe later.

A fast responsive, highly selective and light-up fluorescent probe for the two-photon imaging of carboxylesterase in living cells

A fast responsive and two photon fluorescent probe (HCyNAc) for carboxylesterase (CaE) has been designed and used for the two-photon imaging of the endogenous CaE level in living HeLa cells under 800 nm NIR excitation.

A near-infrared xanthene fluorescence probe for monitoring peroxynitrite in living cells and mouse inflammation model

A novel near-infrared xanthene fluorescence probe for monitoring peroxynitrite in vitro and in vivo.