Dual-Responsive Ratiometric Fluorescent Probe for Hypochlorite and Peroxynitrite Detection and Imaging In Vitro and In Vivo

Development of a dual-responsive ratiometric fluorescent probe for real-time sequential detection of H2O2 and Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2025;333:125855. [PMID: 39946858 DOI: 10.1016/j.saa.2025.125855] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Hydrogen peroxide (H2O2) and silver ions (Ag+) are of considerable interest due to their critical roles in chemical and biological processes and their potential environmental and health risks. In this study, a novel dual-response ratiometric fluorescent probe (FBHP), based on an internal charge transfer (ICT) mechanism, was designed and synthesized for the real-time dual detection of H2O2 and Ag+. The probe utilizes triphenylamine as a luminescent platform, while azacrown [N, S, O] groups and phenylboronic pinacol ester groups serve as recognition sites for Ag+ and H2O2, respectively. Experimental results demonstrate that FBHP exhibits high sensitivity and excellent selectivity for H2O2 and Ag+, achieving detection limits of 0.261 μM for H2O2 and 0.021 μM for Ag+. During sequential real-time detection of H2O2 and Ag+, the probe undergoes distinct three-channel fluorescence color changes, with fluorescence colors transitioning sequentially from red to blue and then to yellow. It also features a large Stokes shift of 194 nm and functions efficiently across a broad pH range (4 to 9). In conclusion, the real-time sequential dual-responsive ratiometric fluorescent probe FBHP offers significant advantages for the detection of H2O2 and Ag+, making it highly suitable for applications in environmental monitoring and biomedical research. This probe represents an efficient and reliable tool for analyzing and detecting H2O2 and Ag+ in various fields. Future work may focus on further structural modifications to enhance its detection performance and broaden its application scope.

Triple-Standard Hypochlorite Quantitative Array Enabled by Precise Stokes Shift Modulation in D-π-A Chemodosimeters

The rational design of the D-π-A chemodosimeter with a significant Stokes shift is of great importance for enhancing the visualization of optical sensing signals. Here, three D-π-A fluorescent chemodosimeters with 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (TCF) as the electron-withdrawing group are synthesized by precisely modulating the electron-releasing strength. By decreasing the ability of electron release, the electrophilicity of the recognition site is increased by 1.449 kcal/mol, the Stokes shift of the chemodosimeter is improved to 201 nm, and the sensing mode changes from fluorescence quenching to ratiometric fluorescence and finally to fluorescence on. Furthermore, the three D-π-A fluorescent chemodosimeters display superior sensing performance toward ClO-, including low limits of detection (LOD, 37.0, 5.1, and 1.0 nM), rapid response (<5 s), and great selectivity in the presence of 16 kinds of interferents. Moreover, the practicality of the chemodosimeters is further validated by a portable triple-standard quantitative array detection platform, which can quantitatively detect ClO- solutions. The proposed design and modulation strategy for chemodosimeters can provide a new pathway for the sensitive and visualized identification of oxidants and other hazardous chemicals.

A novel near-infrared fluorescent probe for peroxynitrite imaging in cellular and organ injury

Peroxynitrite (ONOO-), a crucial reactive oxygen/nitrogen species, plays a significant role in various physiological and pathological processes. However, its excessive accumulation can lead to severe diseases, necessitating effective detection methods. Herein, we report a novel near-infrared fluorescent probe (DCI-ONOO) for sensitive and selective ONOO- detection, utilizing dicyanoisophorone as the fluorophore and a diphenylphosphinic group as the recognition moiety. The probe exhibits excellent photophysical properties, including a large Stokes shift (208 nm), good photostability, and a low detection limit (39.8 nM). Upon interaction with ONOO-, DCI-ONOO demonstrates a significant fluorescence enhancement at 670 nm through an intramolecular charge transfer mechanism. The probe shows remarkable selectivity toward ONOO- over other reactive oxygen/nitrogen species and maintains stability under various pH conditions. Furthermore, DCI-ONOO displays minimal cytotoxicity and effective membrane permeability, enabling successful imaging of both exogenous and endogenous ONOO- in living cells. Notably, the probe effectively monitored ONOO- fluctuations in acetaminophen-induced liver and kidney injury models, revealing previously unreported ONOO- generation patterns in systemic metabolic organs. These findings demonstrate DCI-ONOO potential as a valuable tool for studying ONOO--related biological processes and drug-induced organ damage.

A NIR ratiometric probe for detecting hypochlorite and bisulfite/sulfite in aqueous media

We have designed and synthesized a hemicyanine-based near-infrared (NIR) ratiometric and colorimetric fluorescent probe (AHS) to detect both HSO3-/SO32- and OCl-. AHS probe contains a conjugated -C=C- bond and a -SMe group and exhibits NIR fluorescence emission at 666 nm (λex = 520 nm) because of the intramolecular charge transfer (ICT) mechanism. The probe undergoes a Michael addition reaction with HSO3-/SO32- at the conjugated -C=C- bond, resulting in the formation of an adduct that breaks the π conjugation in the probe and shifts the fluorescence to 488 nm (λex = 420 nm). Similarly, upon reaction with hypochlorite (OCl-), a strong oxidizing agent, the -SMe group is oxidized to -S(O)Me, resulting in a fluorescence shift to 580 nm (λex = 520 nm). AHS demonstrated high selectivity and sensitivity for HSO3-/SO32- and OCl-, with detection limits of 1.96 nM and 164.67 nM, respectively. Additionally, the probe exhibits excellent water solubility and strong anti-interference ability and can detect both the analytes at pH 7-10. AHS was successfully applied for the detection of HSO3-/SO32- and OCl- on paper strips and in real and water samples with a high degree of recovery, demonstrating its potential for practical applications in environmental and biological analysis.

Engineering a swich-on fluorescent probe for the visual detection of HOCl in envirnomental and living system

Normal levels of HOCl can resist pathogen invasion and maintain cellular redox balance. However, excessive HOCl can easily harm the ecological environment and human health. Establishing a reliable approach for detection of HOCl can help resolve controversial issues regarding HOCl in physiological systems and help detect HOCl in complex environmental water samples. This study presents the design and evaluation of a HOCl-specific self-immolative fluorescent probe (OX-OCl), which is based on the N-protected phenoxazine dye structure. In aqueous solution, the probe demonstrates a rapid and highly specific response to HOCl within a brief time frame of 15 s, exhibiting good sensitivity with a limit of detection (LOD) of 15.3 nM. Notably, the reaction of OX-OCl with HOCl results in substantial changes in both UV absorption and fluorescence emission. Benefit from this, smartphone-assisted colorimetric and fluorescent sensing platforms had been developed for real-time monitoring of HOCl. Furthermore, owing to its excellent biocompatibility, OX-OCl has been successfully utilized for near-infrared bioimaging of HOCl in live cells and mouse models of arthritis. In brief, this probe offers a new perspective for the convenient monitoring of HOCl in environmental contexts and provides a visual tool for the early clinical diagnosis of related diseases.

A highly sensitive and fast-response fluorescence nanoprobe for in vivo imaging of hypochlorous acid

Fluorescent probes for in vivo hypochlorous acid (HClO) imaging often face challenges of low selectivity and high cytotoxicity, largely due to poor analyte recognition and water-insoluble aromatic skeletons. To address this, we synthesized fluorescein hydrazide by introducing a spiro-lactam unit into fluorescein, which offers high emission intensity and molar absorption. The five-membered heterocycle in fluorescein hydrazide is selectively disrupted by HClO, enhancing the conjugated system and electron delocalization of the fluorophore, resulting in highly sensitive fluorescence detection of HClO. For in vivo imaging, fluorescein hydrazide was covalently grafted onto the surface of silica nanoparticles via nucleophilic substitution reaction, avoiding complex modifications. This fluorescent nanoprobe (Si-FL) leverages the high-density fluorophores and hydroxyl groups on the silica surface to enrich low-concentrations of HClO through weak supramolecular interactions, thereby accelerating the reaction between HClO and the recognition sites. Compared to other molecular probes, Si-FL demonstrates a superior response speed (within 20 s) and a lower detection limit (72 nM), alongside excellent biocompatibility and water solubility. The nanoprobe Si-FL was successfully applied for HClO detection in living cells, zebrafish, and plants, significantly improving the stability of fluorescence imaging.

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.

Asymmetric D-A-D' Ratiometric Molecule for Highly Specific Hypochlorous Acid Detection

Hypochlorous acid exists as HClO in acidic conditions and as ClO- in alkaline conditions, posing a significant challenge for differentiation due to their strong and closely similar oxidative reaction activities. Addressing this challenge, our study presents an asymmetric donor-acceptor-donor' (D-A-D') molecular architecture for the design of a fluorescent probe (PMT NPs) that demonstrates exceptionally high specificity toward HClO alongside an optimized ratiometric response. The incorporation of the strong electron acceptor 2-(diphenylmethylene)malononitrile (A) modulates the reducing ability of the phenothiazine recognition site, adjusting the probe's oxidation potential to an intermediate level between HClO and ClO-. This adjustment directly dictates the probe's selectivity, enabling it to respond exclusively to HClO. By incorporating D', the probe's response to HClO shifts the intramolecular charge transfer (ICT) from the original D-A to D'-A, instead of the usual Dox-A as presented in previous works. This adjustment controls the blue shift in fluorescence wavelength upon recognition, thereby improving the accuracy of ratiometric signals in vivo. The ability of PMT NPs to precisely recognize HClO in acidic environments was validated through live cell imaging and in vivo experiments using zebrafish and mouse models, enabling real-time monitoring of HClO surges. This dual-pronged molecular design strategy, which combines D-A interaction modulation with a D-A-D' molecular architecture, promises to revolutionize probe designs for various biomolecules and is anticipated to advance the understanding of diseases linked to these analytes.

A Ratiometric Fluorescent Probe Based on Carbon Dots and Quantum Dots for Glucose Detection

Glucose is a critical energy source for human cells, and maintaining stable glucose levels is essential for normal physiological functions. Abnormal glucose levels can lead to health issues such as diabetes, obesity, and hypoglycemia, highlighting the need for precise and rapid glucose detection methods for clinical diagnostics and health management. In this study, a novel ratiometric fluorescent probe was constructed for glucose detection. Using glucose oxidase (GOx) and horseradish peroxidase (HRP) as enzymatic mediators, the probe employs orange-emitting carbon dots (oCDs) as the detection signal and red-emitting quantum dots (rQDs) as the reference signal. Glucose is oxidized by GOx to produce hydrogen peroxide (H2O2), which subsequently generates hydroxyl radicals (·OH) under HRP catalysis. The ·OH interacts electrostatically with oCDs, forming non-fluorescent complexes and quenching the oCDs fluorescence. Glucose concentration is quantified by monitoring the fluorescence intensity ratio (I590/I715) between oCDs and rQDs. The probe has a limit of detection (LOD) of 0.47 µM and a limit of quantification (LOQ) of 1.58 µM. After methodological validation, it has been successfully applied to the detection of glucose in human serum. This study provides a solid basis for accurate glucose monitoring and holds potential for the early diagnosis and treatment of metabolic diseases such as diabetes.

COX-2-targeted fluorescent probe for ClO- monitoring in precise cancer detection

Hypochlorite anion (ClO-) is closely associated with cancer development and progression, necessitating precise monitoring of ClO- in tumor sites, and Cyclooxygenase-2 (COX-2 is highly expressed in tumor cells. So we rationally designed two ClO--specific responsive fluorescent probes COX2-ClO1 and COX2-ClO2, using indomethacin (IMC) as the COX-2 targeting moiety and methylene blue as fluorophore unit. Both probes exhibited high selectivity and sensitivity towards ClO- in the in vitro solution assays and possess excellent biocompatibility in cellular experiments. Compared to COX2-ClO1, COX2-ClO2 exhibited superior targeting specificity for COX-2, enabling precise differentiation between tumor cells and normal cells and allowing imaging of both exogenous and endogenous ClO- in the in vivo experiments. Moreover, COX2-ClO2 could accurately target the tumor site in xenograft mice and is likely metabolized by the kidneys.

Deep learning-assisted surface-enhanced Raman spectroscopy detection of intracellular reactive oxygen species

Realizing the intelligent analysis of the intracellular reactive oxygen species (ROS) is beneficial to quick diagnosis of diseases. Herein, surface-enhanced Raman spectroscopy (SERS) technology was combined with deep learning to establish a smart detection method of intracellular ROS based on neural network to improve the SERS analysis ability. Taking the simultaneous detection of peroxynitrite (ONOO-) and hypochlorite (ClO-) as the templates, 4-mercaptophenylboric acid (4-MPBA) and 2-mercapto-4-methoxyphenol (2-MP) molecules were modified on the AuNPs to prepare AuNP/4-MPBA/2-MP nanoprobes. The SERS spectra of AuNP/4-MPBA/2-MP nanoprobes before and after the specific response of ONOO- and ClO- were collected to construct a database, and the neural network model for extraction (ENN) and one-dimensional convolutional neural network model (1D-CNN) for quantification were built. The cosine similarity values of ENN model for ONOO- and ClO- correlation spectra were 0.997 and 0.995, respectively. In addition, the qualitative and quantitative results of the models were basically consistent with the experimental results. Moreover, the models can accurately extract the SERS response spectral information of ONOO- and ClO- and realize their preliminary prediction of concentration in living cells, which has great potential in the high-throughput smart processing and accurate analysis of large-scale complicated SERS data from biological system.

A novel fluorescent probe based on dicyanoisophorone derivatives for hypochlorite detection in living cells

This study presents a long-wavelength fluorescent probe CNC for the detection of ClO- in vitro and in vivo. Upon interaction with ClO-, this probe exhibited a significant increase in fluorescence, with a significant Stokes shift (169 nm), lower detection limit (1.38 μM), high sensitivity and selectivity. Moreover, the probe demonstrated excellent cell permeability and minimal cytotoxicity, allowing for successful imaging of both endogenous and exogenous ClO- in living cells.

Easy and Fast Detection of Hypochlorite by a Bithiophene-Based Fluorescent Turn-on Sensor and its Applications to Test Strips, Real Water Samples, and Smartphone-Assisted Platform

We report a bithiophene-based fluorescence probe BDT (2,2'-(((1 E, 1'E)-[2,2'-bithiophene]-5,5'-diylbis(methaneylylidene))bis(azaneylylidene))bis(4-(tert-butyl)phenol)) for recognizing ClO-. BDT selectively responded to ClO-, leading to a blue fluorescence enhancement in a mixture of DMF/HEPES buffer (9:1, v/v). Importantly, BDT showed an ultrafast response (within 1 s) to ClO- among the fluorescent turn-on chemosensors based on bithiophene. BDT recognized ClO- through cleavage reaction with a low detection limit of 2.16 µM, and it had the ability to sense ClO- across a pH range of 3-11. The recognition mechanism for ClO- was investigated by 1H nuclear magnetic resonance (NMR) titration, electrospray ionization mass spectrometry (ESI-MS), and density functional theory (DFT) calculations. In addition, BDT could be used to detect ClO- using test strips as a convenient tool, allowing real-time monitoring rapidly. Practically, BDT exhibited reliable recoveries for quantifying ClO- using a smartphone application with a spike-and-recovery method in real water samples such as drinking, tap, mineral, and river water.

Monitoring Endoplasmic Reticulum Peroxynitrite Fluctuations in Primary Tendon-Derived Stem Cells and Insights into Tendinopathy

Tendinopathy is one of the most prevalent musculoskeletal disorders, significantly affecting the quality of life of patients. Treatment outcomes can be improved with an early diagnosis and timely targeted interventions. Increasing evidence indicates that ROS and endoplasmic reticulum (ER) stress play key roles in modulating the differentiation processes of tendon-derived stem cells (TDSCs), thereby contributing to the initiation and progression of tendinopathy. However, the relationship between ONOO- and the differentiation process, as well as the various stages of tendinopathy, remains unexplored. Herein, we developed two highly specific and sensitive fluorescent probes (Rod-Cl and Rod-Br) for detecting ONOO- in the ER. Rod-Br can detect basal levels of ONOO- in the ER of TDSCs and measure ONOO- levels in primary TDSCs stimulated by interleukin-1β over various durations, allowing for comparisons between chondrogenic and osteogenic differentiation and ER stress levels. Additionally, we examined ONOO- variations in different stages of tendinopathy and treatment rat models in vivo and discussed the potential mechanisms. This research provides a robust tool for analyzing ONOO- dynamics in the tenogenic and osteogenic differentiation of TDSCs, offering new insights into the pathophysiology and treatment of tendinopathy.

Fluorescent probes for sensing peroxynitrite: biological applications

Peroxynitrite (ONOO-) is a quintessential reactive oxygen species (ROS) and reactive nitrogen species (RNS), renowned for its potent oxidizing and nitrifying capabilities. Under normal physiological conditions, a baseline level of ONOO- is present within the body. However, its production escalates significantly in response to oxidative stress. ONOO- is highly reactive with various biomolecules in vivo, particularly proteins, lipids, and nucleic acids, thereby playing a role in a spectrum of physiological and pathological processes, such as inflammation, cancer, neurodegenerative diseases, and cardiovascular diseases. Consequently, detecting ONOO- in vivo is of paramount importance for understanding the etiology of various diseases and facilitating early diagnosis. Fluorescent probes have become a staple in the identification of biomolecules due to their ease of use, convenience, and superior sensitivity and specificity. This review highlights the recent advancements in the development of fluorescent probes for the detection of ONOO- in diverse disease models and provides an in-depth examination of their design and application.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Multifunctional Sensors for Successive Detection of Endogenous ONOO- and Mitochondrial Viscosity: Discriminating Normal to Cancer Models

Diagnosing cancer in its early stages can play an important role in prolonging the lifespan of patients, which demands the use of powerful tools to detect biomarkers accurately. However, since most fluorescent probes described for cancer diagnosis are limited to recognizing a single molecule, achieving the high accuracy criteria remains difficult. Here, sensor 1 is constructed for the sequential detection of D, ONOO-, and viscosity. Initially, sensor 1 detected D and underwent an intramolecular charge transfer mechanism, resulting in the formation of 2 and fluorescence quenching at 587 nm. Subsequently, the intermediate (2) monitored ONOO- and reproduced sensor 1 reversibly with fluorescence enhancement at 496 nm, showing concentration-related quantitative analysis. Similar sensing processes were observed in monitoring ONOO- and viscosity by synthetically developed sensor 2. The proposed mechanisms of sensors 1 and 2 are verified through various characterizations (1H NMR, HR-MS, and HPLC) and DFT calculations. Investigations on endogenous ONOO- and mitochondrial viscosity in cancer (HeLa) and normal (NCM460) cells were conducted to distinguish cancerous cells from normal cells. We anticipated that sensor 2 could effectively serve as a reliable bioanalytical reagent for cancer diagnosis at an earlier stage through sequential detection of two cancer markers, ONOO- and mitochondrial viscosity, in living cells. Importantly, sensor 2 has been employed for imaging ONOO- in normal and liver injury mouse models and tissues, achieving outstanding results.

A dual-response ratiometric fluorescent sensor by europium-doped silicon nanoparticles for fluorescent and smartphone imaging detection of tetracycline

Given the threat to human health posed by the abuse of tetracycline (TC), the development of a portable, on-site methods for highly sensitive and rapid TC detection is crucial. In this work, we initially synthesized europium-doped silicon nanoparticles (SiEuNPs) through a facile one-pot microwave-assisted method. Due to its blue-red dual fluorescence emission (465 nm/621 nm), which was respectively attributed to the silicon nanoparticles and Eu3+, SiEuNPs were designed as a ratiometric fluorescent sensor for TC detection. For the dual-signal reverse response mechanism: TC quenched the blue emission from silicon nanoparticles through inner filter effect (IFE), and enhanced the red emission through "antenna effect" (AE) between TC and Eu3+, the nanoprobe was able to detect TC within a range of 0.2-10 μM with a limit of detection (LOD) of 10.7 nM. Notably, the equilibrium detection time was only 1 min, achieving rapid TC detection. Furthermore, TC was also measured in real samples (tap water, milk and honey) with recoveries ranging from 95.7 % to 117.0 %. More importantly, a portable smartphone-assisted on-site detection platform was developed, enabling real-time qualitative identification and semi-quantitative analysis of TC based on fluorescence color changes. This work not only provided a novel doped silicon nanoparticles strategy, but also constructed a ratiometric sensing platform with dual-signal reverse response for intuitive and real-time TC detection.

Fast and easy detection of hypochlorite by a smartphone-based fluorescent turn-on probe: Applications to water samples, zebrafish and plant imaging

We have developed a fluorescent probe DBT-Cl ((E)-2-(2-(4-(diphenylamino)benzylidene) hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for ClO- with an aggregation-induced emission (AIE) strategy depending on solvent polarity. DBT-Cl possessed a prominent solvatochromic emission property with intramolecular charge transfer (ICT) from the TPA (triphenylamine) to the amide group, which was studied by spectroscopic analysis and DFT calculations. These unique AIE properties of DBT-Cl led to the recognition of ClO- with high fluorescent selectivity. DBT-Cl quickly detected ClO- in less than 1 sec with a fluorescent color change from green to cyan. DBT-Cl had a low detection limit of 9.67 μM to ClO-. Detection mechanism of DBT-Cl toward ClO- was illustrated to be oxidative cleavage of DBT-Cl by 1H NMR titrations, ESI-mass, and DFT calculations. We established the viability for dependable detection of ClO- in actual water samples, as well as zebrafish and plant imaging. In particular, DBT-Cl was capable of easily monitoring ClO- through a smartphone application. Therefore, DBT-Cl assured a promising approach for a fast-responsive and multi-applicable ClO- probe in environmental and living organism systems.

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.

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

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

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

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

Construction of CDs@β-CD@CCM ratiometric fluorescence probe for FRET-based ClO--sensing

β-Cyclodextrin (β-CD)-functionalized carbon quantum dots (CDs) loaded with curcumin (CCM) were used for ClO-sensing with high sensitivity and selectivity. This fluorescence resonance energy transfer (FRET)-based sensor was created through attaching CCM to the CDs via β-CD linker. CCM could get into the interior of β-CD triggering the FRET from CDs to CCM, providing an 'off' state of the CDs. However, the effect of FRET was weakened by the ClO-, because the o-methoxyphenol structure from CCM was oxidized to be benzoquinone. The fluorescence intensity of CDs@β-CD@CCM at 440 nm can be heightened and 520 nm from CCM can decrease along with the increased ClO-. Therefore, a ratiometric fluorescence probe for ClO-sensing is successfully constructed. It conforms to a polynomial curve equation which is I440/I520= -0.0268 + 0.0315 CClO-+ 0.0055[CClO-]2(R2= 0.9958) between 0 and 18.4μM ClO-. Furthermore, we also obtain excellent results using this spectrophotometric method for ClO--sensing in pure water and commercial disinfectants, which afford potential in the environment monitoring area. We expect this sensing platform could be helpful in other analogous probes in relevant fields.

Visulization of peroxynitrite variation for accurate diagnosis and assessing treatment response of hepatic fibrosis using a Golgi-targetable ratiometric fluorescent probe

Hepatic fibrosis (HF) is caused by persistent inflammation, which is closely associated with hepatic oxidative stress. Peroxynitrite (ONOO-) is significantly elevated in HF, which would be regarded as a potential biomarker for the diagnosis of HF. Research has shown that ONOO- in the Golgi apparatus can be overproduced in HF, and it can induce hepatocyte injury by triggering Golgi oxidative stress. Meanwhile, the ONOO- inhibitors could effectively relieve HF by inhibiting Golgi ONOO-, but as yet, no Golgi-targetable fluorescent probe available for diagnosis and assessing treatment response of HF through sensing Golgi ONOO-. To this end, we reported a ratiometric fluorescent probe, Golgi-PER, for diagnosis and assessing treatment response of HF through monitoring the Golgi ONOO-. Golgi-PER displayed satisfactory sensitivity, low detection limit, and exceptional selectivity to ONOO-. Combined with excellent biocompatibility and good Golgi-targeting ability, Golgi-PER was further used for ratiometric monitoring the Golgi ONOO- fluctuations and screening of ONOO- inhibitors from polyphenols in living cells. Meanwhile, using Golgi-PER as a probe, the overexpression of Golgi ONOO- in HF and the treatment response of HF to the screened rosmarinic acid were precisely visualized for the first time. Furthermore, the screened RosA has a remarkable therapeutic effect on HF, which may be a new strategy for HF treatment. These results demonstrated the practicability of Golgi-PER for monitoring the occurrence, development, and personalized treatment response of HF.

Dicyanoisophorone-based near-infrared fluorescent probe with large Stokes shift for the monitoring and bioimaging of hypochlorite

Hypochlorite (ClO-), as one of reactive oxygen species (ROS), is closely linked to various illnesses and is essential for the proper functioning of immune system. Hence, monitoring and assessing ClO- levels in organisms are extremely important for the clinical diagnosis of ClO--related disorders. In this study, a novel ClO--selective fluorescent probe, DCP-ClO, was synthesized with dicyanoisophorone-xanthene unit as parent fluorophore, which displayed excellent selectivity towards ClO-, near-infrared emission (755 nm), large Stokes shift (100 nm), real-time response to ClO-, high sensitivity (LOD = 3.95 × 10-8 M), and low cytotoxicity. The recognition mechanism of DCP-ClO towards ClO- was confirmed to be a typical ICT process by HPLC-MS, HR-MS, 1H NMR and theoretical calculations. Meanwhile, DCP-ClO demonstrated remarkable efficacy in monitoring ClO- levels in water samples and eye-catching ability in imaging endogenous/exogenous ClO- in living organisms, which verified its potential as a powerful tool for the recognition of ClO- in complex biological systems.

Preparation and utilization of carbon dots as a nanoprobe for sensitive detection of tartrazine and palladium (II)

We prepared novel green, eco-friendly carbon dots as a dual-channel probe for highly sensitive and selective detection of tartrazine (Trz) and palladium(II) (Pd(II)) involving, respectively, FRET and electron transfer mechanisms. Furthermore, the successful utilization of the carbon dots for detecting Trz and Pd(II) in actual samples implies its potential application prospects in analysis.

Dual-site lysosome-targeted fluorescent sensor for fast distinguishing visualization of HClO and ONOO- in living cells and zebrafish

As two of important highly reactive species / nitrogen species, hypochloric acid (HClO) and peroxynitrite (ONOO-) are involved in various pathological and physiological processes, which are important factors that affect and reflect the functional state of lysosome. Nevertheless, many of their roles are still indefinite because of lack of suitable analytical methods for HClO and ONOO- detection in lysosome. Herein, we designed a lysosome-targeted probe to monitor HClO and ONOO-, which was a hydrid of the benzothiazole derivative, methyl thioether (HClO recognition site) and morpholino hydrazone (ONOO- recognition and lysosome target site). The probe exhibited high sensitivity, good selectivity and fast response toward HClO and ONOO- without spectral crosstalk, and can be employed for quantitative monitoring HClO and ONOO- with LOD of 63 and 83 nM, respectively. In addition, the dual-site probe was lysosome targetable and could be used for detection of HClO and ONOO- in living cells. Furthermore, the excellent behavior made it was suitable for imaging of HClO and ONOO- in zebrafish. Thus, the present probe provides a potent tool for distinguishing monitoring HClO and ONOO- and exploring the role of HClO and ONOO- in biological systems.

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 Fluorescent Probe with Zwitterionic ESIPT Feature for Ratiometric Monitoring of Peroxynitrite In Vitro and In Vivo

Peroxynitrite (ONOO-), as a short-term reactive biological oxidant, could lead to a series of effects in various physiological and pathological processes due to its subtle concentration changes. In vivo monitoring of ONOO- and relevant physiological processes is urgently required. Herein, we describe a novel fluorescent probe termed HBT-Fl-BnB for the ratiometric detection of ONOO- in vitro and in vivo. The probe consists of an HBT core with Fl groups at the ortho and para positions responding to the zwitterionic excited-state intramolecular proton-transfer (zwitterionic ESIPT) process and a boronic acid pinacol ester with dual roles that block the zwitterionic ESIPT and recognize ONOO-. Thanks to the specificity as well as low cytotoxicity, success in imaging of endogenous and exogenous ONOO- in living cells by HBT-Fl-BnB was obtained. Additionally, the applicability of HBT-Fl-BnB to tracking the abnormal expression of ONOO- in vivo induced by inactivated Escherichia coli was also explored. This is the first report of a fluorescent probe for ONOO- sensing via a zwitterionic ESIPT mechanism.

A Photoelectrochemical Sensor for the Detection of Hypochlorous Acid with a Phenothiazine-Based Photosensitizer

This paper presents the development of a photoelectrochemical sensor for hypochlorous acid (HOCl) detection, employing a phenothiazine-based organic photosensitizer (Dye-PZ). The designed probe, Dye-PZ, follows a D-π-A structure with phenothiazine as the electron-donating group and a cyano-substituted pyridine unit as the electron-accepting group. A specific reaction of the phenothiazine sulfur atom with HOCl enables selective recognition. The covalent immobilization of Dye-PZ onto a titanium dioxide nanorod-coated fluorine-doped tin oxide electrode (FTO/TiO2) using bromo-silane coupling agent (BrPTMS) resulted in the fabrication of the photoanode FTO/TiO2/BrPTMS/Dye-PZ. The photoanode exhibited a significant photoresponse under visible-light irradiation, with a subsequent reduction in photocurrent upon reaction with HOCl. The oxidation of the phenothiazine sulfur atom to a sulfoxide diminished the internal charge transfer (ICT) effect. Leveraging this principle, the successful photoelectrochemical sensing of HOCl was achieved. The sensor showed high stability, excellent reproducibility, and selective sensitivity for HOCl detection. Our study provides a novel approach for the development of efficient photoelectrochemical sensors based on organic photosensitizers, with promising applications in water quality monitoring and biosensing.

Recent advances in fluorescent probes for dual-detecting ONOO- and analytes

Although peroxynitrite (ONOO-) plays an essential role in cellular redox homeostasis, its excess ONOO- will affect the normal physiological function of cells. Therefore, real-time monitoring of changes in local ONOO- will contribute to further revealing the biological functions. Reliable and accurate detection of biogenic ONOO- will definitely benefit for disentangling its complex functions in living systems. In the past few years, more fluorescent probes have been developed to help understand and reveal cellular ONOO- changes. However, there has been no comprehensive and critical review of multifunctional fluorescent probes for cellular ONOO- and other analytes. To highlight the recent advances, this review first summarized the recent progress of multifunctional fluorescent probes since 2018, focusing on molecular structures, response mechanisms, optical properties, and biological imaging in the detection and imaging of cellular ONOO- and analytes. We classified and discussed in detail the limitations of existing multifunctional probes, and proposed new ideas to overcome these limitations. Finally, the challenges and future development trends of ONOO- fluorescence probes were discussed. We hoped this review will provide new research directions for developing of multifunctional fluorescent probes and contribute to the early diagnosis and treatment of diseases.

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.

Accurate imaging in the processes of formation and inhibition of drug-induced liver injury by an activable fluorescent probe for ONOO. Mater Today Bio 2023;21:100689. [PMID: 37448665 PMCID: PMC10336156 DOI: 10.1016/j.mtbio.2023.100689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Herein, an activable fluorescent probe for peroxynitrite (ONOO^-), named NOP, was constructed for the accurate imaging in the processes of formation and inhibition of drug-induced liver injury induced by Acetaminophen (APAP). During the in-solution tests on the general optical properties, the probe showed advantages including good stability, wide pH adaption, high specificity and sensitivity in the monitoring of ONOO^-. Subsequently, the probe was further applied in the model mice which used APAP to induce the injury and used inhibiting agents (GSH, Glu, NAC) to treat the induced injury. The construction of the liver injury model was confirmed by the pathological staining and the serum indexes including ALT, AST, ALP, TBIL as well as LDH. During the formation of the drug-induced liver injury, the fluorescence in the red channel enhanced in both time-dependent and dose-dependent manners. In inhibition tests, the inhibition of the liver injury exhibited the reduction of the fluorescence intensity. Therefore, NOP could achieve the accurate imaging in the processes of formation and inhibition of drug-induced liver injury. The information here might be helpful for the early diagnosis and the screening of potent treating candidates in liver injury cases.

Vision for Ratiometric Nanoprobes: In Vivo Noninvasive Visualization and Readout of Physiological Hallmarks

Lesion areas are distinguished from normal tissues surrounding them by distinct physiological characteristics. These features serve as biological hallmarks with which targeted biomedical imaging of the lesion sites can be achieved. Although tremendous efforts have been devoted to providing smart imaging probes with the capability of visualizing the physiological hallmarks at the molecular level, the majority of them are merely able to derive anatomical information from the tissues of interest, and thus are not suitable for taking part in in vivo quantification of the biomarkers. Recent advances in chemical construction of advanced ratiometric nanoprobes (RNPs) have enabled a horizon for quantitatively monitoring the biological abnormalities in vivo. In contrast to the conventional probes whose dependency of output on single-signal profiles restricts them from taking part in quantitative practices, RNPs are designed to provide information in two channels, affording a self-calibration opportunity to exclude the analyte-independent factors from the outputs and address the issue. Most of the conventional RNPs have encountered several challenges regarding the reliability and sufficiency of the obtained data for high-performance imaging. In this Review, we have summarized the recent progresses in developing highly advanced RNPs with the capabilities of deriving maximized information from the lesion areas of interest as well as adapting themselves to the complex biological systems in order to minimize microenvironmental-induced falsified signals. To provide a better outlook on the current advanced RNPs, nanoprobes based on optical, photoacoustic, and magnetic resonance imaging modalities for visualizing a wide range of analytes such as pH, reactive species, and different derivations of amino acids have been included. Furthermore, the physicochemical properties of the RNPs, the major constituents of the nanosystems and the analyte recognition mechanisms have been introduced. Moreover, the alterations in the values of the ratiometric signal in response to the analyte of interest as well as the time at which the highest value is achieved, have been included for most of RNPs discussed in this Review. Finally, the challenges as well as future perspectives in the field are discussed.

Highly selective and sensitive benzopyran-based fluorescent probes for imaging exogenous and endogenous peroxynitrite

Peroxynitrite is widely present in organisms and closely related to many pathophysiological functions. Therefore, it is of great physiological significance to develop capable probes for detecting ONOO^-. In this work, a novel fluorescent probe B-Ch was designed based on the intramolecular charge transfer (ICT) effect. By means of molecular engineering, the replacement from diethylamine group to hydroxyl group has improved the detection sensitivity of the probe. After the addition of ONOO^-, the solution color and fluorescence showed noticeable changes, which were visible to the naked eye. The probe showed excellent advantages: visualization, good selectivity, low sensitivity (22.4 nM), good stability and biocompatibility, exogenous and endogenous imaging of ONOO^- in HeLa cells.

Hyperbranched polysiloxane-based probe with enhanced lipophilicity for visualizing ONOO- fluctuations in endoplasmic reticulum

The endoplasmic reticulum, a cellular signaling regulator, participates in the synthesis and secretion of many proteins, glycogen, lipids and cholesterol substances. Peroxynitrite (ONOO^-) is a highly oxidative and nucleophilic agent. Abnormal fluctuations of ONOO^- induce oxidative stress in the endoplasmic reticulum, further disrupting the normal function of protein folding and transport and glycosylation modification, ultimately leading to neurodegenerative diseases, cancer and Alzheimer's disease. Up to now, most probes have tended to achieve targeting functions by introducing specific targeting groups. However, this approach increased the difficulty of the construction process. Therefore, a simple and efficient construction strategy for fluorescent probes with excellent specificity targeting the endoplasmic reticulum is lacking. To overcome this difficulty and put forward an efficient design strategy for the endoplasmic reticulum targeted probes, in this paper, we constructed alternating rigid and flexible polysiloxane-based hyperbranched polymeric probes (Si-Er-ONOO) by bonding perylenetetracarboxylic anhydride and silicon-based dendrimers for the first time. Efficient and specific targeting of the endoplasmic reticulum was successfully achieved by the excellent lipid solubility of Si-Er-ONOO. Furthermore, we observed different effects of metformin and rotenone on the changes of ONOO^- volatility in the cellular and zebrafish internal environment by Si-Er-ONOO. We believe that Si-Er-ONOO will expand the application of organosilicon hyperbranched polymeric materials in bioimaging and provide an excellent indicator of reactive oxygen species fluctuations in biological systems.

A hypochlorite-activated strategy for realizing fluorescence turn-on, type I and type II ROS-combined photodynamic tumor ablation

The combination of cancer cell-activated fluorescence and the advantages of both type I and type II photodynamic therapy (PDT) capabilities to achieve a synergistic therapeutic effect in a complex tumor environment is highly desirable. Herein, we report an approach by means of tumor intracellular hypochlorite (ClO^-) to turn on fluorescence integrated with type I and II ROS generation for imaging-guided PDT. The resultant PTZSPy functions as a type II photosensitizer with mitochondria-targeting capability. In the presence of ClO^-, PTZSPy is transformed into its oxidized counterpart SPTZSPy, turns on an orange-red fluorescence and triggers the type I ROS generation ability. Biological studies revealed that PTZSPy can accurately distinguishes tumor cells from normal cells, dynamically monitors the cell ablation process and be utilized for theranostics in MCF-7 tumor-bearing nude mice in vivo. This work provides an innovative strategy exploiting the highly abundant ClO^- in tumor cells for the type I and II ROS two-pronged and imaging-guided PDT.

Dual-targetable fluorescent probe for mapping the fluctuation of peroxynitrite in drug-induced liver injury model

Drug-induced liver injury (DILI) is one of the most common and serious adverse drug reactions which can cause acute liver failure or even death in severe cases. With the incidence rate increasing over the years, DILI has became a frequent clinical liver disease and a global public health problem. As a biomarker of DILI, the detection of peroxynitrite (ONOO^-) has became a powerful tool for the early diagnosis of liver injury. Here, we synthesized five mitochondria-targetable probes, 1-5, for detecting endogenous ONOO^-. Through dye-screening, probe 5 was stood out by its excellent performance. In the presence of ONOO^-, the fluorescence signal of probe 5 reduced 40-fold in 19 s with a low detection limit (9.36 nM). At the same time, the transformation can be observed with the naked eye under sunlight or UV lamp without being affected by the other reactive species. Even better, with low toxicity and high biocompatibility, probe 5 could successfully detect endogenous ONOO^- in the mitochondrion of cells. Finally, probe 5 could specifically target the liver, and can be employed for monitoring the therapeutic effect of hepatoprotective medicine after drug-induced hepatotoxicity in vivo. In brief, probe 5 has the practical application capability for diagnosing the severity of the liver injury and researching the therapeutic effect of antidote in complex bio-systems.

A dual-responsive fluorescent turn-on sensor for sensitively detecting and bioimaging of hydrazine and hypochlorite in biofluids, live-cells, and plants

Hydrazine (N₂H₄) and hypochlorite (ClO^-) are extremely harmful to the public health, so it is vitally necessary to detect them in living system. Herein, we developed a new phenthiazine-thiobarbituric acid based dual-analyte responsive fluorescent sensor PT for visually distinguishing and detecting N₂H₄ and ClO^-. PT underwent N₂H₄/ClO^--induced CC breakage, achieving olive-drab/brilliant green fluorescence lighting-up response towards N₂H₄/ClO^- with superb specifity, ultra-sensitivity (detection limit: 15.4 nM for N₂H₄, 13.7 nM for ClO^-), and ultra-fast response (N₂H₄: <15 s, ClO^-: <20 s). The mechanisms for sensing N₂H₄ and ClO^- were investigated with support of spectral measurements and DFT investigation. Sensor based paper-strip/silica-gel device was developed for in-field supervision and on-site monitoring of gaseous and aqueous N₂H₄ and ClO^- solution. In addition, the PT was also applied for quantitatively detecting N₂H₄ and ClO^- in soil, food, plants and bio-fluids. Moreover, PT was utilized to visualize exogenous N₂H₄ and ClO^- in living plants and live-cells, demonstrating this sensor utilized as a powerful tool to detect N₂H₄ and ClO^- in biological fields.

A biotin-guided near-infrared fluorescent probe for imaging hydrogen sulfide and differentiating cancer cells

Imaging cancer specific biomarkers with near-infrared (NIR) fluorescent probes can help inaccurate diagnosis. Hydrogen sulfide (H₂S) has been reported to be involved in many physiological and pathological processes and is considered as one of the key gasotransmitters during the development of cancer. To achieve specific H₂S detection in cancer cells, we reported a biotin-guided NIR fluorescent sensor P1 targeting a cancer cell surface biomarker, based on the H₂S-specific thiolysis of the NBD-amine-hemicyanine conjugate. The probe showed a fast turn-on signal at 754 nm upon H₂S activation and good selectivity towards H₂S over millimolar levels of other biothiols. We successfully employed P1 to image endogenous H₂S and demonstrated its tumor-targeting ability in live cells. P1 could differentiate multiple cancer cells with various levels of H₂S from normal cells, indicating its potential for cancer imaging.

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

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

Rational Design of a Dual-Channel Fluorescent Probe for the Simultaneous Imaging of Hypochlorous Acid and Peroxynitrite in Living Organisms

Hypochlorous acid (HOCl) and peroxynitrite (ONOO^-) are two important highly reactive oxygen/nitrogen species, which commonly coexist in biosystems and play pivotal roles in many physiological and pathological processes. To investigate their function and correlations, it is urgently needed to construct chemical tools that can track the production of HOCl and ONOO^- in biological systems with distinct fluorescence signals. Here, we found that the coumarin fluorescence of coumarin-benzopyrylium (CB) hydrazides (spirocyclic form) is dim, and their fluorescence properties are controlled by their benzopyran moiety via an intramolecular photo-induced electron transfer (PET) process. Based on this mechanism, we report the development of a fluorescent probe CB2-H for the simultaneous detection of HOCl and ONOO^-. ONOO^- can selectively oxidize the hydrazide group of CB2-H to afford the parent dye CB2 (Abs_max/Em_max = 631/669 nm). In the case of HOCl, it undergoes an electrophilic attack on the benzopyran moiety of CB2-H to give a chlorinated product CB2-H-Cl, which inhibits the PET process within the probe and thus affords a turn-on fluorescence response at the coumarin channel (Abs_max/Em_max = 407/468 nm). Due to the marked differences in absorption/emission wavelengths between the HOCl and ONOO^- products, CB2-H enables the concurrent detection of HOCl and ONOO^- at two independent channels without spectral cross-interference. CB2-H has been applied for dual-channel fluorescence imaging of endogenously produced HOCl and ONOO^- in living cells and zebrafish under different stimulants. The present probe provides a useful tool for further exploring the distribution and correlation of HOCl and ONOO^- in more biosystems.

Regulating the activity of boronate moiety to construct fluorescent probes for the detection of ONOO-in vitro and in vivo

Abnormal intracellular peroxynitrite (ONOO^-) concentration is related to oxidative damage, which is correlated with many pathological consequences, such as local inflammation and other diseases. In this work, a series of resorufin benzyl ether-based fluorescent probes were designed using boronate as a recognizing moiety installed on a phenyl moiety for ONOO^- detection via a self-immolation mechanism. The location of the boronate as well as the substitution patterns on the phenyl moiety were investigated and the responding behaviors of the designed probes to ONOO^-, other reactive oxygen species, and biothiols were examined. It was found that all the immolative probes were inevitably dominated by ONOO^-. Compared with other probes, p-Borate possessed favorable selectivity and high sensitivity to ONOO^-. Moreover, p-Borate was successfully used to detect ONOO^- in cells and inflamed mice.

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

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

Rational construction of a fluorescent sensor for simultaneous detection and imaging of hypochlorous acid and peroxynitrite in living cells, tissues and inflammatory rat models

Modern medical research indicates that hypochlorous acid (HClO) and peroxynitrite (ONOO^-) are important biomarkers of oxidative stress. However, the up- or down-regulation of HClO or ONOO^- has been closely associated with the occurrence and development of various diseases. In order to investigate the intrinsic entanglement relationship between HClO and ONOO^- and their relationship with the occurrence and development of inflammation, it is very valuable to develop fluorescent sensors that are capable of displaying different signals towards HClO, ONOO^- and HClO/ONOO^-. In this work, we rationally design and construct a novel robust small organic molecule fluorescent sensor (RhNp-ClO-ONOO) towards ONOO^-, HClO and HClO/ONOO^- with green, red, and green-red three different fluorescent signal outputs, respectively. RhNp-ClO-ONOO has fast responsive time for HClO (∼60 s) and ONOO^- (∼20 s). Also it has markedly low detection limits for HClO (∼25.3 nM) and ONOO^- (12.4 nM) respectively. In addition, RhNp-ClO-ONOO could be further shown to detect endogenous HClO/ONOO^- in living cells, inflammatory tissues and rat model successfully. Therefore, this novel fluorescent sensor with double responsive moiety can offer a powerful tool for studying the role of HClO and ONOO^- and the occurrence and development of inflammatory diseases.

Lysosome-targetable brightly green fluorescence carbon dots for real-time monitoring in cell and highly efficient removal in environment of hypochlorite

Due to the lacks of lysosome localization group and reaction/interaction site for hypochlorite (ClO^-) on the surface of the carbon dots (C-dots), no C-dots-based lysosome-targeted fluorescence probes have, so far, been reported for real-time monitoring intracellular ClO^-. In this work, 1,3,6-trinitropyrene (TNP) was used as a precursor to prepare C-dots with maximum excitation and emission wavelengths at 485 and 532 nm, respectively, and quantum yield ∼ 27% by a hydrothermal approach at 196 °C for 6 h under a reductive atmosphere. The brightly green C-dots can sensitively and quickly respond to ClO^- in aqueous solution through surface chemical reaction, showing a linear relationship in the range of 0.5-120 μΜ ClO^- with 0.27 μΜ of limit of detection (LOD). Most significantly, the C-dots can localize at intracellular lysosome to image ClO^- in lysosomes. Also, the magnetic nanocomposites (C-dots@Fe₃O₄ MNCs) were fabricated via a simple electrostatic self-assembly between Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) and C-dots for highly efficient removal of ClO^- in real samples. Therefore, lysosome-targetable C-dots-based probes for real-time monitoring ClO^- were successfully constructed, opening up a promising door to investigate the biological functions and pathological roles of ClO^- at organelle levels.