Sensitive determination of endogenous hydroxyl radical in live cell by a BODIPY based fluorescent probe

An innovative dual-organelle targeting NIR fluorescence probe for detecting hydroxyl radicals in biosystem and inflammation models

The hydroxyl radical (OH) is highly reactive and plays a significant role in a number of physiological and pathological processes within biosystems. Aberrant changes in the level of hydroxyl radical are associated with many disorders including tumor, inflammatory and cardiovascular diseases. Thus, detecting reactive oxygen species (ROS) in biological systems and imaging them is highly significant. In this work, a novel fluorescent probe (HR-DL) has been developed, targeting two organelles simultaneously. The probe is based on a coumarin-quinoline structure and exhibits high selectivity and sensitivity towards hydroxyl radicals (OH). When reacting with OH, the hydrogen abstraction process released its long-range π-conjugation and ICT processes, leading to a substantial red-shift in wavelength. This probe has the benefits of good water solubility (in its oxidative state), short response time (within 10 s), and unique dual lysosome/mitochondria targeting capabilities. It has been applied for sensing OH in biosystem and inflammation mice models.

Rational design of a ratiometric fluorescent nanoprobe for real-time imaging of hydroxyl radical and its therapeutic evaluation of diabetes

Hydroxyl radical (•OH), one of the most reactive and deleterious substances in organisms, belongs to a class of reactive oxygen species (ROS), and it has been verified to play an essential role in numerous pathophysiological scenarios. However, due to its extremely high reactivity and short lifetime, the development of a reliable and robust method for tracking endogenous •OH remains an ongoing challenge. In this work, we presented the first ratiometric fluorescent nanoprobe NanoDCQ-3 for •OH sensing based on oxidative C-H abstraction of dihydroquinoline to quinoline. The study mainly focused on how to modulate the electronic effects to achieve an ideal ratiometric detection of •OH, as well as solving the inherent problem of hydrophilicity of the probe, so that it was more conducive to monitoring •OH in living organisms. The screened-out probe NanoDCQ-3 exhibited an exceptional ratiometric sensing capability, better biocompatibility, good cellular uptake, and appropriate in vivo retention, which has been reliably used for detecting exogenous •OH concentration fluctuation in living cells and zebrafish models. More importantly, NanoDCQ-3 facilitated visualization of •OH and evaluation of drug treatment efficacy in diabetic mice. These findings afforded a promising strategy for designing ratiometric fluorescent probes for •OH. NanoDCQ-3 emerged as a valuable tool for the detection of •OH in vivo and held potential for drug screening for inflammation-related diseases.

BODIPY-Based Molecules for Biomedical Applications

BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives have attracted attention as probes in applications like imaging and sensing due to their unique properties like (1) strong absorption and emission in the visible and near-infrared regions of the electromagnetic spectrum, (2) strong fluorescence and (3) supreme photostability. They have also been employed in areas like photodynamic therapy. Over the last decade, BODIPY-based molecules have even emerged as candidates for cancer treatments. Cancer remains a significant health issue world-wide, necessitating a continuing search for novel therapeutic options. BODIPY is a flexible fluorophore with distinct photophysical characteristics and is a fascinating drug development platform. This review provides a comprehensive overview of the most recent breakthroughs in BODIPY-based small molecules for cancer or disease detection and therapy, including their functional potential.

Reactive Oxygen Species Suppressive Kraft Lignin-Gelatin Antioxidant Hydrogels for Chronic Wound Repair

Chronic wound is difficult to repair because the normal wound healing mechanism is inhibited by the continuous inflammatory response. The delayed inflammatory responses generate high level of reactive oxygen species (ROS) at the wound sites, which leads to a longer inflammatory phase and induces a vicious cycle that interferes with the normal wound healing process. Therefore, ROS scavenging is an important factor for chronic wound healing. In this study, antioxidant hydrogel is developed by cross-linking kraft lignin, an antioxidant agent, and gelatin (Klig-Gel). Klig-Gel hydrogel is fabricated via ring opening reaction with epichlorohydrin as a cross-linker. High ROS scavenging activities are confirmed by various antioxidant evaluations, and in vitro natural antioxidant expression tests show reduction of oxidative stress. Mechanical properties of Klig-Gel hydrogel are tailorable by introducing different amount of kraft lignin to the hydrogel system. Biocompatibility is confirmed regardless of the kraft lignin content. Klig-Gel hydrogel is a promising ROS scavenging material that can be applied in various chronic wound healing applications.

Deep-Tissue Fluorescence Imaging Study of Reactive Oxygen Species in a Tumor Microenvironment

Tumor microenvironment (TME) is the survival environment for tumor cells to proliferate and metastasize in deep tissue. TME contains tumor cells, immune cells, stromal cells and a variety of active molecules including reactive oxygen species (ROS). Inside the TME, ROS regulate the oxidation-reduction (redox) homeostasis and promote oxidative stress. Due to the rapid proliferation ability and specific metabolic patterns of the TME, ROS pervade virtually all complex physiological processes and play irreplaceable roles in protein modification, signal transduction, metabolism, and energy production in various tumors. Therefore, measurements of the dynamically, multicomponent simultaneous changes of ROS in the TME are of great significance to reveal the detailed proliferation and metastasis mechanisms of the tumor. Near-infrared (NIR) and two-photon (TP) fluorescence imaging techniques possess real-time, dynamic, highly sensitive, and highly signal-to-noise ratios with deep tissue penetration abilities. With the rationally designed probes, the NIR and TP fluorescence imaging techniques have been widely used to reveal the mechanisms of how ROS regulates and constructs complex signals and metabolic networks in TME. Therefore, we summarize the design principles and performances of NIR and TP fluorescence imaging of ROS in the TME in the last four years, as well as discuss the advantages and potentials of these works. This Review can provide guidance and prospects for future research work on TME and facilitate the development of antitumor drugs.

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

Imaging of Hydroxyl-Radical Generation Using Dynamic Nuclear Polarization-Magnetic Resonance Imaging and a Spin-Trapping Agent

Reactive oxygen species (ROS) play an important role in cell metabolism, but they can cause oxidative damage to biomolecules. Among ROS, the hydroxyl radical (·OH) is one of the most reactive molecules in biological systems because of its high reaction rate constant. Therefore, imaging of ·OH could be useful for evaluation of the redox mechanism and diagnosis of oxidative diseases. In vivo dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) is a noninvasive imaging method to obtain spatiotemporal information about free radicals with MRI anatomical resolution. In this study, we investigated the visualization of hydroxyl radicals generated from the Fenton reaction by combining DNP-MRI with a spin-trapping agent (DMPO: 5,5-dimethyl-1-pyrroline N-oxide) for ·OH. Additionally, we demonstrated the radical-scavenging effect using four thiol-related reagents by DNP-MRI. We demonstrated that DNP enhancement could be induced by the DMPO-OH radical using the DNP-MRI/spin-trapping method and visualized ·OH generation for the first time. Maximum DNP enhancement was observed at an electron paramagnetic resonance irradiation frequency of 474.5 MHz. Furthermore, the radical-scavenging effect was simultaneously evaluated by the decrease in the DNP image value of DMPO-OH. An advantage of our methods is that they simultaneously investigate compound activity and the radical-scavenging effect.

Reactive Oxygen Species Imaging in U937 Cells

The U937 cell culture is a pro-monocytic, human histiocytic lymphoma cell line. These monocytes can differentiate into either macrophages or dendritic cells (antigen-presenting cells) depending on the initiators. The U937 cells activated in the presence of phorbol 12-myristate 13-acetate (PMA) change their morphology into macrophage-like cells creating pseudopodia and adhering generously. Macrophages are known to produce reactive oxygen species (ROS) mostly during phagocytosis of foreign particles, an important non-specific immune response. Recently, we have focused on the role of hydroxyl radical (HO^∙) and provide evidence on its importance for differentiation in U937 cells. Based on electron paramagnetic resonance (EPR) spectroscopy combined with confocal laser scanning microscopy (CLSM), formation of HO^∙ was confirmed within the cells undergoing differentiation and/or apoptosis during the PMA treatment. This study aims to increase our knowledge of ROS metabolism in model cell lines used in human research.

A novel fluorescence probe for rapid and sensitive detection of tetracyclines residues based on silicon quantum dots

A novel rapid and sensitive fluorescence probe based on silicon quantum dots (Si QDs) fluorescence was fabricated for selective detection of tetracyclines (TCs) residues. Si QDs were innovatively prepared via facile One-Pot Solvent-Free Method and characterized by TEM, FT-IR, UV absorption, fluorescence, XPS and XRD. In aqueous solution, Cu²⁺ and Si QDs complexed together and the fluorescence of Si QDs quenched (static quenching) to a certain extent. TCs can be early in binding to Cu²⁺ and prevent Si QDs fluorescence quenching. As a consequence, quantitative screening of TCs can be achieved. The assay is highly selective for TCs. Represented by chlortetracycline (CTC), a member of TCs, under optimized conditions, good linear relationship in the range of 11.32-1086.72 nM was obtained, and the detection limit (LOD; S/N ratio = 3) of this assay for CTC is 0.92 nM. It was successfully applied to the determination of CTC in spiked bee honey and total TCs in actual honey samples. And the evaluation of selectivity, reproducibility and stability of the probe were favorable. These results demonstrated that the presented fluorescent probe can be a promising sensing platform for TCs analysis.

A Mitochondrion-Localized Two-Photon Photosensitizer Generating Carbon Radicals Against Hypoxic Tumors

The efficacy of photodynamic therapy is typically reliant on the local concentration and diffusion of oxygen. Due to the hypoxic microenvironment found in solid tumors, oxygen-independent photosensitizers are in great demand for cancer therapy. We herein report an iridium(III) anthraquinone complex as a mitochondrion-localized carbon-radical initiator. Its emission is turned on under hypoxic conditions after reduction by reductase. Furthermore, its two-photon excitation properties (λ_ex =730 nm) are highly desirable for imaging. Upon irradiation, the reduced form of the complex generates carbon radicals, leading to a loss of mitochondrial membrane potential and cell death (IC₅₀ ^light =2.1 μm, IC₅₀ ^dark =58.2 μm, PI=27.7). The efficacy of the complex as a PDT agent was also demonstrated under hypoxic conditions in vivo. To the best of our knowledge, it is the first metal-complex-based theranostic agent which can generate carbon radicals for oxygen-independent two-photon photodynamic therapy.

Detection of Hydroxyl Radicals Using Cerium Oxide/Graphene Oxide Composite on Prussian Blue

A composite sensor consisting of two separate inorganic layers of Prussian blue (PB) and a composite of cerium oxide nanoparticles (CeNPs) and graphene oxide (GO), is tested with •OH radicals. The signals from the interaction between the composite layers and •OH radicals are characterized using cyclic voltammetry (CV). The degradation of PB in the presence of H₂O₂ and •OH radicals is observed and its impact on the sensor efficiency is investigated. The results show that the composite sensor differentiates between the solutions with and without •OH radicals by the increase of electrochemical redox current in the presence of •OH radicals. The redox response shows a linear relation with the concentration of •OH radicals where the limit of detection, LOD, is found at 60 µM (100 µM without the PB layer). When additional composite layers are applied on the composite sensor to prevent the degradation of PB layer, the PB layer is still observed to be degraded. Furthermore, the sensor conductivity is found to decrease with the additional layers of composite. Although the CeNP/GO/PB composite sensor demonstrates high sensitivity with •OH radicals at low concentrations, it can only be used once due to the degradation of PB.

Highly selective ratiometric fluorescent probes for the detection of Fe3+ and its application in living cells

It's of vital importance to detect heavy metals in environment and living cells. In this work, four near-infrared regions boron dipyrromethene (BODIPY) probes (QBPH, PBPH, QBP and PBP) are constructed based on two BODIPY precursors (QB, PB) for sensing of Fe³⁺. As expected, these four probes exhibit obvious colorimetric and ratiometric response to Fe³⁺. In addition, QBP and PBP display highly sensitive and selective performance for detection of Fe³⁺. More importantly, QBP and PBP are successfully applied to near infrared imaging and detection of Fe³⁺ in living A549 cells; it indicates that these novel designed probes could be a useful tool for the studies of Fe³⁺ in living cells.

A sensitive BODIPY-based fluorescent probe for detecting endogenous hydroxyl radicals in living cells

A novel “turn-on” NIR fluorescent probe was designed and used for monitoring endogenous hydroxyl radical in living cells, which also showed higher selectivity toward hydroxyl radical over other reactive oxygen/nitrogen species.

Synthesis and activity of a coumarin-based fluorescent probe for hydroxyl radical detection

As a type of reactive oxygen species (ROS), hydroxyl radical (·OH) is closely associated with many kinds of diseases. The present study aimed to develo p a novel OH fluorescent probe based on coumarin, a new compound that has not been previously reported. This probe exhibited good linear range and selectivity for ·OHl, and is able to avoid interference from some metal ions and other kinds of ROS (H₂ O₂ , O₂ ^.- , ¹ O₂ , and HClO). Meanwhile, this probe has been used to evaluate the ·OH-scavenging efficiency of different compounds, such as isopropyl alcohol, cytosine, uracil, Tempo, Glutathione (GSH), and dimethyl sulfoxide (DMSO). Therefore, the present study shows that this probe not only can effectively measure the level of ·OH, but also can assess the ·OH-scavenging efficiency of different compounds. Furthermore this current study suggested that following further optimization, this probe may be potentially applied in the diagnosis of oxidative stress in human body.

A Naphthalimide-Based Fluorescence "Off-on-Off" Chemosensor for Relay Detection of Al3+ and ClO. Front Chem 2019;7:549. [PMID: 31428604 PMCID: PMC6687763 DOI: 10.3389/fchem.2019.00549]

A novel Al³⁺ chemosensor NPA was designed and synthesized on basis of the mechanism of ICT and CHEF. Upon addition of Al³⁺, the probe NPA displayed a bright green fluorescence under UV radiation and visual color change from yellow to colorless. Spectrum titrations showed that NPA could be recognized as a fluorescent turn-on probe with 10^-8 M detection level. The probe was successfully applied in real water sample and test paper. More important, NPA-Al³⁺ complex were used as a fluorescent turn-off probe for the detection of ClO^- with the detection as low as 2.34 × 10^-8 M. The performance of NPA to Al³⁺ and NPA-Al³⁺ complex to ClO^- demonstrated that NPA could be served as a sensitive probe and exhibit INHIBIT logic gate behavior with Al³⁺ and ClO^- as inputs.

Diameter-optimized high-order waveguide nanorods for fluorescence enhancement applied in ultrasensitive bioassays

Development of fluorescence enhancement (FE) platforms based on ZnO nanorods (NRs) has sparked considerable interest, thanks to their well-demonstrated potential in chemical and biological detection. Among the multiple factors determining the FE performance, high-order waveguide modes are specifically promising in boosting the sensitivity and realizing selective detection. However, quantitative experimental studies on the influence of the NR diameter, substrate, and surrounding medium, on the waveguide-based FE properties remain lacking. In this work, we have designed and fabricated a FE platform based on patterned and well-defined arrays of vertical, hexagonal prism ZnO NRs with six distinct diameters. Both direct experimental evidence and theoretical simulations demonstrate that high-order waveguide modes play a crucial role in FE, and are strongly dependent on the NR diameter, substrate, and surrounding medium. Using the optimized FE platform, a significant limit of detection (LOD) of 10-16 mol L-1 for Rhodamine-6G probe detection is achieved. Especially, a LOD as low as 10-14 g mL-1 is demonstrated for a prototype biomarker of carcinoembryonic antigen, which is improved by one order compared with the best LOD ever reported using fluorescence-based detection. This work provides an efficient path to design waveguiding NRs-based biochips for ultrasensitive and highly-selective biosensing.