Rationally Designed Fluorescence . OH Probe with High Sensitivity and Selectivity for Monitoring the Generation of . OH in Iron Autoxidation without Addition of H2 O2

Pyrazine-based iron metal organic frameworks (Fe-MOFs) with modulated O-Fe-N coordination for enhanced hydroxyl radical generation in Fenton-like process

Rational design of coordination environment of Fe-based metal-organic frameworks (Fe-MOFs) is still a challenge in achieving enhanced catalytic activity for Fenten-like advanced oxidation process. Here in, novel porous Fe-MOFs with modulated O-Fe-N coordination was developed by configurating amino terephthalic acid (H2ATA) and pyrazine-dicarboxylic acid (PzDC) (Fe-ATA/PzDC-7:3). PzDC ligands introduce pyridine-N sites to form O-Fe-N coordination with lower binding energy, which affect the local electronic environment of Fe-clusters in Fe-ATA, thus decreased its interfacial H2O2 activation barrier. O-Fe-N coordination also accelerate Fe(II)/Fe(III) cycling of Fe-clusters by triggering the reactive oxidant species mediated Fe(III) reduction. As such, Fe-ATA/PzDC-7:3/H2O2 system exhibited excellent degradation performance for typical antibiotic sulfamethoxazole (SMX), in which the steady-state concentration of hydroxyl radical (OH) was 1.6 times higher than that of unregulated Fe-ATA. Overall, this study highlights the role of O-Fe-N coordination and the electronic environment of Fe-clusters on regulating Fenton-like catalytic performance, and provides a platform for precise engineering of Fe-MOFs.

The Lifetime of Hydroxyl Radical in Realistic Fuel Cell Catalyst Layer

The lifetime of hydroxyl radicals (⋅OH) in the fuel cell catalyst layer remains uncertain, which hampers the comprehension of radical-induced degradation mechanisms and the development of longevity strategies for proton-exchange membrane fuel cells (PEMFCs). In this study, we have precisely determined that the lifetime of ⋅OH radicals can extend up to several seconds in realistic fuel cell catalyst layers. This finding reveals that ⋅OH radicals are capable of carrying out long-range attacks spanning at least a few centimeters during PEMFCs operation. Such insights hold great potential for enhancing our understanding of radical-mediated fuel cell degradation processes and promoting the development of durable fuel cell devices.

Chiral MoSe2 Nanoparticles for Ultrasensitive Monitoring of Reactive Oxygen Species In Vivo

Reactive oxygen species (ROS) are involved in neurodegenerative diseases, cancer, and acute hepatitis, and quantification of ROS is critical for the early diagnosis of these diseases. In this work, a novel probe is developed, based on chiral molybdenum diselenide (MoSe2 ) nanoparticles (NPs) modified by the fluorescent molecule, cyanine 3 (Cy3). Chiral MoSe2 NPs show intensive circular dichroism (CD) signals at 390 and 550 nm, whereas the fluorescence of Cy3 at 560 nm is quenched by MoSe2 NPs. In the presence of ROS, the probe reacts with the ROS and then oxidates rapidly, resulting in decreased CD signals and the recovery of the fluorescence. Using this strategy, the limit of detection values of CD and fluorescent signals in living cells are 0.0093 nmol/106 cells and 0.024 nmol/106 cells, respectively. The high selectivity and sensitivity to ROS in complex biological environments is attributed to the Mo4+ and Se2- oxidation reactions on the surface of the NPs. Furthermore, chiral MoSe2 NPs are able to monitor the levels of ROS in vivo by the fluorescence. Collectively, this strategy offers a new approach for ROS detection and has the potential to inspire others to explore chiral nanomaterials as biosensors to investigate biological events.

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.

Superoxide Anion-Mediated Afterglow Mechanism-Based Water-Soluble Zwitterion Dye Achieving Renal-Failure Mice Detection

Afterglow materials-based biological imaging has promising application prospects, due to negligible background. However, currently available afterglow materials mainly include inorganic materials as well as some organic nanoparticles, which are difficult to translate to the clinic, resulting from non-negligible metabolic toxicity and even leakage risk of inorganic heavy metals. Although building small organic molecules could solve such obstacles, organic small molecules with afterglow ability are extremely scarce, especially with a sufficient renal metabolic capacity. To address these issues, herein, we designed water-soluble zwitterion Cy5-NF with renal metabolic capacity and afterglow luminescence, which relied on an intramolecular cascade reaction between superoxide anion (O2•-, instead of 1O2) and Cy5-NF to release afterglow luminescence. Of note, compared with different reference contrast agents, zwitterion Cy5-NF not only had excellent afterglow properties but also had a rapid renal metabolism rate (half-life period, t1/2, around 10 min) and good biocompatibility. Unlike prior afterglow nanosystems possessing a large size, for the first time, zwitterion Cy5-NF has achieved the construction of water-soluble renal metabolic afterglow contrast agents, which showed higher sensitivity and signal-to-background ratio in afterglow imaging than fluorescence imaging for the kidney. Moreover, zwitterion Cy5-NF had a longer kidney retention time in renal-failure mice (t1/2 more than 15 min). More importantly, zwitterion Cy5-NF can be metabolized very quickly even in severe renal-failure mice (t1/2 around 25-30 min), which greatly improved biosecurity. Therefore, we are optimistic that the O2•--mediated afterglow mechanism-based water-soluble zwitterion Cy5-NF is very promising for clinical application, especially rapid detection of kidney failure.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

Reactive oxygen species in biological media are they friend or foe? Major In vivo and In vitro sensing challenges

The role of Reactive Oxygen Species (ROS) on biological media has been shifting over the years, as the knowledge on the complex mechanism that lies in underneath their production and overall results has been growing. It has been known for some time that these species are associated with a number of health conditions. However, they also participate in the immunoactivation cascade process, and can have an active role in theranostics. Macrophages, for example, react to the presence of pathogens through ROS production, potentially allowing the development of new therapeutic strategies. However, their short lifetime and limited spatial distribution of ROS have been limiting factors to the development and understanding of this phenomenon. Even though, ROS have shown successful theranostic applications, e.g., photodynamic therapy, their wide applicability has been hampered by the lack of effective tools for monitoring these processes in real time. Thus the development of innovative sensing strategies for in vivo monitoring of the balance between ROS concentration and the resultant immune response is of the utmost relevance. Such knowledge could lead to major breakthroughs towards the development of more effective treatments for neurodegenerative diseases. Within this review we will present the current understanding on the interaction mechanisms of ROS with biological systems and their overall effect. Additionally, the most promising sensing tools developed so far, for both in vivo and in vitro tracking will be presented along with their main limitations and advantages. This review focuses on the four main ROS that have been studied these are: singlet oxygen species, hydrogen peroxide, hydroxyl radical and superoxide anion.

Simultaneous detection of mitochondrial viscosity and peroxynitrite in livers from subjects with drug-induced fatty liver disease using a novel fluorescent probe

Drug-induced fatty liver disease (DIFLD) is a basic clinicopathological example of drug-induced liver injury (DILI). Some drugs can inhibit β-oxidation in hepatocyte mitochondria, leading to steatosis in the liver. Additionally, drug-induced inhibition of β-oxidation and the electron transport chain (ETC) can lead to increased production of reactive oxygen species (ROS) such as peroxynitrite (ONOO^-). Therefore, it is reasonable to suspect that compared to a healthy liver, viscosity and ONOO^- levels are elevated in livers during DIFLD. A novel, smart, dual-response fluorescent probe-Mito-VO-was designed and synthesized for the simultaneous detection of viscosity and ONOO^- content. This probe had a large emission shift of 293 nm and was capable of monitoring the viscosity of, and the ONOO^- content in, cell and animal models alike, either individually or simultaneously. For the first time, Mito-VO was successfully used to demonstrate the elevated viscosity and the amount of ONOO^- in livers from mice with DIFLD.

A turn-on fluorescent nanosensor for H2S detection and imaging in inflammatory cells and mice

Hydrogen sulfide (H₂S) is an endogenously generated gaseous signaling molecule and is known to be involved in the occurrence and development of inflammation. To better understand its physiological and pathological process of inflammation, reliable tools for H₂S detection in living inflammatory models are desired. Although a number of fluorescent sensors have been reported for H₂S detection and imaging, water-soluble and biocompatibility nanosensors are more useful for imaging in vivo. Herein, we developed a novel biological imaging nanosensor, XNP1, for inflammation-targeted imaging of H₂S. XNP1 was obtained by self-assembly of amphiphilic XNP1, which was constructed by the condensation reaction of the hydrophobic, H₂S response and deep red-emitting fluorophore with hydrophilic biopolymer glycol chitosan (GC). Without H₂S, XNP1 showed very low background fluorescence, while a significant enhancement in the fluorescence intensity of XNP1 was observed in the presence of H₂S, resulting in a high sensitivity toward H₂S in aqueous solution with a practical detection limit as low as 32.3 nM, which could be meet the detection of H₂S in vivo. XNP1 also has a good linear response concentration range (0-1 μM) toward H₂S with high selectivity over other competing species. These characteristics facilitate direct H₂S detection of the complex living inflammatory cells and drug-induced inflammatory mice, demonstrating its practical application in biosystems.

Molecular Engineering of pH-Responsive NIR Oxazine Assemblies for Evoking Tumor Ferroptosis via Triggering Lysosomal Dysfunction

Ferroptosis, a newly discovered form of regulated cell death, is emerging as a promising approach to tumor therapy. However, the spatiotemporal control of cell-intrinsic Fenton chemistry to modulate tumor ferroptosis remains challenging. Here, we report an oxazine-based activatable molecular assembly (PTO-Biotin Nps), which is capable of triggering the lysosomal dysfunction-mediated Fenton pathway with excellent spatiotemporal resolution via near-infrared (NIR) light to evoke ferroptosis. In this system, a pH-responsive NIR photothermal oxazine molecule was designed and functionalized with a tumor-targeting hydrophilic biotin-poly(ethylene glycol) (PEG) chain to engineer well-defined nanostructured assemblies within a single-molecular framework. PTO-Biotin Nps possesses a selective tropism to lysosome accumulation inside tumor cells, accommodated by its enhanced photothermal activity in the acidic microenvironment. Upon NIR light activation, PTO-Biotin Nps promoted lysosomal dysfunction and induced cytosolic acidification and impaired autophagy. More importantly, photoactivation-mediated lysosomal dysfunction via PTO-Biotin Nps was found to markedly enhance cellular Fenton reactions and evoke ferroptosis, thereby improving antitumor efficacy and mitigating systemic side effects. Overall, our study demonstrates that the molecular engineering approach of pH-responsive photothermal oxazine assemblies enables the spatiotemporal modulation of the intrinsic ferroptosis mechanism, offering a novel strategy for the development of metal-free Fenton inducers in antitumor therapy.

γ-Glutamyltransferase-Activatable Fluoro-Photoacoustic Reporter for Highly Sensitive Diagnosis of Acute Liver Injury and Tumor

γ-Glutamyltransferase (GGT) has been recognized as an important clinical biomarker that is closely related to many diseases. Visualizing the GGT fluctuation facilitates early disease-related diagnosis and therapy. Herein, an activated probe (NIR-GGT) for the imaging of GGT activity was prepared. The probe consists of a stable NIR fluorophore with the tunable amino group decorated with the γ-glutamate group as a GGT-sensing unit linked by a self-elimination group. NIR-GGT can sensitively recognize GGT and cause a strong turn-on fluorescent and photoacoustic signal. The up-regulation of the GGT expression in acetaminophen-induced acute liver injury was imaged using NIR-GGT. The probe can track changes in the GGT level in the early stages of drug-induced acute liver injury (DIALI) and its remedy process by fluorescent and photoacoustic dual-modality imaging with a high temporal-spatial resolution. NIR-GGT can also be used to differentiate between tumor and para-carcinowa tissues in vivo. The probe may be a potential tool for the diagnosis of early-stage DIALI and accurate tumor resection in the clinical field.

Cerium-terephthalic acid metal-organic frameworks for ratiometric fluorescence detecting and scavenging·OH from fuel combustion gas

Hydroxyl radical (•OH) in fuel combustion gas seriously damages human health. The techniques for simultaneously detecting and scavenging •OH in these gases are limited by poor thermal resistance. To meet this challenge, herein, metal organic frameworks (MOFs) with high thermal stability (80-400 °C) and dual function (•OH detection and elimination) are developed by coordinating Ce ions with terephthalic acid (TA) (Ce-BDC). Due to the reversible conversion between Ce³⁺ and Ce⁴⁺, and the high concentration of Ce³⁺ on the surface of Ce-BDC MOFs (89.6%), an •OH scavenging efficiency over 90% is realized. Ratiometric fluorescence (I_440 nm/I_355 nm) detection of •OH with a low detection limit of ∼4 μM is established by adopting Ce ions as an internal standard and TA as an •OH-responsive fluorophore. For real applications, the Ce-BDC MOFs demonstrate excellent •OH detection sensitivity and high •OH scavenging efficiency in gas produced from cigarettes, wood fiber and machine oil. Mouse model results show that the damage caused by •OH in cigarette smoke can be greatly reduced by Ce-BDC MOFs. This work provides a promising strategy for sensitively detecting and efficiently eliminating •OH in fuel combustion gas.

Ratiometric fluorescence nanoprobe based on carbon dots and terephthalic acid for determining Fe2+ in environmental samples

A ratiometric fluorescent nanoprobe using carbon dots (CDs) and involving oxidation of terephthalic acid (TPA) induced by hydroxyl radicals (·OH) was developed for sensitively and selectively determining Fe²⁺ ions. When Fe²⁺ ions are added to the TPA@CDs/H₂O₂ system, ·OH produced through the Fenton reaction oxidizes the non-fluorescent TPA to give 2-hydroxyl terephthalic acid, which fluoresces at 423 nm when excited at 286 nm. The ·OH and Fe³⁺ produced quench CD fluorescence at 326 nm. The 2-hydroxyl terephthalic acid to CD fluorescence intensity ratio linearly increased as the Fe²⁺ concentration increased in the range 0.5-50 μM, and the detection limit was 0.25 μM. The new assay is very selective because it involves dual-emission reverse change ratio fluorescence sensing, which can exclude matrix effects. The new nanoprobe was used to determine Fe²⁺ concentrations in real water samples, and the recoveries were found to be acceptable. Schematic of the ratiometric fluorometric method for determining Fe²⁺ based on CDs and TPA.

Golgi-Targeted Fluorescent Probe for Imaging NO in Alzheimer's Disease

Nitric oxide (NO) is a crucial neurotransmitter participating in many biological processes via nitrosylation reaction. NO produced in diverse subcellular regions also regulates the function of cells in different manners. A Golgi apparatus is rich in nitric oxide synthase and may serve as a potential therapeutic target for Alzheimer's disease (AD). However, due to the lack of an effective tool, it is difficult to reveal the relationship between Golgi-NO and AD. Herein, we report Golgi-NO as the first Golgi-targeted fluorescent probe for sensing and imaging NO in the Golgi apparatus. The probe is designed and synthesized by incorporating 4-sulfamoylphenylamide as a Golgi-targeted moiety to 6-carboxyrhodamine B, generating a fluorophore of Golgi-RhB with modifiable carboxyl, which is then combined with the NO recognition moiety of o-diaminobenzene. The probe shows superior analytical performance including accurate Golgi-targeted ability and high selectivity for NO. Moreover, using the probe, we disclose a significant increase of NO in Golgi apparatus in the AD model. This study provides a competent tool for studying the function and nitrosylation of NO in the Golgi apparatus in related diseases.

Visual Monitoring of Nucleic Acid Dynamic Structures during Cellular Ferroptosis Using Rationally Designed Carbon Dots with Robust Anti-Interference Ability to Reactive Oxygen Species

Ferroptosis triggered by an iron-dependent accumulation of lipid reactive oxygen species (ROS) has drawn widespread attention. Directly visualizing the dynamic structures of nucleic acids during the ferroptosis of cells is of great importance considering their vital roles in numerous biological functions. However, direct imaging remains challenging, largely due to the extremely high concentrations of ROS generated during ferroptosis, which can affect the imaging of nucleic acid targeted fluorescent probes. To overcome this challenge, nucleic acid-responsive carbon dots (CDs) providing favorable optical properties together with high chemical stability were synthesized. Furthermore, the CDs penetrated the cell membrane quickly and accumulated in the nuclei of cells. The robust anti-interference ability to ROS allows the CDs to visualize the dynamic structures of nucleic acids during ferroptosis. Moreover, the CDs were successfully employed in the imaging of nucleic acids during cell division. The nuclei-targeting CDs show great potential as a powerful tool for imaging nuclei in ferroptosis-related biological and clinical research.

pH-Sensitive Bioprobe for Multichannel Mitochondrial Imaging and Photodynamic Therapy

Tumor targeting therapy and photodynamic therapy are effective anti-cancer therapies. Their research progress has attracted wide attention and is one of the focuses of anti-cancer drug research and development. The design and synthesis of multifunctional organic phototheranostic agents for superior image-guided diagnosis and phototherapy play an increasingly positive role in cancer diagnosis and treatment. Herein, F16M and CyM were obtained through functional design from cyanine and F16. Physicochemical characterization and biological application results showed that CyM is a multifunctional organic biological probe, which can realize intracellular multichannel (green, yellow, red, and NIR) imaging, pH detection, and mitochondrial-targeted photodynamic therapy. As an organic phototheranostic agent, it could not only realize near-infrared imaging and photodynamic therapy in vivo and in vitro but also has excellent biocompatibility and good guiding significance for the development of multichannel imaging and mitochondrial-targeting photodynamic therapy.

Multifunctional Probes with High Utilization Rates: Self-Assembled Merocyanine Nanoparticles in Water as Acid-Base Indicators and Mitochondrion-Targeting Chemotherapeutic Agents

Multifunctional probes with high utilization rates have great value in practical applications in various fields such as cancer diagnosis and therapy. Here we have synthesized two organic molecules based on merocyanine. They can self-assemble in water to form ∼1.5 nm nanoparticles. Both of them have good application potential in fluorescent anticounterfeit printing ink and pH detection. More importantly, they have excellent mitochondrial targeting ability, intracellular red light and near-infrared dual-channel imaging ability, strong antiphotobleaching ability, and in vivo and in vitro near-infrared imaging capabilities, showing superior chemotherapy capabilities and biocompatibility in the 4T1 tumor-bearing mouse model.

Rational Design of a Two-Photon Fluorescent Probe for Human Cytochrome P450 3A and the Visualization of Mechanism-Based Inactivation

Mechanism-based inactivation (MBI) can mediate adverse reactions and hepatotoxicity from drugs, which is a result of their conversion into highly reactive metabolites catalyzed by enzymes such as cytochrome P450 3A (CYP3A). In the present research, we optimized the key interaction domain of the fluorophore with the target protein to develop a two-photon fluorescent probe for CYP3A that is involved in the metabolism of more than half of all clinical drugs. The developed BN-1 probe exhibited appropriate selectivity and sensitivity for the semi-quantitative detection and imaging of endogenous CYP3A activity in various living systems, thereby providing a high-throughput screening system enabling evaluation of MBI-associated hepatotoxicity by CYP3A. Using BN-1 as a fluorescent molecular tool facilitates the efficient discovery and characterization of CYP3A-induced MBI in natural systems.

An Edaravone-Guided Design of a Rhodamine-Based Turn-on Fluorescent Probe for Detecting Hydroxyl Radicals in Living Systems

The hydroxyl radical (·OH), one of the reactive oxygen species (ROS) in biosystems, is found to be involved in many physiological and pathological processes. However, specifically detecting endogenous ·OH remains an outstanding challenge owing to the high reactivity and short lifetime of this radical. Herein, inspired by the scavenging mechanism of a neuroprotective drug edaravone toward ·OH, we developed a new ·OH-specific fluorescent probe RH-EDA. RH-EDA is a hybrid of rhodamine and edaravone and exploits a ·OH-specific 3-methyl-pyrazolone moiety to control its fluorescence behavior. RH-EDA itself is almost nonfluorescent in physiological conditions, which was attributed to the formation of a twisted intramolecular charge transfer (TICT) state upon photoexcitation and the acylation of its rhodamine nitrogen at the 3' position. However, upon a treatment with ·OH, its edaravone subunit was converted to the corresponding 2-oxo-3-(phenylhydrazono)-butanoic acid (OPB) derivative (to afford RH-OPB), thus leading to a significant fluorescence increase (ca. 195-fold). RH-EDA shows a high sensitivity and selectivity to ·OH without interference from other ROS. RH-EDA has been utilized for imaging endogenous ·OH production in living cells and zebrafishes under different stimuli. Moreover, RH-EDA allows a high-contrast discrimination of cancer cells from normal ones by monitoring their different ·OH levels upon stimulation with β-Lapachone (β-Lap), an effective ROS-generating anticancer therapeutic agent. The present study provides a promising methodology for the construction of probes through a drug-guided approach.

Generation of hydroxyl radical-activatable ratiometric near-infrared bimodal probes for early monitoring of tumor response to therapy

Tumor response to radiotherapy or ferroptosis is closely related to hydroxyl radical (•OH) production. Noninvasive imaging of •OH fluctuation in tumors can allow early monitoring of response to therapy, but is challenging. Here, we report the optimization of a diene electrochromic material (1-Br-Et) as a •OH-responsive chromophore, and use it to develop a near-infrared ratiometric fluorescent and photoacoustic (FL/PA) bimodal probe for in vivo imaging of •OH. The probe displays a large FL ratio between 780 and 1113 nm (FL₇₈₀/FL₁₁₁₃), but a small PA ratio between 755 and 905 nm (PA₇₅₅/PA₉₀₅). Oxidation of 1-Br-Et by •OH decreases the FL₇₈₀/FL₁₁₁₃ while concurrently increasing the PA₇₅₅/PA₉₀₅, allowing the reliable monitoring of •OH production in tumors undergoing erastin-induced ferroptosis or radiotherapy.

The hydroxyl radical is generated during radiotherapy and ferroptosis and accurate imaging of this reactive oxygen species may permit the monitoring of response to therapy. Here, the authors develop a ratiometric probe for accurate imaging of hydroxyl radical generation in vivo.

Self-Immolative Dye-Doped Polymeric Probe for Precisely Imaging Hydroxyl Radicals by Avoiding Leakage

For sensing low abundance of biomarkers, utilizing nanocarriers to load dyes is an efficient method to amplify the detected signal. However, the non-specific leak of the internal dyes in this approach is accompanied by false positive signals, resulting in inaccurate signal acquirement. To address this issue, in this work, we reported a novel signal amplification strategy with dye as a scaffold to construct a self-immolative dye-doped polymeric probe (SDPP). In our proposed approach, the dyes were covalently integrated into the main chain of a polymer, which can avoid the non-specific leak of the dye when used in a rigorous biological environment, thus evading the false positive signal. As a prototype of this concept, a SDPP, which responds to hydroxyl radicals (^•OH), was rationally fabricated. Upon being activated by ^•OH, SDPP will liberate the dye through a self-immolative reaction to bind with protein for amplifying the fluorescence signal. Compared with a dye-loaded nanoprobe, SDPP can precisely track intracellular basal ^•OH levels and visualize the ^•OH associated with myocarditis in vivo. More importantly, the attempt in this work not only provides an effective molecular tool to investigate the role of ^•OH in cardiopathy, but also puts forward a new direction to current signal-amplifying strategies for precisely and reliably acquiring the intracellular molecular information.

Nanoparticle-Mediated Inhibition of Mitochondrial Glutaminolysis to Amplify Oxidative Stress for Combination Cancer Therapy

Selective amplification of reactive oxygen species (ROS) generation in tumor cells has been recognized as an effective strategy for cancer therapy. However, an abnormal tumor metabolism, especially the mitochondrial glutaminolysis, could promote tumor cells to generate high levels of antioxidants (e.g., glutathione) to evade ROS-induced damage. Here, we developed a tumor-targeted nanoparticle (NP) platform for effective breast cancer therapy via combining inhibition of mitochondrial glutaminolysis and chemodynamic therapy (CDT). This NP platform is composed of bovine serum albumin (BSA), ferrocene, and purpurin. After surface decoration with a tumor-targeting aptamer and then intravenous administration, this NP platform could target tumor cells and release ferrocene to catalyze hydrogen peroxide (H₂O₂) into the hydroxyl radical (·OH) for CDT. More importantly, purpurin could inhibit mitochondrial glutaminolysis to concurrently prevent the nutrient supply for tumor cells and disrupt intracellular redox homeostasis for enhanced CDT, ultimately leading to the combinational inhibition of tumor growth.

Harnessing Hypoxia-Dependent Cyanine Photocages for In Vivo Precision Drug Release

Photocaging holds promise for the precise manipulation of biological events in space and time. However, current near-infrared (NIR) photocages are oxygen-dependent for their photolysis and lack of timely feedback regulation, which has proven to be the major bottleneck for targeted therapy. Herein, we present a hypoxia-dependent photo-activation mechanism of dialkylamine-substituted cyanine (Cy-NH) accompanied by emissive fragments generation, which was validated with retrosynthesis and spectral analysis. For the first time, we have realized the orthogonal manipulation of this hypoxia-dependent photocaging and dual-modal optical signals in living cells and tumor-bearing mice, making a breakthrough in the direct spatiotemporal control and in vivo feedback regulation. This unique photoactivation mechanism overcomes the limitation of hypoxia, which allows site-specific remote control for targeted therapy, and expands the photo-trigger toolbox for on-demand drug release, especially in a physiological context with dual-mode optical imaging under hypoxia.

Multifunction in One Molecule: Mitochondrial Imaging and Photothermal & Photodynamic Cytotoxicity of Fast-Response Near-Infrared Fluorescent Probes with Aggregation-Induced Emission Characteristics

HJS and DHJS, two near-infrared emissive and mitochondria-targeted therapy probes, have been designed. They exhibited photothermal & photodynamic cytotoxicity and aggregation-induced emission (AIE) characteristics. Interestingly, we could receive fluorescence immediately after adding the probes without washing in 1 min. They could quickly enter cancer cells and selectively localized to the mitochondria firstly. When the concentration of probes was low (<5 μM), they could respond sensitively to the mitochondrial membrane potential and would selectively enter the mitochondria with red fluorescence. However, when the concentration was high (≥5 μM), they would preferentially enter the mitochondria and have the property of dual-channel fluorescence imaging (red and near-infrared) even after 24 h. What's more, they increased the intracellular reactive oxygen species (ROS) levels, decreased the mitochondrial membrane potentials, and then induced apoptosis, which were proved by confocal imaging and flow cytometry experiments. In addition, the results of photothermal experiment and cytotoxicity test showed that the probes had good photothermal and photodynamic toxicity to cancer cells. In vitro and in vivo experiments also proved the excellent near-infrared (NIR) imaging ability, good biocompatibility and certain inhibition of tumor growth ability of DHJS.

Nitric oxide-donating and reactive oxygen species-responsive prochelators based on 8-hydroxyquinoline as anticancer agents

Metal ion chelators based on 8-hydroxyquinoline (8-HQ) have been widely explored for the treatment of many diseases. When aimed at being developed into potent anticancer agent, a largely unmet issue is how to avoid nonspecific chelation of metal ions by 8-HQ in normal cells or tissues. In the current work, a two-step strategy was employed to both enhance the anticancer activity of 8-HQ and improve its cancer cell specificity. Considering the well-known anticancer activity of nitric oxide (NO), NO donor furoxan was first connected to 8-HQ to construct HQ-NO conjugates. These conjugates were screened for their cytotoxicity, metal-binding ability, and NO-releasing efficiency. Selected conjugates were further modified with a ROS-responsive moiety to afford prochelators. Among all the target compounds, prodrug HQ-NO-11 was found to potently inhibit the proliferation of many cancer cells but not normal cells. The abilities of metal chelation and NO generation by HQ-NO-11 were confirmed by various methods and were demonstrated to be essential for the anticancer activity of HQ-NO-11. In vivo studies revealed that HQ-NO-11 inhibited the growth of SW1990 xenograft to a larger extent than 8-HQ. Our results showcase a general method for designing novel 8-HQ derivatives and shed light on obtaining more controllable metal chelators.

Ultra-low background signaling cascade amplifiers for in vivo fluorescence imaging of hydroxyl radical production induced by testosterone

A novel ultra-low background signal cascade amplifier was developed to understand the production mechanism of ˙OH pools in situ stimulated by testosterone.

Visible and Reversible Restrict of Molecular Configuration by Copper Ion and Pyrophosphate

Molecular configuration strongly impacts on its functions; however, due to complicated and diverse configuration as well as easy and rapid conversion among various configurations, research of molecular configuration is extremely difficult. If the free rotation of a molecule could be "slowed down" or even "frozen" by an external stimulus, such as ultralow temperature, then one configuration of the molecule could be captured and characterized relatively easily. Here, we show that the rotation of a hemicyanine-labeled 2-(2'-hydroxyphenyl)-4-methyloxazole (H-HPMO) molecule could be specifically and reversibly restricted by sequential additions of copper ion (Cu²⁺) and pyrophosphate (P₂O₇^4-), reflecting as remarkable fluorescence quenching and recovery, which could be directly observed by naked eyes. Binding affinity tests and cryogenic ¹H NMR indicate that Cu²⁺ forms intensive coordinate bonds with phenolic hydroxyl, oxazole, and methoxyl groups of HPMO, which strongly restricts the free rotations of these groups and blocks charge transfer. This study provides a precise, rapid, visible, reversible, and low-cost method to monitor the molecular configuration, indicating the broad application prospects of near-infrared fluorescent sensors in configuration analysis, biosensing, and drug-substrate complexation.

Epileptic brain fluorescent imaging reveals apigenin can relieve the myeloperoxidase-mediated oxidative stress and inhibit ferroptosis

Myeloperoxidase (MPO)-mediated oxidative stress has been suggested to play an important role in the pathological dysfunction of epileptic brains. However, there is currently no robust brain-imaging tool to detect real-time endogenous hypochlorite (HClO) generation by MPO or a fluorescent probe for rapid high-throughput screening of antiepileptic agents that control the MPO-mediated chlorination stress. Herein, we report an efficient two-photon fluorescence probe (named HCP) for the real-time detection of endogenous HClO signals generated by MPO in the brain of kainic acid (KA)-induced epileptic mice, where HClO-dependent chlorination of quinolone fluorophore gives the enhanced fluorescence response. With this probe, we visualized directly the endogenous HClO fluxes generated by the overexpression of MPO activity in vivo and ex vivo in mouse brains with epileptic behaviors. Notably, by using HCP, we have also constructed a high-throughput screening approach to rapidly screen the potential antiepileptic agents to control MPO-mediated oxidative stress. Moreover, from this screen, we identified that the flavonoid compound apigenin can relieve the MPO-mediated oxidative stress and inhibit the ferroptosis of neuronal cells. Overall, this work provides a versatile fluorescence tool for elucidating the role of HClO generation by MPO in the pathology of epileptic seizures and for rapidly discovering additional antiepileptic agents to prevent and treat epilepsy.

An endoplasmic reticulum-targeted two-photon fluorescent probe for bioimaging of HClO generated during sleep deprivation

With the development of social society, sleep deprivation has become a serious and common issue. Previous studies documented that there is a correlation between sleep deprivation and oxidative stress. However, the information of sleep deprivation related ROS has rarely been obtained. Also, it has been demonstrated that sleep deprivation can induce endoplasmic reticulum (ER) stress. As such, for a better understanding of sleep deprivation as well as its related diseases, it is important to develop probes with ER-targeting ability for detecting ROS generated in this process. Herein, a novel two-photon fluorescent molecular probe, JX-1, was designed for sensing HClO in live cells and zebrafish. The investigation data showed that in addition to real-time response (about 150 s), the probe also exhibited high sensitivity and selectivity. Moreover, the probe JX-1 demonstrated two-photon fluorescence, low cytotoxicity and ER targeting ability. These prominent properties enabled the utilization of the probe for monitoring exogenous and endogenous HClO in both live cells and zebrafish. Using this useful tool, it was found that sleep deprivation can induce the generation of HClO in zebrafish.

Selenium-doped two-photon fluorescent carbon nanodots for in-situ free radical scavenging in mitochondria

Mitochondrial oxidative stress is associated with the occurrence and development of a wide range of human diseases. The development of methodologies to alleviate oxidative stress-mediated injury may have therapeutic potential. Herein, we report the design and preparation of triphenylphosphonium-functionalized selenium-doped carbon nanodots (TPP-Se-CDs) that can efficiently scavenging hydroxyl radicals (OH) and superoxide anions (O₂^-) in mitochondria region. Se-CDs with two-photon blue fluorescence were initially prepared by facile hydrothermal treatment of selenomethionine, followed by the covalent conjugation with TPP. The as-obtained TPP-Se-CDs showed high colloidal stability, strong scavenging abilities towards OH and O₂^-. Moreover, TPP-Se-CDs exhibited low cytotoxicity and mitochondria targeting ability. Taking advantages of these prominent features, TPP-Se-CDs have been successfully applied to combat H₂O₂ and phorbol 12-myristate 13-acetate (PMA) induced oxidative stress in mitochondria.

Sensitive and Selective Measurement of Hydroxyl Radicals at Subcellular Level with Tungsten Nanoelectrodes

Hydroxyl radical (^•OH) is an essential reactive oxygen species involved in critical cell functions. However, the mechanisms controlling its subcellular localization and intracellular level during health and disease remain poorly understood. This is due to the challenge of detecting ^•OH that are highly reactive and consequently short-lived (in vivo half-life of ∼10^-9 s). Herein, we present tungsten nanoelectrodes functionalized with stable 1-hexanethiol (HAT) for selective and sensitive detection of ^•OH at the subcellular level via the destruction of the self-assembled monolayer of HAT on the nanoelectrode tip. Taking advantage of the ultrasmall nanotip and the super mechanical toughness, the tungsten nanoelectrode could easily penetrate a single living cell without inducing any observable damage. Controlled by a high precision micromanipulator, the ^•OH level in RAW 264.7 murine macrophages under amyloid β (Aβ) induced oxidative stress were first investigated by the nanoelectrodes at the subcellular level. Moreover, the results revealed the cordycepin-mediated cytoprotection of macrophages through modulation of PI3K/Akt pathway activity and introduction of heme oxygenase-1 (HO-1). We believe that the developed nanoelectrochemical method has shown great capacities for the study of potential drugs for therapeutic intervention of Alzheimer's disease.