A novel dual-ratiometric-response fluorescent probe for SO2/ClO− detection in cells and in vivo and its application in exploring the dichotomous role of SO2 under the ClO− induced oxidative stress

An ESIPT + AIE based dual-response fluorescent probe for continuous detection of PhSH and HClO and visualization of PhSH-induced oxidative stress in living cells

As a valuable industrial chemical, thiophenol (PhSH) is poisonous, which can be easily absorbed by the human body, leading to many serious health issues. In addition, PhSH-triggered oxidative stress is considered to be related with the pathogenesis and toxicity of PhSH. Therefore, efficient methods for monitoring PhSH and ROS production induced by PhSH in living systems are very meaningful and desired. Herein, we reasonably developed a facile dual-response fluorescent probe (HDB-DNP) by incorporating the dinitrophenyl (DNP) group into a novel methylthio-substituted salicylaldehyde azine (HDB) with AIE and ESIPT features. The probe itself was non-fluorescent owing to the strong quenching effect of DNP group. In the presence of PhSH, HDB-DNP gave an intense red fluorescence (610 nm), which can rapidly switch to green fluorescence (510 nm) upon further addition of HClO, allowing the successive detection of PhSH and HClO in two well-separated channels. HDB-DNP proved to be a very promising dual-functional probe for rapid (PhSH: < 17 min; HClO: 10 s) and selective detection of PhSH and HClO in physiological conditions with low detection limit (PhSH: 13.8 nM; HClO: 88.6 nM). Inspired by its excellent recognition properties and low cytotoxicity, HDB-DNP was successfully applied for monitoring PhSH and PhSH-induced HClO generation in living cells with satisfactory results, which may help to better understand the pathogenesis of PhSH-related diseases.

Ratiometric electrochemiluminescence sensing and intracellular imaging of ClO- via resonance energy transfer

Electrochemiluminescence resonance energy transfer (ECL-RET) is a versatile signal transduction strategy widely used in the fabrication of chem/biosensors. However, this technique has not yet been applied in visualized imaging analysis of intracellular species due to the insulating nature of the cell membrane. Here, we construct a ratiometric ECL-RET analytical method for hypochlorite ions (ClO-) by ECL luminophore, with a luminol derivative (L-012) as the donor and a fluorescence probe (fluorescein hydrazide) as the acceptor. L-012 can emit a strong blue ECL signal and fluorescein hydrazide has negligible absorbance and fluorescence signal in the absence of ClO-. Thus, the ECL-RET process is turned off at this time. In the presence of ClO-, however, the closed-loop hydrazide structure in fluorescein hydrazide is opened via specific recognition with ClO-, accompanied with intensified absorbance and fluorescence signal. Thanks to the spectral overlap between the ECL spectrum of L-012 and the absorption spectrum of fluorescein, the ECL-RET effect is gradually recovered with the addition of ClO-. Furthermore, the ECL-RET system has been successfully applied to image intracellular ClO-. Although the insulating nature of the cell itself can generate a shadow ECL pattern in the cellular region, extracellular ECL emission penetrates the cell membrane and excites intracellular fluorescein generated by the reactions between fluorescein hydrazide and ClO-. The cell imaging strategy via ECL-RET circumvents the blocking of the cell membrane and enables assays of intracellular species. The importance of the ECL-RET platform lies in calibrating the fluctuation from the external environment and improving the selectivity by using fluorescent probes. Therefore, this ratiometric ECL sensor has shown broad application prospects in the identification of targets in clinical diagnosis and environmental monitoring.

Recent development in dual function fluorescence probes for HOCl and interaction with different bioactive molecules

Reactive oxygen species (ROS), reactive sulfur species (RSS), metal ions, and nitrogen species (RNS) play important roles in a variety of biological processes, such as a signal transduction, inflammation, and neurodegenerative damage. These species, while essential for certain functions, can also induce stress-related diseases. The interrelation between ROS, RSS, Metal ions and RNS underscores the importance of quantifying their concentrations in live cells, tissues, and organisms. The review emphasizes the use of small-molecule-based fluorescent/chemodosimeter probes to effectively measure and map the species' distribution with high temporal and spatial precision, paying particular attention to in vitro and in vivo environments. These probes are recognized as valuable tools contributing to breakthroughs in modern redox biology. The review specifically addresses the relationship of HOCl/ClO‾ (hypochlorous acid/Hypochlorite) with other reactive species. (Dual sensing probes).

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

A Fast-Response, Phenanthroimidazole-Based Fluorescent Probe for Selective Detection of HClO

A new phenanthroimidazole-based fluorescence probe for selective detection of HClO was synthesized and characterized using 1HNMR, 13CNMR, IR, and HRMS. With benzenesulfonohydrazide as the identification group, the probe demonstrated a fast fluorescence response from yellow-green to blue when the HC = N double bond was oxidized and broken into an aldehyde group by HClO. The probe showed high selectivity and sensitivity towards HClO with approximately 4.5-fold fluorescence enhancement and has been successfully applied in the molecular logic gate, determination of HClO in environmental water samples, and portable HClO detection.

A novel fluorescence probe for ultrafast detection of SO2 derivatives/biogenic amines and its multi-application: Detecting food and fish freshness, fluorescent dye and bioimaging

In this study, we have effectively prepared a novel fluorescent probe named HDXM based on benzopyran derivatives for the ultrafast detection (within 3 s) of SO2 derivatives or biogenic amines. HDXM showed a noticeable color change after the addition of SO2 derivatives (from purple to colorless) or biogenic amines (from purple to blue), indicating that HDXM can identify two analytes with the naked eye. It is worth noting that HDXM can be used to detect SO2 derivatives in actual sugar samples, and to image HSO3-/SO32- in living cells. More importantly, sensing labels (HDXM-loaded filter paper or agarose hydrogel) enable real-time visual monitoring of salmon freshness through colorimetric and fluorescence dual channels. Compared with the Chinese national standard method, the sensing label is an effective tool for evaluating the freshness of fish. Benefiting from its excellent solubility and fluorescence performance, HDXM can be used as a versatile fluorescent material in various applications, including flexible films, glass coatings, impregnating dyes, printing, and fingerprint ink. HDXM is expected to be a promising and valuable multifunctional tool for food safety and fluorescent materials.

A FRET-based ratiometric fluorescent probe for sensing bisulfite/sulfite and viscosity and its applications in food, water samples and test strips

A FRET-based ratiometric dual-response fluorescent probe, CQI, constructed by combining quinolinium-indole as the acceptor and coumarin as the donor, was developed for sensing HSO3-/SO32- and viscosity. After the interaction of probe CQI with the analyte, we achieved a green channel for the response to HSO3-/SO32- and an orange channel for the response to viscosity. We comprehensively evaluated the ability of CQI to detect SO2 derivatives and viscosity using fluorescence spectroscopy. Probe CQI exhibited a large Stokes shift (196 nm), a high energy transfer efficiency (99.6 %) and a wide detection range (0-250 μM). The fluorescence intensity of the probe increased up to 14-fold with increasing viscosity, and CQI could detect the viscosity of food thickeners. More importantly, probe CQI could not only successfully monitor SO2 derivatives in various food and water samples, but also be prepared as bisulfite test strips.

A near infrared fluorescence probe with dual-site for hydrogen sulfide and sulfur dioxide detection

Both hydrogen sulfide (H2S) and sulfur dioxide (SO2) are regarded as double-edged swords. They are toxic gases at high concentration, and at low concentration they are beneficial to the human. Therefore, it is of great significance to develop single chemosensor which enable to detect them with different fluorescence signal changes. In this work, a novel dual-site fluorescence probe (AMN-SSPy) with near infrared emission (675 nm) was designed, which realized quantitative detection for H2S and SO2 by fluorescence enhancement and fluorescence quenching, respectively. AMN-SSPy showed advantages such as excellent selectivity to H2S and SO2, strong anti-interference ability, high sensitivity for H2S (LOD 1.03 µM for H2S and 77.08 µM for SO2) and low toxicity. In addition, AMN-SSPy possessed the capacity to successfully image the endogenous and exogenous H2S, and it was also used to demonstrate that Ca2+ could induce accumulation of H2S in cell and zebrafish. Finally, the rapid detection of SO2 by AMN-SSPy in real samples was also established.

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.

Bifunctional near-infrared fluorescent probe for the selective detection of bisulfite and hypochlorous acid in food, water samples and in vivo

We report the development of a bifunctional near-infrared fluorescent probe (QZB) for selective sensing of bisulfite (HSO3-) and hypochlorous acid (HOCl). The synergistic detection of HSO3- and HOCl was achieved via a C=C bond recognition site. In comparison with the red-fluorescence QZB, two different products with non-fluorescence and paleturquoise fluorescence were produced by the recognition of QZB towards HSO3- and HOCl respectively, which can realize effectively the dual-functional detection of HSO3- and HOCl. QZB features prominent preponderances of dual-function response, near-infrared emission, reliability at physiological pH, low cytotoxicity and high sensitivity to HSO3- and HOCl. The detection of HSO3- in actual food samples has been successfully achieved using QZB. Utilization of QZB-based test strip to semi-quantitatively detect HSO3- and HOCl in real-world water samples by the "naked-eye" colorimetry are then demonstrated. Simultaneously, the determination of HSO3- and HOCl in real-world water sample has been achieved by smartphone-based standard curves. Additionally, the applications of QZB for imaging HSO3- and HOCl in vivo are successfully demonstrated. Consequently, the successful development of QZB could be promising as an efficient tool for researching the role of HSO3-/HOCl in the regulation of redox homeostasis regulation in vivo and complex signal transduction and for future food safety evaluation.

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

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

A dual-mode probe based on AIE and TICT effects for the detection of the hypochlorite anion and its bioimaging in living cells

Based on aggregation-induced emission (AIE) and twisted intramolecular charge transfer (TICT) mechanisms, a fluorescent probe SWJT-12 for the detection of ClO^- was designed by using the CN bond as a reactive group. This synthesized probe can react with ClO^- in a high aqueous phase, and it shows a large Stokes shift (144 nm) and low biological toxicity. Its limit of detection was calculated to be 0.28 μM. Furthermore, SWJT-12 was successfully used for ratiometric imaging of the exogenous hypochlorite anion in living cells.

A Near-Infrared Fluorescent Probe for Recognition of Hypochlorite Anions Based on Dicyanoisophorone Skeleton

A novel near-infrared (NIR) fluorescent probe (SWJT-9) was designed and synthesized for the detection of hypochlorite anion (ClO^-) using a diaminomaleonitrile group as the recognition site. SWJT-9 had large Stokes shift (237 nm) and showed an excellent NIR fluorescence response to ClO^- with the color change under the visible light. It showed a low detection limit (24.7 nM), high selectivity, and rapid detection (within 2 min) for ClO^-. The new detection mechanism of SWJT-9 on ClO^- was confirmed by ¹H NMR, MS spectrum, and the density functional theory (DFT) calculations. In addition, the probe was successfully used to detect ClO^- in HeLa cells.

Persistent and Efficient Multimodal Imaging for Tyrosinase Based on Two-Photon Excited Fluorescent and Room-Temperature Phosphorescent Probes

Tyrosinase is crucial to regulate the metabolism of phenol derivatives, playing an important role in the biosynthesis of melanin pigments, whereas an abnormal level of tyrosinase would lead to severe diseases. It is rather necessary to develop a sensitive and selective imaging tool to assess the level of tyrosinase in vivo. We thoroughly researched the luminous mechanism of the existing TPTYR probe and provided design strategies to improve its two-photon excited fluorescence properties. The designed probes benza2-TPTYR and product benza2-TPTYR-coumarin have large two-photon absorption cross sections at the NIR spectral region (41 GM/706 nm, 71 GM/852 nm), while benza2-TPTYR-coumarin possesses easily distinguishable spectrum in the visible region and a high fluorescence efficiency (Φ_F = 0.27). What is more, novel two-photon excited multimodal imaging based on the pure organic small molecule benza1-TPTYR-coumarin (61 GM/936 nm) is proposed first, simultaneously possessing strong instantaneous fluorescent (563.79 nm) and persistent room-temperature phosphorescent emissions (767.68 nm, 0.54 ms).

A new ratiometric switch "two-way" detects hydrazine and hypochlorite via a "dye-release" mechanism with a PBMC bioimaging study

A new ratiometric fluorescent probe (E)-2-(benzo[d]thiazol-2-yl)-3-(8-methoxyquinolin-2-yl)acrylonitrile (HQCN) was synthesised by the perfect blending of quinoline and a 2-benzothiazoleacetonitrile unit. In a mixed aqueous solution, HQCN reacts with hydrazine (N₂H₄) to give a new product 2-(hydrazonomethyl)-8-methoxyquinoline along with the liberation of the 2-benzothiazoleacetonitrile moiety. In contrast, the reaction of hypochlorite ions (OCl^-) with the probe gives 8-methoxyquinoline-2-carbaldehyde. In both cases, the chemodosimetric approaches of hydrazine and hypochlorite selectively occur at the olefinic carbon but give two different products with two different outputs, as observed from the fluorescence study exhibiting signals at 455 nm and 500 nm for hydrazine and hypochlorite, respectively. A UV-vis spectroscopy study also depicts a distinct change in the spectrum of HQCN in the presence of hydrazine and hypochlorite. The hydrazinolysis of HQCN exhibits a prominent chromogenic as well as ratiometric fluorescence change with a 165 nm left-shift in the fluorescence spectrum. Similarly, the probe in hand (HQCN) can selectively detect hypochlorite in a ratiometric manner with a shift of 120 nm, as observed from the fluorescence emission spectra. HQCN can detect hydrazine and OCl^- as low as 2.25 × 10^-8 M and 3.46 × 10^-8 M, respectively, as evaluated from the fluorescence experiments again. The excited state behaviour of the probe HQCN and the chemodosimetric products with hydrazine and hypochlorite are studied by the nanosecond time-resolved fluorescence technique. Computational studies (DFT and TDDFT) with the probe and the hydrazine and hypochlorite products were also performed. The observations made in the fluorescence imaging studies with human blood cells manifest that HQCN can be employed to monitor hydrazine and OCl^- in human peripheral blood mononuclear cells (PBMCs). It is indeed a rare case that the single probe HQCN is found to be successfully able to detect hydrazine and hypochlorite in PBMCs, with two different outputs.

Molecular engineering-based a dual-responsive fluorescent sensor for sulfur dioxide and nitric oxide detecting in acid rain and its imaging studies in biosystems

Sulfur dioxide (SO₂) and nitric oxide (NO), known as sulfur oxides and nitrogen oxides, are toxic air pollutants and seriously threaten human health. Herein, for the first time, a robust dual-response fluorescent sensor CGT with two different emission fluorophores and dual well-known response-group for visual bisulphites (HSO₃^-) and nitrites (NO₂^-) detection was reported. Specifically, once CGT was incubated with HSO₃^- firstly, the color of the test solution changed to dark yellow with no-fluorescence emission, following added NO₂^-, the color of the test solution changed to yellow with a bright cyan emission. However, NO₂^- was added firstly, the color of the test solution changed to dark purple with a white emission, and then added HSO₃^-, the color of the test solution changed to yellow with a bright cyan emission. Furthermore, CGT showed high sensitivity and selectivity toward HSO₃^- and NO₂^- detecting with good detection limits as low as 20.17 nM and 4.14 nM, respectively. Impressively, CGT showed good detection capability in complex aqueous samples and was successfully used for the detection of HSO₃^- and NO₂^- in biosystems. Thus, the experimental results indicated CGT as a powerful novel visual detecting tool for HSO₃^- and NO₂^- detecting in complex acid rain and biosystems.

Fluorescent probes for biomolecule detection under environmental stress

The use of fluorescent probes in visible detection has been developed over the last several decades. Biomolecules are essential in the biological processes of organisms, and their distribution and concentration are largely influenced by environmental factors. Significant advances have occurred in the applications of fluorescent probes for the detection of the dynamic localization and quantity of biomolecules during various environmental stress-induced physiological and pathological processes. Herein, we summarize representative examples of small molecule-based fluorescent probes that provide bimolecular information when the organism is under environmental stress. The discussion includes strategies for the design of smart small-molecule fluorescent probes, in addition to their applications in biomolecule imaging under environmental stresses, such as hypoxia, ischemia-reperfusion, hyperthermia/hypothermia, organic/inorganic chemical exposure, oxidative/reductive stress, high glucose stimulation, and drug treatment-induced toxicity. We believe that comprehensive insight into the beneficial applications of fluorescent probes in biomolecule detection under environmental stress should enable the further development and effective application of fluorescent probes in the biochemical and biomedical fields.

A dual-response fluorescent probe for discriminative sensing of hydrazine and bisulfite as well as intracellular imaging with different emission

Bisulfite and hydrazine are harmful to the environment safety and human health. Therefore, it is of great value to develop a smart fluorescent probe with high selectivity for detection of bisulfite and hydrazine. In our report, a dual-response fluorescent probe EDBI with high selectivity, rapid response, and low detection limit for discriminative determination HSO₃^- and N₂H₄ was exploited. The probe EDBI is capable of distinctive sensing HSO₃^- and N₂H₄ based on nucleophilic addition reactions by taking advantage of ratiometric fluorescence and fluorescence "on-off" mode, respectively. The dual-responses behaviors of probe EDBI toward HSO₃^- and N₂H₄ were attribute to different reaction sites, which it has been confirmed by HRMS. More importantly, cytotoxicity experiment authenticated that probe possesses low toxicity and good penetration. The probe EDBI with excellent performance, it was successfully employed to distinguishable sense HSO₃^- and N₂H₄ in living cells by diverse channel patterns. Therefore, this simple dual-response fluorescence probe is expected to be used for real-time monitoring bisulfite and hydrazine in biological samples.

Sequential detection of H2S and HOBr with a novel lysosome-targetable fluorescent probe and its application in biological imaging

Understanding the complex relationship between active small molecules is of great significance in various physiological processes. Herein, we present the design and synthesis of a sequential responsive Lysosome-Naphthalene imide-Azido (lyso-NP-N₃) reporter for probing the H₂S and HOBr within organelle (lysosome) in living cells. Probe lyso-NP-N₃ exhibited high selectivity and sensitivity towards H₂S (LOD = 23.5 nM) and HOBr (LOD = 254 nM). Additionally, lyso-NP-N₃ possessed an excellent lysosome targeting ability and was utilized to visualize the exogenous/endogenous H₂S and HOBr in RAW 264.7, Hela and HepG2 cells. Facilitated by this sequentially activated mechanism, the probe was successfully applied to confirm that the reported scavenger of HOBr, N-acetyl-L-cysteine (NAC) mainly relied on its metabolite H₂S to eliminate excess HOBr, thereby playing the role of cell regulation and protection. These results establish the crosstalk between H₂S and HOBr in lysosome and provide a promising tool to study metabolite interactions.

A novel near-infrared fluorescent probe for the detection of sulfur dioxide derivatives and its application in biological imaging

SO2 plays an important role in our life and is also associated with many diseases, so it is a double-edged sword. Therefore, it is necessary to develop a probe for...

Antibody-siRNA conjugates (ARCs) using multifunctional peptide as a tumor enzyme cleavable linker mediated effective intracellular delivery of siRNA

The tissue-specific targeted delivery and efficient cellular uptake of siRNAs are the main obstacles to their clinical application. Antibody-siRNA-conjugates (ARCs) can deliver siRNA by exploiting the targeting property of antibodies like antibody-drug conjugates (ADCs). However, the effective conjugation of antibodies and siRNAs and the release of siRNAs specifically at target sites have posed challenges to the development of ARCs. In this study, the successful conjugation of antibodies and siRNAs was achieved using a multifunctional peptide as a linker, composed of a cell-penetrating peptide (CPP) and a substrate peptide (SP), which is highly expressed in solid tumors. The resulting antibody-multifunctional peptide (SP-CPP)-siRNA system delivered the siRNA to target tumor cells by the specific binding of the antibody. Once the enzymes on the tumor cell surface hydrolyzed the substrate peptide linker, siRNA-CPP was released from ARCs. The released siRNA-CPP entered the targeted cells via the cellular penetrating ability of CPP, resulting in improved siRNA-mediated gene silencing efficiency, verified both in vitro and in vivo. After intravenous administration, the designed ARCs achieved approximately 66.7% EGFP (Enhanced Green Fluorescent Protein) downregulation efficiency in nude mice xenografted with the HCT116-EGFP tumor model. The proposed system provides a prospective choice for ARC production and the safe and efficient delivery of siRNAs.

Aggregation-induced emission luminogen@manganese dioxide core-shell nanomaterial-based paper analytical device for equipment-free and visual detection of organophosphorus pesticide

Organophosphorus pesticide (OP) residues have gathered considerable attention because of their significant threat to society development and healthy life. Developing a sensitive and practical OPs sensor is highly urgent, whereas remains a huge challenge. To this end, we fabricated a high-performance fluorescence paper analytical device (PAD) for apparatus-free and visual sensing of OPs based on aggregation-induced emission (AIE) luminogen's bright emission in aggregated state, unique response of MnO₂ to thiol compounds, and difference of MnO₂ and Mn²⁺ in quenching fluorescence. AIE nanoparticles PTDNPs-0.10 and MnO₂ respectively acted as core and shell to prepare PTDNPs@MnO₂, which possessed high stability and were dripped on cellulose paper's surface to fabricate AIE-PAD. The sensing mechanism is that OPs-treated acetylcholinesterase (AChE) prevents the formation of thiocholine, thereby minimizing the reduction of MnO₂ into Mn²⁺ and changing the output signal. As a result, equipment-free and visual sensing of OPs was acquired with limit of detection of 1.60 ng/mL. This work justifies the feasibility of applying core-shell material to develop high-performance sensor and substituting complex/expensive solution-phase sensor with PAD, providing a new avenue to bring OPs analysis out of the lab and into the world.

Fluorescence distinguishing of SO2 derivatives and Cys/GSH from multi-channel signal patterns and visual sensing based on smartphone in living cells and environment

Sulfur dioxide (SO₂), cysteine (Cys) and glutathione (GSH), which perform crucial actions in regulating the balance of human, are closely related reactive sulfur species (RSS). Moreover, SO₂ is one of the most concerned air pollutants, which is easily soluble in water and forms its derivatives. Therefore, it is highly desirable to differentiate SO₂ derivatives and Cys/GSH in living cells and environment. Herein, a new near-infrared (NIR) mitochondria-targeted fluorescent probe, NIR-CG, which could distinguish SO₂ derivatives and Cys/GSH by using multiple sets of signal patterns under single excitation was reported. NIR-CG exhibited different fluorescence signal modes to SO₃^2- and Cys/GSH with low limit of detection (17.1 nM for SO₃^2-, 17.3 nM for Cys and 25.9 nM for GSH). The recognition mechanisms of NIR-CG to SO₃^2- and Cys/GSH were verified by HRMS, ¹H NMR and DFT calculation. NIR-CG had good ability of mitochondrial targeted and fluorescence imaging in cells. What's more, NIR-CG showed great recovery rates (101-104%) in the determination of SO₃^2- in actual water samples. It was worth noting that NIR-CG-based paper strip successfully realized the visual quantitative detection of SO₃^2- and Cys/GSH by use of smartphone, which offered a novel method to develop powerful sensing platform.

Tackling the Selectivity Dilemma of Benzopyrylium-Coumarin Dyes in Fluorescence Sensing of HClO and SO2

Benzopyrylium-coumarin fluorescent probes for sensing hypochlorous acid (HClO) or sulfur dioxide (SO₂) are unable to distinguish between HClO and SO₂ because the two compounds can react with the 4-position of benzopyrylium-coumarin dyes through the nucleophilic attack. In the current work, we introduced a phenoxazine moiety to the benzopyrylium-coumarin dye to synthesize a new fluorescent probe PBC1, which can dually sense HClO and SO₂ and generate distinct fluorescence signals with rapid response time and high sensitivity and selectivity. Moreover, probe PBC1 was also successfully utilized to detect intracellular HClO and SO₂ in HeLa cells and zebrafish.

Nanoliposomal Ratiometric Fluorescent Probe toward ONOO- Flux

Peroxynitrite (ONOO^-), a powerful biological oxidant, is produced in the mitochondria and reacts with many biomolecular targets under various pathological conditions, leading to a range of disease states. In this work, we developed a nanoliposome-encapsulated ratiometrically fluorescent probe (NRF) based on a hemicyanine structure Cy-O obtained by facile synthesis. Upon reaction with ONOO^-, the oxidation and hydrolysis of a π-conjugation system within the nanoliposome triggers a ratiometrically fluorescent response and a large-scale emission shift (238 nm), which provides a specific and sensitive means for the ONOO^- detection. Moreover, we have performed DFT calculation at the 6-31+G(d,p) level using a suite of Gaussian 09 programs to obtain insights into the chemical structure optical properties of Cy-O. In addition, the practical applications of the nanoprobe to image exogenous and endogenous ONOO^- were achieved further in live cells and animals triumphantly.

Binary Prodrug of Dichloroacetic Acid and Doxorubicin with Enhanced Anticancer Activity

The inevitable challenge in conventional chemotherapy is to deliver the anticancer drugs to the dense population of tumors cells while minimizing the drug-associated side effects on the normal cells. Cancer cells' preference for glycolysis for energy production is well recognized. Intuitively, taking advantage of such cancer-associated metabolism would be a promising strategy for anticancer drug delivery with minimal side effects. In this investigation, we have designed a binary prodrug PDOX as a sequential drug delivery regimens to realize the combination therapy for cancer. As cancer cells exhibit abrupt metabolism with elevated pyruvate dehydrogenase kinase (PDK) activity, dichloroacetic acid (DCA, a well-known PDK inhibitor) was used in combination with anticancer drug doxorubicin (DOX). The designed molecular prodrug was activated selectively by cancer-associated esterase to deliver DCA and DOX, respectively, and induced synergetic effects. Hence, sequential targeted delivery of molecular prodrug PDOX offers a promising approach to overcome the offside drug toxicity, pharmacokinetics, and biodistribution of individuals and provide an alternative option for cancer treatment.

A three-channel fluorescent probe to image mitochondrial stress

Dual-recognition probes based on one reacting site inevitably encounter competition problems. Here, NPClA, a two-photon fluorescent probe based on a dual-site response for SO2/HOCl, was developed and applied in imaging mitochondrial stress.

The development of a highly selective fluorescent probe for the rapid detection of HClO in living cells and zebrafish

A new turn-on fluorescent probe, BM-HA, for the rapid detection of HClO in living cells and zebrafish is proposed, and DFT/TDDFT calculations provide insights into the optical properties of the BM-HA probe.

Recent development of synthetic probes for detection of hypochlorous acid/hypochlorite

Hypochlorous acid/hypochlorite (HOCl/OCl^-), as one of the most important reactive oxygen species (ROS), plays an important role in various physiological and pathological processes. Nonproperly located or abnormal concentration of OCl^-, however, is associated with many diseases. Thus, developing the fluorescent probe for detecting OCl^- is of great significance. To this end, in last decade, many fluorescent probes have been developed and applied for detecting HOCl/OCl^- in vitro and in vivo. Despite a great progress has achieved, the development and application of near-infrared fluorescent HOCl/OCl^- probe still have some challenges. For example, highly specific and sensitive NIR fluorescent HOCl/OCl^- probes applied in endogenous OCl^- detection and subcellular organelle bioimaging. In this review, we summarized the representative cases of HOCl/OCl^- probes with properties that mentioned above. The discussion contains design strategies, detection mechanisms, as well as applications in bioimaging.

N-doped carbon quantum dots from osmanthus fragrans as a novel off-on fluorescent nanosensor for highly sensitive detection of quercetin and aluminium ion, and cell imaging

In this work, fluorescent N-doped carbon quantum dots (N-CQDs) have been synthesized by simple hydrothermal heating of natural osmanthus fragrans, without any toxic ingredients or surface chemical modifications. The N-CQDs possess a high quantum yield of 21.9 %, outstanding blue fluorescence, good water dispersity, and excellent optical stability. Because the favorable inner filter effect (IFE) between N-CQDs and quercetin (QT) occurs, the addition of QT to N-CQDs can cause their fluorescence quenching. When Al³⁺ was added to the N-CQDs/QT system solution, it was found that the inhibition of IFE leads to the fluorescence intensity of N-CQDs/QT system enhancement by virtue of a specific binding of QT to aluminum ion (Al³⁺). Therefore, we used the N-CQDs as a novel off-on fluorescent nanosensor to detect QT and Al³⁺. Under optimal conditions, the fluorescent nanosensor can detect QT within the wide linear response in the range of 0.003-80 μmol/L with as low as 1 nmol/L detection limit. For the detection of Al³⁺, the N-CQDs/QT system showed linearity response toward Al³⁺ in a range of 0.1∼100 μmol/L and the limit of detection was found at 26 nmol/L. In addition, N-CQDs have been successfully used to efficient quantification QT in human plasma and monitor Al³⁺ in serum samples. Noteworthy, the N-CQDs demonstrated low toxicity toward T24 cells, which realized sensing QT and Al³⁺ in the living cells.

A bifunctional fluorescent sensor for CCCP-induced cancer cell apoptosis imaging

The detailed mechanism and the extent of pH/SO₂ changes during apoptosis remain unknown. The developed sensor NPCF for SO₂ and pH dual detection illustrates that SO₂ can reduce the inflammation caused by LPS and the acidification of the environment. The levels of SO₂ and pH change during carbonyl cyanide m-chlorophenylhydrazone (CCCP)-induced apoptosis.

Highly Efficient Cell Membrane Tracker Based on a Solvatochromic Dye with Near-Infrared Emission

The cell membrane is composed of a phospholipid bilayer with embedded proteins and maintains cell homeostasis through dynamic changes. An abnormal cell membrane shape could be a sign of unhealthy cells. Probes for subcellular fluorescence imaging that can identify the abnormal plasma membrane and record the dynamic changes are needed. Based on a solvatochromic dye with a near-infrared emission strategy, the amphipathic molecule (E)-2,2'-((4-(2-(4-(dicyanomethylene)-4H-chromen-2-yl)vinyl)phenyl)azanediyl)bis(ethane-1-sulfonic acid) (MRL) contained a hydrophilic sulfo group and a hydrophobic chromone group, which was designed and synthesized for staining the cell membrane and monitoring the morphology of the membranes under different conditions. MRL exhibited an excellent photostability and low cytotoxicity; when cells were incubated with MRL, cell membranes were specifically labeled. MRL is capable of long-term monitoring of the morphological changes of cell membrane.

Bioanalytical method by HPLC-FLD for curcumin analysis in supplemented athletes

In sports, curcumin, a substance derived from the rhizome of Curcuma longa (turmeric) plant with antioxidant effect 8 times greater than vitamin E, has attracted the attention of scientists because of its potent antioxidant action, since in athletes subjected to intense exercise the—endogenous mechanisms of neutralization of reactive species are saturated. However, the pharmacokinetic characteristics of curcumin do not favor its medicinal use due to its low absorption, accelerated metabolism and rapid systemic elimination. Thus, the determination of plasma levels in supplemented patients is a crucial step in their pharmacodynamic evaluation. Therefore, the objective of this work was to develop and validate an analytical method by HPLC-FLD for curcumin evaluation in plasma of supplemented athletes. Luna column (C18; 150 × 4 mm; 3 µm), acetonitrile: acetic acid pH 3.2 (45:55 to 60:40) as mobile phase, flow rate of 1 mL min⁻¹, excitation at 429/285 nm and emission at 529 nm and injection of 10 µL were the chromatographic conditions used. Plasma samples were extracted using ethylacetate and methanol (95: 5, 500 µL) and estradiol (30 µg mL⁻¹) as internal standard, with subsequent stirring (3 min) and centrifugation (8 min) (triple extraction). The organic fraction was evaporated under N₂ (20 min) and the dried residue reconstituted in acetonitrile. The method was linear between 44 and 261 ng mL⁻¹, showing intra-day (2.05.6%) and inter-day (4.0–5.1%) precision with accuracy and selectiveness (curcumin t_R = 8.7 min and internal standard t_R = 13.9 min with relative recovery of 83.2%). So, it can be successfully used for curcumin evaluation in plasma samples from supplemented athletes, as well as being an alternative and advantageous method to UV–Vis and MS/MS in bioavailability studies.

A novel self-calibrating strategy for real time monitoring of formaldehyde both in solution and solid phase

Formaldehyde (FA) is a chemical substance with tremendously noxious feature for human health and it causes serious damages to living organisms. The recognition of formaldehyde in the form of fluorescent signals has been extensively explored by using a few molecular scaffolds in buffer mediums. In particular, the study for sensing of formaldehyde both in solution and solid state has generated considerable interests. Herein, a new ratiometric fluorescent probe 1-(5-(9-phenyl-9H-carbazol-3-yl)thiophen-2-yl)but-3-en-1-amine (SO-GJP) has been synthesized for selective detection of FA based on aza-Cope reaction. In the presence of FA from 0 to 1.3 mM, the emission band of SO-GJP varies from 393 nm to 542 nm and the detection limit has been calculated to be 1.55 μM. The entrapment of SO-GJP onto the thin layer chromatography (TLC) plate leads to the successful detection of FA with sensitive color change from white to yellow. Moreover, the response mechanism has been explained by FA-induced 2-aza-Cope rearrangement within SO-GJP and the chemical processes are supported by density functional theory, fluorescence and UV-vis spectra. The integration of responsive units based on carbazole platform can serve as one of the powerful strategies by directly converting signals at different circumstances into fluorescence.

A mitochondrion-targeted dual-site fluorescent probe for the discriminative detection of SO32− and HSO3− in living HepG-2 cells

Sulfur dioxide, known as an environmental pollutant, produced during industrial productions is also a common food additive that is permitted worldwide. In living organisms, sulfur dioxide forms hydrates of sulfite (SO₂·H₂O), bisulfite (HSO₃⁻) and sulfite (SO₃²⁻) under physiological pH conditions; these three exist in a dynamic balance and play a role in maintaining redox balance, further participating in a wide range of physiological and pathological processes. On the basis of the differences in nucleophilicity between SO₃²⁻ and HSO₃⁻, for the first time, we built a mitochondrion-targeted dual-site fluorescent probe (Mito-CDTH-CHO) based on benzopyran for the highly specific detection of SO₃²⁻ and HSO₃⁻ with two diverse emission channels. Mito-CDTH-CHO can discriminatively respond to the levels of HSO₃⁻ and SO₃²⁻. Besides, its advantages of low cytotoxicity, superior biocompatibility and excellent mitochondrial enrichment ability contribute to the detection and observation of the distribution of sulfur dioxide derivatives in living organisms as well as allowing further studies on the physiological functions of sulfur dioxide.

Rational design and sensing mechanism of a dual-site fluorescence probe for HSO₃⁻ and SO₃²⁻.

Simultaneous imaging of mitochondrial viscosity and hydrogen peroxide in Alzheimer's disease by a single near-infrared fluorescent probe with a large Stokes shift

Simultaneous imaging of mitochondrial viscosity and hydrogen peroxide in Alzheimer's disease by a single near-infrared fluorescent probe with a large Stokes shift.

A water soluble ratiometric fluorescent probe for targeting SO2 in mitochondria based on conjugated biquinolines

Despite the unprecedented development of SO₂ fluorescent probes in the past five years, the water-solubility of these probes is still an important factor related to their practical application.

A near-infrared ratiometric fluorescent probe based on the CN double bond for monitoring SO2 and its application in biological imaging

A near-infrared ratiometric fluorescent probe based on CN double bond was developed for monitoring SO₂ and its application in biological imaging.