Coumarin-based near-infrared fluorogenic probes: Recent advances, challenges and future perspectives

Imaging of sulfhydryl fluctuations in mouse models of drug-induced liver injury via a novel near-infrared fluorescence probe

Drug-induced liver injury (DILI), caused by pharmaceuticals or their metabolites, is closely associated with oxidative stress, and it is a serious public health concern. Sulfhydryl groups, due to their antioxidant and detoxification capabilities, play a pivotal role in mitigating oxidative stress-induced cellular damage in related diseases. Therefore, precise monitoring of intracellular sulfhydryl levels is essential for evaluating the severity and progression of such conditions. In this study, we synthesized a series of near-infrared fluorescent probes by incorporating the furan carbonyl group as a novel recognition moiety linked to the dicyanoisophorone structure. Following systematic screening, we identified NIR-Cl as the most effective probe, demonstrating high sensitivity and selectivity for sulfhydryl groups, as well as rapid responsiveness to concentration changes under physiological pH conditions. The application of NIR-Cl in a zebrafish model of oxidative stress and a mouse model of DILI revealed significant fluctuations in sulfhydryl levels, highlighting the probe's capacity to monitor dynamic redox processes in vivo. These results offer important insights into the molecular mechanisms of DILI, positioning NIR-Cl as a promising tool for diagnosing and managing oxidative stress-related diseases. Furthermore, the study highlights the probe's potential to advance redox biology research and support the development of targeted therapeutic strategies.

Advances in fluorescent natural products for imaging localization and biological applications

Natural products play a crucial role in biological activities, yet the quest for novel natural products faces increasing challenges due to the complexities of structural exploration and efficacy evaluation. Besides, traditional methods for evaluating natural products primarily focus on non-fluorescent efficacy studies at animal level or multicellular accumulation level, lacking of intuitive fluorescence presentation at the single cell or organelle level. This limitation disrupts our understanding of the effectiveness of natural products and constrains their biological activities. The most striking example is that fluorescent natural products offer a unique but often overlooked dual function: they not only exhibit biological activities but also may provide real-time fluorescent signals for tracking within biological systems. This review highlights the exciting advances in imaging localization of fluorescent natural products combined with advanced imaging techniques, summarizes the structural characteristics and application criteria of fluorescent natural products, and explores their feasibility in visual localization and biological activities. This synthesis underscores the need for a systematic exploration of fluorescent natural products, towards a transformative impact on drug development and disease understanding.

Experimental and computational insights into the electronic structures and absorption-emission characteristics of coumarin, C-6H, C-153, and C-343 dyes

This paper explores the electronic structure and spectral characteristics of coumarin (C), C-6H, C-153, and C-343 in the protic polar solvent acetonitrile, combining computational methods via Density Functional Theory (DFT) and time-dependent Density Functional Theory (TD-DFT) with experimental analysis of UV-Vis and fluorescence spectra. The optoelectronic features of C, C-6H, C-153, and C-343 are primarily utilized in the solution phase for various applications, such as lasers and dye-sensitized solar cells. Computational studies were conducted using four different Modal Chemistry methods [MC1: CAM-B3LYP/6-311++G(d.p), MC2: CAM-B3LYP/6-31 + G(d.p), MC3: B3LYP/6-311++G(d.p), and MC4: B3LYP/6-31 + G(d.p)]. The excited state features were investigated based on TD-DFT/Polarizable Continuum Model-Linear Response and TD-DFT/Polarizable Continuum Model-State Specific formalisms. Molecular orbital configurations, molecular electrostatic potentials, and electron density difference isosurface of the dyes were analyzed to uncover the factors influencing the absorption and emission properties. The decomposed UV-Vis and fluorescence spectra of compounds indicate that emission characteristics are complex and contribute to low-lying energy transitions. The state-specific solutions provide more reliable estimates for smaller molecular structures with less intramolecular charge transfer, whereas the linear response approach excels when more electron-donating functional groups are present. The effect of the basis set in determining both absorption and emission features is almost negligible compared to Hartree-Fock exchange contributions in DFT functionals. B3LYP appears to provide satisfactory results for systems where long-range HF exchange is not as crucial.

An optimized CYP3A4-activatable fluorogenic sensor for in situ functional imaging and multi-dimensional inhibitor assessment

Cytochrome P450 3A4 (CYP3A4), one of the most important drug-metabolizing enzymes, plays a pivotal role in the oxidative metabolism of a wide range of non-polar xenobiotics and endogenous substances. Deciphering the dynamic changes in CYP3A4 activity under specific physiological or pathological conditions, as well as assessing the modulatory effects of therapeutic agents on CYP3A4, requires highly-efficient and reliable tools for sensing CYP3A4 activity within complex biological matrices. Herein, an integrated strategy was adopted for developing an optimized CYP3A4-activatable fluorogenic sensor that enables in situ detection of CYP3A4 activity in living systems without the interference of P-glycoprotein (P-gp), via integrating computer-aided substrate design, drug-likeness filtering, and biochemical assays. Following screening a range of 1,8-naphthalimide derivatives, N-cyclopropylmethyl-1,8-naphthalimide (NCN) was identified as an optimized fluorogenic substrate for CYP3A4, demonstrating exceptional isoform-specificity, single metabolite formation, ultrahigh sensitivity, high binding-affinity, improved cell-membrane permeability, and favorable bio-safety profiles. Notably, both NCN and its fluorogenic metabolite (HNCN) were identified as non-substrates of P-gp, which greatly facilitated in situ functional imaging of CYP3A4 activities in living systems, such as live cells and organs. It was also found that NCN was an orally bioavailable agent, which significantly facilitated the precise assessment of CYP3A4 inhibitors across multi-dimensional biological systems, including in vitro, ex vivo, and in vivo. Collectively, this work showcases an integrated strategy for the rational engineering of isoform-specific and orally bioavailable CYP3A4-activatable fluorogenic substrates for CYP3A4, with NCN emerging as a practical and reliable CYP3A4-activatable tool for in situ imaging and inhibitor assessment.

Discovery of a Class of Novel Succinate Dehydrogenase Inhibitors Containing a Coumarin Structure

Succinate dehydrogenase (SDH) has emerged as a highly promising target in modern agricultural research, playing a crucial role in developing environmentally friendly and efficient fungicides for combating agricultural pathogens. This study presents the discovery of a novel class of SDH inhibitors (I-III) incorporating coumarin segments achieved through an active fragment swapping and linking strategy. Fungicidal activity assays revealed that several compounds within this series demonstrate significant inhibitory effects against the tested fungal strains. Through comprehensive structure-activity relationship studies, compound N-(1-((3-butyl-4-methyl-2-oxo-2H-chromen-7-yl)oxy)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide (IIk) exhibited potent inhibitory activity against various fungal species. Notably, it demonstrated superior efficacy against S. sclerotiorum with an EC50 value of 1.14 μg/mL, outperforming the commercial control agent thifluzamide (EC50 = 4.90 μg/mL). Molecular docking simulations indicated that hydrophobic interactions serve as the primary binding mechanism between the ligand and SDH. Intriguingly, compound IIk displayed dual functionality, not only acting as an effective fungicide but also promoting the growth of wheat seedlings and Arabidopsis thaliana, resulting in increased plant biomass. Preliminary investigations into its growth-promoting mechanism suggest that IIk enhances the nitrate reductase activity, thereby facilitating plant growth.

A Novel NIR Fluorescence Probe with AIE Property to Image Viscosity in Nystatin-Induced Cell Model

As one of the most significant parameters in cellular microenvironment, viscosity levels could be used to determine the metabolic process of bioactive substances within cells. Abnormal viscosity levels are closely associated with a series of diseases. Therefore, the design and synthesis of fluorescent probes that can monitor changes of intracellular viscosity in real-time is of great significance for the study of disease development process. Here, a new viscosity-recognized NIR fluorescence probe W1 based on quinoline-malonitrile is synthesized, and it is not susceptible to interference substances. Besides, AIE probe W1 shows fast response, excellent photostability, low cytotoxicity, good linear relationship between fluorescence intensity value and viscosity. Based on the above advantages, probe W1 is used to image the change of viscosity level in the cell model induced by nystatin.

A novel self-ratiometric fluorescent sensor of sodium alginate hydrogel bead doping with coumarin derivative with extremely acidic pH visual monitoring of fruit juice freshness

The slight acidic pH changes during food storage and transportation are often difficult to detect in a timely and accurate manner. There is also an urgent need to establish a portable, accurate, and low interference detection method for real-time monitoring of the quality changes of fresh juice that already has its own color. In this paper, a self-ratiometric fluorescent sensor (DCCA/SA bead) was prepared by combining a modified coumarin and sodium alginate (SA), and was used for the extreme pH monitoring of fluorescent by naked eye colorimetry. The derivative of natural active ingredient coumarin (DCCA) exhibited excellent self-fluorescence properties in the ratio of orange red (630 nm) to blue-green (480 nm) under the excitation, and exhibited good linear changes at extreme acid pH range (2.5-5.0), biocompatibility high sensitivity, and anti-interference ability. Based on the multiple interactions between DCCA and SA, DCCA/SA bead could be used for the monitoring small pH changes of fruit juice and storage stage in a fast response time. In addition, analyzing the RGB values of DCCA/SA bead images under ultraviolet light also successfully quantitatively determined changes in pH values. These results indicated that the self-ratiometric fluorescent hydrogel sensor had great user convenience and point-of-care testing (POCT) to monitor extreme acidic pH for freshness of foods.

A molecular sensor for selective recognition of Fe3+ by a functional seven-nuclear Zn(II) cluster compound formed from a quinoline-modified half-salamo-type Precursor

In this paper, we designed and synthesized a novel based on quinoline modification half-salamo-type Zn(II) complex([Zn7(L)6(μ3-OCH3)6]·(ClO4)2), namely ZP. The structure of ZP was determined by X-ray single-crystal diffraction, in which the Zn(II) ions displayed in two different coordination modes, ultimately forming a highly symmetric heptanuclear structure. The Zn(II) complex probe modified by quinoline luminescent group has excellent luminescence properties and selectively recognizes Fe3+ in aqueous solution. When Fe3+ is added to the aqueous solution of ZP, ZP exhibits an obvious fluorescence quenching effect in a relatively short period of time, with a high sensitivity. The lowest detection limit of ZP for Fe3+ was further determined by fluorescence titration to be 5.8 × 10-8 M-1. In order to further explore the mechanism of Fe3+ quenching on ZP fluorescence, we performed fluorescence titration experiments, XPS as well as ESI-MS characterization, which proved that the recognition of Fe3+ by ZP is the substitution of metal ions leading to fluorescence quenching. At the same time, we also examined the practical application of ZP in life, and found that ZP can quantitatively detect the content of Fe3+ in drugs and actual water samples, and the experimental results were highly consistent with test result of ICP-MS, which further demonstrated that the detection of ZP was highly accurate. In addition, the detection of Fe3+ by ZP can be applied over a wide pH range without interference from other metal ions.

Functional Imaging of CYP3A4 at Multiple Dimensions Using an AI-Driven High Performance Fluorogenic Substrate

Cytochrome P450 3A4 (CYP3A4) is a key mediator in xenobiotic metabolism and drug-drug interactions (DDI), developing orally active fluorogenic substrates for sensing and imaging of a target enzyme in biological systems remains challenging. Here, an artificial intelligence (AI)-driven strategy is used to construct a highly specific and orally active fluorogenic substrate for imaging CYP3A4 in complex biological systems. After the fusion of an AI-selected drug-like fragment with a CYP3A4-preferred fluorophore, three candidates are designed and synthesized. Among all evaluated candidates, NFa exhibits excellent isoform-specificity, ultra-high sensitivity, outstanding spatial resolution, favorable safety profiles, and acceptable oral bioavailability. Specifically, NFa excels at functional in situ imaging of CYP3A4 in living systems with exceptional endoplasmic reticulum (ER)-colocalization performance and high imaging resolution, while this agent can also replace hCYP3A4 drug-substrates for high-throughput screening of CYP3A4 inhibitors and for assessing DDI potential in vivo. With the help of NFa, a novel CYP3A4 inhibitor (D13) was discovered, and its anti-CYP3A4 effects are assessed in live cells, ex vivo and in vivo. Collectively, an AI-powered strategy is adapted for developing highly-specific and drug-like fluorogenic substrates, resulting in the first orally available tool (NFa) for sensing and imaging CYP3A4 activities, which facilitates CYP3A4-associated fundamental investigations and the drug discovery process.

Development of Coumarin-Based Probe for Spectrofluorometric Lead Determination in the Human Plasma: Exploring an Association With Otitis Media

Chronic otitis media poses a significant global health challenge, particularly burdening low socioeconomic areas, notably in developing nations. Despite its prevalence, the role of lead in chronic otitis media remains largely overlooked. This study introduces an innovative spectrofluorometric technique for highly sensitive lead detection in human plasma samples at the nano-level. The method capitalizes on the interaction between lead ions and 7,8-dihydroxy-4-phenylcoumarin, generating a distinct fluorescent product. This complex exhibit modified fluorescence characteristics compared to free 7,8-dihydroxy-4-phenylcoumarin, emitting at 505 nm when excited at 330 nm. This shift, accompanied by an increase in fluorescence intensity, enables precise lead quantification even within complex plasma matrices. Validation confirmed a consistent linear relationship within the 200-4000 ng/mL range. Application of the validated method revealed elevated lead levels in plasma samples from chronic otitis media patients compared to healthy controls. These findings suggest a potential link between lead exposure and chronic otitis media development, though further research is warranted for confirmation. This research underscores the importance of considering lead's impact on chronic otitis media etiology and progression, especially in vulnerable populations.

A fluorescent probe based on scopoletin-3-carboxylic acid: pH and micellization evaluation

Coumarins are a class of compounds known for their synthetic and structural versatility, as well as their properties of great interest, such as biological and photophysical activities, and their application in the analysis of molecular microenvironments and their characteristics, such as pH. In this work, the synthesis of 7-hydroxy-6-methoxy-2-oxo-2H-chromene-3-carboxylic acid (3-SCA) was reported, and its absorption, emission and excitation spectral properties, along with photophysical properties such as molar absorption coefficient, lifetime, and Stokes Shift (Δν) in different solvents and pHs, were evaluated for the first time. High values of fluorescence quantum yield were observed for 3-SCA in solvents of different polarities, with a lifetime of approximately 5 ns. The Stokes shift values for 3-SCA were high, with these values greater in aqueous medium. Additionally, the acid equilibrium constant values of 3-SCA were evaluated through absorption, emission, and excitation measurements, resulting in two pKa values of 3.7 for the carboxylic acid group at C-3 and 6.6 for the hydroxyl group at C-7. 3-SCA was successfully applied in determining the critical micellar concentration of the surfactants: anionic (SDS), zwitterionic (SB3-14), neutral (F-127), and cationic (CTAB). The high sensitivity of the spectral properties of 3-SCA as a function of pH, combined with the high Stokes shift values in different media, indicates that 3-SCA is an interesting probe with applications in evaluating local pH and micelle formation.

A turn-on mitochondria-targeted iridium (Ⅲ) Complex-Based probe for glutathione detection and photodynamic therapy of cancer cells

As one of the most abundant biothiols in cells, glutathione (GSH) usually exists in a dynamic equilibrium of oxidized glutathione (GSSG) and reduces glutathione redox, and plays an essential reducing substance to maintain the REDOX balance of the microenvironment. So, the development of a reliable GSH sensor will be important for living cells and organisms. We fabricated a mitochondria targeted "turn-on" fluorescent sensor based on Ir (III) complex and successfully detected endogenous and exogenous GSH in living cells and zebrafish. For the probe Ir-DINI, a robust electron-withdrawing group 2,4-dinitrobenzoyl was introduced to quench the fluorescence, which could be broken through electrostatic interaction with GSH, following exposing a strong fluorescent Ir (Ⅲ) complex Ir-OH. On the other hand, photodynamic therapy (PDT) has attracted much attention in recent years due to its minimally invasive treatment. We found that singlet oxygen yields of probe Ir-DINI displayed an enhancement before and after the detection of GSH. Additionally, photodynamic studies in living cells illustrated that after reacting with GSH, probe Ir-DINI exhibited more obvious phototoxicity than before the detection of GSH. So the probe Ir-DINI could be served as a GSH sensor and potential GSH-activated photosensitizer for photodynamic therapy.

A wash-free AIE fluorescent probe for monitoring lipid droplets and identifying tumors

The abnormal size and number of lipid droplets (LDs) are closely associated with a variety of diseases, including metabolic syndrome related diseases, liver disease and tumors. Therefore, it is particularly important to develop a fluorescent probe that can monitor the abnormal state of LDs. In this study, we designed and synthesized four compounds (namely TCO1, TCO2, TCN1 and TCN2) using coumarin derivatives as the fundamental building blocks. Notably, the fluorescence spectra of compounds TCO1 and TCO2 revealed distinct AIE properties in systems with different ratios of ethanol/water. Furthermore, cell imaging study of compound TCO1 exhibited negligible background fluorescence, indicating its efficacy as a washing-free fluorescent probe targeting LDs within cells. Moreover, cell imaging results for compound TCO1 showed substantial overlap with those obtained from LD commercial dye, thereby confirming its capability to specifically target LDs. Additionally, compound TCO1 was able to monitor changes in both size and quantity of LDs induced by oleic acid stimulation, as well as to discriminate between normal organs and tumours. Based on these properties, compound TCO1 developed in this study provides an effective method for detecting LD abnormalities, a novel technique for visualizing tumor sites in vitro, and also provides new insights for the detection of other related diseases.

Structural and Electronic Properties of D-π-A Coumarin Dyes: A DFT/TD-DFT Assisted Design of Low-Molecular-Weight, Long-Wavelength-Emissive Fluorescent Dyes

This study employs density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to systematically explore the structural and electronic properties of designed D-π-A coumarin dyes, aiming to develop low-molecular-weight fluorescent dyes with long-wavelength emission. The results emphasize the importance of substituent choice and positioning in determining dye spectral profiles. Specifically, placing an electron-withdrawing (EW) substituent at the 4-position of the coumarin ring results in longer emission wavelengths compared to substitution at the 3-position, while disubstitution at both the 3- and 4-positions provides a balance between emission wavelength and intensity. Introducing a julolidine group at the 7-position leads to red-shifted emissions and larger Stokes shifts, although this comes at the cost of reduced fluorescence intensity relative to N, N-diethylamino-substituted analogues. Notably, combining -COOH or -CN groups at the 3, 4-positions with either N, N-diethylamino or julolidine group at the 7-position offers a promising approach for tailored fluorescent dyes for optoelectronics and biological imaging. This work lays a theoretical foundation for guiding future synthesis and application of advanced fluorescent materials.

Synthesis of Coumarinylhydrazone Fluorescent Probe and its Relay Recognition of Cu2+ and HPO42

A novel coumarinylhydrazone fluorescent probe L was designed and synthesized from 4-(diethylamino)salicylaldehyde, its structure was characterized by NMR, IR. Fluorescence emission spectra showed that in ethanol solution, probe L could form a 1:1 complex L-Cu2+ with Cu2+ to realize the "turn-off" detection of Cu2+ with high specificity and sensitivity (3.7 × 10-7 mol/L). Meanwhile, the complex L-Cu2+ had a specific fluorescence-enhanced response to HPO42- with a detection limits down to 5.6 × 10-7 mol/L and was resistant to the effects of many common anions (NO2-, N3-, CO32-, SO32-, HPO42-, I-, Br-, F-, HCO3-, SO42-, NO3-, Cl-, CH3COO-, Cr2O72-, S2O32-, P2O74-). Detection mechanism could be HPO42- captured Cu2+ of the complex and released the free ligand L. At last, the complex L-Cu2+ was successfully applied to the determination of HPO42- in different environmental water samples, and the spiked recoveries ranged from 98.05% to 108.18% and the relative standard deviations of 0.75% ~ 2.9%, which had good application prospects.

Radical-triggered ring-opening of aminocyclopropane for detection of hydroxyl radicals in living cells

Hydroxyl radicals (˙OH), highly reactive oxygen species involved in oxidative stress and cancer therapy, are challenging to detect intracellularly due to their short lifetime, low concentration, and high reactivity. To address this, a novel ˙OH-specific fluorescent probe, CC-7, was developed by integrating an aminocyclopropane group into a coumarin derivative. This design was inspired by the radical-mediated ring-opening of aminocyclopropanes in synthetic chemistry. The ring-opening reaction triggered by ˙OH in CC-7 produces a significant "Fluorescence-ON" response with a 10-fold increase in intensity, demonstrating high selectivity for ˙OH over other reactive oxygen species. CC-7 effectively visualized intracellular ˙OH, distinguished between normal (HEK-293T) and cancer cells (4T1), and monitored ˙OH generated by chemotherapeutic agents like doxorubicin and cisplatin. This study highlights CC-7 as a powerful tool for selectively detecting ˙OH in living cells, with potential applications in investigating oxidative stress-related diseases and monitoring cancer therapy.

Nanocellulose-based functional materials towards water treatment

Water resources are important ecological resources for human survival. To date, advanced water purification technology has become one of the focus of global attention due to the continuous deterioration of the environment and the serious shortage of freshwater resources. Recently, nanocellulose, as a kind of sustainable and carbon-neutral biopolymer, has not only the properties of cellulose, but also the important nature of nanomaterials, including large specific surface area, tailorable surface chemistry, excellent mechanical flexibility, biodegradability, and environmental compatibility. Herein, this review covers several methods of extraction and preparation of nanocellulose and the functional modification strategies. Subsequently, we systematically review the application and latest research progress of nanocellulose-based functional material towards water treatment, from micro/nanoparticles filtration, dyes/organics adsorption/degradation, heavy metal ions adsorption/detection and oil-water separation to seawater desalination. Furthermore, scalable and low-cost nanocellulose synthesis strategies are discussed. Finally, the challenges and opportunities of nanocellulose water purification substrate in industrial application and emerging directions are briefly discussed. This review is expected to provide new insights for the application of advanced functional materials based on nanocellulose in water treatment and environmental remediation, and promote rapid cross-disciplinary development.

An interesting aggregation induced red shifted emissive and ESIPT active hydroxycoumarin tagged symmetrical azine: Colorimetric and fluorescent turn on-off-on response towards Cu2+ and Cysteine, real sample analysis and logic gate application

We report a newly synthesized 7-diethylamino-4-hydroxycoumarin tagged symmetrical azine derivative (SHC), with an interesting color transformation from yellowish green to orange via aggregation induced red shifted emissive (117 nm) feature in THF-H2O mixture. Interestingly, the single crystal X-ray analysis of this molecule demonstrates that two hydroxycoumarin moieties were present in azine unit, among them one of the coumarin units was exist as enol form and another one transferred to keto form via ground state proton transfer reaction. The optical responses of the compound in different solvents exposed the observation of dual emissive bands which corresponds to the presence of ESIPT phenomenon in SHC molecule. Further, this characteristic was confirmed by absorption, emission, solid state structure and time resolved fluorescence decay measurements. Furthermore, the fluorophore, SHC was exploited as a colorimetric and turn on-off-on fluorescent probe for detection of Cu2+ ions and Cysteine (Cys). The 1:1 binding ratio of the probe with Cu2+ and Cys with SHC-Cu2+, was established via Job plot analysis, mass spectral technique and the DFT calculations. The probe, SHC was employed for the detection of copper ions in the environmental real water samples. Finally, the reversible fluorescent turn on-off-on character of the probe, SHC was established to construct the IMPLICATION logic gate application.

Push-pull fluorophores based on NHS esters of bithiophene for labelling of biomolecules containing primary amines

Fluorescent labelling is a versatile tool to visualize biomolecules containing primary amines in their cellular environment, allowing the study of their function or interactions. Here, three organic fluorophores that can irreversibly bind to the primary amine group on the target biomolecule are reported. They consist of push-pull heterocyclic dyes based on bithiophene and incorporating a terminal N-hydroxysuccinimidyl ester as a reactive group for labelling primary amine groups from biomolecules as (poly)amines, peptides or proteins. Their potential as chemosensors for primary amines, using Nα-Boc protected amino acid l-lysine as a model, was assessed through UV-Visible, fluorescence and 1H NMR titrations.

Near-Infrared Visualization of NAD(P)H Dynamics in Live Cells and Drosophila melanogaster Larvae Using a Coumarin-Based Pyridinium Fluorescent Probe

A near-infrared fluorescent probe, A, was designed by substituting the carbonyl group of the coumarin dye's lactone with a 4-cyano-1-methylpyridinium methylene group and then attaching an electron-withdrawing NADH-sensing methylquinolinium acceptor via a vinyl bond linkage to the coumarin dye at the 4-position. The probe exhibits primary absorption maxima at 603, 428, and 361 nm, and fluoresces weakly at 703 nm. The addition of NAD(P)H results in a significant blue shift in the fluorescence peak from 703 to 670 nm, accompanied by a substantial increase in fluorescence intensity. This spectral shift is attributed to the transformation from an A-π-A-π-D configuration to a D-π-A-π-D pyridinium platform in probe AH, owing to the addition of a hydride from NADH to the electron-accepting quinolinium acceptor producing the electron-contributing 1-methyl-1,4-dihydroquinoline donor in probe AH. This conclusion is supported by theoretical calculations. The probe was utilized to investigate NAD(P)H dynamics under various conditions. In HeLa cells, treatment with glucose or maltose resulted in a substantial elevation in near-infrared emission intensity, suggesting increased NAD(P)H levels. Chemotherapeutic agents including cisplatin and fludarabine at concentrations of 5, 10, and 20 μM brought about a dose-dependent increase in emission intensity, reflecting heightened NAD(P)H levels due to drug-induced stress and cellular damage. In vivo experiments with hatched, starved Drosophila melanogaster larvae were also conducted. The results showed a clear relationship between emission intensity and the levels of NADH, glucose, and oxaliplatin, confirming that the probe can detect variations in NAD(P)H levels in a living organism. Our investigation also demonstrates that NAD(P)H levels are significantly elevated in the cystic kidneys of ADPKD mouse models and human patients, indicating substantial metabolic alterations associated with the disease. This near-infrared emissive probe offers a highly sensitive and specific method for monitoring NAD(P)H levels across cellular, tissue and whole-organism systems. The ability to detect NAD(P)H variations in reaction to varying stimuli, including nutrient availability and chemotherapeutic stress, underscores its potential as a valuable resource for biomedical research and therapeutic monitoring.

Water-Soluble Fluorescent Sensors for Quantification of Trace Cisplatin in Body Fluids from Clinical Cancer Patients

Accurate quantification of cisplatin (cDDP) in body fluids (blood, urine, and ascites) is crucial in monitoring therapeutic processes, assessing drug metabolism, and optimizing treatment schedules for cancer patients. Nonetheless, due to the inherent fluorescence and complexity of the body fluid matrix, along with the low cDDP concentrations in these fluids during treatment, using fluorescent sensors for fluid detection remains a subject of ongoing research. Herein, a series of water-soluble cDDP-activatable fluorescent sensors was rationally constructed by introducing thioether groups to the xanthene skeleton based on the chalcogenophilicity of platinum. These sensors exhibit excellent sensitivity and certain anti-interference capabilities for sensing cDDP in living cells, rat tissues, and zebrafish. Especially, with a simplified sample pretreatment procedure, for the first time, Rh3 and Rh4 have enabled quantitative detection of cDDP levels in diversiform body fluids from clinical ovarian and bladder cancer patients. These results are highly consistent with those obtained by ICP-MS detection. This work paves the way for utilizing fluorescent sensors in clinical body fluid analysis, thus potentially revolutionizing the monitoring methods of cDDP in clinic settings.

A novel fluorescent probe for viscosity and polarity detection in real tobacco root cells and biological imaging

The disruption of lipid droplet function is associated with the pathogenesis of various diseases. Clarifying the response behavior of lipid droplets to the microenvironment at the cellular level is of great significance. Plant lipids not only exist in phospholipids in cell membranes, but also in aromatic essential oils. Monitoring the level of lipid droplets in plant cells using fluorescent probes provides a simple method for screening lipid-rich varieties. We synthesized a polarity-viscosity responsive coumarin fluorescent probe, Cou-CN, which achieved sensitive detection of polarity and viscosity in dilute solution environments by constructing this simple probe with ICT and TICT properties and verifying it using Gaussian computational simulation. Cou-CN exhibited good lipid droplet illumination effects in HepG2 cells with a correlation coefficient of 0.92 compared to the commercial lipid droplet dye BODIPY. Additionally, co-staining the probe with the lipophilic commercial dye Nile Red in tobacco root stem seedling cells resulted in a high correlation coefficient of 0.9.

Dynamic insights into mitochondrial function: Monitoring viscosity and SO2 levels in living cells

Mitochondria, central organelles pivotal for eukaryotic cell function, extend their influence beyond ATP production, encompassing roles in apoptosis, calcium signaling, and biosynthesis. Recent studies spotlight two emerging determinants of mitochondrial functionality: intramitochondrial viscosity and sulfur dioxide (SO2) levels. While optimal mitochondrial viscosity governs molecular diffusion and vital processes like oxidative phosphorylation, aberrations are linked with neurodegenerative conditions, diabetes, and cancer. Similarly, SO2, a gaseous signaling molecule, modulates energy pathways and oxidative stress responses; however, imbalances lead to cytotoxic sulfite and bisulfite accumulation, triggering disorders such as cancer and cardiovascular anomalies. Our research focused on development of a dual-channel fluorescent probe, applying electron-withdrawing acceptors within a coumarin dye matrix, facilitating monitoring of mitochondrial viscosity and SO2 in live cells. This probe distinguishes fluorescence peaks at 650 nm and 558 nm, allowing ratiometric quantification of SO2 without interference from other sulfur species. Moreover, it enables near-infrared viscosity determination, particularly within mitochondria. The investigation employed theoretical calculations utilizing Density Functional Theory (DFT) methods to ascertain molecular geometries and calculate rotational energies. Notably, the indolium segment of the probe exhibited the lowest rotational energy, quantified at 7.38 kcals/mol. The probe featured heightened mitochondrial viscosity dynamics when contained within HeLa cells subjected to agents like nystatin, monensin, and bacterial lipopolysaccharide (LPS). Overall, our innovative methodology elucidates intricate mitochondrial factors, presenting transformative insights into cellular energetics, redox homeostasis, and therapeutic avenues for mitochondrial-related disorders.

Isophorone-based crystallization-induced-emission sensors detect proteome aggregation in live cells and tissues with breast cancer

BACKGROUND

Protein misfolding and aggregation can lead to various diseases. Recent studies have shed light on the aggregated protein in breast cancer pathology, which suggests that it is crucial to design chemical sensors that visualize protein aggregates in breast cancer, especially in clinical patient-derived samples. However, most reported sensors are constrained in cultured cell lines.

RESULTS

In this work, we present the development of two isophorone-based crystallization-induced-emission fluorophores for detecting proteome aggregation in breast cancer cell line and tissues biopsied from diseased patients, designated as A1 and A2. These probes exhibited viscosity sensitivity and recovered their fluorescence strongly at crystalline state. Moreover, A1 and A2 exhibit selective binding capacity and strong fluorescence for various aggregated proteins. Utilizing these probes, we detect protein aggregation in stressed breast cancer cells, xenograft mouse model of human breast cancer and clinical patient-derived samples. Notably, the fluorescence intensity of both probes light up in tumor tissues.

SIGNIFICANCE

The synthesized isophorone-based crystallization-induced-emission fluorophores, A1 and A2, enable sensitive detection of protein aggregation in breast cancer cells and tissues. In the future, aggregated proteins are expected to become indicators for early diagnosis and clinical disease monitoring of breast cancer.

A Photoredox Thiol-yne Reaction for the Synthesis of Vinyl Sulfide-Based Coumarins and its Effect on Fluorescence Properties

Coumarins still remain one of the most widely explored fluorescent dyes, with a broad spectrum of applications spanning various fields, such as molecular imaging, bioorganic chemistry, materials chemistry, or medical sciences. Their fluorescence is strongly based on a push-pull mechanism involving an electron-donating group (EDG), mainly located at the C7 or C8 positions of the dye core. Unfortunately, up to now, these positions have been very limited to hydroxyl or amino groups. In this study, we present in detail the synthesis of the first series of coumarins bearing a vinyl sulfide as the EDG at the C7 position. These derivatives were prepared by thiol-yne reaction, promoted by ruthenium- or porphyrin-based photoredox catalysis, enabling rapid late-stage diversification. We also functionalized coumarins with short peptides, and BSA protein as a proof-of-concept study, in a single-step process. This strategy, capable of proceeding under aqueous conditions, overcomes the protection/deprotection steps usually required by traditional methods, which also use strong bases and organic solvents. Moreover, the photophysical properties such as absorption and emission of obtained coumarins (for 3-CF3, 3-benzothiazole, 6-8-difluoro derivatives), predominantly exhibited large Stokes shifts (up to 204 nm) and maintained intramolecular charge transfer (ICT) characteristics.

Molecular engineering to elevate reactive oxygen species generation for synergetic damage on lipid droplets and mitochondria

Photodynamic therapy (PDT), characterized by high treatment efficiency, absence of drug resistance, minimal trauma, and few side effects, has gradually emerged as a novel and alternative clinical approach compared to traditional surgical resection, chemotherapy and radiation. Whereas, considering the limited diffusion distance and short lifespan of reactive oxygen species (ROS), as well as the hypoxic tumor microenvironment, it is crucial to design photosensitizers (PSs) with suborganelle specific targeting ability and low-oxygen dependence for accurate and highly efficient photodynamic therapy. In this study, we have meticulously designed three PSs, namely CIH, CIBr, and CIPh, based on molecular engineering. Theoretical calculation demonstrate that the three compounds possess good molecular planarity with calculated S1-T1 energy gaps (ΔES1-T1) of 1.04 eV for CIH, 0.92 eV for CIBr, and 0.84 eV for CIPh respectively. Notably, CIPh showcases remarkable dual subcellular targeting capability towards lipid droplets (LDs) and mitochondria owing to the synergistic effect of lipophilicity derived from coumarin's inherent properties combined with electropositivity conferred by indole salt cations. Furthermore, CIPh demonstrates exclusive release of singlet oxygen (1O2)and highly efficient superoxide anion free radicals(O2⦁-) upon light irradiation supported by its smallest S1-T1 energy gap (ΔES1-T1 = 0.84 eV). This leads to compromised integrity of LDs along with mitochondrial membrane potential, resulting in profound apoptosis induction in HepG2 cells. This successful example of molecular engineering guided by density functional theory (DFT) provides valuable experience for the development of more effective PSs with superior dual targeting specificity. It also provides a new idea for the development of advanced PSs with efficient and accurate ROS generation ability towards fluorescence imaging-guided hypoxic tumor therapy.

Visualizing the crucial roles of plasma membrane and peroxynitrite during abdominal aortic aneurysm using two-photon fluorescence imaging

Peroxynitrite (ONOO-) and cell plasma membrane (CPM) are two key factors in cell pyroptosis during the progression of abdominal aortic aneurysm (AAA). However, their combined temporal and spatial roles in initiating AAA pathogenesis remain unclear. Herein, we developed a two-photon fluorescence probe, BH-Vis, enabling real-time dynamic detection of CPM and ONOO- changes, and revealing their interplay in AAA. BH-Vis precisely targets CPM with reduced red fluorescence intensity correlating with diminished CPM tension. Concurrently, a blue shift of the fluorescence signal of BH-Vis occurs in response to ONOO- offering a reliable ratiometric detection mode with enhanced accuracy by minimizing external testing variables. More importantly, two photon confocal imaging with palmitic acid (PA) and ganglioside (GM1) manipulation, which modulating cell pyroptosis, showcases reliable fluorescence fluctuations. This groundbreaking application of BH-Vis in a mouse AAA model demonstrates its significant potential for accurately identifying cell pyroptosis levels during AAA development.

Harnessing a simple ratiometric fluorescent probe for albumin recognition and beyond

A commercially available naphthalene fluorophore serves as a ratiometric indicator for albumin, showcasing its applications in albumin-based supramolecular recognition.

A Novel Fluorescence-Based Microplate Assay for High-Throughput Screening of hSULT1As Inhibitors

Human sulfotransferase 1As (hSULT1As) play a crucial role in the metabolic clearance and detoxification of a diverse range of endogenous and exogenous substances, as well as in the bioactivation of some procarcinogens and promutagens. Pharmacological inhibiting hSULT1As activities may enhance the in vivo effects of most hSULT1As drug substrates and offer protective strategies against the hSULT1As-mediated bioactivation of procarcinogens. To date, a fluorescence-based high-throughput assay for the efficient screening of hSULT1As inhibitors has not yet been reported. In this work, a fluorogenic substrate (HN-241) for hSULT1As was developed through scaffold-seeking and structure-guided molecular optimization. Under physiological conditions, HN-241 could be readily sulfated by hSULT1As to form HN-241 sulfate, which emitted brightly fluorescent signals around 450 nm. HN-241 was then used for establishing a novel fluorescence-based microplate assay, which strongly facilitated the high-throughput screening of hSULT1As inhibitors. Following the screening of an in-house natural product library, several polyphenolic compounds were identified with anti-hSULT1As activity, while pectolinarigenin and hinokiflavone were identified as potent inhibitors against three hSULT1A isozymes. Collectively, a novel fluorescence-based microplate assay was developed for the high-throughput screening and characterization of hSULT1As inhibitors, which offered an efficient and facile approach for identifying potent hSULT1As inhibitors from compound libraries.

Bioactive components and mechanisms of Pu-erh tea in improving levodopa metabolism in rats through COMT inhibition

Catechol-O-methyltransferase (COMT) plays a central role in the metabolic inactivation of endogenous neurotransmitters and xenobiotic drugs and hormones having catecholic structures. Its inhibitors are used in clinical practice to treat Parkinson's disease. In this study, a fluorescence-based visualization inhibitor screening method was developed to assess the inhibition activity on COMT both in vitro and in living cells. Following the screening of 94 natural products, Pu-erh tea extract exhibited the most potent inhibitory effect on COMT with an IC50 value of 0.34 μg mL-1. In vivo experiments revealed that Pu-erh tea extract substantially hindered COMT-mediated levodopa metabolism in rats, resulting in a significant increase in levodopa levels and a notable decrease in 3-O-methyldopa in plasma. Subsequently, the chemical components of Pu-erh tea were analyzed using UHPLC-Q-Exactive Orbitrap HRMS, identifying 24 major components. Among them, epigallocatechin gallate, gallocatechin gallate, epicatechin gallate, and catechin gallate exhibited potent inhibition of COMT activity with IC50 values from 93.7 nM to 125.8 nM and were the main bioactive constituents in Pu-erh tea responsible for its COMT inhibition effect. Inhibition kinetics analyses and docking simulations revealed that these compounds competitively inhibit COMT-mediated O-methylation at the catechol site. Overall, this study not only explained how Pu-erh tea catechins inhibit COMT, suggesting Pu-erh tea as a potential dietary intervention for Parkinson's disease, but also introduced a new strategy for discovering COMT inhibitors more effectively.

Quinone Methide Based Self-Immobilizing Molecular Fluorescent Probes for In Situ Imaging of Enzymes

Enzymes play important roles not only in normal physiological processes but in the development of many diseases. In situ imaging of enzymes with high-resolution in living systems would helpful for clinical diagnosis and treatment. However, many molecular fluorescent probes suffer from the drawback of diffusing away from the reaction site of enzymes even out of the cells, losing the in situ information and resulting in poor imaging resolution. Quinone methide (QM) based self-immobilizing probes allow the fluorescent signal to be immobilized near the target for an extended period without deactivating the target enzymes, ensuring that it will provide amplified signals and in situ information of the target with high resolution. In this review, we summarized the recent progress of QM-based self-immobilizing probes including their design strategies, working mechanisms, classifications and applications in in situ enzyme imaging. This review calls for the development of more activatable QM-based probe with the advantages of high stability in the absence of the target but very high labeling efficiency after activation.

Construction of a coumarin-based fluorescent probe for accurately visualizing hydrogen sulfide in live cells and zebrafish

Hydrogen sulfide (H2S), an important gas signaling molecule, is a regulator of many physiological processes, and its abnormal levels are closely related to the onset and progression of disease. It is vital to develop methods for specific tracking of H2S in clinical diagnosis and treatment. In this study, we designed an ultrasensitive and highly stable coumarin-based fluorescent probe Cou-H2S. Through the H2S-initiated tandem reaction, Cou-H2S successfully achieved highly selective and super-fast detection of H2S. Cou-H2S was successfully applied to the monitoring of endogenous and exogenous H2S at the cellular level and verified the validity of the detection of H2S in the LPS-induced zebrafish model. Therefore, Cou-H2S might provide new insights into the study of H2S-related diseases.

D-A-D type based NIR fluorescence probe for monitoring the cysteine levels in pancreatic cancer cell during ferroptosis

Cysteine (Cys) as a crucial precursor for intracellular glutathione (GSH) synthesis, plays an important role in the redox regulation in ferroptosis, Therefore, evaluating intracellular Cys levels is worthy to better understand ferroptosis-related physiological process. In this work, we constructed a novel NIR coumarin-derived fluorescent probe (NCDFP-Cys) based on a dual-ICT system, the NCDFP-Cys can show fluorescence turn-on response at 717 nm toward Cys over other amino acids, and possess large Stokes shift (Δλ = 167 nm), low detection limit, hypotoxicity. More significantly, NCDFP-Cys has been utilized to monitor the intracellular Cys fluctuation in pancreatic cancer cells during ferroptosis induced by Erastin and RSL3 respectively, and revealing the difference of Cys levels changes in different activator-triggered ferroptosis pathways.

Non-destructive real-time monitoring and investigation of the self-assembly process using fluorescent probes

Self-assembly has been considered as a strategy to construct superstructures with specific functions, which has been widely used in many different fields, such as bionics, catalysis, and pharmacology. A detailed and in-depth analysis of the self-assembly mechanism is beneficial for directionally and accurately regulating the self-assembly process of substances. Fluorescent probes exhibit unique advantages of sensitivity, non-destructiveness, and real-time self-assembly tracking, compared with traditional methods. In this work, the design principle of fluorescent probes with different functions and their applications for the detection of thermodynamic and kinetic parameters during the self-assembly process were systematically reviewed. Their efficiency, limitations and advantages are also discussed. Furthermore, the promising perspectives of fluorescent probes for investigating the self-assembly process are also discussed and suggested.

Design, Synthesis, and Biological Activities of Novel Coumarin Derivatives as Pesticide Candidates

Food security is an important issue in the 21st century; preventing and controlling crop diseases and pests are the key to solve this problem. The creation of new pesticides based on natural products is an important and effective method. Herein, coumarins were selected as parent structures, and a series of their derivatives were designed, synthesized, and evaluated for their antiviral activities, fungicidal activities, and insecticidal activities. We found that coumarin derivatives exhibited good to excellent antiviral activities against tobacco mosaic virus (TMV). The antiviral activities of I-1, I-2a, I-4b, II-2c, II-2g, II-3, and II-3b are better than that of ribavirin at 500 μg/mL. Molecular docking research showed that these compounds had a strong interaction with TMV CP. These compounds also showed broad-spectrum fungicidal activities against 14 plant pathogenic fungi. The EC50 values of I-1, I-2a, I-3c, and II-2d are in the range of 1.56-8.65 μg/mL against Rhizoctonia cerealis, Physalospora piricola, Sclerotinia sclerotiorum, and Pyricularia grisea. Most of the compounds also displayed good insecticidal activities against Mythimna separata. Pesticide-likeness analysis showed that these compounds are following pesticide-likeness and have the potential to be developed as pesticide candidates. The present work lays a foundation for the discovery of novel pesticide lead compounds based on coumarin derivatives.

Exploring the impact of novel thiazole-pyrazole fused benzo-coumarin derivatives on human serum albumin: Synthesis, photophysical properties, anti-cholinergic activity, and interaction studies

Derivatives of thiazole-pyrazole fused benzo-coumarin compounds were successfully synthesized and characterized, followed by a comprehensive spectroscopic investigation on various photophysical properties in different media. The multipronged approach using steady state and time resolved fluorescence spectroscopy pointed out the impact of substitution in the estimated spectroscopic and other physicochemical properties of the systems. Further, the evaluation of anti-acetylcholinesterase (anti-AChE) activity yielded significant insight into the therapeutic potential of the synthesized coumarinyl compounds for the treatment of Alzheimer's disease (AD). The findings revealed a non-competitive mode of inhibition mechanism, with an estimated IC50 value of 67.72 ± 2.00 nM observed for one of the investigated systems as AChE inhibitor. Notably, this value is even lower than that of an FDA-approved AD drug Donepezil (DON), indicating the enhanced potency of the coumarin derivatives in inhibiting AChE. Interestingly, significant diminution in inhibition was observed in presence of human serum albumin (HSA) as evidenced by the relative increase in IC50 value by 8 ∼ 39 % in different cases, which emphasized the role of albumin proteins to control therapeutic efficacies of potential medications. In-depth spectroscopic and in-silico analysis quantified the nature of interactions of the investigated systems with HSA and AChE. Overall, the outcomes of this study provide significant understanding into the biophysical characteristics of novel thiazole-pyrazole fused benzo-coumarin systems, which could aid in the development of new cholinergic agents for the treatment of AD and materials based on coumarin motifs.

Design and Application of Fluorescent Probes to Detect Cellular Physical Microenvironments

The microenvironment is indispensable for functionality of various biomacromolecules, subcellular compartments, living cells, and organisms. In particular, physical properties within the biological microenvironment could exert profound effects on both the cellular physiology and pathology, with parameters including the polarity, viscosity, pH, and other relevant factors. There is a significant demand to directly visualize and quantitatively measure the fluctuation in the cellular microenvironment with spatiotemporal resolution. To satisfy this need, analytical methods based on fluorescence probes offer great opportunities due to the facile, sensitive, and dynamic detection that these molecules could enable in varying biological settings from in vitro samples to live animal models. Herein, we focus on various types of small molecule fluorescent probes for the detection and measurement of physical parameters of the microenvironment, including pH, polarity, viscosity, mechanical force, temperature, and electron potential. For each parameter, we primarily describe the chemical mechanisms underlying how physical properties are correlated with changes of various fluorescent signals. This review provides both an overview and a perspective for the development of small molecule fluorescent probes to visualize the dynamic changes in the cellular environment, to expand the knowledge for biological process, and to enrich diagnostic tools for human diseases.

Rational design of an iminocoumarin-based fluorescence probe for peroxynitrite with high signal-to-noise ratio

As a high reactive oxygen species (ROS) and a reactive nitrogen species (RNS), peroxynitrite anion (ONOO- ) is widely present in organisms and plays influential roles in physiological and pathological processes. It is of great significance to develop effective fluorescent probes for imaging peroxynitrite variation in living systems. Herein we present a novel fluorescent probe TQC0 for monitoring ONOO- based on the iminocoumarin platform, and this probe was synthesized by the knoevenagel condensation between a dihydropyridine-salicylaldehyde derivative and 2-benzothiazole-acetonitrile, and subsequently masked with the boronate moiety. The obtained probe TQC0 exhibited a high signal-to-noise ratio (206-fold) and a quick 'turn-on' response (about 10 min) with great selectivity and sensitivity. Furthermore, the probe TQC0 was successfully applied for imaging ONOO- in living cells with low cytotoxicity.

Photonic control of image-guided ferroptosis cancer nanomedicine

Photonic nanomaterials, characterized by their remarkable photonic tunability, empower a diverse range of applications, including cutting-edge advances in cancer nanomedicine. Recently, ferroptosis has emerged as a promising alternative strategy for effectively killing cancer cells with minimizing therapeutic resistance. Novel design of photonic nanomaterials that can integrate photoresponsive-ferroptosis inducers, -diagnostic imaging, and -synergistic components provide significant benefits to effectively trigger local ferroptosis. This review provides a comprehensive overview of recent advancements in photonic nanomaterials for image-guided ferroptosis cancer nanomedicine, offering insights into their strengths, constraints, and their potential as a future paradigm in cancer treatment.

Coumarin-Conjugated Macromolecular Probe for Sequential Stimuli-Mediated Activation

Protein bioconjugation has emerged as one of the most valuable tools for the development of protein-based biochemical assays. Here, we report a fluorescent macromolecular material, RF16_Halo, in which the coumarin derivative RF16 is specifically conjugated onto HaloTag protein to achieve a dual-stimuli-mediated fluorescence response. RF16 is first obtained by installing a H2O2-sensitive boron cage onto the C7 hydroxy moiety of the coumarin fluorophore with a HaloTag ligand attaching to the pH-labile 1,3-dioxane moiety. Upon stimulation, RF16_Halo exhibits a sequential fluorescence response to H2O2/pH at both liquid and solid interfaces. The fluorescence of the RF16_Halo-based protein film increases linearly toward H2O2 with a higher sensitivity when compared with that of RF16. Subsequently, the H2O2-cleaved RF16_Halo presents a pH-dependent fluorescence decrease under acidic conditions. Such a stimulus-responsive fluorescence "off-on-off" multimode enables RF16_Halo to be applied as a sequential logic circuit. In addition, we evaluate the fluorescence labeling ability of RF16 to intracellular IRE1_Halo protein and demonstrate that RF16 containing the HaloTag ligand could be precisely retained in cells to track IRE1_Halo protein. Hence, we provide a unique structural design strategy to construct a fluorescence dual-responsive macromolecular probe for information encryption and protein tracking in cells.

Prediction of Early Atherosclerotic Plaques Using a Sequence-Activated Fluorescence Probe for the Simultaneous Detection of γ-Glutamyl Transpeptidase and Hypobromous Acid

Atherosclerosis is a lipoprotein-driven disease, and there is no effective therapy to reverse atherosclerosis or existing plaques. Therefore, it is urgently necessary to create a noninvasive and reliable approach for early atherosclerosis detection to prevent initial plaque formation. Atherosclerosis is intimately associated with inflammation, which is accompanied by an excess of reactive oxygen species (ROS), leading to cells requiring more glutathione (GSH) to resist severe oxidative stress. Therefore, the GSH-hydrolyzed protein γ-glutamyl transpeptidase (GGT) and the ROS-hypobromous acid (HBrO) are potential biomarkers for predicting atherogenesis. Hence, to avoid false-positive diagnoses caused by a single biomarker, we constructed an ingenious sequence-activated double-locked TP fluorescent probe, C-HBrO-GGT, in which two sequential triggers of GGT and HBrO are meticulously designed to ensure that the probe fluoresces in response to HBrO only after GGT hydrolyzes the probe. By utilization of C-HBrO-GGT, the voltage-gated chloride channel (CLC-1)-HBrO-catalase (CAT)-GGT signaling pathway was confirmed in cellular level. Notably, the forthcoming atherosclerotic plaques were successfully predicted before the plaques could be observed via the naked eye or classical immunofluorescent staining. Collectively, this research proposed a powerful tool to indicate the precise position of mature plaques and provide early warning of atherosclerotic plaques.

Exploring Structural-Photophysical Property Relationships in Mitochondria-Targeted Deep-Red/NIR-Emitting Coumarins

Organic fluorophores operating in the optical window of biological tissues, namely in the deep-red and near-infrared (NIR) region of the electromagnetic spectrum, offer several advantages for fluorescence bioimaging applications owing to the appealing features of long-wavelength light, such as deep tissue penetration, lack of toxicity, low scattering, and reduced interference with cellular autofluorescence. Among these, COUPY dyes based on non-conventional coumarin scaffolds display suitable photophysical properties and efficient cellular uptake, with a tendency to accumulate primarily in mitochondria, which renders them suitable probes for bioimaging purposes. In this study, we have explored how the photophysical properties and subcellular localization of COUPY fluorophores can be modulated through the modification of the coumarin backbone. While the introduction of a strong electron-withdrawing group, such as the trifluoromethyl group, at position 4 resulted in an exceptional photostability and a remarkable redshift in the absorption and emission maxima when combined with a julolidine ring replacing the N,N-dialkylaminobenzene moiety, the incorporation of a cyano group at position 3 dramatically reduced the brightness of the resulting fluorophore. Interestingly, confocal microscopy studies in living HeLa cells revealed that the 1,1,7,7-tetramethyl julolidine-containing derivatives accumulated in the mitochondria with much higher specificity. Overall, our results provide valuable insights for the design and optimization of new COUPY dyes operating in the deep-red/NIR region.

A novel intramolecular charge transfer-based near-infrared fluorescent probe with large Stokes shift for highly sensitive detection of cysteine in vivo

Cysteine (Cys) distribute widely in organisms as the crucial components of proteins, and play important roles in pathophysiological processes of human body. Low level of Cys might induce hepatic injury, edema and growth retardation, while superfluous level of Cys is found to be closely relevant to Alzheimer's and Parkinson's diseases. In this work, a novel near-infrared (NIR) fluorescent probe PFQ-C was developed for highly selective detection of Cys in living cells and mice by utilizing the cyclization removal reaction between acrylate group and Cys. The superior sensitivity (limit of detection, 0.036 μM), NIR emission (655 nm), large Stokes shift (135 nm) and low cytotoxicity of the probe highlight its broad potential for future clinical applications. The response mechanism of the probe towards Cys was clarified by spectroscopy, chromatography and theoretical calculation. In addition, results of fluorescence imaging of cells and mice revealed the good performance of the probe for monitoring the distributions and variations of Cys activity in vivo, which is very useful for the researches on diseases associated with Cys.

Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Group 10 metals including Ni, Pd and Pt have been extensively applied in various essential aspects of human social life, material science, industrial manufactures, medicines and biology. The ionic forms of these metals are involved in several biologically important processes due to their strong binding capability towards different biomolecules. However, the mishandling or overuse of such metals has been linked to serious contamination of our ecological system, more specifically in soil and water bodies with acute consequences. Therefore, the detection of group 10 metal ions in biological as well as environmental samples is of huge significance from the human health point of view. Related to this, considerable efforts are underway to develop adequately efficient and facile methods to achieve their selective detection. Optical sensing of metal ions has gained increasing attention of researchers, particularly in the environmental and biological settings. Innovatively designed optical probes (fluorescent or colorimetric) are usually comprised of three basic components: an explicitly tailored receptor unit, a signalling unit and a clearly defined reporter unit. This review deals with the recent progress in the design and fabrication of fluorescent or colorimetric organic sensors for the detection of group 10 metal ions (Ni(II), Pd(II) and Pt(II)), with attention to the general aspects for design of such sensors.

An aggregation-induced emission sensor combined with UHPLC-Q-TOF/MS for fast identification of anticoagulant active ingredients from traditional Chinese medicine

Xuebijing injection (XBJ) has a good therapeutic effect on the patients with severe coronavirus disease, but the material basis of XBJ with the anticoagulant effect to improve the coagulopathy and thromboembolism is still unclear. Herein, we developed a new strategy based on aggregation-induced emission (AIE) for monitoring thrombin activity and screening thrombin inhibitors from XBJ. The molecule AIE603 and the thrombin substrate peptide S-2238 were formed into AIE nanoparticle (AIENP) which emitted notable fluorescence due to the restriction of intramolecular motions. In the presence of thrombin, AIENP was specifically hydrolyzed and AIE603 was released from AIENP, leading to the decrease of fluorescence intensity. Furthermore, AIENP was combined with ultra-high performance liquid chromatography-fraction collector (UHPLC-FC) and ultra-high performance liquid chromatography quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) for separation, preparation, screening and identification of the thrombin inhibitors from XBJ, a total of 58 chemical constituents were identified, among which 6 compounds possessed higher anticoagulant activity. Notably, the overall inhibition rate of the 6 mixed standards was equivalent to about 60% of the inhibition rate of XBJ. Therefore, this work provides a novel, cheap and simple method for monitoring thrombin activity and is promising to screen active substances from traditional Chinese medicines.

An efficient chitosan-naphthalimide fluorescent probe for simultaneous detection and adsorption of Hg2+ and its application in seafood, water and soil environments

As a virulent heavy metal ion, Hg2+ will lead to a serious threat to ecosystem and human health. In this work, we reported a chitosan-naphthalimide fluorescent probe CS-NA-ITC for specific recognition and efficient adsorption of Hg2+. CS-NA-ITC showed no fluorescence in solution state, while the fluorescence intensity increased obviously at the presence of Hg2+, accompanied by the fluorescence color becomes from colorless to bright yellow. It displayed favorable properties like low detection limit (73 nM), extensive pH detection range (5-10) and excellent anti-interference ability. The binding pattern of CS-NA-ITC to Hg2+ was verified by Job's plot, XPS analysis and FT-IR test. In addition, CS-NA-ITC was utilized to recognition of Hg2+ in actual water and soil samples and seafood products. Furthermore, the CS-NA-ITC hydrogel could be employed as an efficient Hg2+ adsorbent with good reusability, which adsorption ability was enhanced compared to chitosan hydrogel.

Two-Photon Fluorescent Probes for Amyloid-β Plaques Imaging In Vivo

Amyloid-β (Aβ) peptide deposition, hyperphosphorylated tau proteins, reactive astrocytes, high levels of metal ions, and upregulated monoamine oxidases are considered to be the primary pathological markers of Alzheimer's disease (AD). Among them, Aβ peptide deposition or Aβ plaques, is regarded as the initial factor in the pathogenesis of AD and a critical pathological hallmark in AD. This review highlights recently Aβ-specific fluorescent probes for two-photon imaging of Aβ plaques in vivo. It includes the synthesis and detection mechanism of probes, as well as their application to two-photon imaging of Aβ plaques in vivo.

Enzyme-Based Biosensors and Their Applications

Enzymes constitute an extremely important class of biomacromolecules with diverse catalytic functions, which have been validated as key mediators for regulating cellular metabolism and maintaining homeostasis in living organisms [...].