Highly water-soluble BODIPY-based fluorescent probe for sensitive and selective detection of nitric oxide in living cells

A novel donor-acceptor fluorescent probe for the fluorogenic/ chromogenic detection and bioimaging of nitric oxide

Nitric oxide (NO) plays an essential role in regulating various physiological and pathological processes. This has spurred various efforts to develop feasible methods for the detection of NO. Herein we designed and synthesized a novel donor-acceptor fluorescent probe Car-NO for the selective and specific detection of NO. Reaction of Car-NO with NO generated a new donor-acceptor structure with strong intramolecular charge transfer (ICT) effect, and led to remarkable chromogenic change from yellow to blue and dramatic fluorescence quenching. Car-NO exhibited high selectivity, excellent sensitivity, and rapid response for the detection of NO. In addition, the nanoparticles prepared from Car-NO (i.e., Car-NO NPs) showed strong NIR emission and high selectivity/sensitivity. Car-NO NPs was successfully employed to image both endogenous and exogenous NO in HeLa and RAW 264.7 cells. The present findings reveal that Car-NO is a promising probe for the detection and bioimaging of NO.

Mitochondrial-Targeted Ratiometric Near-Infrared Fluorescence Probe for Monitoring Nitric Oxide in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a destructive autoimmune disease, where nitric oxide (NO) is closely implicated in the inflammatory processes of RA. Therefore, direct visualization of NO is essential to assess the pathological changes in RA. Herein, a mitochondrial-targeted near-infrared ratiometric fluorescent probe (NFL-NH2), based on the intramolecular charge transfer effect, was synthesized and applied to monitor the changes of NO content in early RA. Specially, probe NFL-NH2 showed a 44-fold fluorescent intensity ratio (I705/I780) response toward NO with a detection limit of 0.536 nM, enabling qualitative and quantitative analysis of NO. Additionally, NFL-NH2 can accurately target mitochondria and sensitively detect exogenous and endogenous NO in RAW 264.7 cells. Notably, in vivo RA monitoring assays demonstrated that NFL-NH2 can rapidly detect NO levels associated with the inflammatory damage degree in RA mice models by ratiometric fluorescence imaging. These results validate that NFL-NH2 holds significant potential for diagnosing NO-mediated RA diseases.

Engineering giant excitonic coupling in bioinspired, covalently bridged BODIPY dyads

Strong excitonic coupling in photosynthetic systems is believed to enable efficient light absorption and quantitative charge separation, motivating the development of artificial multi-chromophore arrays with equally strong or even stronger excitonic coupling. However, large excitonic coupling strengths have typically been accompanied by fast non-radiative recombination, limiting the potential of the arrays for solar energy conversion as well as other applications such as fluorescent labeling. Here, we report giant excitonic coupling leading to broad optical absorption in bioinspired BODIPY dyads that have high photostability, excited-state lifetimes at the nanosecond scale, and fluorescence quantum yields of nearly 50%. Through the synthesis, spectroscopic characterization, and computational modeling of a series of dyads with different linking moieties, we show that the strongest coupling is obtained with diethynylmaleimide linkers, for which the coupling occurs through space between BODIPY units with small separations and slipped co-facial orientations. Other linkers allow for broad tuning of both the relative through-bond and through-space coupling contributions and the overall strength of interpigment coupling, with a tradeoff observed in general between the strength of the two coupling mechanisms. These findings open the door to the synthesis of molecular systems that function effectively as light-harvesting antennas and as electron donors or acceptors for solar energy conversion.

Ratiometric fluorescent sensing of phosphate ion in environmental water samples using flavin mononucleotide-functionalized Fe3O4 particles

Phosphate ion (PO₄^3-) serves as an important nutrient carrier to support the growth of aquatic animals and plants in aquatic systems. However, excess concentrations of PO₄^3- are the key factor responsible for eutrophication, resulting in rapid deterioration of water quality. Therefore, accurate determination of PO₄^3- is of great significance in water quality and security. In this study, flavin mononucleotide (FMN), an intracellular form of vitamin B₂, was used as fluorophore. A novel "off-on" fluorescent sensing platform (FMN@Fe₃O₄) was fabricated for selective and sensitive detection of PO₄^3-, and showed excellent fluorescence response and good selectivity for PO₄^3- detection. With the addition of PO₄^3-, the fluorescence intensity restored is proportional to PO₄^3- concentration in the quantification range of 50 nM-0.75 μM with a limit of detection as low as 20 nM (0.62 μg.L^-1, calculated by P element). An adsorption/desorption sensing mechanism via an in-depth analysis of the interfacial interaction between PO₄^3- and FMN@Fe₃O₄ is proposed. FMN is first adsorbed by its terminal phosphate group on Fe₃O₄ particles to quench fluorescence. Free PO₄^3- replaces the adsorbed FMN and restores the quenched fluorescence to achieve the aim of PO₄^3- detection. In addition, this sensing system has been successfully validated in real water sample analysis and all reagents involved are nontoxic, environmentally benign, and easily-available. Therefore, this assay has great applicability in water quality monitoring.

Thiophene and diaminobenzo- (1,2,5-thiadiazol)- based DAD-type near-infrared fluorescent probe for nitric oxide: A theoretical research

A near-infrared fluorescent probe (LS-NO) for the real-time detection of nitric oxide (NO) in inflammatory bowel disease (IBD) was developed recently. The probe used oligoglycol morpholine-functionalized thiophene as strong electron donors and diaminobenzene (1,2,5-thiadiazole) as a weak electron acceptor and NO trapping group. It could detect exogenous and endogenous NO in the lysosomes of living cells with high sensitivity and specificity. To further understand the fluorescent mechanism and character of the probes LS-NO and LS-TZ (after the reaction of the probe LS-NO with NO), the electron transfer in the excitation and emitting process within the model molecules DAD-NO and DAD-TZ was analyzed in detail under the density functional theory. The calculation results indicated the transformation from diaminobenzene (1,2,5-thiadiazole) as a weak electron acceptor to triazolo-benzo-(1,2,5-thiadiazole) as a strong electron acceptor made LS-NO an effective "off-on" near-infrared NO fluorescent probe.

Nitric oxide detection using catalytic properties of CuCo-PTC metal organic framework

As a vital gaseous signal molecule involved in various physiological and pathological processes, nitric oxide (NO) has attracted extensive attention in the last few decades. In this work, a copper and cobalt element-doped, biphenyl-(3, 4', 5)-tricarboxylic acid (H₃PTC)-synthesized metal organic framework (CuCo-PTC MOF) composite with catalytic ability was synthesized by solvothermal method. The material can catalyse the oxidation of o-phenylenediamine (OPD) groups by hydrogen peroxide (H₂O₂) to form fluorophores (OPDox) with yellow fluorescence emission and greatly improves its reaction rate. In the presence of NO, OPD will react with NO to produce N-(2-hydrazinophenyl) methylamine, and the group will not react with H₂O₂. Therefore, the concentration of NO can be measured indirectly by comparing the changes of fluorescence intensity in the presence and absence of NO. As the concentration of NO changes, the change of solution colour (from bright yellow to colourless) can also be observed under a 365-nm UV lamp. Furthermore, the method represents high selectivity for NO and shows a fast (within 5 min) and specific fluorescence response toward NO with a linear range from 0.25 to 2.0 μM; the strategy has a limit of detection (LOD) of  0.15 μM. More importantly, the probe was successfully used to detect NO in cell lysate. The recovery was between 98.5 and 103.6%, and the relative standard deviation was between 0.4 and 1.8%. The endogenous NO in cells was successfully detected under the stimulation of L-arginine, which proved the possibility of the probe in real-time and rapid sensing in actual samples and cells. The results indicate that this sensing strategy has the potential to detect NO in the internal environment. Schematic of fluorescence detection of NO.

Highly Sensitive D-A-D-Type Near-Infrared Fluorescent Probe for Nitric Oxide Real-Time Imaging in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a common gastrointestinal inflammatory disease, affecting a huge number of people worldwide with increasing morbidity each year. Although the etiology of IBD has not been fully elucidated, it is understood to be closely related to upregulation of the production of NO. Herein, we first report a donor-acceptor-donor (D-A-D)-type near-infrared (NIR) fluorescent probe LS-NO for real-time detection of NO in IBD by harnessing the enhanced intramolecular charge transfer mechanism. LS-NO exhibited good water solubility, high photostability, and excellent NIR absorbance and emission at 700 and 750/800 nm, respectively. Moreover, it was able to sensitively and specifically detect exogenous and endogenous NO in the lysosomes of living cells. Notably, LS-NO enabled to noninvasively visualize NO generation in a lipopolysaccharide-induced IBD mouse model for 30 h, showing a two- to threefold higher NIR fluorescence intensity in the intestines and feces of IBD mice than normal mice. This work demonstrates that LS-NO is promising as a diagnosis agent for real-time detection of NO in IBD and may promote inflammatory stool examination simultaneously.

Dual Switch Mechanism of Erythropoietin as an Antiapoptotic and Pro-Angiogenic Determinant in the Retina

Constant or intense light degenerates the retina and retinal pigment epithelial cells. Light generates reactive oxygen species and nitric oxide leading to initial reactions of retinal degeneration. Apoptosis is the primary mechanism of abnormal death of photoreceptors, retinal ganglion cells, or retinal pigment epithelium (RPE) in degenerative retinal diseases, including diabetic retinopathy and age-related macular degeneration. The current study evaluated the function of erythropoietin (EPO) on angiogenesis and apoptosis in the retina and RPE under oxidative stress. We determined the pro-angiogenic and antiapoptotic mechanism of EPO under stress conditions using a conditional EPO knockdown model using siRNA, EPO addition, proteomics, immunocytochemistry, and bioinformatic analysis. Our studies verified that EPO protected retinal cells from light-, hypoxia-, hyperoxia-, and hydrogen peroxide-induced apoptosis through caspase inhibition, whereas up-regulated angiogenic reactions through vascular endothelial growth factor (VEGF) and angiotensin pathway. We demonstrated that the EPO expression in the retina and subsequent serine/threonine/tyrosine kinase phosphorylations might be linked to oxidative stress response tightly to determining angiogenesis and apoptosis. Neuroprotective roles of EPO may involve the balance between antiapoptotic and pro-angiogenic signaling molecules, including BCL-xL, c-FOS, caspase-3, nitric oxide, angiotensin, and VEGF receptor. Our data indicate a new therapeutic application of EPO toward retinal degeneration based on the dual roles in apoptosis and angiogenesis at the molecular level under oxidative stress.

Smart Supra- and Macro-Molecular Tools for Biomedical Applications

Stimuli-responsive, “smart” polymeric materials used in the biomedical field function in a bio-mimicking manner by providing a non-linear response to triggers coming from a physiological microenvironment or other external source. They are built based on various chemical, physical, and biological tools that enable pH and/or temperature-stimulated changes in structural or physicochemical attributes, like shape, volume, solubility, supramolecular arrangement, and others. This review touches on some particular developments on the topic of stimuli-sensitive molecular tools for biomedical applications. Design and mechanistic details are provided concerning the smart synthetic instruments that are employed to prepare supra- and macro-molecular architectures with specific responses to external stimuli. Five major themes are approached: (i) temperature- and pH-responsive systems for controlled drug delivery; (ii) glycodynameric hydrogels for drug delivery; (iii) polymeric non-viral vectors for gene delivery; (iv) metallic nanoconjugates for biomedical applications; and, (v) smart organic tools for biomedical imaging.

A FRET-Based Near-Infrared Fluorescent Probe for Ratiometric Detection of Cysteine in Mitochondria

We report a near-infrared fluorescent probe A for the ratiometric detection of cysteine based on FRET from a coumarin donor to a near-infrared rhodamine acceptor. Upon addition of cysteine, the coumarin fluorescence increased dramatically up to 18-fold and the fluorescence of the rhodamine acceptor decreased moderately by 45 % under excitation of the coumarin unit. Probe A has been used to detect cysteine concentration changes in live cells ratiometrically and to visualize fluctuations in cysteine concentrations induced by oxidation stress through treatment with hydrogen peroxide or lipopolysaccharide (LPS). Finally, probe A was successfully applied for the in vivo imaging of Drosophila melanogaster larvae to measure cysteine concentration changes.

Crosstalk between Oxidative Stress and Tauopathy

Tauopathy is a collective term for neurodegenerative diseases associated with pathological modifications of tau protein. Tau modifications are mediated by many factors. Recently, reactive oxygen species (ROS) have attracted attention due to their upstream and downstream effects on tauopathy. In physiological conditions, healthy cells generate a moderate level of ROS for self-defense against foreign invaders. Imbalances between ROS and the anti-oxidation pathway cause an accumulation of excessive ROS. There is clear evidence that ROS directly promotes tau modifications in tauopathy. ROS is also highly upregulated in the patients’ brain of tauopathies, and anti-oxidants are currently prescribed as potential therapeutic agents for tauopathy. Thus, there is a clear connection between oxidative stress (OS) and tauopathies that needs to be studied in more detail. In this review, we will describe the chemical nature of ROS and their roles in tauopathy.

A Novel Ruthenium-based Molecular Sensor to Detect Endothelial Nitric Oxide

Nitric oxide (NO) is a key regulator of endothelial cell and vascular function. The direct measurement of NO is challenging due to its short half-life, and as such surrogate measurements are typically used to approximate its relative concentrations. Here we demonstrate that ruthenium-based [Ru(bpy)₂(dabpy)]²⁺ is a potent sensor for NO in its irreversible, NO-bound active form, [Ru(bpy)₂(T-bpy)]²⁺. Using spectrophotometry we established the sensor’s ability to detect and measure soluble NO in a concentration-dependent manner in cell-free media. Endothelial cells cultured with acetylcholine or hydrogen peroxide to induce endogenous NO production showed modest increases of 7.3 ± 7.1% and 36.3 ± 25.0% respectively in fluorescence signal from baseline state, while addition of exogenous NO increased their fluorescence by 5.2-fold. The changes in fluorescence signal were proportionate and comparable against conventional NO assays. Rabbit blood samples immediately exposed to [Ru(bpy)₂(dabpy)]²⁺ displayed 8-fold higher mean fluorescence, relative to blood without sensor. Approximately 14% of the observed signal was NO/NO adduct-specific. Optimal readings were obtained when sensor was added to freshly collected blood, remaining stable during subsequent freeze-thaw cycles. Clinical studies are now required to test the utility of [Ru(bpy)₂(dabpy)]²⁺ as a sensor to detect changes in NO from human blood samples in cardiovascular health and disease.

Activatable Near-Infrared Fluorescence Imaging Using PEGylated Bacteriochlorin-Based Chlorin and BODIPY-Dyads as Probes for Detecting Cancer

Near infrared (NIR) fluorescent probes are attractive tools for biomedical in vivo imaging due to the relatively deeper tissue penetration and lower background autofluorescence. Activatable probes are turned on only after binding to their target, further improving target to background ratios. However, the number of available activatable NIR probes is limited. In this study, we introduce two types of activatable NIR fluorophores derived from bacteriochlorin: chlorin-bacteriochlorin energy-transfer dyads and boron-dipyrromethene (BODIPY)-bacteriochlorin energy-transfer dyads. These fluorophores are characterized by multiple narrow excitation bands with relatively strong emission in the NIR. Targeted bacteriochlorin-based antibody or peptide probes have been previously limited by aggregation after conjugation. Polyethylene glycol (PEG) chains were added to improve the hydrophilicity without altering pharmacokinetics of the targeting moieties. These PEGylated bacteriochlorin-based activatable fluorophores have potential as targeted activatable, multicolor NIR fluorescent probes for in vivo applications.

Efficient Two-Photon Fluorescent Probe for Imaging of Nitric Oxide during Endoplasmic Reticulum Stress

Nitric oxide (NO) is a vital gaseous signal molecule and plays an important role in diverse physiological and pathological processes including regulation of vascular functions. Endoplasmic reticulum (ER) stress is caused by the accumulation of misfolded or unfolded protein in the ER. Besides, ER stress induced by NO can be involved in the pathogenesis of various vascular diseases. Unfortunately, to the best of our knowledge, no ER-targeting probe for NO is reported to study the relationship between ER stress and the level of NO in a biological system. Herein, an ER-targeted fluorescent probe named ER-Nap-NO for imaging of NO is designed and synthesized. ER-Nap-NO consists of three main parts: naphthalimide (two-photon fluorophore), o-phenylenediamino (NO recognition group), and methyl sulfonamide (ER-targetable group). The probe itself is nonfluorescent because a photoinduced electron transfer (PET) process exists. After the addition of NO, the PET process is inhibited and thus strong fluorescence is released. Moreover, the response mechanism is confirmed by ¹H NMR and mass spectra and DFT calculation in detail. In addition, from the experimental results, we can conclude that the probe displays several obvious advantages including high sensitivity, selectivity, and ER-targetable ability. Based on these excellent properties, the probe is used for the two-photon imaging of exogenous and endogenous NO in ER of living cells. Most importantly, the ER-targetable probe has potential capability as a tool for investigating the level of NO during tunicamycin-induced ER stress in cells and tissues, which is beneficial for revealing the role of NO in ER-associated vascular diseases.

Structure Based Modulation of Electron Dynamics in meso-(4-Pyridyl)-BODIPYs: A Computational and Synthetic Approach

The effects of structural modification on the electronic structure and electron dynamics of cationic meso-(4-pyridyl)-BODIPYs were investigated. A library of 2,6-difunctionalized meso-(4-pyridyl)-BODIPYs bearing various electron-withdrawing substituents was designed, and DFT calculations were used to model the redox properties, while TDDFT was used to determine the effects of functionalization on the excited states. Structural modification was able to restructure the low-lying molecular orbitals to effectively inhibit d-PeT. A new meso-(4-pyridyl)-BODIPY bearing 2,6-dichloro groups was synthesized and shown to exhibit enhanced charge recombination fluorescence. The fluorescence enhancement was determined to be the result of functionalization modulating the kinetics of the excited state dynamics.

Organic Dye Based Nanoparticles for Cancer Phototheranostics

Phototheranostics, which simultaneously combines photodynamic and/or photothermal therapy with deep-tissue diagnostic imaging, is a promising strategy for the diagnosis and treatment of cancers. Organic dyes with the merits of strong near-infrared absorbance, high photo-to-radical and/or photothermal conversion efficiency, great biocompatibility, ready chemical structure fine-tuning capability, and easy metabolism, have been demonstrated as attractive candidates for clinical phototheranostics. These organic dyes can be further designed and fabricated into nanoparticles (NPs) using various strategies. Compared to free molecules, these NPs can be equipped with multiple synergistic functions and show longer lifetime in blood circulation and passive tumor-targeting property via the enhanced permeability and retention effect. In this article, the recent progress of organic dye-based NPs for cancer phototheranostic applications is summarized, which extends the anticancer arsenal and holds promise for clinical uses in the near future.

Luminescent magnetic nanoparticles encapsulated in MOFs for highly selective and sensitive detection of ClO-/SCN- and anti-counterfeiting

It is well-known that ClO- and SCN- can cause adverse effects on the environment and organisms; therefore, development of new strategies for detecting ClO- and SCN-, especially in water, are highly desirable. Here, we present luminous Eu(iii) complex-functionalized Fe3O4 nanoparticles encapsulated into zeolitic imidazolate framework materials (nano-ZIF-8) and successfully employ this nano-MOF as a fluorescence probe for selective and sensitive detection of ClO- and SCN-. The introduction of ClO- into nano-ZIF-8 solution induced a significant decrease in the characteristic fluorescence emission of Eu3+ at 613 nm. However, strong fluorescence emission was again observed when SCN- was successively injected into the prepared nano-ZIF-8-ClO-. Thus, a novel fluorescence system for simultaneous detection of free ClO- and SCN- was established. On the basis of the superior adsorption performance of nano-MOF materials, free residual ClO- and SCN- in water was rapidly, sensitively and selectively detected with a detection limit of 0.133 nM and 0.204 nM, respectively. Moreover, nano-ZIF-8 was successfully used for monitoring the concentration levels of ClO- and SCN- in specimens of tap water and Yellow River water. Furthermore, the reversibility and regeneration of nano-ZIF-8 in sensing ClO- and SCN- is advantageous for applications of nano-ZIF-8 in solid-state sensing and anti-counterfeiting. As far as we know, this is the first time that nano-MOFs have been used as a selective fluorescence probe for ClO-/SCN- detection and anti-counterfeiting.

Aza-BODIPY based polymeric nanoparticles for cancer cell imaging

Near infrared (NIR) fluorescent dyes that are widely used for cancer imaging usually suffer from their hydrophobicity. To overcome this problem, a water-suspendable and biodegradable NIR-light-activating aza-BODIPY (AZB-NO₂) encapsulated in polymeric nanoparticles was prepared as a new class of deep-tissue imaging agent. AZB-NO₂ possesses an intense, broad NIR absorption band (600–800 nm) with a remarkably high fluorescent quantum yield. After being encapsulated with a biodegradable polycaprolactone (PCL) and a Kolliphor P188 surfactant by emulsification-solvent evaporation method, the AZB-NO₂ formed a spherical shape as observed in scanning electron micrographs (SEM) with a hydrodynamic average size of 201 nm (average PDI = 0.185). The results from transmission electron micrographs (TEM) and energy dispersive X-ray spectroscopy (EDS) elemental mapping indicated that the AZB-NO₂ homogeneously distributed in the polymeric shell. UV-visible-NIR and fluorescence spectra of the obtained nanoparticles, AZB-NO₂@PCL, revealed that the nanoparticles prepared by using 0.8 mg dye loading exhibited the highest fluorescence quantum yield. These nanoparticles were then applied for fluorescence imaging in human glioblastoma cell line (U-251). After the cells were exposed to AZB-NO₂@PCL, the materials appeared to be localized inside U-251 cells within 3 h and the fluorescence signal enhanced along with the increased incubation times. Moreover, 3D cell culture was used in this study to mimic in vivo tumor environments. The AZB-NO₂@PCL exhibited bright fluorescence from U-251 cells inside 3D Ca-alginate scaffolds after 24 h incubation. Our study successfully demonstrated that the encapsulation of hydrophobic aza-BODIPY dye could enhance the water-suspendability of the dye yielding biocompatible nanoparticles efficiently used in cancer cell imaging applications.

Encapsulation of hydrophobic aza-BODIPY dye could enhance its hydrophilicity yielding biocompatible nanoparticles which can be efficiently used in cancer cell imaging applications.

Novel cyclodextrin-based pH-sensitive supramolecular host–guest assembly for staining acidic cellular organelles

A novel supramolecular approach for the preparation of new non-toxic systems for staining cellular organelles is described.

BODIPY-Bacteriochlorin Energy Transfer Arrays: Toward Near-IR Emitters with Broadly Tunable, Multiple Absorption Bands

A series of energy transfer arrays, comprising a near-IR absorbing and emitting bacteriochlorin, and BODIPY derivatives with different absorption bands in the visible region (503-668 nm) have been synthesized. Absorption band of BODIPY was tuned by installation of 0, 1, or 2 styryl substituents [2-(2,4,6-trimethoxyphenyl)ethenyl], which leads to derivatives with absorption maxima at 503, 587, and 668 nm, respectively. Efficient energy transfer (>0.90) is observed for each dyad, which is manifested by nearly exclusive emission from bacteriochlorin moiety upon BODIPY excitation. Fluorescence quantum yield of each dyad in nonpolar solvent (toluene) is comparable with that observed for corresponding bacteriochlorin monomer, and is significantly reduced in solvent of high dielectric constants (DMF), most likely by photoinduced electron transfer. Given the availability of diverse BODIPY derivatives, with absorption between 500-700 nm, BODIPY-bacteriochlorin arrays should allow for construction of near-IR emitting agents with multiple and broadly tunable absorption bands. Solvent-dielectric constant dependence of Φf in dyads gives an opportunity to construct environmentally sensitive fluorophores and probes.

An Optimized Two-Photon Fluorescent Probe for Biological Sensing and Imaging of Catechol-O-Methyltransferase

A practical two-photon fluorescent probe was developed for highly sensitive and selective sensing of the activities of catechol-O-methyltransferase (COMT) in complex biological samples. To this end, a series of 3-substituted 7,8-dihydroxycoumarins were designed and synthesized. Among them, 3-BTD displayed the best combination of selectivity, sensitivity, reactivity, and fluorescence response following COMT-catalyzed 8-O-methylation. The newly developed two-photon fluorescent probe 3-BTD can be used for determining the activities of COMT in complex biological samples and bio-imaging of endogenous COMT in living cells and tissue slices with good cell permeability, low cytotoxicity, and high imaging resolution. All these findings suggest that 3-BTD holds great promise for developing therapeutic molecules that target COMT, as well as for exploring COMT-associated biological processes and its biological functions in living systems. Furthermore, the strategy also sheds new light on the development of fluorescent probes for other conjugative enzymes.

Amphiphilic BODIPY-Hydroporphyrin Energy Transfer Arrays with Broadly Tunable Absorption and Deep Red/Near-Infrared Emission in Aqueous Micelles

BODIPY-hydroporphyrin energy transfer arrays allow for development of a family of fluorophores featuring a common excitation band at 500 nm, tunable excitation band in the deep red/near-infrared window, and tunable emission. Their biomedical applications are contingent upon retaining their optical properties in an aqueous environment. Amphiphilic arrays containing PEG-substituted BODIPY and chlorins or bacteriochlorins were prepared and their optical and fluorescence properties were determined in organic solvents and aqueous surfactants. The first series of arrays contains BODIPYs with PEG substituents attached to the boron, whereas in the second series, PEG substituents are attached to the aryl at the meso positions of BODIPY. For both series of arrays, excitation of BODIPY at 500 nm results in efficient energy transfer to and bright emission of hydroporphyrin in the deep-red (640-660 nm) or near-infrared (740-760 nm) spectral windows. In aqueous solution of nonionic surfactants (Triton X-100 and Tween 20) arrays from the second series exhibit significant quenching of fluorescence, whereas properties of arrays from the first series are comparable to those observed in polar organic solvents. Reported arrays possess large effective Stokes shift (115-260 nm), multiple excitation wavelengths, and narrow, tunable deep-red/near-IR fluorescence in aqueous surfactants, and are promising candidates for a variety of biomedical-related applications.

An N-nitrosation reactivity-based two-photon fluorescent probe for the specific in situ detection of nitric oxide

In situ fluorescence imaging of nitric oxide (NO) is a powerful tool for studying the critical roles of NO in biological events. However, the selective imaging of NO is still a challenge because most currently available fluorescent probes rely on the o-phenylenediamine (OPD) recognition site, which reacts with both NO and some abundant reactive carbonyl species (RCS) (such as dehydroascorbic acid and methylglyoxal) and some reactive oxygen/nitrogen species (ROS/RNS). To address this problem, a new fluorescent probe, NCNO, based on the N-nitrosation of aromatic secondary amine was designed to bypass the RCS, ROS, and RNS interference. As was expected, the probe NCNO could recognize NO with pronounced selectivity and sensitivity among ROS, RNS, and RCS. The probe was validated by detecting NO in live cells and deep tissues owing to its two-photon excitation and red-light emission. It was, hence, applied to monitor NO in ischemia reperfusion injury (IRI) in mice kidneys by two-photon microscopy for the first time, and the results vividly revealed the profile of NO generation in situ during the renal IRI process.

Silica nanoparticles based on an AIE-active molecule for ratiometric detection of RNS in vitro

Silica nanoparticles based on an AIE-active molecule were prepared for ratiometric detection of reactive nitrogen species (RNS) in vitro.

Polypyridyl substituted BODIPY derivatives; water switchable imaging probes that exhibit halogen substituent dependent localisation in live cells

The synthesis and photophysical properties of water responsive 1,10-phenanthrolyl and 2,2′-bipyridyl substituted BODIPY derivatives prepared as lipid probes for cell imaging are reported.

A ratiometric mitochondria-targeting two-photon fluorescent probe for imaging of nitric oxide in vivo

A two-photon ratiometric fluorescent probe (Mito-N) has been developed for monitoring mitochondrial nitric oxide (NO) in vivo.

Water-soluble Hantzsch ester as switch-on fluorescent probe for efficiently detecting nitric oxide

A water soluble Hantzsch ester derivative of coumarin, DHPS, was synthesized and successfully applied in the fluorescent sensing nitric oxide (NO) in aqueous solution. The fluorescence of probe DHPS is extremely weak, while its fluorescence was greatly switched on upon the addition of NO solution and showed high selectivity and sensitivity to NO. The limitation of the detection was calculated to be 18nM. The NO-induced aromatization of dihydropyridine in DHPS to pyridine derivative (PYS) proved to be the switching mechanism for the fluorescent sensing process, which was confirmed through spectra characterization and computation study. Cytotoxicity assay demonstrated both DHPS and PYS are biocompatible, the DHPS was successfully applied to track the endogenously produced NO in the RAW 264.7 cells.

An Amphiphilic Fluorescent Probe Designed for Extracellular Visualization of Nitric Oxide Released from Living Cells

Nitric oxide (NO) is an intracellular and intercellular messenger involved in numerous physiological and pathophysiological processes. Small-molecule fluorescent probes coupled with fluorescence microscopy provide excellent tools for real-time detection of NO in situ. However, most probes are designed for imaging intracellular NO, which cannot reflect the release behavior of endogenously produced NO. In order to visualize extracellular NO released from living cells, we report herein a particularly designed amphiphilic fluorescent probe, disodium 2,6-disulfonate-1,3-dimethyl-5-hexadecyl-8-(3,4-diaminophenyl)-4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (DSDMHDAB), in which hydrophilic groups are introduced to keep the fluorophore and recognition domain outside the cell and a hydrophobic C16 alkyl chain acts as the membrane anchor. Based on this design, NO released out of the cells has been visualized on the outer surface of the plasma membrane. Using RAW 264.7 cells and ECV-304 cells as models, the diffusion of NO across the plasma membrane has been directly observed. The amphiphilic design strategy of fluorescent probes holds great promise for developing fluorescent imaging probes to study the release behaviors of other endogenous gasotransmitters.

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Self-assembled hydrophobin for producing water-soluble and membrane permeable fluorescent dye

Low water solubility and poor membrane permeability are major disadvantages that compromise applications of most fluorescent dyes. To resolve these problems, herein, using Boron-dipyrromethene (BODIPY) as a model fluorescent dye, for the first time, we provide a new strategy for the rapid and efficient production of a water-soluble and membrane-permeable dye by mixing with an amphiphilic protein named hydrophobin. Data shows BODIPY could be effectively solubilized and dispersed in 200 μg/mL hydrophobin by simple mixing and sonication. Subsequent experiments indicated that hydrophobin self-assembled into a protein film on the surface of BODIPY forming stable hydrophobin-BODIPY complexes with a size range of 10–30 nm. Furthermore, we demonstrated hydrophobin-functionalized BODIPY are toxicity free to cells. The hydrophobin-BODIPY complex could pass through both the cell plasma membrane and nuclear membrane efficiently. Our work opens a novel route to modify and functionalize fluorescent dyes and may be developed as a general strategy for broadening their applications.

An Approach for the Selective Detection of Nitric Oxide in Biological Systems: An in vitro and in vivo Perspective

A naphthalimide-based fluorescent probe, LyNP-NO, was designed and synthesized for the selective detection of exogenously and endogenously generated nitric oxide (NO) in C6 glial cells. In addition, LyNP-NO was also explored for monitoring endogenous NO levels in rat hippocampus at various tissue depths by stimulating the brain with N-methyl-d-aspartate (NMDA).

Dihydropyridine-based fluorescence probe for nitric oxide

A fluorescence probe for detecting nitric oxide based on dihydropyridine showed high selectivity and sensitivity as well as cell imaging ability.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

Blue ‘turn-on’ fluorescent probes for the direct detection of free radicals and nitric oxide in Pseudomonas aeruginosa biofilms

Novel blue cell-permeable ‘turn-on’ fluorescent probes have been developed to visualize and quantify nitric oxide and free radical formation and reaction within aPseudomonas aeruginosabiofilm.

Acid/Base and H2PO4(-) Controllable High-Contrast Optical Molecular Switches with a Novel BODIPY Functionalized [2]Rotaxane

A novel multifunctional mechanically interlocked switchable [2]rotaxane R4 containing two molecular stations and rotaxane arms terminated with boron-dipyrromethene (BODIPY) fluorophores and its derivatives were synthesized for the first time by CuAAC click reaction. The shuttling motion of macrocycle between the dibenzylammonium and triazolium recognition sites and the distance dependent photoinduced electron transfer process of R4 is demonstrated by utilizing external chemical stimuli (acid/base). Interestingly, the reversible self-assembly process of R4 was recognized by the acid-base molecular switch strategy. Notably, two symmetrical triazolium groups acted as molecular stations, H2PO4(-) receptors, and H-bonded donors. Both [2]rotaxane R4 and thread R2 demonstrated excellent optical responses and high selectivity toward H2PO4(-) ion. The specific motion and guest-host interactions of mechanically interlocked machines (MIMs) were also further explored by quantum mechanical calculations. The thread R2 also demonstrated to enable the detection of H2PO4(-) in RAW 264.7 cells successfully.