Visualizing lysosomes hypochlorous acid in Parkinson's disease models by a novel fluorescent probe

Heightened oxidative stress is the principal driver behind the altered metabolism of neurotransmitters within the brains of Parkinson's disease (PD). Hypochlorous acid (HClO), a variant of reactive oxygen species (ROS), plays a crucial role in several lysosomal activities. An irregular concentration of HClO may result in significant molecular damage and contribute to the onset of neurodegenerative disorders. Despite this, the precise role of lysosomal HClO in PD remains unclear, due to its fast reactivity and low levels. This is further complicated by the lack of effective in situ imaging techniques for accurately tracking its dynamics. Therefore, it is of great significance to use effective tools to map the lysosomal HClO during the pathological process of PD. In this study, we propose a fluorogenic probe named Lys-PTZ-HClO for the specific and sensitive detection of HClO. Lys-PTZ-HClO exhibits features like a fast response time (10 s) and a low detection limit (0.72 μM). Benefiting from its superior properties, the probe was used to visualize the basal HClO levels, and the variation of HClO levels in lysosomal of living cells. More importantly, this probe was successfully applied for the first time to reveal increased lysosomal HClO in a cellular model of PD.

Development of an AIE-active fluorescent probe for the simultaneous detection of Al3+ and viscosity and imaging in Alzheimer's disease model

Alzheimer's disease is associated both with imbalances in Al3+ production and changes in viscosity in cells. Their simultaneous measurement could therefore provide valuable insights into Alzheimer's disease pathology. Their simultaneous measurement would therefore be of great value in investigating the pathological mechanism of Alzheimer's disease. We designed a fluorescent probe YM2T with AIE effect that is capable of selectively responding to Al3+ by fluorescence colormetrics and to viscosity by fluorescence "turn on" modes. Additionally, Al3+ and viscosity were simultaneously detected in PC12 cells using the low cytotoxic probe YM2T via blue and green fluorescence channels. More importantly, the YM2T probe was used to image mice with AD. Hence, the YM2T probe shows potential as a useful molecular instrument for studying the pathological impact of Al3+ and viscosity.

A near-infrared fluorescent probe for simultaneous detection of pH and viscosity

In this work, we developed a ratiometric fluorescent probe (NT) based on ICT framework in near-infrared (NIR) which could detect pH and viscosity simultaneously. Long emission wavelength in NIR could protect the probe from interference of background fluorescence and improve the accuracy of the test. Due to the presence of thiazole-salt, the probe possessed good water solubility and could respond immediately to pH in water system. The pH values measured by NT in the actual samples were not much different from that measured by the pH meter, therefore, NT could give excellent accuracy. NT realized the reversible detection of pH by protonation and deprotonation. NT was used successfully to detect the pH of actual water samples, human serum and meat, as well as the viscosity variation caused by thickeners. Additionally, NT could monitor the changes of pH and viscosity in living cells. Therefore, the novel probe exhibited potential application in the fields of the environment, human health and food safety evaluation.

A near-infrared fluorescent molecular rotor for viscosity detection in biosystem and fluid beverages

Viscosity is closely associated with physiological and pathological processes, as well as food quality. Herein, a novel fluorescent molecular rotor, BMCY-V, was presented and applied for detection of viscosity. BMCY-V contained a benzoindole unit as electron donor and a malononitrile group as acceptor. In low-viscous solvents, the rotor can freely rotate, leading to dissipation of excited-state energy. In high-viscous media, however, the free rotation of the rotor is severely restricted, thus reducing non-radiative transition and resulting in significantly enhanced fluorescence intensity. BMCY-V is extremely sensitive to viscosity, showing about 3968 times increase of fluorescence intensity at 728 nm from water to 95 % glycerol. Due to the excellent photophysical property such as near-infrared emission, BMCY-V was successfully used to visualize viscosity in live cells and in liver tissues. In addition, BMCY-V can also evaluate the thickening effect of various thickeners and visualize the changes of viscosity during deterioration of fluid drinks.

Development of BODIPY-based fluorescent probes for imaging Aβ aggregates and lipid droplet viscosity

Alzheimer's disease (AD), gradually recognized as an untreatable neurodegenerative disorder, has been considered to be closely associated with Aβ plaques, which consist of β-amyloid protein (Aβ) and is one of the crucial pathological features of AD. There are no obvious symptoms in the initial phase of AD, and thus the therapeutic interventions are important for early diagnosis of AD. Moreover, recent researches have indicated that lipid droplets might serve as a potential ancillary biomarker, and its viscosity changes are closely associated to the pathological process of AD. Herein, two newly fluorescent probes 5QSZ and BQSZ have been developed and synthesized for identifying Aβ aggregates and detecting the viscosity of lipid droplet. After selectively binding to Aβ aggregates, 5QSZ and BQSZ exhibited linear and obvious fluorescence enhancements (32.58 and 36.70 folds), moderate affinity (Kd = 268.0 and 148.6 nM) and low detection limits (30.11 and 65.37 nM) in aqueous solutions. Further fluorescence staining of 5QSZ on brain tissue sections of APP/PS1 transgenic mouse exhibited the higher selectivity of 5QSZ towards Aβ aggregates locating at the core of the plaques. Furthermore, 5QSZ and BQSZ displayed strong linear fluorescence emission enhancements towards viscosity changes and would be utilized to monitor variation in cellular viscosity induced by LPS or monensin. These two probes were non-cytotoxic and showed good localization in lipid droplets. Therefore, 5QSZ and BQSZ could serve as potential bi-functional fluorescent probes to image Aβ aggregates and monitor the viscosity of lipid droplets, which have significant implications for the early diagnosis and progression of AD.

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.

Near-infrared fluorescent probe for the imaging of viscosity in fatty liver mice and valuation of drug efficacy

Fatty liver disease affects at least 25 percent of the population worldwide and is a severe metabolic syndrome. Viscosity is closely related to fatty liver disease, so it is urgent to develop an effective tool for monitoring viscosity. Herein, a NIR fluorescent probe called MBC-V is developed for imaging viscosity, consisting of dimethylaniline and malonitrile-benzopyran. MBC-V is non-fluorescent in low viscosity solutions due to intramolecular rotation. In high viscosity solution, the intramolecular rotation of MBC-V is suppressed and the fluorescence is triggered. MBC-V has long emission wavelength at 720 nm and large Stokes shift about 160 nm. Moreover, MBC-V can detect changes in cell viscosity in fatty liver cells, and can image the therapeutic effects of drug in fatty liver cells. By taking advantage of NIR emission, MBC-V can be used as an imaging tool for fatty liver disease and a way to evaluate the therapeutic effect of drug for fatty liver disease.

Red-Emitting Pyrrolyl Squaraine Molecular Rotor Reports Variations of Plasma Membrane and Vesicular Viscosity in Fluorescence Lifetime Imaging

The viscosity that ensures the controlled diffusion of biomolecules in cells is a crucial biophysical parameter. Consequently, fluorescent probes capable of reporting viscosity variations are valuable tools in bioimaging. In this field, red-shifted probes are essential, as the widely used and gold standard probe remains green-emitting molecular rotors based on BODIPY. Here, we demonstrate that pyrrolyl squaraines, red-emissive fluorophores, exhibit high sensitivity over a wide viscosity range from 30 to 4890 mPa·s. Upon alkylation of the pyrrole moieties, the probes improve their sensitivity to viscosity through an enhanced twisted intramolecular charge transfer phenomenon. We utilized this scaffold to develop a plasma membrane probe, pSQ-PM, that efficiently stains the plasma membrane in a fluorogenic manner. Using fluorescence lifetime imaging, pSQ-PM enabled efficient sensing of viscosity variations in the plasma membrane under various conditions and in different cell lines (HeLa, U2OS, and NIH/3T3). Moreover, upon incubation, pSQ-PM stained the membrane of intracellular vesicles and suggested that the lysosomal membranes displayed enhanced fluidity.

A near-infrared fluorescent probe based FRET for ratiometric sensing of H2O2 and viscosity in live cells

Hydrogen peroxide (H2O2) and viscosity play vital roles in the cellular environment as signaling molecule and microenvironment parameter, respectively, and are associated with many physiological and pathological processes in biological systems. We developed a near-infrared fluorescent probe, CQ, which performed colorimetric and ratiometric detection of H2O2 and viscosity based on the FRET mechanism, and was capable of monitoring changes in viscosity and H2O2 levels simultaneously through two different channels. Based on the specific reaction of H2O2 with borate ester, CQ exhibited a significant ratiometric response to H2O2 with a large Stokes shift of 221 nm, a detection limit of 0.87 μM, a near-infrared emission wavelength of 671 nm, a response time of 1 h, a wide detection ranges of 0.87-800 μM and a high energy transfer efficiency of 99.9 %. CQ could also recognize viscosity by the TICT mechanism, and efficiently detect viscosity changes caused by food thickeners. More importantly, CQ could successfully detect endogenous/exogenous H2O2 and viscosity in live HeLa cells, which was expected to be a practical tool for detecting H2O2 and viscosity in live cells.

Mitochondria-Targetable Near-Infrared Fluorescent Probe for Visualization of Hydrogen Peroxide in Lung Injury, Liver Injury, and Tumor Models

Hydrogen peroxide (H2O2) overexpressed in mitochondria has been regarded as a key biomarker in the pathological processes of various diseases. However, there is currently a lack of suitable mitochondria-targetable near-infrared (NIR) probes for the visualization of H2O2 in multiple diseases, such as PM2.5 exposure-induced lung injury, hepatic ischemia-reperfusion injury (HIRI), nonalcoholic fatty liver (NAFL), hepatic fibrosis (HF), and malignant tumor tissues containing clinical cancer patient samples. Herein, we conceived a novel NIR fluorescent probe (HCy-H2O2) by introducing pentafluorobenzenesulfonyl as a H2O2 sensing unit into the NIR hemicyanine platform. HCy-H2O2 exhibits good sensitivity and selectivity toward H2O2, accompanied by a remarkable "turn-on" fluorescence signal at 720 nm. Meanwhile, HCy-H2O2 has stable mitochondria-targetable ability and permits monitoring of the up-generated H2O2 level during mitophagy. Furthermore, using HCy-H2O2, we have successfully observed an overproduced mitochondrial H2O2 in ambient PM2.5 exposure-induced lung injury, HIRI, NAFL, and HF models through NIR fluorescence imaging. Significantly, the visualization of H2O2 has been achieved in both tumor-bear mice as well as surgical specimens of cancer patients, making HCy-H2O2 a promising tool for cancer diagnosis and imaging-guided surgery.

Fluorescent styrenes for mitochondrial imaging and viscosity sensing

Fluorophores bearing cationic pendants, such as the pyridinium group, tend to preferentially accumulate in mitochondria, whereas those with pentafluorophenyl groups display a distinct affinity for the endoplasmic reticulum. In this study, we designed fluorophores incorporating pyridinium and pentafluorophenyl pendants and examined their impact on sub-cellular localization. Remarkably, the fluorophores exhibited a notable propensity for the mitochondrial membrane. Furthermore, these fluorophores revealed dual functionality by facilitating the detection of viscosity changes within the sub-cellular environment and serving as heavy-atom-free photosensitizers. With easy chemical tunability, wash-free imaging, and a favorable signal-to-noise ratio, these fluorophores are valuable tools for imaging mitochondria and investigating their cellular processes.

Turn-on mode probe based on the sustainable xanthohumol extract for the efficient viscosity response in a liquid system

Viscosity is a typical physical parameter and plays an important role in nutrient transferring, diffusion process regulating and safety warning. Aberrant mitochondrial viscosity is closely associated with an imbalance in a liquid system. Nevertheless, there is currently a lack of convenient and efficient tools for the mutation of viscosity detection at the molecular level. Herein, a natural product xanthohumol (XTH) was extracted from Humulus lupulus and used to measure the microenvironmental viscosity. Due to the existence of carbonyl and phenolic hydroxyl groups, a typical twisted intramolecular charge transfer (TICT) was formed. The conjugated single and double bonds can be employed as the rotatable site. Consequently, a turn-on method based on viscosity response is developed. High sensitivity (x = 0.56) with a remarkable enhancement (55-fold) toward viscosity and a visualized fluorescent signal can be found. In addition, it displays a single selectivity with excellent photostability and pH stability in the complex liquid system. Using the extracted XTH, a typical application toward the liquid spoilage process was performed and a positive correlation was noted. Given the comprehensive properties of XTH, liquid safety inspection at a molecular level with natural source-extracted products can be obtained.

Access to 2,4-Disubstituted Pyrrole-Based Polymer with Long-Wavelength and Stimuli-Responsive Properties via Copper-Catalyzed [3+2] Polycycloaddition

Pyrrole-based polymers (PBPs), a type of fascinating functional polymers, play a crucial role in materials science. However, efficient synthetic strategies of PBPs with diverse structures are mainly focused on conjugated polypyrroles and still remain challenging. Herein, an atom and step economy protocol is described to access various 2,4-disubstituted PBPs by in situ formation of pyrrole core structure via copper-catalyzed [3+2] polycycloaddition of dialkynones and diisocyanoacetates. A series of PBPs is prepared with high molecular weight (Mw up to 18 200 Da) and moderate to good yield (up to 87%), which possesses a fluorescent emission located in the green to yellow light region. Blending the PBPs with polyvinyl alcohol, the stretchable composite films exhibit a significant strengthening of the mechanical properties (tensile stress up to 59 MPa, elongation at break >400%) and an unprecedented stress-responsive luminescence enhancement that over fourfold fluorescent emission intensity is maintained upon stretching up to 100%. On the basis of computational studies, the unique photophysical and mechanical properties are attributed to the substitution of carbonyl chromophores on the pyrrole unit.

A multi-functional fluorescent probe for visualization of H2S and viscosity/polarity and its application in cancer imaging

As an important endogenous gasotransmitter, hydrogen sulfide (H2S) plays a critical role in various physiological functions and has been regarded as a biomarker of cancer due to its overexpression in cancer cells. In addition, the early stages of cancer are often accompanied by abnormalities in the intracellular microenvironments, and distinguishing between cancer cell/tissues and normal cell/tissues is of great significance to the accuracy of cancer diagnosis. However, deep insights into the simultaneous detection of H2S and viscosity/polarity variations in cancer cells/tissues are rarely reported. In this work, we designed and synthesized a mitochondria-targeting fluorescent probe PDQHS, which exhibits high selectivity for H2S with an emission peak around 632 nm and excellent response (17-fold) to viscosity/polarity beyond 706 nm. Meanwhile, PDQHS shows good biocompatibility and can specifically accumulate into mitochondria. Using PDQHS, the visual distinguishing of cancer cells from normal cells was achieved via dual-channel detection of H2S and viscosity/polarity. More importantly, PDQHS has been successfully applied to visualize endogenous and exogenous H2S in living cells and tumor tissue. Obviously, compared to the detection of a single biomarker, monitoring multiple biomarkers simultaneously through dual-channel response is conducive to amplifying the detection signal, providing a more sensitive and reliable imaging tool in the tumor region, which is beneficial for cancer prediction.

Design and Application of Fluorescent Probes to Detect Cellular Physical Microenvironments

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

Fluorescent Probe for Investigating the Mitochondrial Viscosity and Hydrogen Peroxide Changes in Cerebral Ischemia/Reperfusion Injury

Cerebral ischemia-reperfusion injury (CIRI), a cause of cerebral dysfunction during cerebral infarction treatment, is closely associated with mitochondrial viscosity and hydrogen peroxide (H2O2). However, the accurate measurement of mitochondrial viscosity and H2O2 levels in CIRI is challenging because of the lack of sufficient selectivity and blood-brain barrier (BBB) penetration of existing monitoring tools related to CIRI, hampering the exploration of the role of mitochondrial viscosity and H2O2 in CIRI. To address this issue, we designed an activatable fluorescent probe, mitochondria-targeting styryl-quinolin-ium (Mito-IQS), with excellent properties including high selectivity, mitochondrial targeting, and BBB penetration, for the visualization of mitochondrial viscosity and H2O2 in the brain. Based on the real-time monitoring capabilities of the probe, bursts of mitochondrial viscosity and H2O2 levels were visualized during CIRI. This probe can be used to monitor the therapeutic effects of butylphthalein treatment. More importantly, in vivo experiments further confirmed that CIRI was closely associated with the mitochondrial viscosity and H2O2 levels. This discovery provides new insights and tools for the study of CIRI and is expected to accelerate the process of CIRI diagnosis, treatment, and drug design.

Carbazole-based mitochondria-targeted fluorescent probes for in vivo viscosity and cyanide detection in cells and zebrafish

Cells of most eukaryotic species contain mitochondria, which play a role in physiological processes such as cellular senescence, metabolism, and autophagy. Viscosity is considered a key marker for many illnesses and is involved in several crucial physiological processes. Cyanide (CN-) can target cytochrome-c oxidase, disrupting the mitochondrial electron transport chain and causing cell death through asphyxiation. In this study, a fluorescent probe named HL-1, which targets mitochondria and measures viscosity and CN- levels, was designed and synthesized. HL-1 is viscosity-sensitive, with a linear correlation coefficient of up to 0.992. In addition, HL-1 was found to change color substantially during a nucleophilic addition reaction with CN-, which has a low detection limit of 47 nM. HL-1 not only detects viscosity and exogenous CN- in SKOV-3 cells and zebrafish but also monitors viscosity changes during mitochondrial autophagy in real time. Furthermore, HL-1 has been used successfully to monitor changes in mitochondrial membrane potential during apoptosis. Endogenous CN- in plant samples was quantified. HL-1 provides new ideas for studying viscosity and CN-.

A dual donor-acceptor fluorescent probe with viscosity response and lipid droplets targeting to initiate oxidative stress for tumor elimination

A dual donor-acceptor photosensitizer TCN-2 prepared based on single donor-acceptor could fulfil lipid droplets targeting to trigger apoptosis and tumor growth arrest. Meanwhile, all of experiments both in phosphate buffer solution and intracellular surroundings have demonstrated that TCN-2 catalyzed the production of type I as well as type II reactive oxygen species, forming a hybrid reactive oxygen species pattern, indicating that TCN-2 could be applied to initiate a series of biological responses triggered by oxidative stress within most high-viscosity solid tumors. In addition, TCN-2 also has the capability of fluorescence imaging, which could perfectly combine therapeutic imaging to achieve therapeutic effects while identifying cancerous lesions. Due to the structural design of double electron-absorbing groups, TCN-2 retained excellent lipophilicity while enhancing solubility in the biological environment. Terrific biocompatibility, minimal phototoxic damage to normal cells and tissues, and specific driving to prescriptive organelles to maximize therapeutic effects were used to enhance the therapeutic effect of photodynamic therapy to cease disease progression.

A near-infrared fluorescent probe for viscosity: Differentiating cancer cells from normal cells and dual-modal imaging in tumor mice

As a basic parameter of the intracellular microenvironment, viscosity is closely related to the development of cancer. Thus, it is necessary to utilize a sensitive tool to visualize the viscosity in tumor cells and mice, which is helpful for the diagnosis of cancer. Herein, a novel dual-modal probe (IX-V) that has a near-infrared fluorescence (NIRF) and photoacoustic (PA) response to viscosity is synthesized. In low viscosity media, the probe has no fluorescence. With the increase of viscosity, the fluorescence is produced in the near-infrared region due to the inhibition of the TICT process. At the same time, the probe shows different photoacoustic (PA) signals in different viscosity media. Most notably, the viscosity in tumor cells has been imaged successfully by the application of IX-V, and the probe can effectively distinguish cancer cells from normal cells co-cultured in one dish by the difference of fluorescence intensity. In addition, the probe has been used for dual-modal imaging (NIRF and PA) of viscosity in tumor mice, which provides a tool for exploring the relationship between viscosity and diseases. That is to say, IX-V can achieve complementary imaging effects and has great application prospects in the tumor diagnosis.

A benzothiazole-salt-based fluorescent probe for precise monitoring the changes of pH and viscosity

This work presented a novel ratiometric fluorescent probe (NBO) based on benzothiazole dye, which could monitor the pH fluctuations with high sensitivity via the intramolecular charge transfer (ICT) process. NBO was developed with a good linear response in the pH range of 5.75-7.00 (pKa = 6.5) and a reversible structural change in acidic and alkaline environments. Besides, NBO also has the potential to detect the viscosity changes. Meanwhile, NBO has been successfully applied to the pH monitoring of a variety of water samples in natural environment and human serum. With the treatment of different solutions at pH 2.0 - pH 9.0, the test strips showed significant color changes under both 365 nm UV lamp and room light. When the test strips were applied to white wine, pH could be detected quickly and easily by the naked eyes. Therefore, a novel probe that can be used to detect pH in environment, human serum and food has been successfully developed.

A near-infrared fluorescent probe with viscosity sensitivity in lysosome for cancer visualization

A viscosity-sensitive, lysosome-targeted near-infrared fluorescent probe (PYATT) was reported in this paper. The fluorescent spectra of PYATT are strongly dependent on viscosity, resulting in a Stokes shift of about 190 nm. Given its photostability, low cytotoxicity, and high fluorescence quantum yield, PYATT is expected to be used in cell imaging. Due to the higher viscosity of tumor cells than normal cells, the fluorescence intensity of PYATT in tumor cells is higher than normal cells, which can realize the visualization of tumors. The near-infrared probe (PYATT) is viscosity-dependent in lysosomes, which is valuable in early diagnosis and treatment of tumor.

Caffeic acid, a natural extract, as an activatable molecular probe for viscosity detection in a liquid system

Liquids, functioning as nutrients and energy systems, regulate various functions during storage programs. Microenvironmental viscosity is one of the most important physical parameters associated with the extent of deterioration, and it is crucial to monitor the mutation of viscosity at a molecular level. Herein, we utilized caffeic acid (CaC), a natural product extracted from thistles, as a molecular probe for viscosity sensing. CaC contains phenol hydroxyl (electron-donor) and carboxyl (electron-acceptor) groups, with both moieties connected by conjugated single and double bonds, forming a typical twisted intramolecular charge transfer system. The fluorescent probe CaC, obtained from a natural product without any chemical processing, exhibits high sensitivity (x = 0.43) toward viscosity, with an obvious visualized turn-on signal. Moreover, it displays good photostability, selectivity, and wide universality in commercial liquids. Utilizing CaC, we have successfully visualized viscosity enhancement during the spoilage process, with a positive correlation between the degree of liquid spoilage and microenvironmental viscosity. Thus, this study will provide a convenient and efficient molecular probe for food safety inspection across the boundaries of traditional biological applications.

Developing a Two-Photon "AND" Logic Probe and Its Application in Alzheimer's Disease Differentiation

In Alzheimer's disease, hypochlorous acid involved in the clearance of invading bacteria or pathogens and butyrylcholinesterase engaged in the hydrolysis of the neurotransmitter acetylcholine are relatively significantly altered. However, there are few dual detection probes for hypochlorous acid and butyrylcholinesterase. In addition, single-response probes suffer from serious off-target effects and near-infrared probes do not easily penetrate the blood-brain barrier due to their excessive molecular weight. In this work, we constructed a two-photon fluorescent probe that recognizes hypochlorous acid and butyrylcholinesterase based on a dual-lock strategy. The thiocarbonyl group is oxidized in the presence of hypochlorous acid, and the hydrolysis occurs at the 7-position ester bond in the existence of butyrylcholinesterase, releasing a strongly fluorescent fluorophore, 4-methylumbelliferone. Excellent imaging was performed in PC12 cells using this probe, and deep two-photon imaging was observed in the brains of AD mice after tail vein injection with this probe. It indicates that the probe can provide a promising tool for the more precise diagnosis of Alzheimer's disease.

Tunable metal-organic frameworks assist in catalyzing DNAzymes with amplification platforms for biomedical applications

Various binding modes of tunable metal organic frameworks (MOFs) and functional DNAzymes (Dzs) synergistically catalyze the emergence of abundant functional nanoplatforms. Given their serial variability in formation, structural designability, and functional controllability, Dzs@MOFs tend to be excellent building blocks for the precise "intelligent" manufacture of functional materials. To present a clear outline of this new field, this review systematically summarizes the progress of Dz integration into MOFs (MOFs@Dzs) through different methods, including various surface infiltration, pore encapsulation, covalent binding, and biomimetic mineralization methods. Atomic-level and time-resolved catalytic mechanisms for biosensing and imaging are made possible by the complex interplay of the distinct molecular structure of Dzs@MOF, conformational flexibility, and dynamic regulation of metal ions. Exploiting the precision of DNAzymes, MOFs@Dzs constructed a combined nanotherapy platform to guide intracellular drug synthesis, photodynamic therapy, catalytic therapy, and immunotherapy to enhance gene therapy in different ways, solving the problems of intracellular delivery inefficiency and insufficient supply of cofactors. MOFs@Dzs nanostructures have become excellent candidates for biosensing, bioimaging, amplification delivery, and targeted cancer gene therapy while emphasizing major advancements and seminal endeavors in the fields of biosensing (nucleic acid, protein, enzyme activity, small molecules, and cancer cells), biological imaging, and targeted cancer gene delivery and gene therapy. Overall, based on the results demonstrated to date, we discuss the challenges that the emerging MOFs@Dzs might encounter in practical future applications and briefly look forward to their bright prospects in other fields.

A BODIPY-based fluorescent probe for simultaneous detection of H2O2 and viscosity during the pyroptosis process

A dual functional BODIPY fluorescent probe was developed for simultaneous detection of H2O2 and viscosity, by collecting fluorescence from 800-1100 nm and 550-750 nm, respectively. Bioimaging based on the probe shows that H2O2 accumulates and cytoplasmic viscosity increases during the palmitic acid (PA)-induced pyroptosis process.

A Fluorescent Probe for Investigating the Role of Biothiols in Signaling Pathways Associated with Cerebral Ischemia-Reperfusion Injury

Cerebral ischemia-reperfusion injury (CIRI) is intimately associated with the redox regulation of biothiol, a crucial antioxidant marker that precludes the onset of ROS. We designed a novel fluorescent probe, DCI-Ac-Py, showing various physicochemical properties, such as high selectivity, exceptional signal-to-noise ratio, near-infrared (NIR) optical window, and blood-brain barrier (BBB) penetrability, for detecting biothiols in the brain. The picolinate serves as a specific recognition group that is rapidly activated by biothiol and undergoes nucleophilic substitution with the adjacent acrylic ester to yield the desired NIR probe. Additionally, the probe's lipid solubility is improved through the inclusion of halogen atoms, which aids in penetrating the BBB. Using DCI-Ac-Py, we investigated changes of biothiols in vivo in the brains of mice during CIRI. We found that biothiol-mediated NF-kB classical (P65-related) and nonclassical (RelB-related) pathways contribute to abundant ROS production induced by CIRI and that biothiols are involved in redox regulation. These findings provide new insights into the study of CIRI and shed light on the physiological and pathological mechanisms of biothiols in the brain.

Design, Synthesis and Evaluation of Fluorescent Properties of Benzothiazole Derivatives

Fluorescence imaging is conducive to establish a bridge between molecular biology and clinical medicine, and provides new tools for disease process research, early diagnosis, and efficacy evaluation, because of the advantages of rapid imaging and nondestructive detection. Herein, a series of fluorescent molecules with thiadiazole, or thiazole, or benzothiazole cores were designed and synthesized to develop more excellent fluorescent molecules in bio-imaging. According to theoretical and experimental methods, we found that benzothiazole derivative 14 B with conjugate expansion by (4-aminophenyl) ethynyl group was the most excellent fluorescent molecule among all the investigated compounds and exhibited low cytotoxicity and strong blue and green fluorescence by confocal cell imaging.

Development of meso-Five-Membered Heterocycle BODIPY-Based AIE Fluorescent Probes for Dual-Organelle Viscosity Imaging

Fluorescent rotors with aggregation-induced emission (AIE) and organelle-targeting properties have attracted great attention for sensing subcellular viscosity changes, which could help understand the relationships of abnormal fluctuations with many associated diseases. Despite the numerous efforts spent, it remains rare and urgent to explore the dual-organelle targeting probes and their structural relationships with viscosity-responsive and AIE properties. Therefore, in this work, we reported four meso-five-membered heterocycle-substituted BODIPY-based fluorescent probes, explored their viscosity-responsive and AIE properties, and further investigated their subcellular localization and viscosity-sensing applications in living cells. Interestingly, the meso-thiazole probe 1 showed both good viscosity-responsive and AIE (in pure water) properties and could successfully target both mitochondria and lysosomes, further imaging cellular viscosity changes by treating lipopolysaccharide and nystatin, attributing to the free rotation and potential dual-organelle targeting ability of the meso-thiazole group. The meso-benzothiophene probe 3 with a saturated sulfur only showed good viscosity-responsive properties in living cells with the aggregation-caused quenching effect and no subcellular localization. The meso-imidazole probe 2 showed the AIE phenomenon without an obvious viscosity-responsive property with a C═N bond, while the meso-benzopyrrole probe 4 displayed fluorescence quenching in polar solvents. Therefore, for the first time, we investigated the structure-property relationships of four meso-five-membered heterocycle-substituted BODIPY-based fluorescent rotors with viscosity-responsive and AIE properties, and among these, 1 with a C═N bond and a saturated sulfur on the meso-thiazole, potentially contributing to their corresponding AIE and viscosity-responsive properties, served as a sensitive AIE fluorescent rotor for imaging dual-organelle viscosity in both mitochondria and lysosomes.

Multifunctional Mitochondria-Targeting Near-Infrared Fluorescent Probe for Viscosity, ONOO-, Mitophagy, and Bioimaging

Irregularities in mitochondrial viscosity and peroxynitrite (ONOO-) concentration can lead to mitochondrial dysfunction. It is still a great challenge to develop near-infrared (NIR) fluorescent probes to simultaneously detect viscosity, endogenous ONOO-, and mitophagy. Herein, a multifunctional mitochondria-targeting NIR fluorescent probe P-1 was first synthesized for simultaneously detecting viscosity, ONOO-, and mitophagy. P-1 used quinoline cations as a mitochondrial targeting moiety, arylboronate as an ONOO- responsive group, and detected the change of viscosity by the twisted internal charge transfer (TICT) mechanism. The probe has an excellent response to the viscosity during inflammation by lipopolysaccharides (LPSs) and mitophagy induced by starvation at 670 nm. The viscosity changes of the probe induced by nystatin in zebrafish showed that P-1 was able to detect microviscosity in vivo. P-1 also showed good sensitivity with a detection limit of 6.2 nM for ONOO- detection and was successfully applied to the endogenous ONOO- detection in zebrafish. Moreover, P-1 has the ability to distinguish between cancer cells and normal cells. All of these features make P-1 a promising candidate to detect mitophagy and ONOO- -associated physiological and pathological processes.

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

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

Utilization of photo-luminescent technique toward viscosity detection in the liquid food system with triphenylamine-michaelitic acid molecular sensor

A noninvasive and effective viscosity inspection method is expected to ease the burden of continued increased health problems caused by liquid food safety. In this study, we proposed the viscosity of the liquid food micro-environment as a marker and further developed a versatile optical sensor, DPTMDD, for monitoring liquid food micro-environmental viscosity alterations. This sensor was strategically constructed by the triphenylamine-thiophene derivate and michaelitic acid, rotatable conjugate structure was utilized as the recognition site. The molecular sensor was synthesized in a one-step facile way, and DPTMDD displayed a longer emission wavelength (592 nm), low detection limit (1.419 cP), and larger Stokes shift (193.7 nm in glycerol and 177.8 nm in water) with narrower energy band, endowing the sensor with the capacity of achieving high signal-to-noise ratio imaging. Meanwhile, DPTMDD exhibits high adaptability, selectivity, sensitivity, and good photo-stability in various liquid foods, bright fluorescent signal (37.5-fold) of DPTMDD is specifically activated in the high viscosity media. Thickening efficiencies can be identified as well. More importantly, the viscosity fluctuations during the metamorphic stages of liquid foods are also screened through in situ monitoring. We expected that this unique strategy will reinvigorate the continued perfection of liquid food safety investigation systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05699-y.

Simultaneous detection of mitochondrial viscosity and peroxynitrite in livers from subjects with drug-induced fatty liver disease using a novel fluorescent probe

Drug-induced fatty liver disease (DIFLD) is a basic clinicopathological example of drug-induced liver injury (DILI). Some drugs can inhibit β-oxidation in hepatocyte mitochondria, leading to steatosis in the liver. Additionally, drug-induced inhibition of β-oxidation and the electron transport chain (ETC) can lead to increased production of reactive oxygen species (ROS) such as peroxynitrite (ONOO^-). Therefore, it is reasonable to suspect that compared to a healthy liver, viscosity and ONOO^- levels are elevated in livers during DIFLD. A novel, smart, dual-response fluorescent probe-Mito-VO-was designed and synthesized for the simultaneous detection of viscosity and ONOO^- content. This probe had a large emission shift of 293 nm and was capable of monitoring the viscosity of, and the ONOO^- content in, cell and animal models alike, either individually or simultaneously. For the first time, Mito-VO was successfully used to demonstrate the elevated viscosity and the amount of ONOO^- in livers from mice with DIFLD.

Mitochondria-targeting fluorescent sensor with high photostability and permeability for visualizing viscosity in mitochondrial malfunction, inflammation, and AD models

Viscosity changes in mitochondria are closely associated with numerous cellular processes and diseases. Currently available fluorescence probes used in mitochondrial viscosity imaging are not very photostable or sufficiently permeable. Herein, a highly photostable and permeable mitochondria-targeting red fluorescent probe (Mito-DDP) was designed and synthesized for viscosity sensing. Viscosity was imaged in living cells using a confocal laser scanning microscope, and the results suggested that Mito-DDP penetrated the membrane and stained the living cells. Importantly, practical applications of Mito-DDP were demonstrated: viscosity visualization was realized for mitochondrial malfunction, cellular and zebrafish inflammation, and Drosophila Alzheimer's disease models, i.e., for subcellular organelles, cells, and organisms. The excellent analytical and bioimaging performance of Mito-DDP in vivo makes it an effective tool for exploring the physiological and pathological effects of viscosity.

Green extract rosemary acid as a viscosity-sensitive molecular sensor in liquid systems

The liquid micro-environment plays a momentous role in the regulation of various activities, and the abnormal changes are often closely related to the deterioration phenomena in multiple beverages. The local viscosity fluctuation has long been regarded as a key indicator to reflect the micro-environmental status changes. Herein, we proposed a versatile optical sensor, rosmarinic acid (RA), one kind of green natural product extracted from rosemary, for monitoring liquid micro-environmental viscosity alterations. RA displays a larger Stokes shift (123.8 nm) with narrow-band energy and exhibits wide adaptability, high selectivity, good sensitivity, and excellent photostability in various commercial liquids. When in high viscous media, a bright fluorescent signal of RA is specifically activated, and a high signal-to-noise ratio signal was released (58-fold). With the assistance of the fluorescence analytical technique, we have successfully achieved tracking the viscosity fluctuations during the deterioration stage of liquids via an in situ and visualization method. Our study will spur additional research on the molecular tools extracted from natural products for liquid safety inspection, and a convenient and sustainable application pathway has been established.

Cysteine-Activatable Near-Infrared Fluorescent Probe for Dual-Channel Tracking Lipid Droplets and Mitochondria in Epilepsy

Dual-channel fluorescent probes could respond to a specific target and emit different wavelengths of fluorescence before and after the response. Such probes could alleviate the influence caused by the variation of the probe concentration, excitation intensity, and so on. However, for most dual-channel fluorescent probes, the probe and fluorophore faced spectral overlap, which reduced sensitivity and accuracy. Herein, we introduced a cysteine (Cys)-responsive and near-infrared (NIR) emissive AIEgen (named TSQC) with good biocompatibility to dual-channel monitor Cys in mitochondria and lipid droplets (LDs) during cell apoptosis through wash-free fluorescence bio-imaging. TSQC can label mitochondria with bright fluorescence around 750 nm, and after reacting with Cys, the reaction product TSQ could spontaneously target LDs with emissions around 650 nm. Such spatially separated dual-channel fluorescence responses could significantly improve detection sensitivity and accuracy. Furthermore, the Cys-triggered dual-channel fluorescence imaging in LDs and mitochondria during apoptosis induced by UV light exposure, H₂O₂, or LPS treatment is clearly observed for the first time. Besides, we also report here that TSQC can be used to image subcellular Cys in different cell lines by measuring the fluorescence intensities of different emission channels. In particular, TSQC shows superior utility for the in vivo imaging of apoptosis in acute and chronic epilepsy mice. In brief, the newly designed NIR AIEgen TSQC can respond to Cys and separate two fluorescence signals to mitochondria and LDs, respectively, to study Cys-related apoptosis.

Mitochondrial Membrane Potential Independent Near-Infrared Mitochondrial Viscosity Probes for Real-Time Tracking Mitophagy

Mitophagy is a vital cellular process playing vital roles in regulating cellular metabolism and mitochondrial quality control. Mitochondrial viscosity is a key microenvironmental index, closely associated with mitochondrial status. To monitor mitophagy and mitochondrial viscosity, three molecular rotors (Mito-1, Mito-2, and Mito-3) were developed. All probes contain a cationic quinolinium unit and a C₁₂ chain so that they can tightly bind mitochondria and are not affected by the mitochondrial membrane potential. Optical studies showed that all probes are sensitive to viscosity changes with an off-on fluorescence response, and Mito-3 shows the best fluorescence enhancement. Bioimaging studies showed that all these probes can not only tightly locate and visualize mitochondria with near-infrared fluorescence but also effectively monitor the mitochondrial viscosity changes in cells. Moreover, Mito-3 was successfully applied to visualize the mitophagy process induced by starvation, and mitochondrial viscosity was found to show an increase during mitophagy. We expect Mito-3 to become a useful imaging tool for studying mitochondrial viscosity and mitophagy.

Light, Water, and Melatonin: The Synergistic Regulation of Phase Separation in Dementia

The swift rise in acceptance of molecular principles defining phase separation by a broad array of scientific disciplines is shadowed by increasing discoveries linking phase separation to pathological aggregations associated with numerous neurodegenerative disorders, including Alzheimer’s disease, that contribute to dementia. Phase separation is powered by multivalent macromolecular interactions. Importantly, the release of water molecules from protein hydration shells into bulk creates entropic gains that promote phase separation and the subsequent generation of insoluble cytotoxic aggregates that drive healthy brain cells into diseased states. Higher viscosity in interfacial waters and limited hydration in interiors of biomolecular condensates facilitate phase separation. Light, water, and melatonin constitute an ancient synergy that ensures adequate protein hydration to prevent aberrant phase separation. The 670 nm visible red wavelength found in sunlight and employed in photobiomodulation reduces interfacial and mitochondrial matrix viscosity to enhance ATP production via increasing ATP synthase motor efficiency. Melatonin is a potent antioxidant that lowers viscosity to increase ATP by scavenging excess reactive oxygen species and free radicals. Reduced viscosity by light and melatonin elevates the availability of free water molecules that allow melatonin to adopt favorable conformations that enhance intrinsic features, including binding interactions with adenosine that reinforces the adenosine moiety effect of ATP responsible for preventing water removal that causes hydrophobic collapse and aggregation in phase separation. Precise recalibration of interspecies melatonin dosages that account for differences in metabolic rates and bioavailability will ensure the efficacious reinstatement of the once-powerful ancient synergy between light, water, and melatonin in a modern world.

Configuration-Induced Multichromism of Phenanthridine Derivatives: A Type of Versatile Fluorescent Probe for Microenvironmental Monitoring

Fluorescent probes are attractive in diagnosis and sensing. However, most reported fluorophores can only detect one or few analytes/parameters, notably limiting their applications. Here we have designed three phenanthridine-based fluorophores (i.e., B1, F1, and T1 with 1D, 2D, and 3D molecular configuration, respectively) capable of monitoring various microenvironments. In rigidifying media, all fluorophores show bathochromic emissions but with different wavelength and intensity changes. Under compression, F1 shows a bathochromic emission of over 163 nm, which results in organic fluorophore-based full-color piezochromism. Moreover, both B1 and F1 exhibit an aggregation-caused quenching (ACQ) behavior, while T1 is an aggregation-induced emission (AIE) fluorophore. Further, F1 and T1 selectively concentrate in cell nucleus, whereas B1 mainly stains the cytoplasm in live cell imaging. This work provides a general design strategy of versatile fluorophores for microenvironmental monitoring.

Recent Advancements in the Design and Development of Near Infrared (NIR) Emitting Fluorescent Probes for Sensing and their Bio-Imaging Applications

Fluorescent bio-imaging will be the future in the medical diagnostic for visualising inner cellular and tissues. Near-infrared (NIR) emitting fluorescent probes serve dynamically for targeted fluorescent imaging of live cells and tissues. NIR imaging is advantageous because of its merits like deep tissue penetration, minimum damage to the tissue, reduced auto fluorescence from the background, and improved resolution in imaging. The Development of the NIR emitting probe was well explored recently and growing drastically. In this review, we summarise recent achievements in NIR probes in between 2018-2021. The merits and future applications have also been discussed in this review.

Activity-Based Sensing for Chemistry-Enabled Biology: Illuminating Principles, Probes, and Prospects for Boronate Reagents for Studying Hydrogen Peroxide

Activity-based sensing (ABS) offers a general approach that exploits chemical reactivity as a method for selective detection and manipulation of biological analytes. Here, we illustrate the value of this chemical platform to enable new biological discovery through a case study in the design and application of ABS reagents for studying hydrogen peroxide (H2O2), a major type of reactive oxygen species (ROS) that regulates a diverse array of vital cellular signaling processes to sustain life. Specifically, we summarize advances in the use of activity-based boronate probes for the detection of H2O2 featuring high molecular selectivity over other ROS, with an emphasis on tailoring designs in chemical structure to promote new biological principles of redox signaling.

Multiple organelle-targeted near-infrared fluorescent probes toward pH and viscosity

Organelles, including mitochondria (mito), lysosomes (lyso), endoplasmic reticulum (ER), Golgi apparatus (Golgi), and ribosome et al., play a vital role in maintaining the regular work of the cell. Viscosity is an essential parameter in the cellular microenvironment. Herein, four viscosity-sensitive near-infrared fluorescent probes DMPC, DEPC, DHDM and DHDV that can simultaneously target multiple organelles were synthesized. As the viscosity increased, the fluorescence intensity of the probes gradually increased due to the hindrance of the rotation of the carbon-carbon single bond. The fluorescence intensity of DHDV increased by about 453 times, and the fluorescence quantum yield also increased from 0.051 to 0.681. Cell experiments indicated the probes could simultaneously target four kinds of organelles, and the four probes could also track mitochondria with no dependence on membrane potential. Further experiments showed that the probes could detect viscosity changes in lyso and mito. In addition, the probes also demonstrated the advantages of low cytotoxicity, good anti-interference and stability, providing a simple and effective tool for studying the activity of organelles with changing viscosity signals.

Visualization of HOCl in the brains of Alzheimer's disease models using an easily available two-photon fluorogenic probe

As an inflammatory signaling molecule, hypochlorous acid (HOCl), which is generated by myeloperoxidase (MPO) catalysis, is associated with neuronal cell death during neuroinflammation and the etiology of Alzheimer's disease (AD). Thus, it is significant to employ effective tools for the in vivo mapping of HOCl during the early pathology of AD. In this study, we propose the use of an easily available two-photon fluorogenic probe, named Q-HOCl, for the specific and sensitive detection of HOCl in AD brains. The Q-HOCl probe displayed favorable selectivity and rapid response (20 s) to HOCl with a limit of detection of 12.5 nM. In addition, the Q-HOCl probe manifested splendid ability to penetrate the blood-brain barrier. Subsequently, it was utilized to visualize HOCl fluctuation induced by LPS in PC12 cells via two-photon imaging. Importantly, we monitored the elevated level of HOCl in AD brains compared to normal brains. Ultimately, based on the two-photon imaging of the hippocampus of brain slices and Morris water maze test, the cognitive ability of the AD model mice was effectually ameliorated by treatment with an MPO inhibitor. Thus, we expect that the Q-HOCl probe can be applied to reveal the capacity of HOCl in AD pathology and develop efficacious MPO inhibitor drugs for the treatment of AD.

Novel Meso-Benzothiazole-Substituted BODIPY-Based AIE Fluorescent Rotor for Imaging Lysosomal Viscosity and Monitoring Autophagy

Meso-substituted boron dipyrromethenes (BODIPYs) provide a potential and innovative strategy for the synergistic construction of aggregation-induced emission (AIE) probes and fluorescent rotors for monitoring cellular viscosity changes, which play critical roles in understanding the function of viscosity in its closely associated diseases. Therefore, for the first time, a BODIPY-based fluorescent probe (1) with a rotatable meso-benzothiazole group was rationally designed and synthesized, showing both good viscosity-responsive and AIE properties. Probe 1 through direct linkage with the thiazole group, showed nearly no emission in low viscous solvents; however, a strong emission at 534 nm appeared and increased gradually with the increase in viscosity, attributing to the efficient restriction of the rotatable meso-benzothiazole group. The intensity (log I₅₃₄) displayed a good linear relationship with viscosity (log η) in the viscous range of 0.59-945 cP in methanol/glycerol mixtures. Interestingly, 1 showed enhanced emission at 534 nm in 70% water compared to pure acetonitrile due to the aggregation-induced inhibited rotations. Cellular imaging suggested that 1 could successfully sense lysosomal viscosity changes induced by lipopolysaccharide, nystatin, low temperature, and dexamethasone in living cells, which could be further applied in autophagy monitoring by tracing viscosity changes. As a comparison, its analogue 2 directly linking with the phenyl group showed no viscosity-responsive or AIE properties. Therefore, for the first time, we reported a meso-benzothiazole-BODIPY-based fluorescent rotor with AIE and lysosomal viscosity-responsive properties in nervous cells, which was further applied in monitoring autophagy, and this work thus could provide an innovative strategy for the design of potential AIE and viscosity-responsive probes.

Synergistic Modulation by Halogens and Pyridine Crossing the Blood-Brain Barrier for In Situ Visualization of Thiol Flux in the Epileptic Brain

Epilepsy is a nervous system disease, and seizures are closely related to oxidative stress. Thiols, as the main antioxidant in an organism, play a key role in regulating the redox balance and defending from oxidative stress. As a result of the complexity of the brain structure, there is still a lack of suitable in situ detection methods of thiols to reveal the relationship between epilepsy and thiol level fluctuations. Therefore, by combining picolinate as the new recognition site for thiols, parallel synthesis, and the fluorescence rapid screening method, DCI-Br-3 was developed as a rapid, highly sensitive, and selective probe to monitor thiols in vitro and in vivo. It is worth noting that DCI-Br-3 effectively crossed the blood-brain barrier (BBB) to reveal the negative relationship between the level of thiols and the occurrence of epilepsy and may further provide important information for the prevention and treatment of thiol-related neurological diseases.

Application of Fluorescent Probes in Reactive Oxygen Species Disease Model

Reactive oxygen species (ROS) play an important role in living activities as signaling molecules that regulate the living activities of organisms. There are many types of ROS, mainly including hydrogen peroxide (H2O2), hypochlorous acid (HOCl), hydroxyl radical (•OH), peroxyl radical (ROO•), singlet oxygen (1O2), peroxynitrite (ONOO-) and superoxide anion radical (O2-•) etc. Existing studies have shown that changes in ROS levels are closely associated with the development of many diseases, such as inflammation, cancer, cardiovascular disease, and neurodegenerative damage. Small molecule fluorescent probes have been widely used in biology, pathology and medical diagnosis due to their advantages of noninvasive, high sensitivity and in vivo real-time detection. It is extremely important to better apply small-molecule fluorescent probes to detect ROS levels in organisms to achieve early diagnosis of diseases and assessment of therapeutic conditions. This work focuses on summarizing the representative applications of some fluorescent probes in ROS disease models in recent years. This article focuses on summarizing the construction methods of various ROS-related disease models, and classifying and analyzing the basic ideas and methods of fluorescent probes applied to disease models according to the characteristics of various diseases.

Dual-channel detection of viscosity and pH with a near-infrared fluorescent probe for cancer visualization

Compared to ordinary cells, tumor cells have a unique microenvironment, characterized by high viscosity, low pH, high reactive oxygen species level and the overexpression of certain proteases. Therefore, viscosity and pH can be used as important parameters for visualizing cancer. We designed a spiro-oxazolidine compound (In-1) for the dual-channel detection of viscosity and pH, with the red channel for detecting viscosity and the blue channel for pH. Interestingly, In-1 can locate different organelles under different conditions. Under physiological conditions, In-1 efficiently targeted lysosomes and showed that the viscosity of lysosomes increases in cancer cells while the pH decreases, which can be used to distinguish and detect cancer cells and normal cells. When we treated HL-7702 cells with CCCP, the probe could effectively target the mitochondria, and the fluorescence intensity in the pH channel decreased. This indicates that In-1 can be used as a powerful tool to simultaneously monitor viscosity and pH in different organelles, and may have a guiding role in diseases caused by mitochondrial and lysosomal microenvironments.