Rationally Optimized Fluorescent Probe for Imaging Mitochondrial SO2 in HeLa Cells and Zebrafish

Advances in small-molecule fluorescent probes for the study of apoptosis

Apoptosis, as type I cell death, is an active death process strictly controlled by multiple genes, and plays a significant role in regulating various activities. Mounting research indicates that the unique modality of cell apoptosis is directly or indirectly related to different diseases including cancer, autoimmune diseases, viral diseases, neurodegenerative diseases, etc. However, the underlying mechanisms of cell apoptosis are complicated and not fully clarified yet, possibly due to the lack of effective chemical tools for the nondestructive and real-time visualization of apoptosis in complex biological systems. In the past 15 years, various small-molecule fluorescent probes (SMFPs) for imaging apoptosis in vitro and in vivo have attracted broad interest in related disease diagnostics and therapeutics. In this review, we aim to highlight the recent developments of SMFPs based on enzyme activity, plasma membranes, reactive oxygen species, reactive sulfur species, microenvironments and others during cell apoptosis. In particular, we generalize the mechanisms commonly used to design SMFPs for studying apoptosis. In addition, we discuss the limitations of reported probes, and emphasize the potential challenges and prospects in the future. We believe that this review will provide a comprehensive summary and challenging direction for the development of SMFPs in apoptosis related fields.

Construction of a Colorimetric and Near-Infrared Ratiometric Fluorescent Sensor and Portable Sensing System for On-Site Quantitative Measurement of Sulfite in Food

Sulfites play imperative roles in food crops and food products, serving as sulfur nutrients for food crops and as food additives in various foods. It is necessary to develop an effective method for the on-site quantification of sulfites in food samples. Here, 7-(diethylamino) quinoline is used as a fluorescent group and electron donor, alongside the pyridinium salt group as an electron acceptor and the C=C bond as the sulfite-specific recognition group. We present a novel fluorescent sensor based on a mechanism that modulates the efficiency of intramolecular charge transfer (ICT), CY, for on-site quantitative measurement of sulfite in food. The fluorescent sensor itself exhibited fluorescence in the near-infrared light (NIR) region, effectively minimizing the interference of background fluorescence in food samples. Upon exposure to sulfite, the sensor CY displayed a ratiometric fluorescence response (I447/I692) with a high sensitivity (LOD = 0.061 μM), enabling accurate quantitative measurements in complex food environments. Moreover, sensor CY also displayed a colorimetric response to sulfite, making sensor CY measure sulfite in both fluorescence and colorimetric dual-signal modes. Sensor CY has been utilized for quantitatively measuring sulfite in red wine and sugar with recoveries between 99.65% and 101.90%, and the RSD was below 4.0%. The sulfite concentrations in live cells and zebrafish were also monitored via fluorescence imaging. Moreover, the sulfite assimilated by lettuce leaves was monitored, and the results demonstrated that excessive sulfite in leaf tissue could lead to leaf tissue damage. In addition, the sulfate-transformed sulfite in lettuce stem tissue was tracked, providing valuable insights for evaluating sulfur nutrients in food crops. More importantly, to accomplish the on-site quantitative measurement of sulfite in food samples, a portable sensing system was prepared. Sensor CY and the portable sensing system were successfully used for the on-site quantitative measurement of sulfite in food.

Neo-construction of a SO2-tunable near-infrared ratiometric fluorescent probe for high-fidelity diagnosis and evaluation hazards of Cd2+-induced liver injury

Cadmium-contaminated water and food are seriously hazardous to the human health, especially liver injury. To understand the entanglement relationship between cadmium ion (Cd2+)-induced liver injury and the biomarker sulfur dioxide (SO2), a reliable bioanalytical tool is urgently needed, detecting SO2 to diagnose and evaluate the extent of liver injury in vivo. Herein, based on the Förster resonance energy transfer (FRET) mechanism, a novel SO2-tunable NIR ratiometric fluorescent probe (SMP) was developed, it was used to diagnose and treat liver injury induced by Cd2+ in biosystems. Specifically, it was constructed by conjugating a NIR dicyanoisophorone with a NIR benzopyranate as the donor and acceptor, respectively, and the ratiometric response of SO2- regulated by the Michael addition reaction. In addition, SMP exhibits rapid reaction time (<15 s), two well-resolved emission peaks (68 nm) with less cross-talk between channels for high imaging resolution, superior selectivity, and low limit of detection (LOD=80.3 nM) for SO2 detection. Impressively, SMP has been successfully used for intracellular ratiometric imaging of Cd2+-induced SO2 and diagnostic and therapeutic evaluation in liver injury mice models with satisfactory results. Therefore, SMP may provide a powerful molecular tool for revealing the occurrence and development relationship between SO2 and Cd2+-induced liver injury. ENVIRONMENTAL IMPLICATION: Cadmium ions are one of the well-known toxic environmental pollutants, which are enriched in the human body through inhalation of cadmium-contaminated air or from the food chain, leading to damage in various organs, especially liver injury. Therefore, we developed a novel fluorescent probe that can specifically detect SO2 in Cd2+-induced liver injury, which is critically important for the diagnosis and evaluation of Cd2+-induced liver injury diseases. The specific detection of SO2 of this probe has been successfully demonstrated in live HepG2 cells and Cd2+-induced liver injury mice.

A rationally designed fluorescent probe for sulfur dioxide and its derivatives: applications in food analysis and bioimaging

Exogenous sulfur dioxide (SO2) and its derivatives (SO32-/HSO3-) have been extensively utilized in food preservation and endogenous SO2 is recognized as a significant gaseous signaling molecule that can mediate various physiological processes. Overproduction and/or extensive intake of these species can trigger allergic reactions and even tissue damage. Therefore, it is highly desirable to monitor SO2 and its derivatives effectively and quantitatively both in vitro and in vivo. Herein, a new mitochondria-targeted fluorescent probe (PIB) had been constructed, which could ratiometrically recognize SO2 and its derivatives with excellent sensitivity (DL = 15.9 nM) and a fast response time (200 s). The obtained high selectivity and good adaptability of this SO2-specific probe in a wide pH range (6.5-10.0) allowed for quantitatively tracking of SO2 and its derivatives in real food samples (granulated sugar, crystal sugar, and white wine). In addition, PIB could locate at mitochondrion and was capable of imaging exogenous/endogenous SO2 in the cells and zebrafish. In particular, our findings represented one of the rare examples that have demonstrated endogenous SO2 is closely related with the apoptosis of cells. Importantly, probe PIB was successfully employed for in situ metabolic localization in mouse organs, implying the potential applications of our probe in further exploration on SO2-releated pathological and physiological processes.

hROS-Responsive Behavior for Long-Term Stability of Cellulosic Gold Nanoclusters

Understanding the gold core-ligand interaction in gold nanoclusters (GNCs) is essential for the on-demand tailoring of their photoluminescence properties and long-term stability. Here, inspired by the suckers arranged directionally on the tentacles of octopus, a series of GNCs with regulating ligand structures are grown and stabilized on the cellulose nanocrystals (CNCs). The carboxylated CNCs providing an electron-rich environment to promote the luminescence of GNCs and stabilize it within a long-term of 1 year through anchoring and diluting effects, and the highest quantum yields reaches 31.02% in ultrapure water. Interestingly, this bionic preparation strategy is generally applicable to various ligands for tailoring on-demand hROS-responsive and nonresponsive GNCs to construct tunable-emission wavelength dual GNCs ratiometric probes. The results show that designing a specific ligand structure to inhibit the transformation of Au-Au to Au (I)-ligand in GNCs is crucial to regulate the hROS-responsive characteristics. As expected, the interfacial compatible dual GNCs ratiometric probe with a hROS limit of detection of 0.74 µmol L-1 can diagnose certain diseases through intracellular hROS imaging. This work provides important insights for understanding the gold core-ligand interaction in GNCs during the oxidation process triggered by intracellular hROS.

Polysiloxane-Based Molecular Logic Gate for Dual-Channel Visualizing Mitochondrial pH and Sulphite Changes during Cuproptosis

Intracellular Cu-induced regulated cell death, characterized by the aggregation of lipidizing mitochondrial enzymes, is called cuproptosis. Mitochondria play a vital role in the metabolic regulation of cell injury and stressful immune responses. The pH levels and sulfur dioxide (SO2) content in mitochondria have important indicative roles in the regulation of cuproptosis. However, fluorescent probes that simultaneously detect changes in pH and SO2 in mitochondria during cuprotosis have not been reported. To fill this blank, in this study, we dexterously used functional polysiloxane as a fluorescent platform to propose a molecular logic gate probe P0-pH-SO2 for detecting changes in intramitochondrial pH and SO2 content through a dual-channel mode. In addition, we defined a new function to reflect the cellular state of the elesclomol-induced cuproptosis process based on the input and output of the relevant logic relationship. This new fluorescent molecular logic gate probe P0-pH-SO2 can be rapidly activated by mitochondrial sulfites to induce green fluorescence, while the red fluorescence is quenched with the proton in the mitochondria. Overall, this study developed a novel logic-gated molecular probe that provided a versatile strategy for monitoring the role played by intramitochondrial sulfites and H+ in cuproptosis. This work will open the way to broaden the applications of molecular logic gates and fluorescent polysiloxanes.

"One stone, two birds": a mitochondria-targeted fluorescent probe for the detection of viscosity and HSO3- in living cells

The material transport and physiological events of mitochondria need to be supported by a suitable microenvironment. For example, high viscosity will seriously hinder material exchange, and SO2, as the precursor of HSO3-, is an endogenous signal molecule that plays a key role in information transmission. It is very important to detect viscosity and HSO3- in mitochondria. Here, we developed a dual-responsive fluorescent probe (named Hcy-NT) to image the changes in mitochondrial viscosity and HSO3- in a "killing two birds with one stone" manner. Hcy-NT showed an OFF-ON fluorescence signal for the increase in cell viscosity induced by nystatin, while an ON-OFF fluorescence signal for intracellular and endogenous HSO3-. Its limits of detection for HSO3- were calculated by both absorption and fluorescence methods, which were 1.200 and 1.291 μM, respectively. This work provides a valuable tool for the study of viscosity and HSO3- related physiological processes and the diagnosis of potential diseases.

A multifunctionally reversible detector: Photoacoustic and dual-channel fluorescence sensing for SO2/H2O2

In this work, the phenothiazine fragment with powerful electron-donating ability was specifically selected to construct a multifunctional detector (noted as T1) in double-organelle with near-infrared region I (NIR-I) absorption. The changes of SO₂/H₂O₂ content in mitochondria and lipid droplets were observed through red/green channels respectively, which was due to the reaction between benzopyrylium fragment of T1 and SO₂/H₂O₂ to achieve red/green fluorescence conversion. Additionally, T1 was endowed with photoacoustic properties deriving from NIR-I absorption to reversibly monitor SO₂/H₂O₂in vivo. This work was significant for more accurately deciphering the physiological and pathological processes in living organisms.

A dual-channel fluorescent nanoprobe for accurate cancer diagnosis by sequential detection of adenosine triphosphate and sulfur dioxide

Cancer is one of the major diseases that seriously endanger the health of all mankind. Accurate diagnosis of early cancer is the most promising way to reduce cancer harm and improve patient survival. However, many developed fluorescent probes for cancer imaging only have the function of identifying one marker, which cannot meet the needs of accurate diagnosis. Here, a fluorescent nanoprobe (CPH@ZIF-90) utilizing ZIF-90 to encapsulate SO₂-sensitive dye (CPH) is synthesized for the sequential detection of ATP and SO₂. The nanoprobe first interacts with ATP to release CPH, thus increasing the fluorescence at 685 nm and realizing the near-infrared (NIR) fluorescence detection of ATP. Then, SO₂ acts on the released CPH through nucleophilic addition, affecting the π-conjugated structure of CPH and resulting in enhanced fluorescence at 580 nm. CPH@ZIF-90 exhibits satisfactory sensitivity and selectivity for sequential detection of ATP and SO₂. Excitedly, CPH@ZIF-90 can sequentially image the endogenous ATP and SO₂ in cells, showing sensitive fluorescence changes in dual channels (red and green). Due to the NIR emission properties of CPH@ZIF-90 and its ability to enrich in tumor, it is applied to monitor ATP and SO₂ in mice and distinguish normal mice from tumor mice. The ability of CPH@ZIF-90 to sequentially detect two cancer-related biomarkers makes it provide meaningful assistance in accurate early diagnosis of cancer.

FRET-based fluorescent probe with favorable water solubility for simultaneous detection of SO2 derivatives and viscosity

The intracellular viscosity is an important parameter of the microenvironment and SO₂ is a vital gas signal molecule. At present, some dual-response fluorescence probes for simultaneous measurements of viscosity and SO₂ derivatives (HSO₃^-/SO₃^2-) possessed poor water solubility. In this work, we developed a water-soluble fluorescence probe CIJ (0.0864 g/100 mL of water at 20 °C) for simultaneous measurements of viscosity and SO₂ derivatives. CIJ exhibited a sensitive fluorescence enhancement to environmental viscosity from 0.97 to 28.04 cP based on a twisted intramolecular charge transfer mechanism and was applied to effective measurement of viscosity in vitro and in vivo. CIJ could also respond to SO₂ derivatives with a low detection limit (44 nM) and a fast response time (5 min) based on the nucleophilic addition reaction. Furthermore, CIJ was applied to monitor SO₂ derivatives in ratiometric response manner in living cells.

Viscosity & SO2-sensitive dual colorimetric effect fluorescent sensor enabled imaging detection within plant onion and biological system

The biological microenvironment includes important parameters such as viscosity, polarity, temperature, oxygen content and pH. In particular, abnormal cell viscosity is associated with the development of major diseases. Sulphur dioxide (SO₂) serves not only as an essential atmospheric pollutant but also an influential signalling molecule in biological cells, predisposing individuals to increased respiratory disease. In this work, we designed and synthesized a novel fluorescent probe CouCN-V&S with dual response to micro environmental viscosity and SO₂. The probe monitored viscosity and SO₂ separately through dual emission channels with a difference of 135 nm. The probe responded sensitively to SO₂ (<1s) and exhibited satisfactory immunity to interference and pH stability. The probe was successfully applied to imaging cellular, intra-zebrafish viscosity and SO₂ changes. Interestingly, we took onion epidermal cells as model and explored the capability of probe CouCN-V&S to image SO₂ in plant cells for the first time.

Dual-response and lysosome-targeted fluorescent probe for viscosity and sulfur dioxide derivatives

Viscosity and sulfur dioxide levels are important factors to evaluate the changes of cell micro-environment because a series of diseases usually occur when they are abnormal. At present, dual-response probes that can detect both viscosity and sulfur dioxide are rare. Therefore, we developed a novel fluorescent probe CBN for simultaneous detection of sulfur dioxide and viscosity. Besides, probe CBN could target lysosome of which normal function will be disrupted by the abnormality of viscosity. Therefore, probe CBN has the potential to be served as an effective biological tool to monitor the intracellular micro-environment.

A NIR Fluorescent Probe Benzopyrylium Perchlorate-based for Visual Sensing and Imaging of SO2 Derivatives in Living Cells

Endogenous sulfur dioxide (SO₂), as a gas signal molecule, has a certain physiological functions. Understanding the role of endogenous SO₂ in human physiology and pathology is of great significance to the biological characteristics of SO₂,which bring challenges to develop fluorescent probes with excellent performance. Herein, we rationally designed and constructed a novel near-infrared bioprobe benzaldehyde-benzopyrylium (BBp) by employing the nucleophilic addition benzopyrylium perchlorate fluorophore and benzaldehyde moiety by means of C = C/C = O group that serves as both fluorescence reporting unit. Probe BBp exhibit excellent sensing performance with fluorescent "On - Off"rapid response (100 s) and long-wavelength emission (670 nm). With the treatment of HSO₃^-, the color of BBp solution obviously varies from purple to colorless, and the fluorescent color varies from red to colorless. By the fluorescence and colorimetric changes, probe BBp was capable of sensitive determination HSO₃^- with low limits of detection (LOD) of 0.43 μM, realizing visual quantitative monitoring SO₂ derivative levels. Due to the low phototoxicity and good biocompatibility, it was successfully applied to monitor SO₂ derivatives and fluorescence imaging in HepG2 and HeLa living cells. Hopefully, this work supplies a new strategy for designing NIR fluorescent probes for quantitative determination SO₂ derivatives in biological samples.

Hypochlorite Detection by Fluorescent Sensors Bearing Long Alkyl Chains: The Role of Chain Length in Sensing Properties

Three pyridinium derivatives bearing alkyl chains of different lengths (C1, C8, and C18) that show aggregation-enhanced emission were synthesized. These compounds can be used to detect ClO- ion as the reaction releases the fluorescent core with an increase in emission intensity and change in absorption wavelength. The lowest detection limit of TPA-Pyr-18C was 6.04 μM. The length of the alkyl chain and resulting lipophilicity allowed the targeting of different subcellular structures. TPA-Pyr-18C could be used for staining yolk lipids in zebrafish.

Rational Construction of a Mitochondria-Targeted Reversible Fluorescent Probe with Intramolecular FRET for Ratiometric Monitoring Sulfur Dioxide and Formaldehyde

Sulfur dioxide (SO₂) and formaldehyde (FA) are important species that maintain redox homeostasis in life and are closely related to many physiological and pathological processes. Therefore, it is of great significance to realize the reversible monitoring of them at the intracellular level. Here, we synthesized a reversible ratiometric fluorescent probe through a reasonable design, which can sensitively monitor SO₂ derivatives and FA, and the detection limit can reach 0.16 μM. The probe can specifically target mitochondria and successfully monitor the fluctuations of SO₂ and FA in living cells. It also works well in the detection of SO₂ and FA in zebrafish. This high-performance probe is expected to find broad in vitro and in vivo applications.

A susceptible multifunctional fluorescent probe based on levulinic acid for the practical detection of SO2

Sulfites (HSO₃^-) are used as preservatives and additives in many foods and medicines. However, a high sulfite concentration can cause asthma attacks and even breathing difficulties. Sulfites can also accumulate from the environment into the body, so it is necessary to develop a probe capable of detecting SO₂ in the environment and in organisms. A multifunctional sensor, SO-2, based on levulinic acid was designed and synthesized. SO-2 showed an excellent response to SO₂ with a detection limit of 2.0 × 10^-8 M and a fast response equilibrium time (within 10 min), which indicated that the probe could detect SO₂ with high sensitivity. The probe also successfully traced exogenous bisulfite in cells and was applied to analyze water samples in a natural environment.

Insight into sulfur dioxide and its derivatives metabolism in living system with visualized evidences via ultra-sensitive fluorescent probe

Sulfur dioxide (SO₂) and its derivatives have long been considered as hazardous environmental pollutants but commonly used as food additives in safe dose range. They also could be produced from biological metabolism process of sulfur-containing amino acids. However, their physiological roles remain extremely obscure mainly due to lack of efficient tools for monitoring and imaging strategy establishment. Furthermore, most of current studies of this aspect focus on novel probe design or just imaging them rather than on the ins and outs. Therefore, there is a high significance of establishing highly sensitive detection strategy for monitoring SO₂ derivatives in living systems, food and environment. Herein, we design a fluorescent probe MS-Bindol for sensitively detecting SO₂ derivatives with a low detection limit (0.2 nM). We have established an imaging strategy for investigation of SO₂ derivatives metabolism in living cells and zebrafish, providing visualize evidences and verified that SO₂ derivatives could be synthetized from thiosulfate and glutathione(GSH) and be hardly consumed by using sulfite oxidase inhibitors (ferricyanide or arsenite). Moreover, the probe also exhibits excellent practicability in food as well as environmental samples. Our studies may help biologist for better understanding SO₂ derivatives metabolism and deeply explore their physiological roles in biological systems.

A novel fluorescent probe based on triphenylamine for detecting sulfur dioxide derivatives

According to the nucleophilicity of sulfur dioxide derivatives, a reactive fluorescent probe was designed and synthesized by linking triphenylamine with benzoindole.

Sequential detection of hypochlorous acid and sulfur dioxide derivatives by a red-emitting fluorescent probe and bioimaging applications in vitro and in vivo

A red-emitting fluorescence probe (DP) has been successfully developed for the sequential detection of hypochlorous acid (HOCl) and sulfur dioxide derivatives (SO32−/HSO3−) in vitro and in vivo.

Optical/electrochemical methods for detecting mitochondrial energy metabolism

This review highlights the biological importance of mitochondrial energy metabolism and the applications of multiple optical/electrochemical approaches to determine energy metabolites. Mitochondria, the main sites of oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis, provide the majority of energy required by aerobic cells for maintaining their physiological activity. They also participate in cell growth, differentiation, information transmission, and apoptosis. Multiple mitochondrial diseases, caused by internal or external factors, including oxidative stress, intense fluctuations of the ionic concentration, abnormal oxidative phosphorylation, changes in electron transport chain complex enzymes and mutations in mitochondrial DNA, can occur during mitochondrial energy metabolism. Therefore, developing accurate, sensitive, and specific methods for the in vivo and in vitro detection of mitochondrial energy metabolites is of great importance. In this review, we summarise the mitochondrial structure, functions, and crucial energy metabolic signalling pathways. The mechanism and applications of different optical/electrochemical methods are thoroughly reviewed. Finally, future research directions and challenges are proposed.

Water-soluble fluorescent probes for bisulfite and viscosity imaging in living cells: Pyrene vs. anthracene

We have designed two mitochondria targetable probes P-Py and P-An by the π-conjugation of polyaromatic hydrocarbons (pyrene vs. anthracene) with 4-dimethylamino pyridinium. They present an amphiphilic property with excellent solubility in the common polar and non-polar solvents. Both of them demonstrated a significant fluorescence response to bisulfite in Tris-HCl buffer solutions (5 mM, pH = 7.4). By a combination of fluorescence, UV-vis, time-resolved emission, ¹H NMR, and ESI-MS, their sensing mechanisms have been elaborated to be a Michael addition. Notably, P-Py also exhibits a sensitivity to the viscosity change with a Stokes shift of 140 nm, due to the restriction of C-C bond rotation. By taking advantages of its good water solubility, low toxicity, and high mitochondrial target, the dual responses of P-Py to exogenous SO₂ derivatives and viscosity change in mitochondria were explored by confocal fluorescence microscopy.

Mitochondria selective trackers for long-term imaging based on readily accessible neutral BODIPYs

We report the design of a new model based on a small neutral 8-aryl-3-formylBODIPY and its suitability to develop privileged highly bright and photostable fluorescent probes for selective and, more importantly, covalent staining of mitochondria.

A photostable reaction-based A-A-A type two-photon fluorescent probe for rapid detection and imaging of sulfur dioxide

In this study, a novel reaction-based A-A-A (acceptor-acceptor-acceptor) type two-photon fluorescent probe, BTC, is prepared using the benzothiadiazole (BTD) scaffold as the two-photon fluorophore and electron-accepting centre. Two β-chlorovinyl aldehyde moieties are symmetrically connected to both ends of the BTD scaffold and act as reaction groups to recognize SO2 and quenching groups to make the dis-activated probe stay at off-state due to their weak electron-withdrawing effect. In the presence of SO2 derivatives, the aldehyde groups are consumed through aldehyde addition, resulting in the activation of intramolecular charge transfer (ICT) processes and therefore recovering the fluorescence of the probe. The designed probe shows excellent two-photon properties including large two-photon absorption cross-sections (TPA) of 91 GM and photostability. Beyond these, the BTC probe exhibits a fast response to SO2 within 30 s, high specificity without foreign interference and a broad detection range from 500 nM to 120 μM with a detection limit of 190 nM. The designed fluorescent probe is further applied to the two-photon imaging of exogenous and endogenous SO2 derivatives under different physiological processes in HeLa cells and zebrafish with satisfactory results. We believe that the proposed design strategy can be extended to fabricate versatile BTD-based two-photon fluorescent probes through molecular engineering for further applications in bioassays and two-photon imaging.

A distinctive mitochondrion-targeting, in situ-activatable near-infrared fluorescent probe for visualizing sulfur dioxide derivatives and their fluctuations in vivo

Sulfur dioxide derivatives are intimately involved in some physiological processes in organisms, and high levels of these substances can cause many diseases. Herein, we rationally prepared a mitochondrion-targeting, in situ-activatable near-infrared (NIR) fluorescent probe (DCQN) by coupling 2-(3,5,5-trimethylcyclohex-2-enylidene)malononitrile with 3-quinolinium carboxaldehyde. DCQN displayed a NIR fluorescence turn-on signal to indicate the presence of HSO3-, along with a considerable hyperchromic shift from light yellow to purple via a 1,4-nucleophilic addition reaction. We were able to use DCQN to instantaneously and quantitatively determine the concentration of HSO3- with high specificity, a low detection limit (24 nM), a large Stokes shift (∼110 nm), and a high contrast ratio. Moreover, DCQN displayed good mitochondrion-targeting abilities and was in situ-activated by HSO3- to produce NIR fluorescence for imaging HSO3- in the mitochondria of live breast cancer cells. Furthermore, DCQN was used to monitor HSO3- in zebrafish with a high contrast ratio.

A mitochondria-targeted fluorescent probe for the detection of endogenous SO2 derivatives in living cells

A unique fluorescent probe (ZACA) for the monitoring of SO2 derivatives was developed from coumarin and benzoindoles based on FRET and ICT. ZACA exhibited an active emission signal, large Stokes shift, wide emission window distance, and high photostability. It also possessed many advantages in the ratiometric detection of HSO3-/SO32- including low detection limit and high selectivity and sensitivity. Importantly, ZACA was successfully applied in the ratiometric detection of endogenous HSO3-/SO32- in living cells with excellent cellular imaging capability (1 μM) and mitochondria-targeting ability (co-localization coefficient: 0.91).

ESIPT silent and mitochondrial-targeted rapid response for SO2 regulated by pyridinium and its real-time detection in living cells

ESIPT has been widely used in fluorescence recognition because of its advantages such as large Stokes shift.

A novel dual-function fluorescent probe for the rapid detection of bisulfite and hydrogen peroxide in aqueous solution and living cells

In this work, Hcy-OB, a novel hemicyanine-based biocompatible dual-function fluorescence probe for bisulfite and H₂O₂ detection is designed and synthesized. Based on a 1,4-addition reaction, Hcy-OB can be used for bisulfite detection with fast response, high sensitivity and low detection limit (120 nM). In addition, the probe is successfully applied to the detection of bisulfite in aqueous solution. Furthermore, Hcy-OB shows excellent performance for hydrogen peroxide detection with the oxidation of phenylboronic acid. Hcy-OB shows excellent selectivity to H₂O₂ over other interfering substances with detection limit of H₂O₂ is calculated to be 70 nM. Most importantly, due to its good cell membrane permeability and low cytotoxicity, Hcy-OB has been applied to monitor and image H₂O₂ in living cells and mice.

Synergistic effect of uniform lattice cation/anion doping to improve structural and electrochemical performance stability for Li-rich cathode materials

There has been extensive research into lithium-rich layered oxide materials as candidates for the nextgeneration of cathode materials in lithium-ion batteries, due to their high energy density and low cost; however, their poor cycle life and fast voltage fade hinder their large-scale commercial application. Here, we propose a novel cation/anion (Na⁺/PO₄ ^3-) co-doping approach to mitigate the discharge capacity and voltage fade of a Co-free Li_1.2Ni_0.2Mn_0.6O₂ cathode. Our results show that the synergistic effect of cation/anion doping can promote long cycle stability and rate performance by inhibiting the phase transformation of the layered structure to a spinel or rock-salt structure and stabilizing the well-ordered crystal structure during long cycles. The co-doped sample exhibits an outstanding cycle stability (capacity retention of 86.7% after 150 cycles at 1 C) and excellent rate performance (153 mAh g^-1 at 5 C). The large ionic radius of Na⁺ can expand the Li slab to accelerate Li diffusion and the large tetrahedral PO₄ ^3- polyanions with high electronegativity stabilize the local structure to improve the electrochemical performance.

A FRET-based ratiometric fluorescent probe to detect cysteine metabolism in mitochondria

As an important biothiol in living cells, cysteine is closely related to oxidative damage in living organisms. Sulfite from cysteine metabolism in living cells plays a crucial role in maintaining homeostasis in an organism, and the unbalance of sulfite in vivo would lead to multiple diseases. Thus the development of a new fluorescent probe for cysteine metabolism is needed urgently in mitochondria which are the main place of cysteine metabolism. Herein we construct a novel targeting mitochondria fluorescent probe CP-K based on the FRET mechanism to visualize sulfite in living MCF-7 cells. Probe CP-K displays a large Stokes shift of 150 nm, a low detection limit (26.3 nM) and "naked eye" detection after the addition of HSO3-. Importantly, it is appropriate for imaging the endogenous sulfite from cysteine metabolism in living cells.

A novel mitochondria-targeted ratiometric fluorescent probe for endogenous sulfur dioxide derivatives as a cancer-detecting tool

A new mitochondria-targeted fluorescent probe RBC, constructed using a coumarin moiety which was selected as the donor and a benzothiazole derivative as the acceptor, for SO₂ derivatives (HSO₃^-/SO₃^2-) was presented. The probe designed on a new FRET platform showed high selectivity and a low detection limit. Importantly, the probe could respond to HSO₃^-/SO₃^2- within 35 s. Furthermore, the probe could target mitochondria and was successfully used for fluorescence imaging of endogenous bisulfite in HepG2 with low cytotoxicity, which significantly assisted in cancer diagnosis.

Red-Emission Probe for Ratiometric Fluorescent Detection of Bisulfite and Its Application in Live Animals and Food Samples

Key roles of bisulfite (HSO3 -) in food quality assurance and human health necessitate a reliable analytical method for rapid, sensitive, and selective detection of HSO3 -. Herein, a new red-emitting ratiometric fluorescence probe, BIQ, is reported for sensitive and selective detection of HSO3 - in food samples and live animals. Probe BIQ recognizes HSO3 - via a 1,4-nucleophilic addition reaction. As a result of this specific reaction, emission intensities at 625 and 475 nm are dramatically changed, allowing the detection of HSO3 - in a ratiometric fluorescence model in an aqueous solution. The obvious changes of solution color from pink to transparent and fluorescence color from rose-red to cyan allow the detection of HSO3 - by naked eyes. Furthermore, probe BIQ has fast response in color and fluorescence (<2 min), excellent selectivity, and a low detection limit (0.29 μM), which enables its application in HSO3 - detection in food samples and live organisms. The practical applications of probe BIQ are then demonstrated by the visualization of HSO3 - in live animals (zebrafish and nude mouse) as well as the determination of HSO3 - in white wine and sugar.

A near-infrared fluorescent probe for ratiometric sensing of SO2 in cells and zebrafish

SO₂ sensing and imaging: the first near-infrared fluorescent probe Mito-HN with AIEE characteristics for ratiometric sensing of SO₂ derivatives in vitro, in cells, and in zebrafish was rationally designed and synthesized.

An effective biocompatible fluorescent probe for bisulfite detection in aqueous solution, living cells, and mice

Sulfur dioxide, an air pollutant, is easily hydrated to sulfites and bisulfites and extremely harmful to human health. On the other hand, endogenous sulfur dioxide is the fourth gasotransmitter. In view of the above, it is worth developing an effective method for the detection of these compounds. In this paper, a novel colorimetric fluorescent probe (Hcy-Mo), based on hemi-cyanine, for bisulfites is reported. Hcy-Mo shows excellent selectivity for bisulfites over various other species including cysteine, glutathione, CN⁻, and HS⁻, and undergoes 1,4-addition reactions at the C-4 atom of the ethylene group. The reaction can be completed in 30 s in a PBS buffer solution and displays high sensitivity (limit of detection is 80 nM) for bisulfites. Test paper experiments show that the probe can be used for bisulfite detection in aqueous solutions. In addition, Hcy-Mo exhibits excellent cell permeability and low cytotoxicity for the successful detection of bisulfites in living MDA-MB-231 cells and in living mice, implying that this probe would be of great benefit to biological researchers for investigating the detailed biological and pharmacological functions of bisulfites in biological systems.

Sulfur dioxide, an air pollutant, is easily hydrated to sulfites and bisulfites and extremely harmful to human health.

Independent bi-reversible reactions and regulable FRET efficiency achieving real-time visualization of Cys metabolizing into SO2

An independent bi-reversible reaction sensor BPC detected cysteine (Cys) and sulfur dioxide (SO₂) based on the regulable FRET efficiency, and achieved real-time process visualization of Cys metabolizing into SO₂ in subcellular organelles and tumors.

Recent progress in the small-molecule fluorescent probes for the detection of sulfur dioxide derivatives (HSO3-/SO32-)

Sulfur dioxide (SO₂) had been recognized as an environmental pollutant produced from industrial processes. SO₂ is water soluble and forms hydrated SO₂ (SO₂·H₂O), bisulfite ion (HSO₃^-), and sulfite ion (SO₃^2-) upon dissolution in water. SO₂ could be also produced endogenously from sulfur-containing amino acids l-cysteine in mammals. Endogenous SO₂ can maintain the balance of biological sulfur and redox equilibrium in vivo, regulate blood insulin levels and reduce blood pressure. Excess intake of exogenous SO₂ can result in respiratory diseases, cardiovascular diseases and neurological disorders. As a result, fluorescent probes to detect HSO₃^-/SO₃^2- have attracted great attention in recent years. Herein, a general overview was provided with the aim to highlight the typical examples of the HSO₃^-/SO₃^2- fluorescent probes reported since 2010, especially those in the past five years. We have classified HSO₃^-/SO₃^2- fluorescent probes through different chemical reaction mechanisms and wish this review will give some help to the researchers in this field.

AND-Logic Based Fluorescent Probe for Selective Detection of Lysosomal Bisulfite in Living Cells

Sulfur dioxide (SO₂) plays significant roles in regulating cell apotosis and inflammation. However, there are complex interactions between small biomolecules in cells, and the identification of these coexisting biomarkers remains a challenge. Herein, we report an AND logic gate based fluorescent probe (NY-Lyso), operating by responding to pH differences between organelles in cell and selectively reacting with bisulfite (HSO₃^-). This approach allows the fluorescence of the probe to remain silent under neutral or alkaline conditions, notably, is activated by costimulation of lower pH and bisulfite. Furthermore, it was confirmed to be biocompatible and could be employed to monitor HSO₃^- in lysosomes of living cells. The proposed method demonstrated more practical and outstanding capabilities in targeted and real-time monitoring, providing an effective optical tool for biomarker sensing.

A chromenoquinoline-based two-photon fluorescent probe for the highly specific and fast visualization of sulfur dioxide derivatives in living cells and zebrafish

Sulfur dioxide (SO₂) derivatives play critical roles in various biological processes. Therefore, effective methods for monitoring SO₂ are of vital importance in bisulfite/sulfite biology. In this study, a two-photon (TP) imaging probe (CQ-SO₂) for detecting SO₂ derivatives was designed and constructed, based on the chromenoquinoline (CQ) fluorophore and a β-chlorovinyl aldehyde sensing moiety. The TP properties of the CQ derivatives were revealed for the first time in this study. This study enriched the biological application range of CQ derivatives and also provided a new choice for the development of TP dyes. In particular, the CQ-SO₂ probe exhibited a fast response time (about 5 s), low detection limit (16 nM) and ultrahigh specificity towards SO₂ derivatives. Furthermore, the probe was successfully applied to the highly specific TP bioimaging of SO₂ derivatives in living cells and zebrafish.

A near-infrared and mitochondria-targeted fluorescence probe for ratiometric monitoring of sulfur dioxide derivatives in living cells

A promising near-infrared emissive and mitochondria-targeted fluorescence probe (SNB) for the ratiometric detection of sulfur dioxide derivatives with a novel reaction mechanism was developed on the basis of FRET and the ICT platform.

A real-time ratiometric fluorescent probe for imaging of SO2 derivatives in mitochondria of living cells

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer (ICT) of the hemicyanine dye platform. The mechanism of using the probe is mainly through the Michael addition that occurs between IN-CZ and sulfite with a detection limit of 2.99 × 10⁻⁵ M. IN-CZ displays a fast response (within 1 minute) and is highly selective for SO₃²⁻/HSO₃⁻ over ROS, biologically relevant ions, biological mercaptans and other reactive species. More importantly, IN-CZ was suitable for ratiometric fluorescence imaging in living cells, by real-time monitoring of SO₃²⁻/HSO₃⁻ changes in mitochondria targeted in living cells.

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer of the hemicyanine dye platform.

Dual-site functionalized NIR fluorescent material for a discriminative concentration-dependent response to SO2 in cells and mice

Sulfur dioxide (SO₂), as an important anti-oxidant and gaseous signaling molecule, plays fundamental roles in the regulation of intracellular signaling and cell death cellular bioenergetics.