Redox-Responsive Fluorescent Probes with Different Design Strategies

A selenium-based fluorescent sensor for the reversible detection of ClO- and H2S in foods

HClO/ClO- and H2S are two kinds of momentous biological small molecules in the organism, and the redox balance between them is considerable for the physiological and pathological properties of organisms. Hence, it is very crucial to monitor the redox course between HClO and H2S. Herein, a reversible fluorescent sensor (IPSe) for ClO- and H2S was firstly constructed with the selenium atom as the response site and the dicyanoisophorone as the fluorophore. The sensor IPSe could detect ClO- with good selectivity and sensitivity due to the oxidation reaction of the selenium atom triggered by ClO-. The recognition of IPSe to hypochlorite induced a hypsochromic shift of the absorption maximum from 420 nm to 380 nm. IPSe exhibited the prominent low detection limit of 55.3 nM for detecting ClO-, accompanied by distinct fluorescent attenuation. Moreover, H2S could efficiently return the fluorescence of the IPSe solution to the original level by H2S reducing selenoxide. The experimental results show that the suggested method has high precision and accuracy for the detection of ClO- and H2S. The applications in real water samples, beverages and cell imaging verified that the IPSe was capable of monitoring the changes in the concentration of ClO-/H2S, which indicates that it is of great meaning to survey the biological functions of ClO- and H2S via IPSe.

Ratiometric Fluorescent Probe for Sensitive Tracking of Peroxynitrite during Drug-Induced Hepatotoxicity

As an essential component of reactive oxygen species (ROS), peroxynitrite (ONOO-) plays an indispensable role in redox homeostasis and signal transduction, with anomalous levels implicated in various clinical conditions. Therefore, accurate and rapid detection of intracellular ONOO- levels is crucial for revealing its role in physiological and pathological processes. In this study, we developed a ratiometric fluorescent probe to detect ONOO- levels in biological systems. The probe demonstrated a fast reaction rate (within 15 min), outstanding selectivity, high sensitivity (limit of detection=13.32 nM), and stability in the presence of ONOO-. The proposed probe was successfully used for visualizing endogenous ONOO- in living cells and tracking changes in intracellular ONOO- levels during drug-induced hepatotoxicity using ratiometric fluorescence.

Nickel(II) complexes with covalently attached quinols rely on ligand-derived redox couples to catalyze superoxide dismutation

Although nickel is found in the active sites of a class of superoxide dismutase (SOD), nickel complexes with non-peptidic ligands normally do not catalyze superoxide degradation, and none has displayed activity comparable to those of the best manganese-containing SOD mimics. Here, we find that nickel complexes with polydentate quinol-containing ligands can exhibit catalytic activity comparable to those of the most efficient manganese-containing SOD mimics. The nickel complexes retain a significant portion of their activity in phosphate buffer and under operando conditions and rely on ligand-centered redox processes for catalysis. Although nickel SODs are known to cycle through Ni(II) and Ni(III) species during catalysis, cryo-mass spectrometry studies indicate that the nickel atoms in our catalysts remain in the +2 oxidation state throughout SOD mimicry.

Naphthalene peri-Diselenide-Based BODIPY Probe for the Detection of Hydrogen Peroxide, tert-Butylhydroperoxide, Hydroxyl Radical, and Peroxynitrite Ion

Dimethoxynaphthalene peri-diselenide-based BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) probe has been synthesized. The probe demonstrated selectivity and sensitivity for hydrogen peroxide (H2O2) and tert-butylhydroperoxide (t-BuOOH), hydroxyl radical (•OH), and peroxynitrite ion (ONOO-) detection and reversibility upon treatment with glutathione. The limits of detection of the probe were observed to be 0.40 μM for H2O2, 0.41 μM for t-BuOOH, 0.95 μM for •OH, and 0.46 μM for ONOO-, respectively. A proposed mechanism for the "turn-on" event has been suggested and corroborated by spectroscopic and computational data. It has been proposed that electron transfer occurred from the Se center to the BODIPY moiety, followed by the photoinduced electron transfer (PET) mechanism.

Development of diselenide-based fluorogenic system for the selective and sensitive detection of the Hg(II) in aqueous media

Mercury(II) is highly toxic thus the selective and sensitive detection of Hg(II) is important. This research article deals with the synthesis and characterization of the fluorogenic system based on diselenide containing rhodamine by single crystal XRD. The probe has been used for selective detection of Hg(II) in aqueous media with detection limit of 62.3 nM. The reaction of the Hg(II) with the probe induces opening of the spirolactam ring triggering fluorescence turn-on response. This reaction causes color change of the probe solution from colorless to pink. In addition, the probe showed the reversible binding behavior with Hg(II) and S2-. The effectiveness of the probe was evaluated using prostate cancer cell line through live cell imaging.

New horizons in nanoelectrochemistry: concluding remarks

The aim of this paper is to overview the meeting on New horizons in nanoelectrochemistry held at Nanjing University in China in October 2024 and to give some perspective to the work presented. This paper is based on my summary talk and breaks down the subjects in the following areas of nanoelectrochemistry presented at the meeting: nanowires, nanonets, and nanoarrays; nanopores; nanopipettes; spectroelectrochemistry, scanning ion-conductance microscopy and light-active processes at nanointerfaces; scanning electrochemical microscopy and scanning electrochemical cell microscopy; and nanosensors. I end with some discussion of online meetings and where the field might go including artificial intelligence and by asking AI to define the challenges and future of nanoelectrochemistry.

The electrochemical modulation of single molecule fluorescence

Recently it has been shown that electrochemistry, instead of using high intensity lasers, can be used to modulate the intensity of emission of fluorophores and even switch fluorophores between their ON and OFF states as required for single molecule localisation microscopy. This modulation of fluorescence does not necessarily correlate with direct oxidation and reduction of the dyes. Questions arise from this unexpected observation related to what is the electrochemistry that occurs, what are the important variables in switching fluorophores electrochemically and what range of dyes can be modulated with electrochemistry. Herein we seek to answer some of these questions. We demonstrate how to effectively modulate the fluorescence intensity of organic dye-labelled cell samples on an indium tin oxide surface using electrochemistry with redox-active mediators present in an oxygen scavenger buffer. We showed the electrochemical fluorescence modulation is sensitive to the applied potential and the excitation laser intensity, indicating the possibility of coupled photochemical and electrochemical reactions occurring. We also compared the electrochemical fluorescence modulation of representative oxazine, rhodamine, and cyanine dyes using ATTO 655, Alexa Fluor 488, and Alexa Fluor 647. Different dyes with distinctly different structural cores show fluorescence modulation to different extents. The electrochemical fluorescence modulation will be applicable in fluorescence imaging techniques as well as biosensing.

Anthracene carboxyimide-based selenide as a fluorescent probe for the ultrasensitive detection of hypochlorous acid

In situ detection of hypochlorous acid (HOCl) is critical for understanding its complex physiological and pathological roles. Fluorescent probes, known for their sensitivity and selectivity, are the preferred approach for such detections. Anthracene carboxyimide, an analog of naphthalimide, offers extended excitation and emission wavelengths, making it an excellent candidate for developing new fluorescent probes that address the limitations of naphthalimide. In this study, we designed a novel HOCl-specific fluorescent probe, AC-Se, by incorporating highly reactive selenium into anthracene carboxyimide. The probe exhibits a 104-fold fluorescence enhancement, a large Stokes shift of 72 nm, and a low detection limit of 36.2 nM. Moreover, AC-Se responds rapidly to HOCl within 4 seconds, enabling real-time intracellular monitoring of both exogenous and endogenous HOCl.

Click Coupling of Flavylium Dyes with Plasmodione Analogues: Towards New Redox-Sensitive Pro-Fluorophores

The development of redox-sensitive molecular fluorescent probes for the detection of redox changes in Plasmodium falciparum-parasitized red blood cells remains of interest due to the limitations of current genetically encoded biosensors. This study describes the design, screening and synthesis of new pro-fluorophores based on flavylium azido dyes coupled by CuAAC click chemistry to alkynyl analogues of plasmodione oxide, the key metabolite of the potent redox-active antimalarial plasmodione. The photophysical and electrochemical properties of these probes were evaluated, focusing on their fluorogenic responses. The influence of both the redox status of the quinone and the length of the PEG chain separating the fluorophore from the electrophore on the photophysical properties was investigated. The fluorescence quenching by photoinduced electron transfer is reversible and of high amplitude for probes in oxidized quinone forms and fluorescence is reinstated for reduced hydroquinone forms. Our results demonstrate that shortening the PEG chain has the effect of enhancing the fluorogenic response, likely due to non-covalent interactions between the two chromophores. All these systems were evaluated for their antiparasitic activities and fluorescence imaging suggests the efficacy of the fluorescent flavylium dyes in P. falciparum-parasitized red blood cells, paving the way for future parasite imaging studies to monitor cellular redox processes.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

Recent advances of versatile fluorophores for multifunctional biomedical imaging in the NIR-II region

Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) enables high-resolution visualization of deep-tissue biological architecture and physiopathological events, due to the reduced light absorption, scattering and tissue autofluorescence. Numerous versatile NIR-II fluorescent probes have been reported over the past decades. In this review, we first provide a detailed account of the advantages of fluorescence imaging in the NIR-II region. Following this, the classification, design and performance optimization strategies of NIR-II fluorescent probes are systematically discussed, along with a broad range of biomedical applications in vivo. Finally, the discussion extends to the next generation of fluorescent probes for in vivo imaging and the challenges and perspectives for the clinical translation of fluorescence imaging technology in the NIR-II region.

Light/X-ray/ultrasound activated delayed photon emission of organic molecular probes for optical imaging: mechanisms, design strategies, and biomedical applications

Conventional optical imaging, particularly fluorescence imaging, often encounters significant background noise due to tissue autofluorescence under real-time light excitation. To address this issue, a novel optical imaging strategy that captures optical signals after light excitation has been developed. This approach relies on molecular probes designed to store photoenergy and release it gradually as photons, resulting in delayed photon emission that minimizes background noise during signal acquisition. These molecular probes undergo various photophysical processes to facilitate delayed photon emission, including (1) charge separation and recombination, (2) generation, stabilization, and conversion of the triplet excitons, and (3) generation and decomposition of chemical traps. Another challenge in optical imaging is the limited tissue penetration depth of light, which severely restricts the efficiency of energy delivery, leading to a reduced penetration depth for delayed photon emission. In contrast, X-ray and ultrasound serve as deep-tissue energy sources that facilitate the conversion of high-energy photons or mechanical waves into the potential energy of excitons or the chemical energy of intermediates. This review highlights recent advancements in organic molecular probes designed for delayed photon emission using various energy sources. We discuss distinct mechanisms, and molecular design strategies, and offer insights into the future development of organic molecular probes for enhanced delayed photon emission.

Cobalt-catalyzed hydrothiolation of alkynes for the diverse synthesis of branched alkenyl sulfides

Alkenyl sulfides have gained increasing prominence in medicinal chemistry and materials. Hydrothiolation of alkynes for the diverse synthesis of alkenyl sulfides is an appealing method. Herein, we report a cobalt-catalyzed Markovnikov hydromethylthiolation of alkynes to afford branched alkenyl methylsulfanes with good yields and high regioselectivity. This method also enables the diverse synthesis of branched alkenyl sulfides. The reaction shows good functional group tolerance and could be scaled up. The mechanistic studies including control experiments, deuterium-labeling experiments, and Hammett plot indicated alkynes insertion followed by electrophilic thiolation pathway.

Fast Intramolecular Thiol-Activated Arylselenoamides Provide Access to Triggered, Fluorogenic H2Se Donors

H2Se is the precursor for the biosynthesis of selenocompounds and is a potential gasotransmitter. Chemical tools for H2Se delivery and detection are important for Se-related biology research. Key challenges in the field include developing compound platforms that are triggered to release H2Se under various stimuli and developing fluorogenic donors that allow for real-time tracking of H2Se delivery. Here we report a new general platform for triggered H2Se donors based on controllable deprotection of a thiol, which can quickly activate an intramolecular arylselenoamide (t1/2 < 1 min) to release H2Se efficiently. Furthermore, we leverage this platform to develop the first examples of fluorogenic H2Se donors, which can be used to monitor H2Se release by fluorescence in real time. We anticipate that the well-defined donation chemistries will significantly advance the development of H2Se donors and stimulate further in-depth studies of H2Se biomedicine.

Reversible Fluorescent Probes for Dynamic Imaging of Liver Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion injury (HIRI) is an inevitable complication of clinical surgeries such as liver resection or transplantation, often resulting in postoperative liver dysfunction, hepatic failure in up to 13% of postresection patients, and early graft failure in 11-18% of liver transplantation patients. HIRI involves a series of biochemical events triggered by abnormal alterations in multiple biomarkers, characterized by short lifespans, dynamic changes, subcellular regional distribution, and multicollaborative regulation. However, traditional diagnosis, including serology, imaging, and liver puncture biopsy, suffers from low sensitivity, poor resolution, and hysteresis, which hinder effective monitoring of HIRI markers. Thus, to address the unique properties of HIRI markers, there is a pressing demand for developing novel detection strategies that are highly selective, transiently responsive, dynamically reversible, subcellular organelle-targeted, and capable of simultaneous multicomponent analysis. Optical probe-based fluorescence imaging is a powerful tool for real-time monitoring of biomarkers with the advantages of high sensitivity, noninvasiveness, rapid analysis, and high-fidelity acquisition of spatiotemporal information on signaling molecules compared with conventional methods. Moreover, with the growing demand for continuous monitoring of biomarkers, probes with reversible detection features are receiving more and more attention. Importantly, reversible probes can not only monitor fluctuations in marker concentrations but also distinguish between transient bursts of markers during physiological events and long-term sustained increases in pathological marker levels. This can effectively avoid false-positive test results, and in addition, reversible probes can be reutilized with green and economical features. Therefore, our team has employed various effective methods to design reversible optical probes for HIRI. We proposed reversible recognition strategies based on specific reactions or interactions to detect dynamic changes in markers. Given the biomarkers' unique signaling in subcellular organelles and the synergistic regulatory properties of multiple markers for HIRI, bifunctional reversible detection strategies are exploited, including organelle-targeted reversible and multicomponent simultaneous detection. With these strategies, we have tailored a variety of high-fidelity fluorescent probes for a series of HIRI markers, including reactive oxygen/nitrogen species (O2•- and ONOO-), ATP, protein (Keap1), mitochondrial DNA, etc. Utilizing the probes, the in situ dynamic imaging detection of the HIRI markers was successfully achieved. While performing the precise examination of the earlier occurrence of HIRI disease and visualizing the real-time monitoring of the disease process, we have also further elucidated the HIRI-associated signaling pathways. It is envisioned that our summarized work will inspire the design of future reversible fluorescent probes and help to improve the clinical diagnosis and therapeutic efficiency of these diseases.

Synthesis and characterization of organoselenium based BODIPY and its application in living cells

Phenylselenide based BODIPY probe was successfully synthesized and characterized by NMR spectroscopic techniques (1H, 13C and 77Se NMR), mass spectrometry and single crystal XRD. Surprisingly, crystal packing diagram of the probe showed formation of 1-D strip through intermolecular F---H interaction. The probe was screened with various Reactive Oxygen Species (ROS) and found to be selective for superoxide ion over other ROS via "turn-on" fluorescence response. The probe selectively and sensitively detects superoxide with a lower detection limit (43.34 nM) without interfering with other ROS. The quantum yield of the probe was found to increase from 0.091 % to 30.4 % (334-fold) after oxidation. Theoretical calculations (DFT and TD-DFT) were also performed to understand the sensing mechanism of the probe. The probe was able to effectively detect superoxide inside living cells without any toxic effect.

Stimuli-responsive linkers and their application in molecular imaging

Molecular imaging is a non-invasive imaging method that is widely used for visualization and detection of biological events at cellular or molecular levels. Stimuli-responsive linkers that can be selectively cleaved by specific biomarkers at desired sites to release or activate imaging agents are appealing tools to improve the specificity, sensitivity, and efficacy of molecular imaging. This review summarizes the recent advances of stimuli-responsive linkers and their application in molecular imaging, highlighting the potential of these linkers in the design of activatable molecular imaging probes. It is hoped that this review could inspire more research interests in the development of responsive linkers and associated imaging applications.

Expedient, regioselective C-H chalcogenation of 3,4-dihydro-1,4-benzoxazines using a palladium-copper catalyst

The palladium-catalysed regioselective C-H chalcogenation of benzoxazines with disulfides and diselenides in air has been described. In this protocol, palladium acetate serves as the catalyst in conjunction with copper as an oxidizing agent. Through this approach, a wide array of sulfenylation and selenylation reactions of benzomorpholines have been effected, yielding results ranging from good to excellent. Thus, the established procedure demonstrates superb regioselectivity and a strong tolerance towards various functional groups and is suitable for gram-scale synthesis. Additionally, this synthetic approach offers a practical and convenient pathway for late-stage functionalization leading to the Rosenmund-von Braun reaction.

Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species

Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) serve as vital mediators essential for preserving intracellular redox homeostasis within the human body, thereby possessing significant implications across physiological and pathological domains. Nevertheless, deviations from normal levels of ROS, RNS, and RSS disturb redox homeostasis, leading to detrimental consequences that compromise bodily integrity. This disruption is closely linked to the onset of various human diseases, thereby posing a substantial threat to human health and survival. Small-molecule fluorescent probes exhibit considerable potential as analytical instruments for the monitoring of ROS, RNS, and RSS due to their exceptional sensitivity and selectivity, operational simplicity, non-invasiveness, localization capabilities, and ability to facilitate in situ optical signal generation for real-time dynamic analyte monitoring. Due to their distinctive transition from their spirocyclic form (non-fluorescent) to their ring-opened form (fluorescent), along with their exceptional light stability, broad wavelength range, high fluorescence quantum yield, and high extinction coefficient, rhodamine fluorophores have been extensively employed in the development of fluorescent probes. This review primarily concentrates on the investigation of fluorescent probes utilizing rhodamine dyes for ROS, RNS, and RSS detection from the perspective of different response groups since 2016. The scope of this review encompasses the design of probe structures, elucidation of response mechanisms, and exploration of biological applications.

Detection of redox potential evolution during the initial stage of an acute wound based on a redox-sensitive SERS-active optical fiber

To detect redox potential evolution during the initial stage of an acute wound, a redox-sensitive SERS-active optical fiber was fabricated by integrating redox-sensitive SERS probes in a hole of an optical fiber. The redox-sensitive SERS-active optical fibers carried redox-sensitive SERS probes into the inside of a wound to sense its redox potential. The laser was transmitted to the redox-sensitive SERS probes in the body by optical fibers, and the SERS signals of the redox-sensitive SERS probes were transferred out of the body by optical fibers to indicate the redox potentials in the wound. The redox-sensitive SERS probes dynamically sensed the redox potential in vivo, and their SERS signals were collected constantly to indicate the redox potentials. The assessments in vivo and in vitro proved the responsiveness of redox-sensitive SERS-active optical fibers. The redox potential evolution during the initial stage of an acute wound with the treatments of different concentrations of glucose was detected to verify the feasibility of redox-sensitive SERS-active optical fibers to dynamically detect redox potentials in vivo. The redox-sensitive SERS-active optical fiber would be a versatile tool to explore the roles of redox potentials in living organisms.

Iodine-Catalyzed Cyclization of o-Nitrothiophenols with Cyclohexanones to Phenothiazines

Here, a novel iodine-catalyzed direct cyclization of o-nitrothiophenols with cyclohexanones to phenothiazines has been described without external oxidants and hydrogen acceptors. The nitro of o-nitrothiophenol works as both a hydrogen acceptor and a coupling group, and water is the only byproduct. The reaction involves the reduction of nitro groups, C-H bond thioetherification, and C-H bond dehydroaromatization. This scheme offers broad synthetic value for further elaborations, as exemplified by a 3-step total synthesis of antipsychotic chlorpromazine.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Single-molecule electrochemical imaging resolves the midpoint potentials of individual fluorophores on nanoporous antimony-doped tin oxide

We report reversible switching of oxazine, cyanine, and rhodamine dyes by a nanoporous antimony-doped tin oxide electrode that enables single-molecule (SM) imaging of electrochemical activity. Since the emissive state of each fluorophore is modulated by electrochemical potential, the number of emitting single molecules follows a sigmoid function during a potential scan, and we thus optically determine the formal redox potential of each dye. We find that the presence of redox mediators (phenazine methosulfate and riboflavin) functions as an electrochemical switch on each dye's emissive state and observe significantly altered electrochemical potential and kinetics. We are therefore able to measure optically how redox mediators and the solid-state electrode modulate the redox state of fluorescent molecules, which follows an electrocatalytic (EC') mechanism, with SM sensitivity over a 900 μm2 field of view. Our observations indicate that redox mediator-assisted SM electrochemical imaging (SMEC) could be potentially used to sense any electroactive species. Combined with SM blinking and localization microscopy, SMEC imaging promises to resolve the nanoscale spatial distributions of redox species and their redox states, as well as the electron transfer kinetics of electroactive species in various bioelectrochemical processes.

Selenium-Based Catalytic Scavengers for Concurrent Scavenging of H2 S and Reactive Oxygen Species

Hydrogen sulfide (H2 S) is an endogenous gasotransmitter that plays important roles in redox signaling. H2 S overproduction has been linked to a variety of disease states and therefore, H2 S-depleting agents, such as scavengers, are needed to understand the significance of H2 S-based therapy. It is known that elevated H2 S can induce oxidative stress with elevated reactive oxygen species (ROS) formation, such as in H2 S acute intoxication. We explored the possibility of developing catalytic scavengers to simultaneously remove H2 S and ROS. Herein, we studied a series of selenium-based molecules as catalytic H2 S/H2 O2 scavengers. Inspired by the high reactivity of selenoxide compounds towards H2 S, 14 diselenide/monoselenide compounds were tested. Several promising candidates such as S6 were identified. Their activities in buffers, as well as in plasma- and cell lysate-containing solutions were evaluated. We also studied the reaction mechanism of this scavenging process. Finally, the combination of the diselenide catalyst and photosensitizers was used to achieve light-induced H2 S removal. These Se-based scavengers can be useful tools for understanding H2 S/ROS regulations.

Dual-responsive probe and DNA interstrand crosslink precursor target the unique redox status of cancer cells

Elevated GSH and H2O2 in cancer cells is sometimes doubted due to their contrary reactivities. Here, we construct a dual-responsive fluorescent probe to confirm the conclusion, and employ this to exploit a redox-inducible DNA interstrand crosslink (ICL) precursor. It crosslinks DNA upon activation by GSH and H2O2, affording an alternative dual-responsive strategy.

New dual-responsive fluorescent sensor for hypochlorite and cyanide sensing and its imaging application in live cells and zebrafish

Excessive levels of cyanide (CN-) and hypochlorite (ClO-) anions are the significant threats to the human health and the environment. Thus, great efforts have been to design and synthesize molecular sensors for the simple, instantaneous and efficient detecting environmentally and biologically important anions. Currently, developing a single molecular sensor for multi-analyte sensing is still a challenging task. In our present work, we developed a new molecular sensor (3TM) based on oligothiophene and Meldrum's acid units for detecting cyanide and hypochlorite anions in biological, environmental and food samples. The detecting ability of 3TM has been examined to various testing substances containing amino acids, reactive oxygen species, cations and anions, showing its high selectivity, excellent sensitivity, short response time (ClO-: 30 s, CN-: 100 s), and broad pH working range (4-10). The detection limits were calculated as 4.2 nM for ClO- in DMSO/H2O (1/8, v/v) solution and 6.5 nM for CN- in DMSO/H2O (1/99, v/v) solution. Sensor 3TM displayed sharp turn-on fluorescence increasement (555 nm, 435 nm) and sensitive fluorescence color changes caused by CN-/ClO-, which is ascribed to the nucleophilic addition and oxidation of ethylenic linkage by cyanide and hypochlorite, respectively. Moreover, sensor 3TM was applied for hypochlorite and cyanide detecting in real-world water, food samples and bio-imaging in live cells and zebrafish. To our knowledge, the developed 3TM sensor is the seventh single-molecular sensor for simultaneous and discriminative detecting hypochlorite and cyanide in food, biological and aqueous environments using two distinct sensing modes.

A Smart Single-Fluorophore Polymer: Self-Assembly Shapechromic Multicolor Fluorescence and Erasable Ink

A novel smart fluorescent polymer polyethyleneimine-grafted pyrene (PGP) is developed by incorporating four stimuli-triggers at molecular level. The triggers are amphiphilicity, supramolecular host-guest sites, pyrene fluorescence indicator, and reversible chelation sites. PGP exhibits smart deformation and shape-dependent fluorescence in response to external stimuli. It can deform into three typical shapes with a characteristic fluorescence color, namely, spherical core-shell micelles of cyan-green fluorescence, standard rectangular nanosheets of yellow fluorescence, and irregular branches of deep-blue fluorescence. A quasi-reversible deformation between the first two shapes can be dynamically manipulated. Moreover, driven by reversible coordination and the resulting intramolecular photoinduced electron transfer, PGP can be used as an aqueous fluorescence ink with erasable and recoverable properties. The fluorescent patterns printed by PGP ink on paper can be rapidly erased and recovered by simple spraying a sequence of Cu2+ and ethylene diamine tetraacetic acid aqueous solutions. This erase/recover transformation can be repeated multiple times on the same paper. The multiple stimulus responsiveness of PGP makes it have potential applications in nanorobots, sensing, information encryption, and anticounterfeiting.

Ionic liquids revolutionizing biomedicine: recent advances and emerging opportunities

Ionic liquids (ILs), due to their inherent structural tunability, outstanding miscibility behavior, and excellent electrochemical properties, have attracted significant research attention in the biomedical field. As the application of ILs in biomedicine is a rapidly emerging field, there is still a need for systematic analyses and summaries to further advance their development. This review presents a comprehensive survey on the utilization of ILs in the biomedical field. It specifically emphasizes the diverse structures and properties of ILs with their relevance in various biomedical applications. Subsequently, we summarize the mechanisms of ILs as potential drug candidates, exploring their effects on various organisms ranging from cell membranes to organelles, proteins, and nucleic acids. Furthermore, the application of ILs as extractants and catalysts in pharmaceutical engineering is introduced. In addition, we thoroughly review and analyze the applications of ILs in disease diagnosis and delivery systems. By offering an extensive analysis of recent research, our objective is to inspire new ideas and pathways for the design of innovative biomedical technologies based on ILs.

A Reversible Fluorescent Probe for In Situ Monitoring Redox Imbalance during Mitophagy

Mitophagy is the lysosome-dependent degradation of damaged and dysfunctional mitochondria, which is closely associated with H2O2-related redox imbalance and pathological processes. However, development of fast-responding and highly sensitive reversible fluorescent probes for monitoring of mitochondrial H2O2 dynamics is still lacking. Herein, we report a reversible fluorescent probe (M-HP) that enables real-time imaging of H2O2-related redox imbalance. In vitro studies demonstrated that M-HP had a rapid response and high sensitivity to the H2O2/GSH redox cycle, with a detection limit of 17 nM for H2O2. M-HP was applied to imaging of H2O2 fluctuation in living cells with excellent reversibility and mitochondrial targeting. M-HP reveals an increase in mitochondrial H2O2 under lipopolysaccharide stimulation and a decrease in H2O2 following the combined treatment with rapamycin. This suggests that the level of oxidative stress is significantly suppressed after the enhancement of mitophagy. The rationally designed M-HP offers a powerful tool for understanding redox imbalance during mitophagy.

Computational Insights into Excited State Intramolecular Double Proton Transfer Behavior Associated with Atomic Electronegativity for Bis(2'-benzothiazolyl)hydroquinone

Inspired by the distinguished regulated photochemical and photophysical properties of 2-(2'-hydroxyphenyl)benzazole derivatives, in this work, the novel bis(2'-benzothiazolyl)hydroquinone (BBTHQ) fluorophore is explored, looking at its photo-induced behaviors associated with different substituted atomic electronegativities, i.e., BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds. From the structural changes, infrared (IR) vibrational variations and simulated core-valence bifurcation (CVB) indexes for the dual hydrogen bonds for the three BBTHQ derivatives, we see that low atomic electronegativity could be conducive to enhancing hydrogen bonding effects in the S1 state. Particularly, the O4-H5⋯N6 of BBTHQ-SO and the O1-H2⋯N3 of BBTHQ-SSe could be strengthened to be more intensive in the S1 state, respectively. Looking into the charge recombination induced by photoexcitation, we confirm a favorable ESDPT trend deriving from the charge reorganization of the dual hydrogen bonding regions. By constructing the potential energy surfaces (PESs) along with the ESDPT paths for the BBTHQ-SO, BBTHQ-SS and BBTHQ-Se compounds, we not only unveil stepwise ESDPT behaviors, but also present an atomic electronegativity-regulated ESDPT mechanism.

Exploring the distinct conformational preferences of allyl ethyl ether and allyl ethyl sulfide using rotational spectroscopy and computational chemistry

The conformational energy landscapes of allyl ethyl ether (AEE) and allyl ethyl sulfide (AES) were investigated using Fourier transform microwave spectroscopy in the frequency range of 5-23 GHz aided by density functional theory B3LYP-D3(BJ)/aug-cc-pVTZ calculations. The latter predicted highly competitive equilibria for both species, including 14 unique conformers of AEE and 12 for the sulfur analog AES within 14 kJ mol-1. The experimental rotational spectrum of AEE was dominated by transitions arising from its three lowest energy conformers, which differ in the arrangement of the allyl side chain, while in AES, transitions due to the two most stable forms, distinct in the orientation of the ethyl group, were observed. Splitting patterns attributed to methyl internal rotation were analyzed for AEE conformers I and II, and the corresponding V3 barriers were determined to be 12.172(55) and 12.373(32) kJ mol-1, respectively. The experimental ground state geometries of both AEE and AES were derived using the observed rotational spectra of the 13C and 34S isotopic species and are highly dependent on the electronic properties of the linking chalcogen (oxygen vs sulfur). The observed structures are consistent with a decrease in hybridization in the bridging atom from oxygen to sulfur. The molecular-level phenomena that drive the conformational preferences are rationalized through natural bond orbital and non-covalent interaction analyses. These show that interactions involving the lone pairs on the chalcogen atom with the organic side chains favor distinct geometries and energy orderings for the conformers of AEE and AES.

A bio-friendly biotin-coupled and azide-functionalized naphthalimide for real-time endogenous hydrogen sulfide analysis in living cells

Hydrogen sulfide (H₂S) is involved in various biological processes. Thereby, abnormal levels of H₂S are reported to be related to various human diseases including cancer. Currently, many fluorescent probes are pioneered to detect H₂S by taking advantages of naphthalimides' unique internal charge transfer (ICT) property. However, most probes often require a high content of organic solvents or surfactants, and are limited to the analysis of exogenous H₂S treated externally in live cell studies, and have difficulties in analyzing endogenous H₂S, thus limiting their practical use. In this study, we developed a bio-friendly biotin-coupled and azide-functionalized naphthalimide (1) as a fluorescent probe enabling real-time analysis of H₂S in living system. Probe was able to provide a fluorescence at 545 nm via H₂S-mediated azide reduction selectively without interference by biologically abundant constituents and pH effects. In a biological study using A549 cells, probe readily penetrated living cells without cytotoxicity, and unreacted probes showed almost no fluorescence, enabling real-time detection of H₂S in living cells without requiring separate washing process. More importantly, under stimulation with various H₂S inducers and inhibitors, probe was able to provide an effective fluorescence response against fluctuations in endogenous H₂S, a key requirement for H₂S studies. Probe 1 can be applied as a useful chemical tool and enables the analysis of H₂S and the study of H₂S-related cell functions in a variety of environments.

A NIR BODIPY-based ratiometric fluorescent probe for HClO detection with high selectivity and sensitivity in real water samples and living zebrafish

Hypochlorous acid (HClO) plays an important role in many physiological and pathological activities. In this work, a novel BODIPY-based Near-infrared (NIR) ratiometric fluorescent probe BODIPY-Hyp was designed for the rapid detection of HClO. The probe BODIPY-Hyp was highly selective and sensitive for HClO with a low detection limit of 16.74 nM and short response time of less than 60 s. The probe BODIPY-Hyp in response to HClO exhibited a significant blue-shifted fluorescence emission from 700 nm to 530 nm, and its fluorescence intensity ratio (I_{530 nm}/I_{700 nm}) increased about 1200 times before and after adding HClO. Moreover, the reaction mechanism of BODIPY-Hyp with HClO was verified by HRMS analysis, ¹H NMR titration and DFT calculations. Furthermore, BODIPY-Hyp was successfully processed into a portable test strip-based device for the detection of HClO. In addition, the probe BODIPY-Hyp could be used in real time to monitor the levels of HClO in living zebrafish larvae. In conclusion, BODIPY-Hyp has great application potential in the life and environmental sciences.

A DFT/TDDFT Investigation on Fluorescence and Electronic Properties of Chromone Derivatives

The development of quick and precise detection technologies for active compounds in vivo is critical for disease prevention, diagnosis and pathological investigation. The fluorescence signal of the fluorophore usually defines the probe's sensitivity to the chemical being examined. Many natural compounds containing flavone and isoflavone scaffolds exhibit a certain amount fluorescence, albeit with poor fluorescence quantum yields. Therefore, we used density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations to investigate the fluorescence characteristics of chromium-derived fluorophores in more depth. Different substituents are introduced at different positions of the chromone. As weak electron donor groups, alkyl and aromatic groups were discovered to have varying quantum yields on the fluorophore scaffold, and longer alkyl chains are favorable to enhance fluorescence quantum yield. In comparison to the amino group, substituted amino group can avoid group rotation, and the introduction of cyclic amines such as pyrrolidine and heterocyclic amines can improve optical characteristics. The electron-donating methoxy group at position 6 helps to increase the fluorescence quantum yield.

Synthesis and Photophysical Study of Tetraphenyl Substituted BODIPY Based Phenyl-Monoselenide Probe for Selective Detection of Superoxide

Selenium containing tetraphenyl substituted BODIPY probe was successfully synthesized from respective selenium aldehyde and tetraphenyl pyrrole using Knoevenagel-type condensation. The product was characterized using various spectroscopic techniques (¹ H, ¹³ C, ⁷⁷Se, ¹¹B, and ¹⁹ F) and mass spectrometry. The probe was found to be selective and sensitive towards detection of superoxide over other ROS with a "turn-off" (quenched) fluorescence response. The detection limit of the probe was found to be 4.87 µM. The probe reacted with superoxide in less than a sec with a stoke shift of 35 nm.

Redox-Reversible Near-Infrared Fluorescent Probe for Imaging of Acute Kidney Oxidative Injury and Remedy

Drug-induced acute kidney injury (DIAKI) is associated with high morbidity and mortality. It remains a diagnostic and therapeutic dilemma due to failure of providing unambiguous real-time feedback on nephrotoxicity, which is regarded as a serious problem in clinics. Herein, we report a reversible fluorescence probe, NRN, to monitor the ONOO^-/GSH in an acute kidney injury model. The NRN near-infrared fluorescent probe features a big Stokes shift (83 nm), which was oxidized by ONOO^- and reduced by succussive glutathione (GSH) with excellent selectivity and good sensitivity (detection limit: 418 nM and 0.28 mM, respectively). Taking the reversibility of NRN toward ONOO^- and GSH, real-time evaluations in vivo with cisplatin (CP) alone and CP combined with acetaminophen-stimulated acute kidney injury and the following remedy process with l-carnitine were realized for the first time. The experiments revealed that acute kidney injury caused by combined drugs might be more serious and irreversible under certain conditions. Therefore, NRN could act as a potential tool for understanding oxidative stress-related DIAKI disease processes.

Fluorescent proteins and genetically encoded biosensors

The genetically encoded fluorescent sensors convert chemical and physical signals into light. They are powerful tools for the visualisation of physiological processes in living cells and freely moving animals. The fluorescent protein is the reporter module of a genetically encoded biosensor. In this study, we first review the history of the fluorescent protein in full emission spectra on a structural basis. Then, we discuss the design of the genetically encoded biosensor. Finally, we briefly review several major types of genetically encoded biosensors that are currently widely used based on their design and molecular targets, which may be useful for the future design of fluorescent biosensors.

ROS-responsive ADPH nanoparticles for image-guided surgery

In recent years, organic fluorescent probes with tumor microenvironment (TME)-responsive fluorescence turn-on properties have been increasingly used in imaging-guided tumor resection due to their higher signal-to-noise ratio for tumor imaging compared to non-responsive fluorescent probes. However, although researchers have developed many organic fluorescent nanoprobes responsive to pH, GSH, and other TME, few probes that respond to high levels of reactive oxygen species (ROS) in the TME have been reported in imaging-guided surgery applications. In this work, we prepared Amplex^® Red (ADHP) with excellent ROS response performance as an ROS-responsive nanoprobe and studied its application in image-guided tumor resection for the first time. To confirm whether the nanoprobe can be used as an effective biological indicator to distinguish tumor sites, we first detected 4T1 cells with the ADHP nanoprobe, demonstrating that the probe can utilize ROS in tumor cells for responsive real-time imaging. Furthermore, we conducted fluorescence imaging in vivo in 4T1 tumor-bearing mice, and the ADHP probe can rapidly oxidize to form resorufin in response to ROS, which can effectively reduce the background fluorescence signal compared with the single resorufin probe. Finally, we successfully carried out image-guided surgery of 4T1 abdominal tumors under the guidance of fluorescence signals. This work provides a new idea for developing more TME-responsive fluorescent probes and exploring their application in image-guided surgery.

An ESIPT-based reversible ratiometric fluorescent sensor for detecting HClO/H2S redox cycle in living cells

HClO and H₂S, as two kinds of crucial small biomolecules, are endowed various roles in biological organisms. The redox balance between HClO and H₂S is closely related to the physiological and pathological processes. Thus, it is significant to monitor the redox process between HClO and H₂S. Inspired by the advantages of ratiometric fluorescent probes, we firstly developed a reversible ratiometric fluorescent probe (BT-Se) for HClO and H₂S via combination of phenyl selenide as the response group and 2-(2'-hydroxyphenyl)benzothiazole dye as the fluorophore. The proposed probe BT-Se could detect HClO with well-separated dual emission (110 nm), fast response, good selectivity and sensitivity owing to the oxidation reaction of the Se atom induced by HClO. Moreover, only H₂S could effectively recover the fluorescence of the detection system to the original state via H₂S induced-reduction of selenoxide. Cell imaging studies demonstrated that the probe BT-Se was capable of ratiometric monitoring the changes of intracellular HClO/H₂S, which suggested that it has great potential for researching the biological functions of HClO and H₂S.

Design strategies and applications of smart optical probes in the second near-infrared window

Over the last decade, a series of synergistic advances in the synthesis chemistries and imaging instruments have largely boosted a significant revolution, in which large-scale biomedical applications are now benefiting from optical bioimaging in the second near-infrared window (NIR-II, 1000-1700 nm). The large tissue penetration and limited autofluorescence associated with long-wavelength imaging improve translational potential of NIR-II imaging over common visible-light (400-650 nm) and NIR-I (750-900 nm) imaging, with ongoing profound effects on the studies of precision medicine. Unfortunately, the majority of NIR-II probes are designed as "always-on" luminescent imaging contrasts, continuously generating unspecific signals regardless of whether they reach pathological locations. Thus, in vivo imaging by traditional NIR-II probes usually suffers from weak detect precision due to high background noise. In this context, the advances of optical imaging now enter into an era of precise control of NIR-II photophysical kinetics. Developing NIR-II optical probes that can efficiently activate their luminescent signal in response to biological targets of interest and substantially suppress the background interferences have become a highly prospective research frontier. In this review, the merits and demerits of optical imaging probes from visible-light, NIR-I to NIR-II windows are carefully discussed along with the lens of stimuli-responsive photophysical kinetics. We then highlight the latest development in engineering methods for designing smart NIR-II optical probes. Finally, to appreciate such advances, challenges and prospect in rapidly growing study of smart NIR-II probes are addressed in this review.

Tagging Peptides with a Redox Responsive Fluorescent Probe Enabled by Photoredox Difunctionalization of Phenylacetylenes with Sulfinates and Disulfides

Herein, we describe a photoredox three-component atom-transfer radical addition (ATRA) reaction of aryl alkynes directly with dialkyl disulfides and alkylsulfinates, circumventing the utilization of chemically unstable and synthetically challenging S-alkyl alkylthiosulfonates as viable addition partners. A vast array of (E)-β-alkylsulfonylvinyl alkylsulfides was prepared with great regio- and stereoselectivity. Moreover, this powerful tactic could be employed to tag cysteine residues of complex polypeptides in solution or on resin merging with solid phase peptide synthesis (SPPS) techniques. A sulfonyl-derived redox responsive fluorescent probe could be conveniently introduced on the peptide, which displays green fluorescence in cells while showing blue fluorescence in medium. The photophysical investigations reveal that the red shift of the emission fluorescence is attested to reduction of carbonyl group to the corresponding hydroxyl moiety. Interestingly, the fluorescence change of tagged peptide could be reverted in cells by treatment of H₂O₂, arising from the reoxidation of hydroxyl group back to ketone by the elevated level of reactive oxygen species (ROS).

Development of peroxynitrite-responsive fluorescence probe for recognition of drug-induced liver injury

Peroxynitrite (ONOO^-) as an active substance, is produced during normal physiological process, which plays an important role in maintaining cell REDOX balance and cell function. Moreover, the peroxynitrite is involved in many diseases and especially can be used as a biomarker of drug-induced liver injury (DILI). Therefore, in this work, we synthesized a fluorescent probe JQ-3 for detecting ONOO^-. The results showed the probe JQ-3 possessed excellent selectivity, fast response time (10 min) and low detection limit (32 nM). The probe JQ-3 is almost unaffected by pH, showing the potential application in biological systems. Moreover, the probe JQ-3 can be successfully used for the detection of exogenous and endogenous ONOO^- in living cells and zebrafish. At the same time, the DILI was successfully recognized by visualizing ONOO^- with JQ-3 in living cells and zebrafish. Therefore, the probe JQ-3 provides a potential tool for detecting ONOO^- to understand physiological and pathology processes of disease.

3-Aminophenylboronic acid-functionalized molybdenum disulfide quantum dots for fluorescent determination of hypochlorite

A simple method is reported for hypochlorite determination based on fluorescence 3-aminophenylboronic acid-functionalized molybdenum disulfide quantum dots (B-MoS₂ QDs). B-MoS₂ QDs with strong fluorescence at 380 nm have been successfully synthesized by the amidation reaction between APBA and hydrothermal MoS₂ QDs. Hypochlorite sensing was proposed utilizing the fluorescent quenching effect of 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB) on B-MoS₂ QDs and the fast redox reaction between hypochlorite and TMB. The fluorescent quenching effect of TMB to B-MoS₂ QDs was proved to be caused by static dynamic quenching and inner filter effect. A good linear relationship was obtained in the hypochlorite concentration range from 1 to 20 μM, and the limit of detection (LOD) was 36.8 nM. The proposed fluorescent detection assay was simple and fast, taking only 5 min at room temperature. Satisfactory results were obtained in the standard spike recovery tests on tap water and milk samples, which indicate high potential in constructing fluorescent bio-detection assays.

Decarboxylative ring-opening of 2-oxazolidinones: a facile and modular synthesis of β-chalcogen amines

We report herein the synthesis of primary and secondary β-chalcogen amines through the regioselective ring-opening reaction of non-activated 2-oxazolidinones promoted by in situ generated chalcogenolate anions. The developed one-step protocol enabled the preparation of β-selenoamines, β-telluroamines and β-thioamines with appreciable structural diversity and in yields of up to 95%.