Selective Visualization of the Endogenous Peroxynitrite in an Inflamed Mouse Model by a Mitochondria-Targetable Two-Photon Ratiometric Fluorescent Probe

A novel hypochlorous acid-activated NIR fluorescent probe with a large Stokes shift for bioimaging and early diagnosis of arthritis

In this work, we synthesized a novel hypochlorous acid-activated near-infrared (NIR) fluorescent probe (RhSBZ) by a strategy of enhancing π-conjugation through modification the 3,6-substituents of xanthene. Specifically designed for HClO bioimaging and arthritis diagnosis, RhSBZ displayed exceptional performance. RhSBZ exhibited a Stokes shift of 148 nm, high sensitivity, excellent selectivity, and a detection limit as low as 4.95 nM for HClO. Especially, upon reaction with HClO, the fluorescence intensity of RhSBZ enhanced dramatically by 61-fold. Notably, RhSBZ not only can detect exogenous and endogenous HClO in MCF-7 cells, but also has impressive imaging depth of up to 140 μm in rat liver tissues. More encouragingly, RhSBZ can be successfully used for the early diagnosis of abdominal inflammation and arthritis in mice. In summary, RhSBZ displayed excellent bioimaging capabilities and will have the potential application in the early diagnosis of inflammation diseases.

An activatable β-diketonate europium(III) complex-based probe for time-gated luminescence detection and imaging of peroxynitrite in vitro and in vivo

Peroxynitrite (ONOO-), one of representative reactive nitrogen species with strong oxidative and nitrative properties, is known to be associated with various human diseases, such as Alzheimer's disease, drug-induced liver injury (DILI), inflammation, and cancer. Probing its fluctuations throughout diseases holds profound promise for advancing early diagnosis and enabling prompt intervention. In this work, we designed and synthesized a β-diketonate Eu3+ complex-based probe, [Eu(Cy-CDHH)3(terpy)], for the time-gated luminescence (TGL) detection of ONOO-. The probe, composed of a cyanine-dye-conjugated β-diketonate-Eu3+ coordination structure, is non-luminescent due to the intramolecular energy transfer from β-diketonate to cyanine-dye, which inhibits the energy transfer from β-diketonate to central Eu3+ ion. Upon reaction with ONOO-, the unsaturated CC bond of cyanine-dye is cleaved. This process leads to the recovery of the intense long-lived luminescence of the β-diketonate-Eu3+ complex (ϕ = 17.3 %, τ = 436 μs), showcasing characteristics of rapid response (within 10 s), high selectivity, low detection limit (17.4 nM), and low cytotoxicity. These features enable the probe to be used for the quantitative TGL detection of ONOO- in aqueous media as well as for the background-free TGL imaging of ONOO- in living cells under assorted stimuli. Furthermore, the probe was effectively implemented for imaging of ONOO- in livers of drug-induced liver injury mice, revealing the up-regulation of ONOO- levels in this disease and the therapeutic efficacy of glutathione (GSH) via precluding the onset of reactive oxygen/nitrogen species. This research paves a new way for the fabrication of lanthanide complex bioprobes, providing a useful tool for understanding the interconnection between ONOO- and disease-related physiological processes.

Peroxynitrite and amyloid-β dual-activated near-infrared theranostic probe for oxidative stress monitoring in Alzheimer's disease

Amyloid-β (Aβ), the hallmark of Alzheimer's disease (AD), is known to induce reactive oxygen species, peroxynitrite (ONOO-) which plays a crucial role in the pathogenesis and progression of this incurable disease. However, the development of tools that can directly detect the presence and monitor the level of Aβ-induced ONOO- remains a great challenge. We report herein the development of an Aβ and ONOO- synergistically activated NIR fluorescent probe for highly selective imaging of Aβ-induced ONOO- level in vivo. Importantly, this responsive probe exhibits not only synergistically strong enhancement of fluorescence at 655 nm upon reacting with ONOO- in the presence of Aβ but also high sensitivity down to 13 nM with minimal interference. The strong Aβ binding and low cytotoxicity enable the probe to successfully apply for detecting and visualizing endogenous ONOO- level induced by Aβ in AD cell model. Remarkably, this ONOO--responsive probe can be applied effectively to detect, monitor, and distinguish varying ONOO- levels induced by Aβ in different age groups of AD mice, in which cerebral ONOO- level rises with increasing age of AD mice along with Aβ plaque accumulation. Furthermore, the potent neuroprotection against Aβ-induced toxicity and anti-Aβ aggregation effect of the ONOO--reaction product of the probe offer an extra therapeutic advantage of this ONOO--responsive probe. In essence, this multifunctional theranostic probe can serve as a highly sensitive and specific imaging tool for visualizing and monitoring of ONOO- level in the presence of Aβ in vivo, thereby facilitating more accurate early diagnosis and therapy of AD.

A sequence-activatable dual-locked fluorescent probe for simultaneous detection of hypochlorous acid and peroxynitrite during drug-induced liver injury

Drug-induced liver injury (DILI) is a crucial factor that poses a significant threat to human health. DILI process leads to the changes of reactive oxygen species and reactive nitrogen species content in cells, which leads to oxidative and nitrosative stress in cells. However, the high reactivity of hypochlorous acid (HOCl) and peroxynitrite (ONOO⁻), combined with a lack of in situ imaging techniques, has hindered a detailed understanding of their roles in DILI. Therefore, this paper reports a novel sequence-activatable dual-locked molecular probe HA-P3 for the identification and imaging of two DILI-related biomarkers. First, HA-P3 selectively reacts with reactive oxygen species HOCl to leave the recognition receptor diethyl thiocarbamate to form HA-P2. Subsequently, HA-P2 reacts with ONOO⁻, liberating the fluorophore 4-hydroxy-1,8-naphthalimide, which emits a strong fluorescence signal. The two-step reaction effectively reduces the probability of false positive in predicting DILI. HA-P3 achieved the sensitive detection of HOCl and ONOO- in different cells and zebrafish. Furthermore, HA-P3 can distinguish between normal liver cells and hepatoma cells and monitored the elevated levels of HOCl and ONOO⁻ during acetaminophen (APAP)-induced cellular damage. It is worth noting that in the APAP-induced mouse model, the positive correlation between HOCl and ONOO- and DILI was revealed, providing strong direct evidence for the relationship between oxidative/nitrosative stress and DILI.

A NIR-II emissive sonosensitized biotuner for pyroptosis-enhanced sonodynamic therapy of hypoxic tumors

Pyroptosis is considered as a new way to effectively boost the immune response of tumors and inhibit tumor growth. Effective strategies to induce pyroptosis mainly rely on chemotherapeutic drugs and phototherapy, but their potential biotoxicity and phototoxicity limit their application in biomedicine. Herein, we designed a NIR-II emitting pyroptosis biotuner, Rd-TTPA, which induced pyroptosis under ultrasound irradiation to achieve pyroptosis-enhanced sonodynamic therapy (SDT) and immunogenic cell death (ICD) for tumors. Benefiting from its A-π-D1-D2 structure enhanced donor-acceptor interaction, Rd-TTPA can induce cell pyroptosis under both normoxia (21 % O2) and hypoxia (2 % O2) conditions by rapidly generating superoxide radicals (O2-•) upon ultrasound irradiation. The sonodynamic biotuner of pyroptosis overcomes the longstanding weakness of chemical drug and photosensitizer-based pyroptosis, such as drug resistance and limited penetration depth. In-depth studies demonstrated that Rd-TTPA can selectively target tumor cell mitochondria and possess excellent in vivo NIR-II fluorescence imaging capabilities. Administrating a tumor-bearing mouse model with Rd-TPPA, satisfying antitumor efficacy via pyroptosis-augmented SDT was achieved upon the guidance of NIR-II fluorescence imaging.

Novel nitrogen-doped carbon dots with triple targetability as a fluorescent probe for bioimaging of living cells

Investigating the interactions between various organelles can effectively reveal the corresponding biological problems. Currently, studies of organelle interactions typically employ multiple fluorescent probes that can concurrently target different organelles. However, the simultaneous use of multiple probes is complicated to operate, and the probes can interact with each other, affecting the imaging results. Therefore, targeting multiple organelles using a single probe can enhance the process of studying organelle interactions. Carbon dots (CDs), with their abundant surface groups, are expected to solve the abovementioned problems. Herein, we successfully used m-aminophenol and ethylenediamine to prepare high anti-interference capability and triple targetability CDs (n-CDs) with hydrothermal method. The co-localization experiments with commercial probes confirmed that it can target nucleolus, mitochondria and Lysosome at the same time. The preparation of n-CDs provides a new and convenient strategy to study the interaction between various organelles for solving corresponding biological problems, thus revealing the mysteries of life.

An Activatable Chemiluminescent Self-Reporting Sulfur Dioxide Donor for Inflammatory Response and Regulation of Gaseous Vasodilation

Sulfur dioxide (SO2), being a novel gaseous signaling molecule, exhibits significant potential for application in the field of cardiovascular diseases. SO2 donors serve as crucial tools for the transportation and regulation of SO2 in vivo, facilitating the investigation of physiological roles associated with this molecule. However, the current therapeutic SO2 donors lack the capability to monitor the real-time release of SO2, thereby hindering accurate assessment of their therapeutic efficacy and target localization. Herein, we present an activatable chemiluminescent self-reporting SO2 donor (CL-SO2D) that can be selectively activated by peroxynitrite (ONOO-) to release SO2 and enable real-time visualization of the extent of release through chemiluminescent imaging. In vitro and cellular experiments demonstrate that CL-SO2D exhibits high selectivity and signal-to-noise ratio toward ONOO- and effectively facilitates the SO2 release process. Finally, CL-SO2D successfully achieved the response to the mouse inflammatory model and relieved vasoconstriction in zebrafish by releasing SO2 stimulated by ONOO-. The findings suggest that CL-SO2D exhibits impressive attributes in the diagnosis and treatment of SO2-related diseases, opening the gateway for developing low-background and high-sensitivity self-reporting SO2 donors.

A Dual-Channel Fluorescence Probe for Early Diagnosis and Treatment Monitoring of Acute Kidney Injury by Detecting HOCl and Cys with Different Fluorescence Signals

The pathogenesis of acute kidney injury (AKI) is a multifaceted process involving various mechanisms, with oxidative stress playing a crucial role in its development. Hypochlorite (HOCl) and cysteine (Cys) are indicators of oxidative stress in AKI pathophysiology, directly reflecting the degree of oxidative stress and disease severity. However, their exact mechanism of action in AKI pathophysiology remains unknown. Herein, we developed a dual-channel fluorescent probe, MB-NAP, which allowed for the simultaneous detection of HOCl and Cys. The probe exhibited distinct fluorescence responses in the green channel (λex = 450 nm, λem = 560 nm) and red channel (λex = 610 nm, λem = 690 nm), without any spectral crosstalk, allowing for accurate measurement of both analytes. We successfully applied MB-NAP to monitor the levels of HOCl and Cys in cellular and in vivo models of AKI, revealing a significant increase in their concentrations compared to normal models. Furthermore, MB-NAP was demonstrated to exhibit outstanding capabilities for drug screening by effectively real-time monitoring HOCl and Cys. This study not only provides a more sensitive and reliable method/tool for tracking AKI-related pathological processes but also offers a potential breakthrough in the early diagnosis and identification of therapeutic agents aimed at mitigating oxidative stress-induced damage in AKI.

Visualizing Endoplasmic Reticulum Stress and Autophagy in Alzheimer's Model Cells by a Peroxynitrite-Responsive AIEgen Fluorescent Probe

Endoplasmic reticulum (ER) stress and autophagy (ER-phagy) occurring in nerve cells are crucial physiological processes closely associated with Alzheimer's disease (AD). Visualizing the two processes is paramount to advance our understanding of AD pathologies. Among the biomarkers identified, peroxynitrite (ONOO-) emerges as a key molecule in the initiation and aggravation of ER stress and ER-phagy, highlighting its significance in the underlying mechanisms of the two processes. In this work, we designed and synthesized an innovative ONOO--responsive AIEgen-based fluorescent probe (DHQM) with the ability to monitor ER stress and ER-phagy in AD model cells. DHQM demonstrated excellent aggregation-induced emission (AIE) properties, endowing it with outstanding ability for washing-free intracellular imaging. Meanwhile, it exhibited high sensitivity, remarkable selectivity to ONOO-, and exceptional ER-targeting ability. The probe was successfully applied for fluorescence imaging of ER ONOO- fluctuations to assess the ER stress status in aluminum-induced AD model cells. Our findings revealed that aluminum-induced ferroptosis, a regulated cell death process, was pivotal in the excessive ONOO- production, which in turn activated and exacerbated ER stress. Furthermore, the aluminum-stimulated ER-phagy was observed utilizing DHQM, which might be crucial in inhibiting ferroptosis and mitigating aberrant ER stress. Overall, this study not only offers valuable insights into the pathological mechanisms of AD at the ER level but also opens new potential therapeutic avenues targeting these pathways.

An activatable near-infrared fluorescent probe with large Stokes shift for visualizing peroxynitrite in Alzheimer's disease models

Alzheimer's disease (AD), characterized by its incurable nature and prevalence among the elderly, has remained a focal point in medical research. Increasing evidence suggests that peroxynitrite (ONOO-) serves as a crucial biomarker for the diagnosis of AD. In this study, we present a novel, easily available, high-yield, and cost-effective near-infrared (NIR) fluorescent probe, CDCI-ONOO. This probe utilizes a coumarin-dicyanoisophorone conjugate as the fluorophore and diphenylphosphinic chloride as the recognition site, enabling the detection of ONOO- both in vitro and in vivo. Upon interaction with ONOO-, CDCI-ONOO exhibits a distinct maximum emission peak at 715 nm with a substantial Stokes shift of 184 nm. The probe demonstrates excellent selectivity and sensitivity (LOD = 144 nM), along with noticeable colorimetric and fluorescence changes after the reaction. Comprehensive analyses using high-performance liquid chromatography (HPLC), high-resolution mass spectrometry (HRMS), and density functional theory (DFT) calculations confirm that the reaction with ONOO- restores the initially quenched Intramolecular Charge Transfer (ICT), resulting in the formation of CDCI-OH, a product that emitting fluorescence in the near-infrared region. Furthermore, we demonstrated the successful application of CDCI-ONOO for ONOO- detection in neuronal cells and imaging of ONOO- in the brains of mice. These findings underscore the potential of CDCI-ONOO as a near-infrared fluorescent probe for in vivo ONOO- detection, offering a significant avenue for advancing our understanding of AD pathology and diagnosis.

Simultaneous Imaging of pH and Peroxynitrite in the Endoplasmic Reticulum and Mitochondria: Revealing Organelle Interactions in Alzheimer's Disease Pathogenesis

pH and peroxynitrite (ONOO-) are two critical biomarkers to unveil the corresponding status of endoplasmic reticulum (ER) stress and mitochondrial dysfunction, which are closely related to Alzheimer's disease (AD). Simultaneously monitoring pH and ONOO- fluctuations in the ER and mitochondria during AD progression is pivotal for clarifying the interplay between the disorders of the two organelles and revealing AD pathogenesis. Herein, we designed and synthesized a dual-channel fluorescent probe (DCFP) to visualize pH and ONOO- in the ER and mitochondria. DCFP possessed excellent sensitivity and selectivity to pH and ONOO- without spectral crosstalk and was utilized in monitoring the two analytes within AD model cells and larval zebrafish. Importantly, DCFP could preferentially target mitochondria in normal cells and be enriched in the ER after mitochondrial depolarization. With the aid of DCFP, the slower acidification rate of the ER than that of mitochondria induced by Aβ oligomers (AβOs) was first identified, which could be ascribed to the relief of the AβOs-triggered ER stress through the Ca2+ migration from the ER to mitochondria. Moreover, continuous exposure to AβOs led to mitochondrial Ca2+ overload, accelerating the acidification and ONOO- overproduction within mitochondria. As a result, intracellular oxidative stress levels were elevated, further exacerbating ER stress and aggravating ER acidification in turn. The advanced understanding of the potential interplay between the ER and mitochondria in this work may offer new insights and methodologies for studying AD pathogenesis. The DCFP developed in this work could also be employed to study other diseases related to ER stress and mitochondrial dysfunction.

Rational design of an ultrabright quinolinium-fused rhodamine turn-on fluorescent probe for highly sensitive detection of SO2 derivatives: Applications in food safety and bioimaging

Sulfur dioxide (SO2) is an essential signaling molecule involved in various physiological processes within living organisms. Bisulfite (HSO3-) possesses antioxidant, antimicrobial, and preservative properties, making it a common food additive. However, elevated levels of SO2 or excessive HSO3- intake can lead to a range of diseases, highlighting the importance of detecting SO2 and its derivatives (HSO3-/SO32-). This study presents a quinolinium-fused rhodamine fluorogenic probe (RQB-R) for ultrafast, highly selective, and sensitive detection of HSO3-. The probe operates via a dual-response mechanism, exhibiting a visible color change and a transition from nonemissive to intense red fluorescence upon interaction with HSO3-. The detection mechanism involves a 1,4-nucleophilic addition reaction of HSO3- at the 4-position of the quinolinium unit, which bypasses the photoinduced electron-transfer fluorescence quenching pathway and activates the intramolecular charge transfer mechanism, thereby enhancing fluorescence emission. Practical applications of the RQB-R probe include rapid quantification of HSO3- levels in sugar samples and integration into smartphone-assisted detection platforms. This method demonstrates excellent biocompatibility and enables visualization of both exogenous and endogenous HSO3- within MCF-7 cells, with a specific focus on targeting mitochondria.

A Novel Colon-Targeting Ratiometric Probe with Large Emission Shift for Imaging Peroxynitrite in Ulcerative Colitis

Ulcerative colitis (UC) is an inflammatory disease that leads to the overexpression of peroxynitrite (ONOO-). Up to now, it has been a challenge to design a colon-targeted fluorescent probe with a large emission shift that can detect and image ONOO- in UC mice. Here, a fluorophore (pyran-coumarin) is linked with cholic acid to develop a colon-targeted fluorescent probe (CPC) for the detection of ONOO-. The fluorescent probe showed strong near-infrared emission at 725 nm. After reacting with ONOO-, it can be observed that the fluorescence intensity at 725 nm decreases obviously, and the signal at 490 nm increases clearly with an obvious emission shift (235 nm). This response mechanism causes the probe to have good sensitivity and selectivity. Additionally, the probe CPC shows good targeting ability for the cells with overexpressingTGR5 receptors and displays good results for detecting exogenous and endogenous ONOO- in the cells. More importantly, the probe CPC can be especially assembled in the colon site to distinguish normal and UC mice and provide significant information for the diagnosis of UC.

A near-infrared frequency upconversion fluorescent probe for rapid and sensitive visual detection of sulfur dioxide

Inflammation is a complex physiological response involving various cellular and molecular events. Sulfur dioxide (SO2), which is usually in the form of HSO3- and SO32- under physiological conditions, plays a crucial role in the regulation of inflammation and diseases. Frequency upconversion luminescence (FUCL) can realize the unique anti-Stokes process of long-wavelength excitation to short-wavelength emission; thus, it is a highly promising optical method for in vivo imaging due to its deep tissue penetration, low photo-damage, etc. Therefore, we developed a near-infrared FUCL NIRX-1 probe for the detection of HSO3-. NIRX-1 had a fast response (80 s), a low detection limit (0.43 μM), and high selectivity towards HSO3-. In addition, NIRX-1 had deep light penetration ability due to the near-infrared excitation at 808 nm and was able to detect HSO3- in living cells and mice. Lastly, NIRX-1 was employed in the imaging of HSO3- in an inflammation mouse model through FUCL imaging techniques. All these features make NIRX-1 a good candidate for the investigation of SO2-associated physiological and pathological processes.

A Cascade Activation Probe with Double-Enhanced Near-Infrared Imaging for Monitoring Peroxynitrite Fluctuations in Vivo

Monitoring peroxynitrite (ONOO-) fluctuations is particularly important for assessing pathological progression and oxidative damage due to their crucial role in maintaining the redox balance of organisms. However, due to the lack of efficient tools for differentially monitoring ONOO- fluctuations at different concentration ranges in vivo, the precise detection of endogenous ONOO- fluctuations under pathological conditions in living systems remains challenging. Herein, we rationally designed a double-enhanced emission cascade activatable near-infrared (NIR) fluorescent probe (B-TCF) for the measurement of ONOO-, which consists of a borate ester response group and a malononitrile hemicyanine fluorophore. Especially, after sequential oxidative hydrolysis of the borate ester group and xanthene skeleton, B-TCF exhibited a sequentially double-enhanced NIR emission response at 776 and 625 nm for different ONOO- concentration ranges. Moreover, B-TCF revealed excellent and promising performance for ONOO- in terms of high selectivity, sensitivity, and reaction rate (k = 28.2 M-1 s-1). Motivated by the two-step emission signal enhancement and large wavelength shift in the NIR region, B-TCF enabled discriminative imaging of ONOO- with the low and high concentrations in living cells. Importantly, B-TCF was successfully applied for assessing the pathological progression of isoniazid and acetaminophen-induced liver damage in vivo by detecting the endogenous different ONOO- levels. Overall, this study not only demonstrates the first double-enhanced emission cascade activatable NIR fluorescent probe for measuring the dynamic variation of ONOO- in related diseases but also shows great potential as an effective molecular tool for evaluating the various stages of drug-induced liver damage.

Single Side-Chain-Modulatory of Hemicyanine for Optimized Fluorescence and Photoacoustic Dual-Modality Imaging of H2S In Vivo

Near-infrared fluorescence (NIRF)/photoacoustic (PA) dual-modality imaging integrated high-sensitivity fluorescence imaging with deep-penetration PA imaging has been recognized as a reliable tool for disease detection and diagnosis. However, it remains an immense challenge for a molecule probe to achieve the optimal NIRF and PA imaging by adjusting the energy allocation between radiative transition and nonradiative transition. Herein, a simple but effective strategy is reported to engineer a NIRF/PA dual-modality probe (Cl-HDN3) based on the near-infrared hemicyanine scaffold to optimize the energy allocation between radiative and nonradiative transition. Upon activation by H2S, the Cl-HDN3 shows a 3.6-fold enhancement in the PA signal and a 4.3-fold enhancement in the fluorescence signal. To achieve the sensitive and selective detection of H2S in vivo, the Cl-HDN3 is encapsulated within an amphiphilic lipid (DSPE-PEG2000) to form the Cl-HDN3-LP, which can successfully map the changes of H2S in a tumor-bearing mouse model with the NIRF/PA dual-modality imaging. This work presents a promising strategy for optimizing fluorescence and PA effects in a molecule probe, which may be extended to the NIRF/PA dual-modality imaging of other disease-relevant biomarkers.

Molecular Logic Gate for Sensing pH/Peroxynitrite with Potential Applications in Cisplatin Treatment

Cisplatin is a common chemotherapy drug for multiple solid tumors; however, due to the nitrification of peroxynitrite (ONOO-), a series of side effects seriously affect its dose and efficacy. Considering that the reactivity of ONOO- is significantly affected by pH in vitro, revealing their roles in living cells contributes to understanding the side-effect process induced by cisplatin. Herein, we present a near-infrared fluorescent logic gate for sensing pH/ONOO-, which can accurately discriminate four scenarios (no analyte, analyte H+ alone, analyte ONOO- alone, and H+ + ONOO-) and which one comes first. With this probe, the significant roles of pH and ONOO- in cisplatin treatment are disclosed, in which the cell account shows a dramatic reduction accompanied by decreased pH and upregulated ONOO- levels. By artificially recovering the pH, the ONOO- content and cell account can maintain a stable state, possibly due to the protection from acidification and nitration. This work provides an ideal pH/ONOO- logical sensor for revealing their potential roles under cisplatin, which is expected to proffer new insights into more related diseases and drug research.

A new FRET-based fluorescent probe: Colorimetric and ratiometric detection of hypochlorite and anti-counterfeiting applications

Hypochlorite (ClO-), as the main component of widely used disinfectants in daily life, comes into closer contact with the human body, which can lead to a number of diseases. The high-performance method is increasingly needed to detect ClO- in our daily life. In this report, we successfully synthesized a FRET ratiometric fluorescent probe (NDAC) containing benzoxadiazole moieties and coumarin moieties bound via ethylenediamine. As expected, NDAC has excellent selectivity and anti-interference ability toward ClO-, and the ratio of fluorescence intensity (I471 nm/I533 nm) has a very good linear relationship with the concentration of ClO-, with a wide linear range (2.5-1750 μM) and low detection limit (0.887 μM). Furthermore, we have successfully applied it for the quantitative detection of ClO- in water samples in daily life. At the same time, there is a very clear change in the fluorescence color after the reaction of the NDAC with ClO-. The blue/green value (B/G) of this color change also shows a very good linear relationship to ClO- (5.0-1000 μM). Therefore, the NDAC has also been successfully used for test strip detection and quantitative detection of ClO- in actual samples through smartphone-based fluorescence image analysis, and this method can provide faster, more convenient and more accessible detection. In addition, NDAC sensors also have potential applications in the field of information anti-counterfeiting.

Development of a ratiometric fluorescent probe for the detection of peroxynitrite

Peroxynitrite is one of the important reactive oxygen species in the human body and is closely related to the physiological and pathological processes of many diseases. Therefore, the development of probes to detect peroxynitrite is important for diagnostic and pathologic studies of many diseases. In this work, a ratiometric probe was designed using benzopyran as the recognition site, and the sensitivity and selectivity of the probe were tuned by modification of substituents on benzopyran. Upon reaction with peroxynitrite, the color of the solution changes to the naked eye (from blue to yellow), and the fluorescence changes from red to blue. The probe SJ has the advantages of large Stokes shift (237 nm), fast response (≤10 s), wide linear range, good selectivity, low detection line (21.3 nm), and low cytotoxicity. Probe SJ has been successfully used for bioimaging of endogenous and exogenous peroxynitrite.

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.

Nanostructured rhodamine B/aluminosilicate extracted sugarcane bagasse modified with tobacco-derived carbon quantum dot as ratiometric fluorescence probe for determination of tetracycline

Tetracycline (TC), as a widely used antibiotic, is very useful in treating bacterial infections. However, its residues in animal foodstuffs can enter the human body through the food cycle and causes severe and chronic diseases. On the other hand, due to its weak non-biodegradability, it is considered a threat to the environment. In this regard, the development of sensing methods to detect and measure TC is need of the hour. Herein, a dual-emission fluorescence sensor based on porous aluminosilicate structure (ASS) with rough surface hexagonal shape morphology and pore diameter less than 2 nm was prepared. The porous AAS was modified by post-modification method with blue carbon dots (CDT) and rhodamine B (RB) as two fluorophores to develop the ratiometric fluorescence (RF) sensor (CDT-AAS/RB). Nanostructured CDT-AAS/RB emitted two resolved peaks at 445 and 585 nm , which were dramatically quenched in the presence of TC. The RF sensor, with excellent sensitivity, was able to measure TC over the linear range of 0.001-150 μM with a limit of detection of 5.4 nM in the aqueous phosphate buffer. Moreover, the AAS component granted high selectivity and anti-interference ability to the sensor. In addition, the stability of the sensor was greatly improved due to the non-accumulation of CDT nanoparticles and RB molecules in the presence of the AAS. The proposed method was able to determine TC in complex real samples with satisfactory recovery, and the obtained results were validated with standard high-performance liquid chromatography technique.

Molecular Engineering of a Doubly Quenched Fluorescent Probe Enables Ultrasensitive Detection of Biothiols in Highly Diluted Plasma and High-Fidelity Imaging of Dihydroartemisinin-Induced Ferroptosis

The occurrence and development of diseases are accompanied by abnormal activity or concentration of biomarkers in cells, tissues, and blood. However, the insufficient sensitivity and accuracy of the available fluorescence probes hinder the precise monitoring of associated indexes in biological systems, which is generally due to the high probe intrinsic fluorescence and false-negative signal caused by the reactive oxygen species (ROS)-induced probe decomposition. To resolve these problems, we have engineered a ROS-stable, meso-carboxylate boron dipyrromethene (BODIPY)-based fluorescent probe, which displays quite a low background fluorescence due to the doubly quenched intrinsic fluorescence by a combined strategy of the photoinduced electron transfer (PET) effect and "ester-to-carboxylate" conversion. The probe achieved a high S/N ratio with ultrasensitivity and good selectivity toward biothiols, endowing its fast detection capability toward the biothiol level in 200×-diluted plasma samples. Using this probe, we achieved remarkable distinguishing of liver injury plasma from normal plasma even at 80× dilution. Moreover, owing to its good stability toward ROS, the probe was successfully employed for high-fidelity imaging of the negative fluctuation of the biothiol level in nonsmall-cell lung cancer (NSCLC) during dihydroartemisinin-induced ferroptosis. This delicate design of suppressing intrinsic fluorescence reveals insights into enhancing the sensitivity and accuracy of fluorescent probes toward the detection and imaging of biomarkers in the occurrence and development of diseases.

Fluorescent Probes for Disease Diagnosis

The identification and detection of disease-related biomarkers is essential for early clinical diagnosis, evaluating disease progression, and for the development of therapeutics. Possessing the advantages of high sensitivity and selectivity, fluorescent probes have become effective tools for monitoring disease-related active molecules at the cellular level and in vivo. In this review, we describe current fluorescent probes designed for the detection and quantification of key bioactive molecules associated with common diseases, such as organ damage, inflammation, cancers, cardiovascular diseases, and brain disorders. We emphasize the strategies behind the design of fluorescent probes capable of disease biomarker detection and diagnosis and cover some aspects of combined diagnostic/therapeutic strategies based on regulating disease-related molecules. This review concludes with a discussion of the challenges and outlook for fluorescent probes, highlighting future avenues of research that should enable these probes to achieve accurate detection and identification of disease-related biomarkers for biomedical research and clinical applications.

A Phenanthrenequinone-Based Ratiometric Fluorescent Probe for Rapid Detection of Peroxynitrite with Imaging in Osteoblast Precursor Cells

In the current situation, peroxynitrite (ONOO-) is drawing the increasing attention of researchers for its pivotal role in diverse pathological and physiological processes on grounds of robust oxidation and nitrification. Herein, we have successfully designed and synthesized a phenanthrenequinone benzyl borate-based chemosensor for fast and selective detection of ONOO-. The probe PTDP itself had an orange fluorescence, which was changed to strong blue fluorescence upon the addition of ONOO-, indicating the ratiometric response of the probe. This is so because of the cleavage of the benzyl boronate-protecting group of PTDP upon the addition of ONOO- with simultaneous releasing of pyridinyl-based chemosensor PPI. The PTDP showed outstanding performance in the various photophysical studies such as good selectivity, excellent sensitivity with a very low detection limit of 2.74 nM, and a very fast response time (<15 s). Furthermore, for practical applicability, it was successfully applied in the ratiometric detection of ONOO- in osteoblast precursor cells.

Ratiometric Near-Infrared Fluorescent Probe Monitors Ferroptosis in HCC Cells by Imaging HClO in Mitochondria

Hypochlorous acid (HClO) is a typical endogenous ROS produced mainly in mitochondria, and it has strong oxidative properties. Abnormal HClO levels lead to mitochondrial dysfunction, strongly associated with various diseases. It has been shown that HClO shows traces of overexpression in cells of both ferroptosis and hepatocellular carcinoma (HCC). Therefore, visualization of HClO levels during ferroptosis of HCC is important to explore its physiological and pathological roles. So far, there has been no report on the visualization of HClO in ferroptosis of HCC. Thus, we present a ratiometric near-infrared (NIR) fluorescent probe Mito-Rh-S which visualized for the first time the fluctuation of HClO in mitochondria during ferroptosis of HCC. Mito-Rh-S has an ultrafast response rate (2 s) and large emission shift (115 nm). Mito-Rh-S was constructed based on the PET sensing mechanism and thus has a high signal-to-noise ratio. The cell experiments of Mito-Rh-S demonstrated that Fe2+- and erastin-induced ferroptosis in HepG2 cells resulted in elevated levels of mitochondrial HClO and that high concentration levels of Fe2+ and erastin cause severe mitochondrial damage and oxidative stress and had the potential to kill HepG2 cells. By regulating the erastin concentration, erastin induction time, and treatment of the ferroptosis model, Mito-Rh-S can accurately detect the fluctuation of mitochondrial HClO levels during ferroptosis in HCC.

A near-infrared AIE fluorescent probe for accurate detection of sulfur dioxide derivatives and visualization of fingerprints

In most biophysiological processes, sulfur dioxide (SO2) is an important intracellular signaling molecule that plays an important role. The change of SO2 in cells are closely related to various diseases such as neurological disorders and lung cancer, so it is necessary to develop fluorescent probes with the ability to accurately detect SO2 during physiological processes. In this work, we designed and synthesized a multifunctional fluorescent probe TIS. TIS has excellent properties such as near-infrared emission, large stokes shift, excellent SO2 detection capabilities, low detection limit, high specificity and visualization of color change before and after reaction. Simultaneously, TIS has low cytotoxicity, good biocompatibility, clear cell imaging capability and mitochondrial targeting ability. In addition, the ability of TIS to be applied to different material surfaces for latent fingerprint fluorescence imaging was also explored. TIS provides an excellent method for the accurate detection of SO2 derivatives and shows great potential applications in near-infrared cellular imaging and latent fingerprint fluorescence imaging.

Carboxylesterase-activated near-infrared fluorescence probe for highly sensitive imaging of liver tumors

Carboxylesterases (CESs) are critical for metabolizing ester-containing biomolecules and are specifically important in liver metabolic disorders. The modulation of CESs is also an important issue in pharmacology and clinical applications. Herein, we present a near-infrared (NIR) CES fluorescent probe (NCES) based on the protection-deprotection of the hydroxyl group for monitoring CES levels in living systems. The NCES probe has good selectivity and sensitivity for CESs with a limit of detection (LOD) of 5.24 mU mL-1, which allows for tracing the fluctuation of cellular CES after treatment with anticancer drugs and under inflammation and apoptosis states. Furthermore, NCES can be successfully applied for guiding liver cancer surgery with high-contrast in vivo imaging and detecting clinical serum samples from liver cancer patients. This work showed that the NCES probe has great potential in drug development, imaging applications for medical diagnosis, and early-stage detection for clinical liver diseases.

Design a dual-response two-photon fluorescent probe for simultaneous imaging of mitochondrial viscosity and peroxynitrite in a thrombosis model

BACKGROUND

Venous thromboembolism is a sudden cardiovascular disease that can lead to death, and its pathologic development is closely related to vascular viscosity and inflammation. However, direct evidence from in vivo is really scarce. The key limitation is that the combined probes cannot detect multiple markers simultaneously, which may lead to unreliable results. Therefore, to develop a single probe that can simultaneously monitor the variations of viscosity in the vascular microenvironment as well as inflammation level during venous thrombosis.

RESULTS

A dual-responsive two-photon fluorescent probe, Cou-ONOO, was designed and synthesized. Cou-ONOO provides a visualization tool for monitoring the viscosity of the vascular as well as the inflammatory marker ONOO‾ during thromboembolism via dual-channel simultaneous imaging. As a single probe that can recognize dual targets, Cou-ONOO effectively avoids the problems from unreliable results caused by complex synthesis and differences in intracellular localization, diffusion, and metabolism of different dyes as using combinatorial probes. Using Cou-ONOO, simultaneous imaging the variations of viscosity and ONOO‾at the cellular and tissue levels was successfully performed. In addition, Cou-ONOO also successfully visualized and tracked the viscosity of the vascular microenvironment and ONOO‾ during venous embolism in mice.

SIGNIFICANCE

Experimental results show that both viscosity and inflammation are abnormally overexpressed in the microenvironment at the thrombus site during venous thrombosis. An intuitive visualization tool to elucidate the variations of viscosity as well as inflammation level in the vascular microenvironment during thrombosis was provided, which will facilitate a better clinical understanding of the pathological process of thrombosis.

Engineering an activatable fluorescent probe for studying ONOO- in pyroptotic process

Pyroptosis, a recently discovered form of programmed cell death, plays a pivotal role in oncological treatment. Howbeit, the mechanisms underlying pyroptosis in tumor treatment remain unclear. Previous research has demonstrated that the occurrence of pyroptosis generally accompanies a surge of reactive oxygen species (ROS) generation, with ONOO- being one of these ROS and closely linked to numerous diseases. Therefore, it is imperative to investigate the potential association between ONOO- and pyroptosis. Herein, a highly sensitive and rapidly responsive near-infrared (NIR) probe, Rd700-PN, is fabricated for exploring unrevealed relationships between ONOO- and pyroptosis. We successfully harness Rd700-PN to detect ONOO- fluctuation during cellular pyroptosis for the first time. Furthermore, the results demonstrate that Rd700-PN can scout the chemotherapeutic drug's induction ability of tumor pyroptosis in vivo. Notably, this study provides an excellent means to shed light on the correlation between ONOO- and pyroptosis and to screen antitumor drugs activating pyroptosis.

De Novo Design of Near-Infrared Fluorescent Agents Activated by Peroxynitrite and Glutathione-Responsive Imaging for Diabetic Liver Disease

Diabetes and its complications, such as diabetes liver disease, is a major problem puzzling people's health. The detection of redox states in its pathological process can effectively help us gain a deeper understanding of the disease. The pair of oxidation-reduction substances peroxynitrite (ONOO- ) and glutathione (GSH) is considered to be closely related to their occurrence and development. Thus, direct visualization of ONOO- and GSH in diabetes liver disease is critical to evaluate the disease at the molecular level. Herein, two activatable agents NTCF-ONOO- and NTCF-GSH are prepared for selectively detecting ONOO- and GSH through protection and deprotection strategies based on hydroxyl and amino groups of near-infrared fluorophore. Fluorescence imaging of exogenous and endogenous ONOO- and GSH changes in living cells and in vivo is observed. The ONOO- and GSH level in the diabetes liver disease cellular model are visualized and the possible redox imbalance mechanism related to the oxidized (NAD+ ) and reduced (NADH) nicotinamide adenine dinucleotides is explored in this process. Moreover, these probes can sensitively recognize ONOO- and GSH in the process of oxidative stress resulting from streptozotocin and streptozotocin/acetaminophen-induced complex diabetic liver disease in vivo. In addition, they can be applied for monitoring the clinical serum sample related with diabetic patients.

Applications of Pyrrole and Pyridine-based Heterocycles in Cancer Diagnosis and Treatment

BACKGROUND

The escalation of cancer worldwide is one of the major causes of economy burden and loss of human resources. According to the American Cancer Society, there will be 1,958,310 new cancer cases and 609,820 projected cancer deaths in 2023 in the United States. It is projected that by 2040, the burden of global cancer is expected to rise to 29.5 million per year, causing a death toll of 16.4 million. The hemostasis regulation by cellular protein synthesis and their targeted degradation is required for normal cell growth. The imbalance in hemostasis causes unbridled growth in cells and results in cancer. The DNA of cells needs to be targeted by chemotherapeutic agents for cancer treatment, but at the same time, their efficacy and toxicity also need to be considered for successful treatment.

OBJECTIVE

The objective of this study is to review the published work on pyrrole and pyridine, which have been prominent in the diagnosis and possess anticancer activity, to obtain some novel lead molecules of improved cancer therapeutic.

METHODS

A literature search was carried out using different search engines, like Sci-finder, Elsevier, ScienceDirect, RSC etc., for small molecules based on pyrrole and pyridine helpful in diagnosis and inducing apoptosis in cancer cells. The research findings on the application of these compounds from 2018-2023 were reviewed on a variety of cell lines, such as breast cancer, liver cancer, epithelial cancer, etc. Results: In this review, the published small molecules, pyrrole and pyridine and their derivatives, which have roles in the diagnosis and treatment of cancers, were discussed to provide some insight into the structural features responsible for diagnosis and treatment. The analogues with the chromeno-furo-pyridine skeleton showed the highest anticancer activity against breast cancer. The compound 5-amino-N-(1-(pyridin-4- yl)ethylidene)-1H-pyrazole-4-carbohydrazides was highly potent against HEPG2 cancer cell. Redaporfin is used for the treatment of cholangiocarcinoma, biliary tract cancer, cisplatin-resistant head and neck squamous cell carcinoma, and pigmentation melanoma, and it is in clinical trials for phase II. These structural features present a high potential for designing novel anticancer agents for diagnosis and drug development.

CONCLUSION

Therefore, the N- and C-substituted pyrrole and pyridine-based novel privileged small Nheterocyclic scaffolds are potential molecules used in the diagnosis and treatment of cancer. This review discusses the reports on the synthesis of such molecules during 2018-2023. The review mainly discusses various diagnostic techniques for cancer, which employ pyrrole and pyridine heterocyclic scaffolds. Furthermore, the anticancer activity of N- and C-substituted pyrrole and pyridine-based scaffolds has been described, which works against different cancer cell lines, such as MCF-7, A549, A2780, HepG2, MDA-MB-231, K562, HT- 29, Caco-2 cells, Hela, Huh-7, WSU-DLCL2, HCT-116, HBL-100, H23, HCC827, SKOV3, etc. This review will help the researchers to obtain a critical insight into the structural aspects of pyrrole and pyridine-based scaffolds useful in cancer diagnosis as well as treatment and design pathways to develop novel drugs in the future.

Visualization of peroxynitrite/GSH cross-talk in the oxidant-antioxidant balance by a dual-fluorophore and dual-site based mito-specific fluorescent probe

Peroxynitrite (ONOO-) and glutathione (GSH) play mutually regulating roles in the oxidant-antioxidant balance of organisms, which has a profound relationship with people's health and disease. In this study, we designed a two-photon fluorescent probe CD-NA that could simultaneously detect ONOO- and GSH via dual-fluorophore and dual-site properties. CD-NA shows different fluorescence responses to ONOO- (annihilated red fluorescence) and GSH (enhanced green emission) with high specificity and sensitivity. Notably, the response of CD-NA to ONOO- was unaffected by GSH, and the reverse is also true. It allows the ONOO-/GSH cross-talk to be successfully imaged. Given these excellent properties, CD-NA has been favorably employed in detecting ONOO- and GSH in living cells with the ability to target mitochondria. Therefore, CD-NA offers an efficient method for understanding the oxidant-antioxidant balance and interrelated physiological functions of ONOO- and GSH in living systems, and provides a new strategy to sort out the complex relationships and roles of various analytes in complex physiological processes.

FRET Luminescent Probe for the Ratiometric Imaging of Peroxynitrite in Rat Brain Models of Epilepsy-Based on Organic Dye-Conjugated Iridium(III) Complex

Epilepsy is a chronic neurological disorder characterized by recurrent seizures globally, imposing a substantial burden on patients and their families. The pathological role of peroxynitrite (ONOO-), which can trigger oxidative stress, inflammation, and neuronal hyperexcitability, is critical in epilepsy. However, the development of reliable, in situ, and real-time optical imaging tools to detect ONOO- in the brain encounters some challenges related to the depth of tissue penetration, background interference, optical bleaching, and spectral overlapping. To address these limitations, we present Ir-CBM, a new one-photon and two-photon excitable and long-lived ratiometric luminescent probe designed specifically for precise detection of ONOO- in epilepsy-based on the Förster resonance energy transfer mechanism by combining an iridium(III) complex with an organic fluorophore. Ir-CBM possesses the advantages of rapid response, one-/two-photon excitation, and ratiometric luminescent imaging for monitoring the cellular levels of ONOO- and evaluating the effects of different therapeutic drugs on ONOO- in the brain of an epilepsy model rat. The development and utilization of Ir-CBM offer valuable insights into the design of ratiometric luminescent probes. Furthermore, Ir-CBM serves as a rapid imaging and screening tool for antiepileptic drugs, thereby accelerating the exploration of novel antiepileptic drug screening and improving preventive and therapeutic strategies in epilepsy research.

A Small-Molecule Fluorescent Probe for the Detection of Mitochondrial Peroxynitrite

Reactive oxygen species (ROS) are pivotal signaling molecules that control a variety of physiological functions. As a member of the ROS family, peroxynitrite (ONOO-) possesses strong oxidation and nitrification abilities. Abnormally elevated levels of ONOO- can lead to cellular oxidative stress, which may cause several diseases. In this work, based on the rhodamine fluorophore, we designed and synthesized a novel small-molecule fluorescent probe (DH-1) for ONOO-. Upon reaction with ONOO-, DH-1 exhibited a significant fluorescence signal enhancement (approximately 34-fold). Moreover, DH-1 showed an excellent mitochondria-targeting capability. Confocal fluorescence imaging validated its ability to detect ONOO- changes in HeLa and RAW264.7 cells. Notably, we observed the ONOO- generation during the ferroptosis process by taking advantage of the probe. DH-1 displayed good biocompatibility, facile synthesis, and high selectivity, and may have potential applications in the study of ONOO--associated diseases in biosystems.

A near-infrared fluorescent probe with remarkably large stokes shift for specifical imaging of peroxynitrite fluctuations in Hela cells

Peroxynitrite (ONOO-), an endogenous reactive nitrogen species, plays an important role in maintaining intracellular homeostasis. Abnormal levels of ONOO- in cells could cause protein oxidation which is confirmed that related with Alzheimer's diseases, so accurate monitoring of ONOO- in cells is crucial. Herein, a novel fluorescent probe (XPC) based on dicyanomethylene-4H-benzothiopyran was developed by regulating its intramolecular charge transfer (ICT) effect to detect ONOO-. Once reaction with ONOO-, the fluorescence of XPC was turned on and the emission wavelength could reach up to 750 nm. Furthermore, XPC exhibited satisfactory performances for ONOO- such as large Stokes shift (200 nm), good sensitivity (Limit of detection = 13 nM), high selectivity to ONOO- over other a reactive nitrogen species (RNS)/reactive oxygen species (ROS). More importantly, XPC was successfully applied for monitoring the fluctuations of ONOO- in living cells.

Dual Ratio and Ultraprecision Quantification of Mitochondrial Viscosity in Ferroptosis Enabled by a Vibration-Based Triple-Emission Fluorescent Probe

Ferroptosis is a new mode of cell death with major morphological changes in mitochondria, including structural shrinkage and increased membrane density, indicating the mitochondrial abnormality during this process. Viscosity, as one of the crucial microenvironmental parameters for characterizing the mitochondrial state, is thought to be highly involved in the ferroptosis. Herein, we present a single fluorescent probe (PPAC-C4) for the dual ratio and ultrahigh-accuracy quantification of mitochondrial viscosity. This probe is constructed by linking a mitochondria-targeting cation fragment on a vibration-based fluorescent scaffold whose fluorescence exhibits the rare triple emission (480, 533, and 628 nm) depending on the viscosity. The intensity ratios of 480 nm/628 nm and 533 nm/628 nm can be used to monitor the viscosity changes in a double self-calibration manner and finally afford an average viscosity value with improved precision. By virtue of this pattern, we reveal that the mitochondrial viscosity will increase from 43.58 to 152.05 cP in A549 cells during the ferroptosis. This dual-ratio probe with triemission not only shows great potential in the study of ferroptosis and ferroptosis-related diseases but also proposes a new concept for ultraprecision quantitative analysis.

A dual-channel fluorescence probe for simultaneously visualizing cysteine and viscosity during drug-induced hepatotoxicity

Cysteine (Cys), one of the important participants in protecting cells from oxidative stress, is closely associated with the occurrence and development of various diseases. Moreover, cell viscosity as a pivotal microenvironmental parameter has recently attracted increasing attention due to its dominant role in governing intracellular signal transduction and diffusion of reactive metabolites. Thus, simultaneous detection of Cys and viscosity is imperative for investigating their pathophysiological functions and cross-link. Herein we present a mitochondria-targetable dual-channel fluorescence probe ABDSP by grafting the acrylate modified pyridinium unit to dimethylaminobenzene. Whilst the probe is a seemingly simple, it could simultaneously discriminate Cys and viscosity in a fashion of distinguishable signals. Furthermore, the probe was successfully employed for visualizing mitochondrial Cys and viscosity, and probe into their cross-link during acetaminophen-induced hepatotoxicity.

Precise Spatiotemporal Identification of Mitochondrial H2S Fluctuations through Exploiting an On-Demand Photoactivated Probe

Various signal molecules participate in complex biological processes in mitochondria. However, most currently available probes have problems in elucidating the functions of these active species in mitochondria due to the inability to light up these probes exclusively at the desired mitochondrial location, thereby compromising the specificity and accuracy. In this study, we present an on-demand photoactivation approach to the molecular design of optimized probes for precise spatiotemporal identification of mitochondrial H2S fluctuations. The designed probe with native yellow fluorescence can monitor the process into mitochondria but maintains nonfluorescent response to H2S during cellular delivery, providing the accurate timing of accumulation in mitochondria. On-demand photoactivation exclusively at the desired mitochondrial location affords a significant aggregation-enhanced and emissive response to H2S with lighting up red fluorescence at 690 nm, which is the only way to get such an emissive phenomenon and greatly improves the specificity and accuracy of targeting mitochondrial H2S. By using this photocontrolled fluorescence responsiveness to H2S, precise spatiotemporal identification of mitochondrial H2S fluctuations is successfully performed. Our work could facilitate advances toward interrogating the physiological and pathological consequences of mitochondrial H2S in various biological events.

Multiple fluorescence and hydrogen peroxide-responsive properties of novel triphenylamine-benzothiazole derivatives

A novel fluorescent dye molecule - triphenylamine (TPA)-benzothiazole (BZT) - based on excited state intramolecular proton transfer (ESIPT) was prepared by the Suzuki coupling reaction. The photophysical property assay indicates that BZT-TPA appeared in distinguishable colors in mixed solvents with different water contents. Moreover, BZT-TPA exhibited observable AIE behavior. On this basis, a fluorescent probe BZT-TPA-BO was synthesized for detecting H2O2. This probe molecule was found to have excellent selectivity, rapid response, and good linear relationship (R2 = 0.989) for detecting H2O2 in aqueous medium. Through DFT calculation, fluorescence spectrum, nuclear magnetic titration and HR-MS, the mechanism of recognition of H2O2 by the probe BZT-TPA-BO is proposed. In addition, the probe BZT-TPA-BO to some extent exhibited better performance for detecting exogenous H2O2 in HeLa cells.

Recent Progress of Spectroscopic Probes for Peroxynitrite and Their Potential Medical Diagnostic Applications

Peroxynitrite (ONOO-) is a crucial reactive oxygen species that plays a vital role in cellular signal transduction and homeostatic regulation. Determining and visualizing peroxynitrite accurately in biological systems is important for understanding its roles in physiological and pathological activity. Among the various detection methods, fluorescent probe-based spectroscopic detection offers real-time and minimally invasive detection, high sensitivity and selectivity, and easy structural and property modification. This review categorizes fluorescent probes by their fluorophore structures, highlighting their chemical structures, recognition mechanisms, and response behaviors in detail. We hope that this review could help trigger novel ideas for potential medical diagnostic applications of peroxynitrite-related molecular diseases.

Activatable fluorescent probes for imaging and diagnosis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease that is primarily manifested as synovitis and polyarticular opacity and typically leads to serious joint damage and irreversible disability, thus adversely affecting locomotion ability and life quality. Consequently, good prognosis heavily relies on the early diagnosis and effective therapeutic monitoring of RA. Activatable fluorescent probes play vital roles in the detection and imaging of biomarkers for disease diagnosis and in vivo imaging. Herein, we review the fluorescent probes developed for the detection and imaging of RA biomarkers, namely reactive oxygen/nitrogen species (hypochlorous acid, peroxynitrite, hydroxyl radical, nitroxyl), pH, and cysteine, and address the related challenges and prospects to inspire the design of novel fluorescent probes and the improvement of their performance in RA studies.

Evaluation of peroxynitrite fluxes in inflammatory mice with a ratiometric fluorescence probe

Inflammation is a critical physiological process in the human body, which is closely related to numerous disorders and cancers. ONOO^- is generated and functionalized in the inflamed process, but the roles of ONOO^- are still blurred. To illuminate the roles of ONOO^-, we fabricated an intramolecular charge transfer (ICT)-based fluorescence probe, HDM-Cl-PN, for the ratiometric determination of ONOO^- in the inflamed mouse model. The probe displayed a gradual fluorescence increase at 676 nm and a fluorescence drop at 590 nm toward 0-10.5 μM ONOO^-, and the ratio of 676 nm fluorescence and 590 nm fluorescence varied from 0.7 to 24.7. The significantly changed ratio and favorable selectivity ensure the sensitive detection of subtle changes in cellular ONOO^-. Thanks to the excellent sensing performance, HDM-Cl-PNin vivo ratiometrically visualized ONOO^- fluctuations in the LPS-triggered inflammatory process. Overall, this work not only expatiated the rational design for a ratiometric ONOO^- probe but also built a bridge to investigate the connections between ONOO^- and inflammation in living mice.

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 long-wavelength mitochondria-targeted fluorescent probe for imaging of peroxynitrite during dexamethasone treatment

Peroxynitrite (ONOO^-), as a strong oxidizing reactive nitrogen substance (RNS), is generated endogenously by cells. Its visualization research is crucial to understand relevant disease processes. Herein, we reported a long-wavelength mitochondria-targeted fluorescence "turn on" probe TL. The probe TL could react with ONOO^- by using 4-(Bromomethyl)benzeneboronic as a reactive site, which exhibited outstanding characteristics for detection of ONOO^-, thus improving response time (about 50 s), sensitivity (DL, 10.1 nM), and emission wavelength (667 nm). Besides, TL displayed well mitochondria targeting and biological visualizing of exogenous and endogenous ONOO^- in biological systems. Finally, TL was used to monitor high concentration of dexamethasone-induced an up-regulation of ONOO^-. This indicated that TL has excellent potential to study the fluctuation of ONOO^- in the physiological and pathological system.

Supramolecular Host-Guest Strategy for the Accelerating Detection of Nitroreductase

Identifying nitroreductase (NTR) with fluorescent techniques has become a research hotspot, due to its good sensitivity and selectivity toward the early-stage cancer diagnosis and monitoring. Herein, a host-guest reporter (NAQA⊂Zn-MPPB) is successfully achieved by encapsulating the NTR probe NAQA into a new NADH-functioned metal-organic cage Zn-MPPB, which makes the reporter for ultrafast detection of NTR within dozens of seconds in solution. The host-guest strategy fuses the Zn-MPPB and NAQA to form a pseudomolecule material, which changes the reaction process of NTR and NAQA from a double substrates mechanism to a single substrate one, and accelerates the reduction efficiency of NAQA. This advantage make the new host-guest reporter exhibit a linear relationship between emission changes and NTR concentration, and it shows better sensitively toward NTR than that of NAQA. Additionally, the positively charged water-soluble metal-organic cage can encapsulate NAQA in the cavity, promote it to dissolve in an aqueous environment, and facilitate their accumulation into tumor cells. As expected, such host-guest reporter displays a fast and high efficiently imaging capability toward NTR in tumor cells and tumor-bearing mice, and flow cytometry assay is conducted to corroborate the capability as well, implying the considerably potential of host-guest strategy for early tumor diagnosis and treatment.

An endoplasmic reticulum-specific ratiometric fluorescent probe for imaging esterase in living cells

Esterase is primarily distributed in the endoplasmic reticulum (ER) and often overexpressed in cancer cells. Therefore, the detection of esterase in ER is significant for monitoring the metabolic process of various esters and evaluating the efficacy of chemotherapeutic prodrugs. However, only few fluorescent probes can detect esterase in the ER due to the lack of ER-specificity. More seriously, these probes are often limited by low pearson's colocalization coefficient and one single wavelength emission. To solve those problems, an ER-specific ratiometric fluorescent probe (ER-EST) is designed for detecting esterase in living cells. The ER-EST shows a ratiometric and red-shifted emission (125 nm) from 435 to 560 nm after hydrolysis by esterase. The fluorescence intensity ratio of ER-EST displays quantitative response to the esterase activity (0-0.5 U/mL) with low detection limit of 1.8 × 10^-4 U/mL. Importantly, the ER-EST with good biocompatibility and excellent ER-targeted ability was successfully employed to ratiometric image the endogenous endoplasmic reticulum esterase in living cells.

A robust high selectivity fluorescence turn-on nanoprobe for peroxynitrite detection in inflammatory cells and mice

Changed levels of intracellular peroxynitrite anion (ONOO^-) are closely related to the occurrence and development of inflammation. Specific imaging of ONOO^- at sites of inflammation can be of great significance not only for inflammation diagnosis but also for obtaining a deeper understanding of the role of ONOO^- in inflammation. Therefore, there is an urgent need for constructing some reliable tools to study the relationship between ONOO^- and inflammation in biosystems. In this work, we developed a robust high selectivity fluorescence turn-on nanoprobe (Rhb-ONOO) for inflammation-targeted imaging of ONOO^-. The Rhb-ONOO was obtained by self-assembly of amphiphilic Rhb-ONOO, which was constructed by the condensation reaction of the hydrophobic, ONOO^--response and deep red-emitting fluorophore (Rhb) with hydrophilic biopolymer glycol chitosan (GC). Rhb-ONOO showed rapid response towards ONOO^- during 60 s, high sensitivity with 19-fold enhancement of fluorescence intensity ratio (I₆₂₈/I₀), and excellent selectivity towards ONOO^- over other analytes as well as a good linear relationship was observed between the I₆₂₈/I₀ and the ONOO^- concentration range 0-1 μM, with an excellent limit of detection (LOD) of 33 nM. Impressively, it was successfully employed Rhb-ONOO for ONOO^- imaging in living inflammatory cells and drug-induced inflammatory mice, illustrating nanoprobe Rhb-ONOO has excellent potential for further study ONOO^--related inflammatory diseases.

Endoplasmic Reticulum Peroxynitrite Fluctuations in Hypoxia-Induced Endothelial Injury and Sepsis with a Two-Photon Fluorescence Probe

Sepsis is a serious systemic inflammatory disease that frequently results in death. Early diagnosis and timely targeted interventions could improve the therapeutic effect. Recent work has revealed that the reactive oxygen species (ROS) in the endoplasmic reticulum (ER) and hypoxia-induced endothelial injury play significant roles in sepsis. However, the relationship between the levels of peroxynitrite (ONOO^-) and hypoxia-induced endothelial injury as well as different states of sepsis remain unexplored. Herein, we developed a unique two-photon fluorescent probe (ER-ONOO^-) for detecting ONOO^- in aqueous solution that has high sensitivity, high selectivity, and ultrafast response time. In addition, ER-ONOO^- was successfully used to evaluate the levels of ONOO^- at the ER with three kinds of methods in a hypoxia-induced endothelial injury model. Furthermore, ER-ONOO^- is capable of monitoring the changes in organ fluorescence through ONOO^- variation in different stages of a cecum ligation and puncture (CLP) mouse model. Moreover, we also confirmed that the endoplasmic reticulum stress and oxidative stress participated in the CLP model. Consequently, this research can provide a reliable tool for studying ONOO^- fluctuation in sepsis and provide new insights into the pathogenic and therapeutic mechanisms involved.

Visual and quantitative monitoring of thiophenol by a novel deep-red emitting fluorescent probe in environmental and biological systems

Detection of highly toxic thiophenols in biological or environmental systems is of great importance. Therefore, fast, reliable, and sensitive probes are needed to detect thiophenols. Herein, a novel triphenylamine conjugated dicyanoisophorone-based near infrared fluorescence probe is reported to determine trace thiophenol (PhSH) levels. The probe demonstrates a distinct "turn-on" fluorescence response to thiophenol among the tested analytes and its quantum yield (Φ) increases from 0.011 to 0.142. It has low cytotoxicity with cell viability of 90-100% up to 10.0 μM of the probe, a strong anti-interference capability, a large Stokes shift (150 nm), and a fast response time (<1 min). In addition, the probe exhibits a good linear response to PhSH over the range from 0 to 15.0 μM with a detection limit of 32.3 nM (R² = 0.9978). The detection process is also confirmed through HPLC. The practical applicability of the probe is proved by a smartphone platform, TLC kit, plant tissue imaging, soil assay, tap, and lake water analysis with good recovery values (92.3-117%), and concentration-dependent live cell bioimaging PhSH from 5.0 to 15.0 μM. Therefore, the present probe is a robust candidate for monitoring PhSH levels in biological and environmental systems.

Molecular Engineering of Near-Infrared Fluorescent Probes for Cell Membrane Imaging

Cell membrane (CM) is a phospholipid bilayer that maintains integrity of a whole cell and relates to many physiological and pathological processes. Developing CM imaging tools is a feasible method for visualizing membrane-related events. In recent decades, small-molecular fluorescent probes in the near-infrared (NIR) region have been pursued extensively for CM staining to investigate its functions and related events. In this review, we summarize development of such probes from the aspect of design principles, CM-targeting mechanisms and biological applications. Moreover, at the end of this review, the challenges and future research directions in designing NIR CM-targeting probes are discussed. This review indicates that more efforts are required to design activatable NIR CM-targeting probes, easily prepared and biocompatible probes with long retention time regarding CM, super-resolution imaging probes for monitoring CM nanoscale organization and multifunctional probes with imaging and phototherapy effects.