Employing an ICT-FRET Integration Platform for the Real-Time Tracking of SO2 Metabolism in Cancer Cells and Tumor Models

Boosting responses of fluorescent imaging probes toward sulfur dioxide through engineering side chain length

Development of fluorescent probes with high sensitivity and specificity is always desirable, yet, challenging. Conventionally, improving the responses of probes relied on optimizing the reactivities of recognition sites, either by increasing the binding affinity or reaction rates. Herein, we found the sensitivity and response kinetics could be improved by changing the aggregation behaviors of probes. As a proof-of-concept, benzothiazole derivatives with different side chain lengths were prepared and the enhanced responses toward sulfur dioxide (SO2) were observed for the probe with longer side chain. We demonstrated that the long side chain facilitates formation of tightly aggregates, which possessed higher positive charges and susceptible recognition sites as compared with probes possessing short side chains, resulting in better sensitivity and faster responses. In addition, we also demonstrated the generality of such design protocols with probes displaying aggregation induced emission (AIE) properties. Thus, the proposed side chain engineering strategy provides new paradigm for probe design.

Insight into Cys and its derivatives metabolism in living system with 3D-printed portable smartphone platform via multifunctional fluorescent probe

Cysteine (Cys) is a crucial biological thiol that facilitates broad range of biological circumstances and health conditions. Especially the aberrant Cys level in human serum is an independent risk factor for cardiovascular diseases. What more, Cys metabolism (Cys to SO2) is typically connected with illnesses such as lung cancer, and are recognized as biomarker. Herein, an innovative multifunctional fluorescent probe was rudimentarily designed and utilized, not only for realizing real-time visualization of the metabolism of Cys to SO2 in tumors through two self-sufficient channels without spectral cross-interference, but also for sensitive, real-time, on-site, and quantitative visual recognition of Cys in human serum through 3D-printed smartphone sensing platform. In addition, the probe's unique response to Cys/HSO3- in distinct spectral behaviors, which have been characterized theoretically using UV-Vis, fluorescence, DFT calculations, and 1H NMR. More importantly, the methodology reported herein enables an available pathway for real-time/on-site and visual determination of Cys in human serum and is expected to extend the use of potential cardiovascular disease biomarker studies for initial monitoring and clinical diagnosis.

Revealing the elevated sulfite levels in acute kidney injury using a promising ratiometric fluorescent probe

The development of novel biomarkers for the early diagnosis of acute kidney injury (AKI) is critical for enabling timely protective interventions and predicting potential drug toxicity. Recent studies have highlighted metabolic abnormalities in sulfur-containing compounds during AKI progression. A ratiometric fluorescent probe, BP-BT-OH, has been designed for sulfite detection, featuring a covalent bond between benzothiazole and benzopyran-oxonium. The probe's ratio intensity is highly sensitive to sulfite concentration with an almost 80-fold increase. BP-BT-OH showed a rapid response of 50 s, an excellent detection limit of 0.21 μM, and a high selectivity and anti-interference capabilities. The probe can efficiently detects fluctuations in intracellular sulfite, both exogenous and endogenous. In cisplatin-treated cells, the ratio intensity between the two channels was significantly higher compared to untreated cells. More promisingly, BP-BT-OH was successfully used for imaging cisplatin-induced AKI in mice, revealing elevated sulfite levels in the kidneys. These findings validate sulfite as a potential biomarker for AKI. Further analysis of specific kidney proteins indicated that the increased sulfite concentration may be linked to downregulation of sulfur-containing compound metabolic enzymes. This approach offers a novel perspective on using molecular imaging tools for diagnosing early-stage diseases that lack obvious symptoms.

A Hemicyanine-based dual function fluorescent probe for rapid detecting sulfur dioxide and viscosity in food sample and living cells

Sulfur dioxide is a critical factor in evaluating food safety, as excessive intake can lead to various adverse reactions. Additionally, viscosity is a key indicator of food quality. However, to date, dual-response probes capable of detecting both viscosity and sulfur dioxide in food remain scarce. In this study, we present a novel fluorescent probe, BZID-OH, designed for the simultaneous detection of sulfur dioxide and viscosity in food. Moreover, BZID-OH is also effective for sulfur dioxide detection in living cells. These findings suggest that BZID-OH has the potential to serve as an effective dual-response fluorescent probe for monitoring both sulfur dioxide levels and viscosity in food, offering a valuable tool for food safety and quality assessment.

A Kidney-Targeted Rapid Photoacoustic Probe Activated by Sulfur Dioxide for 3D Visual Diagnosis of Iodinated Contrast-Induced Acute Kidney Injury

Sulfur dioxide (SO2) dysmetabolism is closely associated with various diseases such as acute kidney injury (AKI). Nevertheless, the relationship between SO2 levels and iodinated contrast-induced AKI remains largely unclear. Therefore, accurate imaging of SO2 level fluctuations in vivo is therefore critically important. However, no photoacoustic (PA) imaging method is currently available for the detection of SO2. To address this gap, we designed and synthesized a PA probe toward SO2, namely, Rho-QL, for the first time and performed in situ PA imaging of SO2 in deep tissues in vivo. A novel method was accordingly developed for the 3D visual diagnosis of AKI based on PA imaging of SO2 in kidney tissues with high spatial resolution. Rho-QL exhibited a PA response time of 5 s for SO2 and displayed remarkable turn-on absorption changes at 700 nm, making it a suitable probe for detecting SO2 levels via PA imaging. Moreover, Rho-QL exhibited an excellent targeting ability to the kidney, thereby facilitating in situ imaging of SO2 in the kidney. Notably, through real-time PA imaging, Rho-QL was successfully applied for 3D visualization of the detailed SO2 distribution with high spatial resolution and revealed a remarkable increase in the SO2 levels in the kidney during a contrast-induced AKI process. Based on the current findings, Rho-QL is expected to become a powerful tool for the study and diagnosis of AKI-related diseases.

Functional nucleic acid-based fluorescence imaging for tumor microenvironment monitoring: A review

BACKGROUND

The tumor microenvironment (TME) refers to the complex ecological system surrounding tumor cells, which is intimately associated with regulating tumor cell growth, invasive behavior, and metastatic capacity. Hence, in situ imaging of related bioactivity with resolution in the TME is critical for early cancer detection and accurate diagnosis. In recent years, fluorescence imaging technology has become a widely used tool in TME research due to its non-invasive nature, high spatiotemporal resolution, and capability for real-time monitoring. Among these advancements, signal probes designed based on functional nucleic acids (FNAs) provide a promising and innovative toolkit for targeted imaging analysis of the TME.

RESULTS

This review provides a comprehensive discussion on the construction of FNA-based biosensors and their advancements in TME monitoring. In this review, we initially provide a systematic summary of the current targeting strategies of FNA-based biosensors for visual monitoring of the TME, focusing on targeting cell surface and extracellular matrix components. Subsequently, we further explore the application of FNA-based biosensors in monitoring the TME. These biosensors have successfully achieved the monitoring of key parameters, bioactive molecules and other tumor markers in the tumor microenvironment due to their excellent molecular recognition ability and high sensitivity. Finally, we discuss some of the challenges currently faced in the field. In response to these challenges, we propose potential research directions and look forward to the future development prospects of this field.

SIGNIFICANCE

Unlike previous reviews of biosensors based on FNAs for imaging tumor markers in the TME, this work is the first to review how such biosensors can be anchored in the TME. With continued efforts and advancements, we believe an increasing number of FNA-based fluorescence imaging probes will be utilized for TME imaging. This progress will significantly enhance our understanding of disease pathogenesis and progression, thereby offering substantial potential in biosensing and imaging analysis.

Multifunctional Fluorescent Probes for Profiling Cys, Hcy, GSH, and SO₂: Illuminating Their Dynamics in Apoptosis and Ferroptosis

The ability to perform simultaneous fluorescence imaging of multiple targets is essential, providing crucial multi-parametric information necessary for understanding complex biological interactions and processes. In this study, TBC, a novel multi-signal fluorescent probe is presented, crafted for simultaneous differentiation and in situ real-time monitoring of homocysteine (Hcy), cysteine (Cys), sulfur dioxide (SO2), and glutathione (GSH), illuminating the dynamic metabolic status of endogenous reactive sulfur species. TBC achieves an ultrahigh signal-to-background ratio, enabling wash-free direct fluorescence imaging of the dynamics and distribution of these entities in living cells and zebrafish. Notably, TBC has revealed distinctive dynamic metabolic features of Hcy/Cys/SO2/GSH during apoptosis and ferroptosis. This innovative probe acts as a key tool for unraveling the conversion networks of multiple reactive sulfur species and assessing the impact of metabolic oscillations during programmed cell death and the progression of diverse diseases, effectively uncovering concurrent biochemical dynamics in various biological settings and cell death events.

A dual-cascade-activatable molecular probe with microenvironment-adapted performance for accurate differentiation of hepatopathy

Fluorescence imaging utilizing biomarker-activatable fluorescent probes has emerged as a powerful tool for the precise and early diagnosis of hepatopathy. However, the development of effective molecular probes remains challenging due to limitations, such as single-stimulus responsiveness and incompatible with microenvironment characteristic of hepatopathy. These limitations often result in a lower signal-to-noise ratio, false positives and ultimately reduced diagnostic accuracy. In this study, we developed a novel dual-lock-controlled fluorescent probe (Hdual) based on basic blue 3 dye. This probe was designed to be sequentially activated by two potential hepatopathy biomarkers, leucine aminopeptidase (LAP) and monoamine oxidase (MAO), through a cascade mechanism. Moreover, after addition LAP and MAO, Hdual exhibited a linear fluorescence change within a pH range of 6.2-6.8, ensuring high compatibility with the weakly acidic microenvironment characteristic of hepatopathy. The dual-cascade-activatable design, combined with the probe's microenvironment-adapted property, enabled Hdual to achieve a significantly higher target-to-noise ratio (T/N) of 2.40 in in vivo imaging for drug-induced liver injury, compared to "single-locked" probe (T/N < 0.79). Notably, Hdual demonstrated the ability to differentiate between cirrhotic and hepatitis B samples by analyzing patient blood samples through both fluorescent imaging and a distinct colorimetric change, observable either visually or via smartphone-based color analysis. These findings highlight Hdual's high specificity and accuracy in fluorescence imaging-based detection, underscoring its potential to improve the early diagnosis of hepatopathy.

Simultaneous Monitoring of Tyrosinase and ATP in Thick Brain Tissues Using a Single Two-Photon Fluorescent Probe

Cellular redox homeostasis and energy metabolism in the central nervous system are associated with neurodegenerative diseases. However, their real-time and concurrent monitoring in thick tissues remains challenging. Herein, a single dual-emission two-photon fluorescent probe (named DST) is designed for the simultaneous tracking of tyrosinase (TYR) and adenosine triphosphate (ATP), thereby enabling the real-time monitoring of both neurocellular redox homeostasis and energy metabolism in brain tissue. The developed DST probe exhibits excellent sensitivity and selectivity toward TYR and ATP, with distinctive responses in the blue and red fluorescence channels being observed without spectra crosstalk. Using this probe, the correlation and regulatory mechanism between TYR and ATP during oxidative stress are uncovered. Additionally, the two-photon nature of this probe allows alterations in the TYR and ATP levels to be monitored across different brain regions in an Alzheimer's disease (AD) mouse model. Notably, a significant decrease in ATP levels is revealed within the somatosensory cortex (S1BF) and caudate putamen brain regions of an AD mouse, alongside an increase in TYR levels within the S1BF and laterodorsal thalamic nucleus brain regions. These findings indicate the potential of applying the spatially resolved regulation of neurocellular redox homeostasis and energy metabolism to treat neurodegenerative diseases.

Sequential metabolic probes illuminate nuclear DNA for discrimination of cancerous and normal cells

Elucidating the timing and spatial distribution of DNA synthesis within cancer cells is vital for cancer diagnosis and targeted therapy. However, current probes for staining nucleic acids rely on electrostatic interactions and hydrogen bonds with the nucleic acid, resulting in "static" DNA staining and the inability to distinguish cell types. Here, we present a proof-of-concept study of sequential metabolic probes, for the first time allowing for cancer-cell-specific illumination of DNA. This breakthrough is achieved by the combination of a "dual-locked" nucleoside analog VdU-Lys, and a new tetrazine-based bioorthogonal probe. Specifically, 5-vinyl-2'-deoxyuridine (VdU) release is only conducted in programmatically triggered histone deacetylases (HDACs) and cathepsin L (CTSL) as "sequential keys", enabling the modification of vinyl groups into the nuclear DNA of cancerous cells rather than normal cells. Subsequently, tetrazine-based Et-PT-Tz could in situ light-up DNA containing VdUs with significant fluorescence illumination (120-fold enhancement) through rapid bioorthogonal reaction. We demonstrated the compatibility of our probe in cancer-specific sensing of DNA with a high signal-to-noise ratio ranging from in vitro multiple cell lines to whole-organism scale. This approach would serve as a benchmark for the development of cell-specific metabolic reporters for DNA labelling, to characterize DNA metabolism in various types of cell lines.

Bifunctional fluorescent probe revealing viscosity and SO2 in cell, zebrafish and NASH model

Clarifying the presence of viscosity and endogenous sulfur dioxide (SO2) in mitochondria is crucial for advancing the diagnosis and treatment of illnesses. Nevertheless, the advancement of fluorescent probes that concurrently satisfy the criteria of mitochondrial viscosity and endogenous recognition of SO2 remains significantly insufficient. In this work, we have engineered and synthesized two probes ID-OH and BID-OH, which exhibit a ratio-type response to SO2 and an off-on fluorescence response to viscosity. Due to the superior selectivity coupled with its outstanding wavelength and fluorescence quantum yield, BID-OH has been effectively utilized for the detection of exogenous SO2, endogenous SO2 and viscosity within living HepG2 cells. Additionally, BID-OH demonstrates the capability to offer comprehensive insights into the distribution of endogenous SO2 as it traverses through the transfer pathway in zebrafish. Notably, the remarkable capacity of BID-OH to differentiate between normal mice and nonalcoholic steatohepatitis (NASH) mice has been demonstrated, indicating its potential as an excellent diagnostic tool for detecting SO2 levels and viscosity under physiological conditions. It is anticipated that BID-OH will emerge as a valuable instrument for diagnosing mitochondrial irregularities, thereby contributing to the advancement of related medical research in this field.

A Bifunctional Fluorescence Probe for the Detection of Hypochlorous Acid and Viscosity in Living Cells and Zebrafish

As two significant indicators in the microenvironment, hypochlorous acid and viscosity play important roles in multitudinous physiological metabolic processes. However, it is challenging to determine the dynamic levels of hypochlorous acid and viscosity in living cells and organisms because of the absence of effective molecular tools that can simultaneously detect hypochlorous acid and viscosity in organisms. Herein, a molecular design strategy was presented to fabricate a single fluorescence probe that can simultaneously detect hypochlorous acid and viscosity by using two different emission channels. In JXR, TICT-based 4-(2-(5-(dimethylamino)thiophen-2-yl)vinyl)-1-methylpyridin-1-ium-iodide chromophore serves as energy acceptor in the FRET process and sensors for hypochlorous acid and viscosity. JXR showed a large Stokes shift, wide emission peak distance, high photostability, and low toxicity. JXR could detect hypochlorous acid and viscosity rapidly, sensitively, and selectively by emitting different fluorescence signals. Importantly, JXR was successfully applied to track the intracellular hypochlorous acid and viscosity in living cells. Meanwhile, the generation of endogenous hypochlorite in living cells can be observed by using JXR.

A bio-mimicking cobalt tetramenthol-substituted phthalocyanine-based electrochemical sensor for selective and sensitive detection of tert-butylhydroquinone

Healthy eating choices and adequate nutritional foods are the most important factors in extending a person's life expectancy. Synthetic antioxidants are frequently used in the food industry as preservatives despite their toxicity and hence have drawn much attention for their accurate monitoring. This study explores the newly designed cobalt tetramenthol substituted phthalocyanine (CoTMPc) for the electrocatalytic detection of an artificial food preservative, i.e., tertiary butylhydroquinone (TBHQ). A highly selective, cost-effective electrochemical probe is developed for the nanomolar detection of TBHQ. Its efficacy is evaluated and validated by different electrochemical techniques, namely cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry (CA) and the CA results demonstrated a good sensitivity of 1.3102 μA nM-1 cm-2 with a linear range of 20-200 nM and a detection limit (LOD) of 4.5 nM in comparison to other techniques. The developed sensor was successfully applied to real samples. The CoTMPc electrode exhibited superior sensitivity, excellent selectivity, repeatability, and reproducibility, with anti-interference ability, over a broad linear range towards TBHQ detection. The mechanism of electrochemical detection is supported by fluorescence resonance energy/electron transfer and provides insights into the design of high-performing electroactive molecules that induce specificity and selectivity.

Computational Chemistry-Assisted Design of a Dual-Function Fluorescent Probe for Viscosity Sensing in Liver Damage and SO2 Detection In Vitro

A new dual-channel and dual-functional fluorescent probe, DX3-AXI, is developed with the aid of computational chemistry, enabling viscosity and SO2 detection in separate fluorescence emission channels. The probe DX3-AXI exhibits significant fluorescence changes in the detection, demonstrating excellent interference resistance and a linear response. Through Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) calculations, along with hole-electron molecular analysis, energy level structure, and molecular local attachment energy analysis, the mechanism of the dual-channel response of the DX3-AXI probe is systematically revealed, demonstrating that the regulation of interactions between the rotatable bond and double bond drives the fluorescence changes. Furthermore, a portable sensing platform for on-site sulfite detection in water samples was developed by coupling the probe with a smartphone, enabling the rapid qualitative and semiquantitative detection of sulfite. Significantly, DX3-AXI has demonstrated successful application in detecting changes in the microenvironment of normal and cancer cells while also enabling the visualization of viscosity variations in the liver tissue of mice with liver injury. The DX3-AXI probe has shown significant potential for application in disease diagnostics, drug assessment, and environmental monitoring.

A FRET/TICT based multifunctional fluorescent probe for the monitoring of SO2 derivatives and viscosity in living cells and real samples

SO2 derivatives and viscosity are important intracellular indicators, which are closely associated with various physiological metabolisms in organisms. The unregulated contents of SO2 derivatives and viscosity in vivo commonly related to some disorders. In this work, probe JFT was developed relying on FRET and TICT mechanisms for the simultaneous detection of SO2 derivatives and viscosity. JFT can rapidly detect viscosity levels with continuously enhanced fluorescence signals at 582 nm basing on the increasing of viscosity. Moreover, JFT was also sensitive to the changes of SO2 derivatives level with a low detection limit (61.5 nM), rapid responding time (with 16 min), excellent selectivity and anti-interference capacity. JFT could detect bisulfite in real water, wine and food samples with high accuracy and recovery rate. Cell imaging indicated that JFT could monitor the endogenous SO2 derivatives and viscosity in mitochondria. Importantly, JFT could recognize the cancer cells basing on the cell imaging difference of JFT in AGS and GES-1 cells.

A ratiometric two-photon fluorescent probe for the quantification of nitroreductase in hypoxic neurons

We developed a novel ratiometric two-photon fluorescent probe for the selective and precise detection of nitroreductase (NTR) in neurons. Using this probe, we found that hypoxic stimulation could up-regulate endogenous NTR levels.

FRET-Based Nanoprobe with Adaptive Background Suppression for Reliable Detection of ONOO-/ClO- in Whole Blood: Facilitating Monitoring of Sepsis Progression and Hemolytic Disorders

Abnormal fluctuations in blood biomarker levels serve as critical indicators of the disease. However, detecting endogenous substances in whole blood using fluorescent probes is challenging due to its complex composition. This challenge primarily arises from two factors: the high autofluorescence of whole blood and the intrinsic fluorescence of the probe, both contributing to significant background fluorescence in the detection system. To overcome these obstacles, we introduced a donor-acceptor "one-to-many" FRET-based sensing strategy integrated with blood autofluorescence suppression to design a multifunctional fluorescent nanoprobe. The donor effectively suppresses blood autofluorescence through the inner filter effect and efficiently quenches donor fluorescence by adjusting the acceptor-to-donor ratio, achieving a "zero" background in whole blood detection. Leveraging this excellent background fluorescence quenching effect, we successfully detected endogenous ONOO- and ClO- levels in whole blood samples from mice with sepsis or hemolytic diseases. Furthermore, we monitored the changes in the ONOO- and ClO- levels throughout the disease course, revealing a positive correlation between the ONOO- and ClO- concentrations and disease severity. This innovative sensing strategy for achieving a "zero" background in whole blood detection provides valuable insights for designing fluorescent probes to directly detect endogenous substances in whole blood.

H2O2 accumulation promoting internalization of ox-LDL in early atherosclerosis revealed via a synergistic dual-functional NIR fluorescence probe

The equilibrium of lipid metabolism is critical to sustaining human health. Metabolic disorders often result in a variety of cardiovascular illnesses, especially atherosclerosis. Atherosclerosis is characterized by complicated complications and high mortality. Cholesterol deposition and oxidative stress have been considered as critical mechanisms in the occurrence and progression of atherosclerosis, however, the relationship between oxidative stress and lipid accumulation remains a puzzle in foam cells during the early stages of atherosclerosis development. Hydrogen peroxide (H2O2) has been reported to participate in various signaling pathways associated with atherosclerotic diseases. Additionally, the excessive intake of oxidized low-density lipoprotein (ox-LDL) leads to cholesterol accumulation and viscosity increasing in foam cells. Therefore, it is critical to investigate the internalization and modification of ox-LDL by H2O2 in foam cells. Herein, we developed a near-infrared, synergistic dual-functional fluorescent probe capable of detecting H2O2 and viscosity simultaneously with high selectivity and sensitivity. Through in situ imaging of H2O2 and viscosity in vivo, we discovered that H2O2 accumulation leads to an increased intake of ox-LDL in the early stages of plaque formation. This finding establishes a new experimental approach and theoretical foundation for the diagnosis and treatment of atherosclerosis, as well as the development of new medications.

A coumarin-naphthalimide-based ratiometric fluorescent probe for nitroxyl (HNO) based on an ICT-FRET mechanism

Nitroxyl (HNO) is an important reactive nitrogen that is associated with various states in physiology and pathology and plays a unique function in living systems. So, it is important to exploit fluorescent probes with high sensitivity and selectivity for sensing HNO. In this paper, a novel ratiometric fluorescent probe for HNO was developed utilizing intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) mechanisms. The probe selected coumarin as energy donor, naphthalimide as energy receptor and 2-(diphenylphosphino)benzoate as the sensing site for detecting HNO. When HNO was not present, the 2-(diphenylphosphino)benzoate unit of the probe restricted electron transfer and the ICT process could not occur, leading to the inhibition of FRET process as well. Thus, in the absence of HNO the probe displayed the intrinsic blue fluorescence of coumarin. When HNO was added, the HNO reacted with the 2-(diphenylphosphino)benzoate unit of the probe to yield a hydroxyl group which resulting in the opening of ICT process and the occurring of FRET process. Thus, after providing HNO the probe displayed yellow fluorescence. In addition, the probe showed good linearity in the ratio of fluorescence intensity at 545 nm and 472 nm (I545 nm/I472 nm) with a concentration of HNO (0.1-20 μM). The probe processed a detection limit of 0.014 μM and a response time of 4 min. The probe also specifically identified HNO over a wide pH scope (pH = 4.00-10.00), including physiological conditions. Cellular experiments had shown that this fluorescent probe was virtually non-cytotoxic and could be applied for ratiometric sensing of HNO in A549 cells.

A unique near-infrared fluorescent probe based on dual-DNP binding sites for rapid monitoring of hydrogen sulfide in food samples and living cells

A new NIR fluorescent probe (DCIQ-2DNP), which combined the thiolysis of dinitrophenyl (DNP) ether and DNP-marked electron-deficient quaternary carbon, was reported for the first time for detection of H2S. The DCIQ-2DNP probe showed an NIR emission signal (740 nm), a large Stokes shift (128 nm), and rapid monitoring of hydrogen sulfide (within 60 s) in food samples and living cells.

A fluorescent probe for detecting bisulfite/sulfite in lipid droplets and tracking the dynamics of lipid droplets

Intracellular lipid droplets (LDs) are important organelles regulating intracellular redox processes. Endogenous bisulfite/sulfite (HSO3-/SO32-) is one of the metabolites of thiol metabolism. The variation in HSO3-/SO32- content around LDs is closely related to cellular homeostasis. However, there is currently no effective method to visualize and quantify the dynamic changes in HSO3-/SO32- content around LDs. In this work, a fluorescent probe MC-BEN utilizing a triphenylamine basic framework was developed to selectively recognize HSO3-/SO32- via a nucleophilic addition reaction. The probe exhibits excellent anti-interference capability, short response time, outstanding photostability, and a low fluorescence detection limit (6.1 μM) for HSO3-/SO32- recognition. More interesting, there is a trend of accelerated contact between LDs and lysosomes after MC-BEN targeting LDs and reacting with endogenous/exogenous HSO3-/SO32-, which may provide new ideas for the study of intracellular lysosomal lipophagy.

Recent advances in fluorescent probes for ATP imaging

Adenosine-5'-triphosphate (ATP) is a critical biological molecule that functions as the primary energy currency within cells. ATP synthesis occurs in the mitochondria, and variations in its concentration can significantly influence mitochondrial and cellular performance. Prior studies have established a link between ATP levels and a variety of diseases, such as cancer, neurodegenerative conditions, ischemia, and hypoglycemia. Consequently, researchers have developed many fluorescent probes for ATP detection, recognizing the importance of monitoring intracellular ATP levels to understand cellular processes. These probes have been effectively utilized for visualizing ATP in living cells and biological samples. In this comprehensive review, we categorize fluorescent sensors developed in the last five years for ATP detection. We base our classification on fluorophores, structure, multi-response channels, and application. We also evaluate the challenges and potential for advancing new generations of fluorescence imaging probes for monitoring ATP in living cells. We hope this summary motivates researchers to design innovative and effective probes tailored to ATP sensing. We foresee imminent progress in the development of highly sophisticated ATP probes.

An Acid-Activatable Fluorescent Probe for Sulfur Dioxide in Traditional Chinese Medicines and Living Cells

Excessive sulfur dioxide (SO₂) disturbs physiology of lysosomes causing diseases and threatening human health. A fluorescent probe has been regarded as one of the most attractive approaches, which is compatible with living cells and possesses high sensitivity. However, most of fluorescent probes' reaction sites are activated before they reach the destination. In this work, an acid-activatable fluorescent probe PT1 was synthesized, characterized, and used for SO2 detection. The introduction of oxazolines in PT1 enables the intelligent response of probe to release the activation stie for SO2 derivatives through Michael addition upon exposure to acid. In vitro studies showed a remarkable selectivity of PT1 to SO₂ derivatives than other biothiols with a limit of detection as low as 62 nM. By using this acidic pH-controlled fluorescence responsiveness to SO₂, precise spatiotemporal identification of lysosomal SO2 fluctuations has been successfully performed. Furthermore, probe PT1 can be applied for monitoring SO₂ derivatives in traditional Chinese medicines.

A remarkable membrane-permeable fluorescent probe for real-time imaging of mitochondrial SO2 with high fidelity during ferroptosis

Mitochondrial sulfur dioxide (SO2) plays a double-edged role in cells, and the real-time and in situ tracing of its dynamic behaviors to elucidate its complicated functions in detail is of great significance. Here, we developed a simple mitochondria-targeted fluorescent probe ZW for tracing SO2 with good membrane permeability. In probe ZW, the 1-phenylpyrrolidine-decorated benzopyrylium unit is employed as the selective response site for SO2. Besides, it also acts as the main fluorophore for signal conversion. The spectral results displayed that ZW could emit near-infrared (NIR) fluorescence (670 nm) and has a highly sensitive and selective response to SO2 (LOD = 0.19 μM). For biological imaging, compared with the control probe ZE, concentration- and time-dependent results verified that probe ZW has remarkable cell delivery with low concentration (200 nM) and fast response time (3 min). Furthermore, the NIR emission of ZW rendered high-fidelity imaging in living cells. Owing to its positive charge, ZW showed favorable mitochondria-targeting properties by colocalization experiments. Probe ZW could detect SO2 in real-time and in situ with high photostability in cells. Significantly, it has the ability to monitor the changes of endogenous SO2 during ferroptosis.

Near-infrared and multifunctional fluorescent probe enabled by cyanopyridine cyanine dye for bisulfite recognition and biological imaging

SO2 derivatives, sulfite/bisulfite, are widely employed in both the food processing and drug synthesis industries. Despite their widespread application, excessive levels of sulfite/bisulfite can negatively impact human health. Most probes for detecting sulfite/bisulfite are restricted by their fluorescence within the visible spectrum range and poor solubility in aqueous solution, which limit their use in food testing and biological imaging. Herein, a near-infrared probe comprising of the cyanopyridine cyanine skeleton, 4-((Z)-2-((E)-2-chloro-3-(2-cyano-2-(1-methylpyridine-4(1H)-ylidene)ethylidene)cyclohex-1-en-1-yl)-1-cyanovinyl)-1-methylpyridin-1-ium (abbreviated as CCP), was developed. This probe enables precise quantification of bisulfite (HSO3-) in almost pure buffered solutions, showing a near-infrared fluorescence emission at 784 nm with an impressively low detection limit of 0.32 μM. The probe stands out for its exceptional selectivity, minimal susceptibility to interference, and strong adaptability. The probe CCP utilizes the CC bond to trigger a near-infrared fluorescence quenching reaction with HSO3- via nucleophilic addition, which effectively disrupts the large delocalization within the molecule for accurate HSO3- identification. Moreover, the probe has been successfully applied in detecting HSO3- in various food products and living cells, simplifying the measurement of HSO3- content in water samples. This advancement not only enhances the analytical capabilities but also contributes to ensuring food safety and environmental protection. ENVIRONMENTAL IMPLICATION: SO2 derivatives including sulfite/bisulfite, serving dual roles as preservatives and antioxidants, have widespread application across various sectors including food preservation, water sanitation, and the pharmaceutical industry. Despite their widespread application, excessive levels of sulfite/bisulfite can affect human health. Developing methods for precisely and sensitively detecting sulfite/bisulfite in food products and biological samples is important for ensuring food safety and environmental protection. Here, a sensitive near-infrared and multifunctional fluorescent probe in a 99.9 % buffered solution, along with water gel encapsulation, has been successfully applied for the detection of bisulfite in food, authentic water samples, and biological cells.

A ratiometric fluorescent probe with dual-targeting capability for heat shock imaging

HSO3- is an important reactive sulfur species that maintains the normal physiological activities of living organisms and participates in a variety of redox homeostatic processes. It has been found that changes in HSO3- levels is closely related to the heat stroke phenomenon of the organism. Heat stroke causes damage to normal cells, which in turn causes damage to the body and even death. It is crucial to accurately monitor and track the physiological behavior of HSO3- during heat stroke. Herein, a ratiometric multifunctional fluorescent probe DRM-SO2 with dual-targeting ability to rapidly and precisely recognize HSO3- being constructed based on the FRET mechanism. DRM-SO2 has extra Large Stokes shift (216 nm), very high sensitivity (DL = 12.2 nM), fast response time and good specificity. When DRM-SO2 undergoes Michael addition with HSO3-, the fluorescence emission peak was blue-shifted from 616 nm to 472 nm, and a clear ratiometric signal appeared. The interaction between lysosomes and mitochondria in maintaining cellular homeostasis was investigated by the dual-targeting ability of the probe using HSO3- as a mediator. DRM-SO2 achieved successful targeting and real-time monitoring of exogenous and endogenous HSO3- in the cells. More importantly, imaging experiments in heat stroke mice revealed high HSO3- expression in intestinal tissues. This provides new ideas and research tools for early prevention of heat stroke-induced diseases such as intestinal injuries. In addition, the semi-quantitative monitoring experiments for paper-based visualization of HSO3- make the probe promising for the design of portable detectors.

Developing a fluorescent probe containing benzofuranone moiety for imaging sulphite in living hypoxia pulmonary cells

In this work, a benzofuranone-derived fluorescent probe BFSF was developed for imaging the sulphite level in living hypoxia pulmonary cells. Under the excitation of 510 nm, BFSF showed a strong fluorescence response at 570 nm when reacted with sulphite. In the solution system, the constructed hypercapnia and serious hypercapnia conditions did not affect the fluorescence response. In comparison with the recently reported probes, BFSF suggested the advantages including rapid response, steady signal reporting, high specificity and low cytotoxicity upon living lung cells. Under a normal incubation atmosphere, BFSF realized the imaging of both exogenous and endogenous sulphite in living pulmonary cells. In particular, BFSF achieved imaging the decrease of the sulphite level under severe hypoxia as well as the recovery of the sulphite level with urgent oxygen supplement. With the imaging capability for the sulphite level in living pulmonary cells under hypoxia conditions, BFSF together with the information herein was meaningful for investigating the anaesthesia-related biological indexes.

Dual-Site Chemosensor for Visualizing •OH-GSH Redox and Tracking Ferroptosis-Inducing Pathways In Vivo

Oxidative stress, characterized by an imbalance between oxidative and antioxidant processes, results in excessive accumulation of intracellular reactive oxygen species. Among these responses, the regulation of intracellular hydroxyl radicals (•OH) and glutathione (GSH) is vital for physiological processes. Real-time in situ monitoring these two opposing bioactive species and their redox interactions is essential for understanding physiological balance and imbalance. In this study, we developed a dual-site fluorescence chemosensor OG-3, which can independently image both exogenous and endogenous •OH and GSH in separate channels both within cells and in vivo, eliminating issues of spatiotemporal inhomogeneous distribution and cross-interference. With its imaging capabilities of monitoring •OH-GSH redox, OG-3 elucidated two different pathways for ferroptosis induction: (i) inhibition of system xc- to block cystine uptake (extrinsic pathway) and (ii) GPX4 inactivation, leading to the loss of antioxidant defense (intrinsic pathway). Moreover, we assessed the antiferroptotic function and effects of ferroptosis inhibitors by monitoring •OH and GSH fluctuations during ferroptosis. This method provides a reliable platform for identifying potential ferroptosis inhibitors, contributing to our understanding of relevant metabolic and physiological mechanisms. It shows potential for elucidating the regulation of ferroptosis mechanisms and investigating further strategies for therapeutic applications.

Covalent Interactions of Anthocyanins with Proteins: Activity-Based Protein Profiling of Cyanidin-3-O-glucoside

Anthocyanins are common natural pigments with a variety of physiological activities. Traditional perspectives attribute their molecular mechanism to noncovalent interactions influencing signaling pathways. However, this ignores the nature of its benzopyrylium skeleton, which readily reacts with the electron-rich groups of proteins. Here, we modified cyanidin-3-O-glucoside (C3G) via activity-based protein profiling technology by our previous synthesis route and prepared the covalent binding probe (C3G-Probe) and the noncovalent photoaffinity probe (C3G-Diazirine). The properties of C3G's covalent binding to proteins were also discovered by comparing the labeling of the two probes to the whole HepG2 cell proteome. We further explored its target proteins and enriched pathways in HepG2 and HeLa cells. Western blot analysis further confirmed the covalent binding of C3G to four target proteins: insulin-degrading enzyme, metal cation symporter ZIP14, spermatid perinuclear RNA-binding protein, and Cystatin-B. Pathway analysis showed that covalent targets of C3G were concentrated in metabolic pathways and several ribonucleoprotein complexes that were also coenriched. The results of this study provide new insights into the interaction of the naturally active molecule C3G with proteins.

A FRET-based multifunctional fluorescence probe for the simultaneous detection of sulfite and viscosity in living cells

Viscosity and sulfur dioxide derivatives were significant indicators for the assessment of health threat and even cancers, therefore, on-site and real time detection of viscosity and sulfur dioxide derivatives has obtained considerable attentions. An FRET-based fluorescence probe JZX was designed and synthesized based on a novel energy donor of N,N-diethyl-4-(1H-phenanthro[9,10-d]imidazol-2-yl)benzamide fluorophore. JZX exhibited a large Stokes shift (230 nm), high energy transfer efficiency, wide emission channel gap (135 nm) and excellent stability and biocompatibility. JZX detected sulfur dioxide with low detection limit (55 nM), fast responding (16 min), high selectivity and sensitivity. Additionally, JZX tend to target endoplasmic reticulum of which normal metabolism will be disturbed by the abnormal levels of viscosity and sulfur dioxide derivatives. Prominently, JZX could concurrently detect viscosity and sulfur dioxide derivatives depending on different fluorescence signals in living cells for the screening of cancer cells. Hence, probe JZX will be a promising candidate for the detection of viscosity and sulfur dioxide derivatives, and even for the diagnosis of liver cancers.

A mitochondria-specific NIR fluorescence probe for dual-detection of sulfur dioxide and viscosity in living cells and mice

The level of sulfur dioxide (SO2) and viscosity in mitochondria play vital roles in various physiological and pathological processes. Abnormalities in mitochondrial SO2 and viscosity are closely associated with numerous biological diseases. It is of great significance to develop novel fluorescence probes for simultaneous detection of SO2 and viscosity within mitochondria. Herein, we have developed a water-soluble, mitochondrial-targeted and near-infrared fluorescent probe, CMBT, for the simultaneous detection of SO2 and viscosity. The probe CMBT incorporates benzothiazolium salt as a mitochondrial targeting moiety and 7-diethylaminocoumarin as a rotor for viscosity detection, respectively. Based on the prompt reaction between nucleophilic HSO3-/SO32- and the backbone of the benzothiazolium salt derivative, probe CMBT displayed high sensitivity and selectivity toward SO2 with a limit of detection as low as 0.17 μM. As viscosity increased, the twisted intramolecular charge transfer (TICT) process was restricted, resulting in fluorescence emission enhancement at 690 nm. Moreover, probe CMBT demonstrated exceptional mitochondrial targeting ability and was successfully employed to image variations of SO2 and viscosity in living cells and mice. The work highlights the great potential of the probe as a convenient tool for revealing the relationship between SO2 and viscosity in biological systems.

A benzothiophene-based fluorescent probe with dual-functional to polarity and cyanide for practical applications in living cells and real water samples

Polarity is a significant intracellular environmental parameter associated with cancer, while cyanide (CN-) is known to be highly toxic to humans. In this work, we designed a dual-functional fluorescent probe (TPABT) for simultaneous detection of polarity and CN-. As a polarity sensor, the probe exhibits NIR emission at 766 nm in 1,4-dioxane (non-polar solvent), whose emission intensity is 71-fold stronger than that in water (polar solvent). Meanwhile, the fluorescence intensity and quantum yield are linearly related to solvent polarity, confirming the polarity response ability of TPABT. For cell polarity detection, low cytotoxicity and polarity sensitivity of probe enable the applications for differentiating cancer cells (HeLa, 4TI) from normal cells (HUV, 3 T3) and monitoring the polarity changes of 4TI cells. As a CN- sensor, TPABT displays a turn-on fluorescence at 640 nm upon the addition of CN-, with advantages of anti-interference, response in aqueous media and low detection limit (22 nM). Additionally, we further explored the practical applications of TPABT for CN- determination in three types of real water samples (drinking water, tap water and lake water) and living cells. Notably, TPABT responses to polarity and CN- in two independent fluorescence channels of 766 and 640 nm, respectively, ensuring the dual functions for polarity and CN- sensing. Consequently, this multi-responsive fluorescent probe TPABT is promising to diagnose polarity-related diseases and detect CN- in real environments.

Lysosomal-targeted fluorescent probe based pH regulating reactivity for tracking cysteine dynamics under oxidative stress

The ability to detect and visualize cellular events and associated biological analytes is essential for the understanding of their physiological and pathological functions. Cysteine (Cys) plays a crucial role in biological systems and lysosomal homeostasis. This puts forward higher requirements on the performance of the probe. Herein, we rationally designed a coumarin-based probe for the reversible, specific, sensitive, and rapid detection of Cys based on pH regulating reactivity. The obtained probe (ECMA) introduces a morpholine moiety to target lysosomes, and α,β-unsaturated-ketone with an electron-withdrawing CN group served as a reversible reaction site for Cys. Importantly, ECMA was successfully applied to the real-time monitoring of Cys dynamics in living cells. Furthermore, cell imaging clearly revealed that exogenous Cys could induce the up-regulation of lysosomal ROS, which provided a powerful tool for investigating the relationship between oxidative stress and lysosomal Cys.

A multipurpose mitochondrial NIR probe for imaging ferroptosis and mitophagy

This paper explores the use of a di-cationic fluorophore for visualizing mitochondria in live cells independent of membrane potential. Through the synthesized di-cationic fluorophore, we investigate the monitoring of viscosity, ferroptosis, stress-induced mitophagy, and lysosomal uptake of damaged mitochondria. The designed fluorophore is based on DQAsomes, cationic vesicles responsible for transporting drugs and DNA to mitochondria. The symmetric fluorophores possess two charge centres separated by an alkyl chain and are distinguished by a pyridinium group for mitochondrial selectivity, the C-12 alkyl substitution for membrane affinity, and an electron donor-π-acceptor fluorescent scaffold for intramolecular charge transfer. The synthesized fluorophores, PP and NP, emit wavelengths exceeding 600 nm, with a significant Stokes shift (130-211 nm), and NP demonstrates near-infrared emission (∼690 nm). Our study underscores the potential of these fluorophores for live-cell imaging, examining physiological responses such as viscosity and ferroptosis, and highlights their utility in investigating mitophagy damage and lysosomal uptake.

Beyond Explored Functionals: A Computational Journey of Two-Photon Absorption

We present a thorough investigation into the efficacy of 19 density functional theory (DFT) functionals, relative to RI-CC2 results, for computing two-photon absorption (2PA) cross sections (σ2PA) and key dipole moments (|μ00|, |μ11|, |Δμ|, |μ01|) for a series of coumarin dyes in the gas-phase. The functionals include different categories, including local density approximation (LDA), generalized gradient approximation (GGA), hybrid-GGA (H-GGA), range-separated hybrid-GGA (RSH-GGA), meta-GGA (M-GGA), and hybrid M-GGA (HM-GGA), with 14 of them being subjected to analysis for the first time with respect to predicting σ2PA values. Analysis reveals that functionals integrating both short-range (SR) and long-range (LR) corrections, particularly those within the RSH-GGA and HM-GGA classes, outperform the others. Furthermore, the range-separation approach was found more impactful compared to the varying percentages of Hartree-Fock exchange (HF Ex) within different functionals. The functionals traditionally recommended for 2PA do not appear among the top 9 in our study, which is particularly interesting, as these top-performing functionals have not been previously investigated in this context. This list is dominated by M11, QTP variants, ωB97X, ωB97X-V, and M06-2X, surpassing the performance of other functionals, including the commonly used CAM-B3LYP.

Dual-Functional AIE Fluorescent Probe for Visualization of Lipid Droplets and Photodynamic Therapy of Cancer

Abnormal lipid droplets (LDs) are known to be intimately bound with the occurrence and development of cancer, allowing LDs to be critical biomarkers for cancers. Aggregation-induced emission luminogens (AIEgens), with efficient reactive oxygen species (ROS) production performance, are prime photosensitizers (PSs) for photodynamic therapy (PDT) with imaging. Therefore, the development of dual-functional fluorescent probes with aggregation-induced emission (AIE) characteristics that enable both simultaneous LD monitoring and imaging-guided PDT is essential for concurrent cancer diagnosis and treatment. Herein, we reported the development of a novel LD-targeting fluorescent probe (TDTI) with AIE performance, which was expected to realize the integration of cancer diagnosis through LD visualization and cancer treatment via PDT. We demonstrated that TDTI, with typical AIE characteristics and excellent photostability, could target LDs with high specificity, which enables the dynamic tracking of LDs in living cells, specific imaging of LDs in zebrafish, and the differentiation of cancer cells from normal cells for cancer diagnosis. Meanwhile, TDTI exhibited fast ROS generation ability (achieving equilibrium within 60 s) under white light irradiation (10 mW/cm2). The cell apoptosis assay revealed that TDTI effectively induced growth inhibition and apoptosis of HeLa cells. Further, the results of PDT in vivo indicated that TDTI had a good antitumor effect on the tumor-bearing mice model. Collectively, these results highlight the potential utility of the dual-functional fluorescent probe TDTI in the integrated diagnosis and treatment of cancer.

Microenvironment-differential Imaging of Demethylated Metabolites of Methionine for Identifying Ferroptosis Regional Preferences with Path-independent Equifinal Fluorescence Probes

We realized the microenvironment-differential Imaging of demethylated metabolites of methionine and the regional regulation of ferroptosis.

Dual-Mode Nanoprobes Based on Lanthanide Doped Fluoride Nanoparticles Functionalized by Aryl Diazonium Salts for Fluorescence and SERS Bioimaging

The design of dual-mode fluorescence and Raman tags stimulates a growing interest in biomedical imaging and sensing applications as they offer the possibility to synergistically combine the versatility and velocity of fluorescence imaging with the specificity of Raman spectroscopy. Although lanthanide-doped fluoride nanoparticles (NPs) are among the most studied fluorescent nanoprobes, their use for the development of bimodal fluorescent-Raman probes has never been reported yet, to the best of the authors knowledge, probably due to the difficulty to functionalize them with Raman reporter groups. This gap is filled herein by proposing a fast and straightforward approach based on aryl diazonium salt chemistry to functionalize Eu3+ or Tb3+ doped CaF2 and LaF3 NPs by Raman scatters. The resulting surface-enhanced Raman spectroscopy (SERS)-encoded lanthanide-doped fluoride NPs retain their fluorescence labeling capacity and display efficient SERS activity for cell bioimaging. The potential of this new generation of bimodal nanoprobes is assessed through cell viability assays and intracellular fluorescence and Raman imaging, opening up unprecedented opportunities for biomedical applications.

Long-Chain Fluorescent Probe for Straightforward and Nondestructive Staining Mitochondria in Fixed Cells and Tissues

Normally, small-molecule fluorescent probes dependent on the mitochondrial membrane potential (MMP) are invalid for fixed cells and tissues, which limits their clinical applications when the fixation of pathological specimens is imperative. Given that mitochondrial morphology is closely associated with disease, we developed a long-chain mitochondrial probe for fixed cells and tissues, DMPQ-12, by installing a C12-alkyl chain into the quinoline moiety. In fixed cells stained with DMPQ-12, filament mitochondria and folded cristae were observed with confocal and structural illumination microscopy, respectively. In titration test with three major phospholipids, DMPQ-12 exhibited a stronger binding force to mitochondria-exclusive cardiolipin, revealing its targeting mechanism. Moreover, mitochondrial morphological changes in the three lesion models were clearly visualized in fixed cells. Finally, by DMPQ-12, three kinds of mitochondria with different morphologies were observed in situ in fixed muscle tissues. This work breaks the conventional concept that organic fluorescent probes only stain mitochondria with normal membrane potentials and opens new avenues for comprehensive mitochondrial investigations in research and clinical settings.

Simultaneous detection of SO2 and viscosity in drug-induced inflammation in live cells and zebrafish

The viscosity within cells is a crucial microenvironmental factor, and sulfur dioxide (SO2 ) has essential functions in regulating cellular apoptosis and inflammation. Some evidence has been confirmed that changes in viscosity and overexposure of SO2 within the cell may cause detrimental effects including, but not limited to, respiratory and cardiovascular illnesses, inflammation, fatty liver, and various types of cancer. Therefore, precise monitoring of SO2 and viscosity in biological entities holds immense practical importance. Therefore, in this research, we developed a versatile fluorescent TCF-Cou that enables the dual detection of SO2 and viscosity in the living system. Probe TCF-Cou possessed a response to viscosity and SO2 through red and green emissions. The alteration of SO2 and viscosity levels in live cells and zebrafish were also monitored using probe TCF-Cou. We hope that this fluorescent probe could be a potential tool for revealing the related pathological and physiological processes through monitoring the changes in SO2 and viscosity.

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

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

Tetrazine-Based Ratiometric Nitric Oxide Sensor Identifies Endogenous Nitric Oxide in Atherosclerosis Plaques by Riding Macrophages as a Smart Vehicle

Atherosclerosis (AS) is the formation of plaques in blood vessels, which leads to serious cardiovascular diseases. Current research has disclosed that the formation of AS plaques is highly related to the foaming of macrophages. However, there is a lack of detailed molecular biological mechanisms. We proposed a "live sensor" by grafting a tetrazine-based ratiometric NO probe within macrophages through metabolic and bio-orthogonal labeling. This "live sensor" was proved to target the AS plaques with a diameter of only tens of micrometers specifically and visualized endogenous NO at two lesion stages in the AS mouse model. The ratiometric signals from the probe confirmed the participation of NO during AS and indicated that the generation of endogenous NO increased significantly as the lesion progressed. Our proposal of this "live sensor" provided a native and smart strategy to target and deliver small molecular probes to the AS plaques at the in vivo level, which can be used as universal platforms for the detection of reactive molecules or microenvironmental factors in AS.

Mitochondrial nucleoid condensates drive peripheral fission through high membrane curvature

Mitochondria are dynamic organelles that undergo fusion and fission events, in which the mitochondrial membrane and DNA (mtDNA) play critical roles. The spatiotemporal organization of mtDNA reflects and impacts mitochondrial dynamics. Herein, to study the detailed dynamics of mitochondrial membrane and mtDNA, we rationally develop a dual-color fluorescent probe, mtGLP, that could be used for simultaneously monitoring mitochondrial membrane and mtDNA dynamics via separate color outputs. By combining mtGLP with structured illumination microscopy to monitor mitochondrial dynamics, we discover the formation of nucleoid condensates in damaged mitochondria. We further reveal that nucleoid condensates promoted the peripheral fission of damaged mitochondria via asymmetric segregation. Through simulations, we find that the peripheral fission events occurred when the nucleoid condensates interacted with the highly curved membrane regions at the two ends of the mitochondria. Overall, we show that mitochondrial nucleoid condensates utilize peripheral fission to maintain mitochondrial homeostasis.

A highly selective ratio-metric fluorescent sensor for visualizing nitroreductase in hypoxic cells

Herein, we have developed a novel single-molecular probe (NORP) for selective and accurate determination of NTR in living cells. It was discovered that up-regulation of endogenous NTR occurred in response to hypoxic stimulation, and there was a dependence between the NTR levels and the degree of hypoxia.

Bioimaging of a chromenoquinoline-based ratiometric fluorescent probe for detecting ClO. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023;303:123256. [PMID: 37579661 DOI: 10.1016/j.saa.2023.123256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Hypochlorous acid (HClO) is a reactive oxygen species and a relatively strong antibacterial substance in the immune defense system. The normal concentration of HClO in the human body is approximately 200 μM, and its high concentration can cause tissue damage and some diseases. Herein, a chromenoquinoline-based ratiometric fluorescent probe was developed to detect and quantify HClO. The developed Probe 1 exhibited the advantages of large Stokes shift (137 nm), high synthetic yield (84.7 %), simple synthesis method, short response time (<4 min), low detection limit (5.1 nM), and low toxicity. The probe was successfully validated in live cells and zebrafish.

TPE-based fluorescent probe for dual channel imaging of pH/viscosity and selective visualization of cancer cells and tissues

The development of efficient fluorescence-based detection tools with high contrast and accuracy in cancer diagnosis has recently attracted extensive attention. Changes in the microenvironments between cancer and normal cells provide new biomarkers for precise and comprehensive cancer diagnosis. Herein, a dual-organelle-targeted probe with multiple-parameter response is developed to realize cancer detection. We designed a tetraphenylethylene (TPE)-based fluorescent probe TPE-PH-KD connected with quinolinium group for simultaneous detection of viscosity and pH. Due to the restriction on the double bond's rotation, the probe respond to viscosity changes in the green channel with extreme sensitivity. Interestingly, the probe exhibited strong emission of red channel in acidic environment, and the rearrangement of ortho-OH group occurred in the basic form with weak fluorescence when pH increased. Additionally, cell colocalization studies revealed that the probe was located in the mitochondria and lysosome of cancer cells. Following treatment with carbonyl cyanide m-chloro phenylhydrazone (CCCP), chloroquine, and nystatin, the pH or viscosity changes in the dual channels are also monitored in real-time. Furthermore, the probe TPE-PH-KD could effectively discriminate cancer from normal cells and organs with high-contrast fluorescence imaging, which sparked more research on an efficient tool for highly selectively visualizing tumors at the organ level.

A novel multi-functional fluorescent probe for dual-channel detection of SO2 and Hg2+ and dynamic visualization of SO2 fluctuations in vivo upon mercury exposure

Although there are many drugs used for the treatment of mercury poisoning, it is remains confused that pathological symptoms associated with Hg2+-induced oxidative stress. It is reported that SO2 can be generated as the anti-oxidant, and plays an important role in maintaining redox balance in cells. There has not yet been a study to precisely track the changes in SO2 during mercury ion poisoning. We developed a novel dual-response fluorescence probe (CY-SPH) for respective or successive determination of Hg2+ and SO2 in neutral aqueous media. The nucleophilic addition of HSO3- toward CY-SPH caused a significant fluorescence enhancement at 455 nm while the Hg2+ -triggered desulfurization of CY-SPH to the final phenolic product (CY-OH) elicited a markedly enhanced emission at 760 nm, allowing for two-color visualization of Hg2+ and SO2 with good selectivity (detection limit: 67.2 nM for Hg2+ and 34.7 nM for SO2). Moreover, CY-OH could undergo further nucleophilic addition reaction with HSO3- and resulted in a decrease in emission at 760 nm and an increase in emission at 438 nm, enabling the ratiometric determination of SO2 with better sensitivity (detection limit, 3.50 nM). Significantly, CY-SPH can monitor the endogenous SO2 fluctuations upon mercury exposure by means of confocal fluorescence imaging, which may prove valuable for deciphering the relationship between SO2 levels and the mercury induced oxidative stress. We anticipated that this research will promote to understand the functions of SO2 under the oxidative stress by Hg2+.

Burst of hopping trafficking correlated reversible dynamic interactions between lipid droplets and mitochondria under starvation

Dynamic membrane contacts between lipid droplets (LDs) and mitochondria play key roles in lipid metabolism and energy homeostasis. Understanding the dynamics of LDs under energy stimulation is thereby crucial to disclosing the metabolic mechanism. Here, the reversible interactions between LDs and mitochondria are tracked in real-time using a robust LDs-specific fluorescent probe (LDs-Tags). Through tracking the dynamics of LDs at the single-particle level, spatiotemporal heterogeneity is revealed. LDs in starved cells communicate and integrate their activities (i.e., lipid exchange) through a membrane contact site-mediated mechanism. Thus the diffusion is intermittently alternated between active and confined states. Statistical analysis shows that the translocation of LDs in response to starvation stress is non-Gaussian, and obeys nonergodic-like behavior. These results provide deep understanding of the anomalous diffusion of LDs in living cells, and also afford guidance for rationally designing efficient transporter.

Two near-infrared phosphorescent iridium(III) complexes for the detection of GSH and photodynamic therapy

GSH is one of the most important reducing agents in biological systems. The depletion of GSH in the human body is linked to many diseases. Therefore, it is necessary to develop suitable and efficient probes for detecting GSH concentrations in real samples. In this work, we designed and synthesized two near-infrared emitting iridium(III) complex probes containing a novel ligand functionalized with an α,β-unsaturated ketone for the rapid and sensitive detection of GSH. The molecular structure of Ir2 was determined by X-ray crystallography. Due to their large Stokes shift, long luminescence lifetime and NIR emission, these probes were successfully applied in the imaging of GSH in living cells. In addition, two iridium(III) complexes have strong singlet oxygen generation ability which can be used for photodynamic therapy (PDT) upon visible light irradiation. On the basis of these findings, our iridium(III) complexes may serve as GSH probes for HeLa cell imaging and as photosensitizers for PDT.

Structure-regulated mitochondrial-targeted fluorescent probe for sensing and imaging SO2in vivo

SO2 and its derivatives play an important role in the antioxidation and anticorrosion of food and medicine. In biological systems, abnormal levels of SO2 lead to the occurrence of many biological diseases. Hence, the development of suitable tools for monitoring SO2 in mitochondria is beneficial for studying the biological effect of SO2 in subcellular organelles. In this research, DHX-1 and DHX-2 are fluorescent probes designed on the basis of dihydroxanthene skeletons. Importantly, DHX-1 (650 nm) and DHX-2 (748 nm) show near-infrared fluorescence response toward endogenous and exogenous SO2, which showed advantages of great selectivity, good sensitivity and low cytotoxicity, and the detection limit is 5.6 μM and 4.08 μM of SO2, respectively. Moreover, DHX-1 and DHX-2 realized SO2 sensing in HeLa cells and zebrafish. Moreover, cell imaging demonstrated that DHX-2 with a thiazole salt structure possesses good mitochondria-targeting ability. Additionally, DHX-2 was perfectly achieved by in situ imaging of SO2 in mice.