Chameleon-Like Fluorescent Probe for Monitoring Interplays between Three Organelles and Reporting Cell Damage Processes through Dramatic Color Change

Wash-free and ultra-low concentration monitor lysosomal viscosity in apoptosis with a noteworthy fluorescent probe

The visualization and subsequent monitoring of apoptosis holds paramount significance in the domains of physiology, pathology, and pharmacology. However, traditional probes require high staining concentrations and multiple washing steps, which would alter the specimen's micro-environment, potentially inducing harm to specimen. To overcome these challenging issues, we have rationally designed and prepared a pH-inert lysosomal probe (named IVTI) to wash-free visualize apoptosis with ultra-low concentration to alleviate the disturbance of probe concentration, washing procedure and pH variations. Compared with general lysosomal probes, IVTI showed a significant fluorescence boost in reflex to elevated viscosity, while its fluorescence intensity remained mostly still when altering pH values, which could achieve more accurate visualization of lysosomes. Moreover, the probe can detect minute viscosity fluctuations in lysosomes under extra-low concentration, greatly eliminating the effect of probe concentration and washing steps to live bio-samples. Furthermore, compared to LTR (Lyso-Tracker Red, a commercial lysosome probe), IVTI offered exceptional imaging capabilities, and the fluorescence images of IVTI was still clear when lysosomal pH increased, which attributed to the pH-inert properties of IVTI. In view of the excellent imaging abilities, the pH-inert probe was applied to in-situ and real time visualize viscosity changes of live cells under extra-low concentration without washing procedure, and the increase of lysosomal viscosity during apoptosis was also monitored by the probe, thereby minimizing the disturbance of probe concentration, washing procedure and pH variations during apoptosis. The probe possesses tremendous potential in the visualization of dynamic changes related to lysosomes in various physiological processes.

Mitochondria-Nucleus Migration Probe for Ultrasensitive Monitoring of mtDNA Damage in Living Cells

Mitochondrial DNA (mtDNA) damage is a prevalent phenomenon that has been proven to be implicated in a wide spectrum of diseases. However, the progressive attenuation of probe signals in response to mtDNA damage within living cells inherently limits the sensitivity and precision of current probes for detecting mtDNA damage. Herein, we employ an innovative organelle signal ratio imaging approach, utilizing the mitochondria-nucleus migration probe MCQ, to achieve unparalleled sensitivity in detecting mtDNA damage in living cells. MCQ exhibited an initial preferential binding to mtDNA, facilitated by its cationic quinolinium moiety, but migrated to the nucleus upon mtDNA damage. This unique migration behavior not only enhanced the spatial identifiability of mtDNA damage but also amplified detection sensitivity and precision significantly by harnessing the intensified nucleus signal against the attenuated mitochondrial signal. This innovative approach established a positive correlation between the signal and mtDNA damage, enabling the detection of even subtle mtDNA damage at the early stage of apoptosis with a remarkable 23-fold enhancement following just 5 min H2O2 induction in living cells, whereas conventional methods relying solely on the fading of mitochondrial signals proved insufficient. Furthermore, MCQ's ability to monitor the occurrence of mtDNA damage achieved the intricate differentiation between apoptosis and ferroptosis. By monitoring mtDNA damage, drug-induced apoptosis in cancer cells was further conducted using MCQ to evaluate the therapeutic efficacy of four anticancer drugs at very low concentrations. This innovative strategy not only paves the way for ultrasensitive detection of mtDNA damage but also holds immense promise for early monitoring of mtDNA damage-associated diseases.

Intramolecular Charge Transfer Inhibition Strategy toward a Desired Solvatochromic Fluorescent Platform: Visualization of Duple Organelles and Detection of Carbon Dioxide

Solvatochromic fluorescent probes are crucial molecular tools to investigate and aggregate proteins' fold, visualize fine structures in biomembranes, and label different organelles in dual emission colors. However, solvatochromic fluorogens often displayed a weak emission at high polarity, hindering their bioimaging applications. To resolve this problem, herein, we propose an intramolecular charge transfer (ICT) inhibition strategy. The probe was designed with a single electronic donor and two acceptors in order to split and inhibit the ICT procedure. As a result, the probe displayed an intense emission at both low and high polarities and showed a large emission shift (84 nm) upon polarity change. Using the probe, we successfully imaged lipid droplets and the endoplasmic reticulum in different fluorescence colors. Moreover, the different degrees of lipid accumulation by oleic acid, stearic acid, and cholesterol (oleic acid > stearic acid > cholesterol) have been revealed. The lipid accumulation induced by the three lipids could be rapidly consumed under lipid-less conditions, and the lipids with stearic acid were the most difficult to be consumed. The biological results could facilitate the understanding and treatment of lipid accumulation and obesity. Furthermore, utilizing the polarity increase of diethylamine after the reaction with CO2, the ratiometric detection of CO2 has been achieved for the first time with the probe.

Mitochondria-Specific Fluorescent Probe for Revealing the Interaction between Mitochondria and Lysosomes during Apoptosis

The mitochondria, as one of the essential organelles in cells, are closely associated with numerous biological processes. Therefore, the realization of clear and real-time imaging for tracking mitochondria is of profound significance. Here, we present a mitochondria-targeting fluorescent probe, N(CH2)3-PD-NEt, for the real-time fluorescence imaging of mitochondria in living cells. Using the probe, the fluorescence changes of mitochondria stimulated by different drugs were successfully observed by fluorescence imaging. In addition, the dynamic processes of mitochondria and lysosomes during apoptosis were also explored. Importantly, we observed several novel dynamic interaction patterns between mitochondria and lysosomes. Among them, the most prominent pattern involved the noncontact movements of two lysosomes, that is, one lysosome gradually approached the other lysosome over time, eventually coming into contact and merging with it while gradually combining with mitochondria to form new mitochondria. Notably, the protrusions of the mitochondria became increasingly evident during this process. Meanwhile, we successfully observed the dynamic changes of mitochondria with SIM super-resolution imaging. The study provides promising help for the in-depth study of the dynamic processes of mitochondrial physiology and pathology and the study of the interactions between organelles.

Unveiling Cellular Microenvironments with a Near-Infrared Fluorescent Sensor: A Dual-Edge Tool for Cancer Detection and Drug Screening

Mitochondria and lysosomes are pivotal intracellular organelles, and the injury or dysfunction of these organelles can trigger a range of pathological processes. Early diagnosis and treatment of cancer are of paramount importance due to cancer's status as a leading health threat. This study introduces a novel fluorescent probe, BDHV, for detecting mitochondrial and lysosomal viscosity and pH abnormalities in tumors, facilitating early cancer detection and screening of anticancer drugs. Under acidic conditions, the red fluorescence of the probe gradually increases with increasing viscosity. Conversely, in alkaline environments, an increase in viscosity leads to a decrease in green fluorescence and an increase in red fluorescence. The inclusion of a benzothiazole group endows BDHV with strong dual-targeting capability for mitochondria and lysosomes and without being affected by the mitochondrial membrane potential. Most notably, BDHV has potential applications for early cancer diagnosis and in effectively assessing the efficacy of various anticancer drugs.

Development of a fluorescent scaffold by utilizing quercetin template for selective detection of Hg2+: Experimental and theoretical studies along with live cell imaging

Quercetin is an important antioxidant with high bioactivity and it has been used as SARS-CoV-2 inhibitor significantly. Quercetin, one of the most abundant flavonoids in nature, has been in the spot of numerous experimental and theoretical studies in the past decade due to its great biological and medicinal importance. But there have been limited instances of employing quercetin and its derivatives as a fluorescent framework for specific detection of various cations and anions in the chemosensing field. Therefore, we have developed a novel chemosensor based on quercetin coupled benzyl ethers (QBE) for selective detection of Hg2+ with "naked-eye" colorimetric and "turn-on" fluorometric response. Initially QBE itself exhibited very weak fluorescence with low quantum yield (Φ = 0.009) due to operating photoinduced electron transfer (PET) and inhibition of excited state intramolecular proton transfer (ESIPT) as well as intramolecular charge transfer (ICT) within the molecule. But in presence of Hg2+, QBE showed a sharp increase in fluorescence intensity by 18-fold at wavelength 444 nm with high quantum yield (Φ = 0.159) for the chelation-enhanced fluorescence (CHEF) with coordination of Hg2+, which hampers PET within the molecule. The strong binding affinity of QBE towards Hg2+ has been proved by lower detection limit at 8.47 µM and high binding constant value as 2 × 104 M-1. The binding mechanism has been verified by DFT study, Cyclic voltammograms and Jobs plot analysis. For the practical application, the binding selectivity of QBE with Hg2+ has been capitalized in physiological medium to detect intracellular Hg2+ levels in living plant tissue by using green gram seeds. Thus, employing QBE as a fluorescent chemosensor for the specific identification of Hg2+ will pave the way for a novel approach to simplifying the creation of various chemosensors based on quercetin backbone for the precise detection of various biologically significant analytes.

Fluorescent Probe as Dual-Organelle Localizer Through Differential Proton Gradients Between Lipid Droplets and Mitochondria

Dual-organelle molecular localizers represent powerful new tools allowing the exploration of interorganelle physical contacts and subcellular chemical communication. Here, we describe new dynamic molecular probes to localize mitochondria and lipid droplets taking advantage of the differential proton gradients present in these organelles as well as the activity of mitochondrial esterase. We unveil their potential utility when organelle retention mechanisms and proton gradients are synchronized, an insight that has not been documented previously. Our discoveries indicate that dual-organelle probes serve as a valuable multiplexing assay during starvation-induced autophagy. The pioneering molecular mechanism they employ opens doors to avoid using labile esters such as acetoxymethyl derivatives which are not optimal in imaging microscopy assays.

pH-triggered hydrophility-adjustable fluorescent probes for simultaneously imaging lipid droplets and lysosomes and the application in fatty liver detection

To study the collaboration between lipid droplets (LDs) and lysosomes, and the lipid change in nonalcoholic fatty liver disease (NAFLD), herein two pH-triggered hydrophility-adjustable fluorescent probes (LD-Lyso and LD-Lyso 1) are designed. The mechanism is based on cyclization and ring-opening with thorough consideration of pH and hydrophilic differences between LDs and lysosomes. Both of the two probes exist in ring-opening form and emit red fluorescence in acidic environment, while they exist in cyclized form and the emission is blueshifted in alkaline environment due to reduced conjugate planes. Moreover, LD-Lyso exhibits near infrared fluorescence at 740 nm under ring-opening form, which facilitates further cell, tissue, and in vivo imaging. The cell imaging results show that LD-Lyso can simultaneously target LDs and lysosomes by two different colors. Impressively, LD-Lyso cannot only detect NAFLD tissues from the normal tissue, but also distinguish different degrees of NAFLD tissues and mice, which provides a very promising tool for timely diagnosis of early NAFLD.

Single Fluorescent Probe for Multiple Tasks: Illuminating Lipid Droplets and Lysosomes in Dual Channels and Distinguishing Autophagy and Apoptosis

Lipid droplets (LDs) and lysosomes play key roles in autophagy and cell apoptosis, and the discriminative visualization of the two organelles and simultaneously of autophagy and apoptosis is very helpful to understand their internal relationships. However, fluorescent probes that can concurrently achieve these tasks are not available currently. Herein, we delicately fabricate a robust probe CAQ2 for multiple tasks: illumination of LDs and lysosomes in dual emission colors as well as discriminative visualization of cell apoptosis and autophagy. The probe exhibited both lipophilic and basic properties and displayed different emission colors in neutral and protonated forms; thus, LDs and lysosomes emitted blue and red fluorescence colors, respectively. Because of the lysosomal acidification during autophagy, CAQ2 detected autophagy with evidently enhanced red emission. Because of the lysosomal alkalization during apoptosis, CAQ2 imaged apoptosis with a drastically decreased red fluorescence intensity. With the robust probe, the autophagy under starvation and lipidless conditions was visualized, and the apoptosis induced by H2O2, ultraviolet (UV) irradiation, and rotenone treatment was successfully observed. The efficient detoxification of Na2S against rotenone treatment was successfully revealed.

Mild synthesis of ultra-bright carbon dots with solvatochromism for rapid lipid droplet monitoring in varied physiological processes

Lipid droplets (LDs) participating in various cellular activities and are increasingly being emphasized. Fluorescence imaging provides powerful tool for dynamic tracking of LDs, however, most current LDs probes remain inconsistent performance such as low Photoluminescence Quantum Yield (PLQY), poor photostability and tedious washing procedures. Herein, a novel yellow-emissive carbon dot (OT-CD) has been synthesized conveniently with high PLQY up to 90%. Besides, OT-CD exhibits remarkable amphiphilicity and solvatochromic property with lipid-water partition coefficient higher than 2, which is much higher than most LDs probes. These characters enable OT-CD high brightness, stable and wash-free LDs probing, and feasible for in vivo imaging. Then, detailed observation of LDs morphological and polarity variation dynamically in different cellular states were recorded, including ferroptosis and other diseases processes. Furthermore, fast whole imaging of zebrafish and identified LD enrichment in injured liver indicate its further feasibility for in vivo application. In contrast to the reported studies to date, this approach provides a versatile conventional synthesis system for high-performance LDs targeting probes, combing the advantages of easy and high-yield production, as well as robust brightness and stability for long-term imaging, facilitating investigations into organelle interactions and LD-associated diseases.

Dual-Labeled Single Fluorescent Probes for the Simultaneous Two-Color Visualization of Dual Organelles and for Monitoring Cell Autophagy

Dual-labeled single fluorescent probes are powerful tools for studying autophagy on the molecular scale, yet their development has been hampered by design complexity and a lack of valid strategies. Herein, for the first time, we introduce a combinatorial regulation strategy to fabricate dual-labeled probes for studying autophagy by integrating the specific organelle-targeting group and the functional fluorescence switch into a pentacyclic pyrylium scaffold (latent dual-target scaffold). For proof of concept, we prepared a range of dual-labeled probes (TMOs) that display different emission colors in duple organelles. In these probes, TMO1 and TMO2 enabled the simultaneous two-color visualization of the lysosomes and mitochondria. The other probes (TMO3 and TMO4) discriminatively targeted lysosomes/nucleolus and lysosomes/lipid droplets (LDs) with dual-color emission characteristics, respectively. Intriguingly, by simply connecting the endoplasmic reticulum (ER) targeting group to the pentacyclic pyrylium scaffold, we created the first dual-labeled probe TMO5 for simultaneously labeling lysosomes/ER in distinctive fluorescent colors. Subsequently, using the dual-labeled probe TMO2, drug-induced mitophagy was successfully recorded by evaluating the alterations of multiple mitophagy-related parameters, and the mitophagy defects in a cellular model of Parkinson's disease (PD) were also revealed by simultaneous dual-color/dual-organelle imaging. Further, the probe TMO4 can track the movement of lysosomes and LDs in real time and monitor the dynamic process of lipophagy. Therefore, this work not only presents attractive dual-labeled probes to promote the study of organelle interactions during autophagy but also provides a promising combinatorial regulation strategy that may be generalized for designing other dual-labeled probes with multiple organelle combinations.

A Benzil- and BODIPY-Based Turn-On Fluorescent Probe for Detection of Hydrogen Peroxide

Faced with rising threats of terrorism, environmental and health risks, achieving sensitive and selective detection of peroxide-based explosives (PEs) has become a global focus. In this study, a turn-on fluorescent probe (BOD) based on benzil (H2O2-recognition element) and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivative (fluorophore) was developed to sensitively and specifically detect hydrogen peroxide (H2O2). The synthesized BOD had a very weak fluorescence due to intramolecular donor-excited photo-induced electron transfer (d-PET) effect; however, it could emit a strong fluorescence since H2O2 selectively oxidized the benzil moiety and released free BODIPY fluorophore (BOD-COOH). As a result, the proposed BOD detected H2O2 in linear detection ranged from 25 to 125 µM with a detection limit of 4.41 µM. Meanwhile, the proposed BOD showed good selectivity toward H2O2, which is not affected by other common reactive oxygen species (ROS) and ions from explosive residues. In addition, a blue shift from 508 to 498 nm was observed in the absorption spectra upon addition of H2O2. More importantly, the BOD was successfully applied for rapid detection of H2O2 vapor with good sensitivity (down to 7 ppb), which holds great potential for practical use in public safety, forensic analysis and environmental monitoring.

Rational Design of Cost-Effective 4-Styrylcoumarin Fluorescent Derivatives for Biomolecule Labeling

Fluorescent labels are key tools in a wide range of modern scientific applications, such as fluorescence microscopy, flow cytometry, histochemistry, direct and indirect immunochemistry, and fluorescence in situ hybridization (FISH). Small fluorescent labels have important practical advantages as they allow maximizing the fluorescence signal by binding multiple fluorophores to a single biomolecule. At present, the most widely used fluorescent labels available present small Stokes shifts and are too costly to be used in routine applications. In this work we present four new coumarin derivatives, as promising and inexpensive fluorescent labels for biomolecules, obtained through a cost-effective, efficient, and straightforward synthetic strategy. Density functional theory and time-dependent density functional theory calculations of the electronic ground and lowest-lying singlet excited states were carried out in order to gain insights into the observed photophysical properties.

New Advances in the Exploration of Esterases with PET and Fluorescent Probes

Esterases are hydrolases that catalyze the hydrolysis of esters into the corresponding acids and alcohols. The development of fluorescent probes for detecting esterases is of great importance due to their wide spectrum of biological and industrial applications. These probes can provide a rapid and sensitive method for detecting the presence and activity of esterases in various samples, including biological fluids, food products, and environmental samples. Fluorescent probes can also be used for monitoring the effects of drugs and environmental toxins on esterase activity, as well as to study the functions and mechanisms of these enzymes in several biological systems. Additionally, fluorescent probes can be designed to selectively target specific types of esterases, such as those found in pathogenic bacteria or cancer cells. In this review, we summarize the recent fluorescent probes described for the visualization of cell viability and some applications for in vivo imaging. On the other hand, positron emission tomography (PET) is a nuclear-based molecular imaging modality of great value for studying the activity of enzymes in vivo. We provide some examples of PET probes for imaging acetylcholinesterases and butyrylcholinesterases in the brain, which are valuable tools for diagnosing dementia and monitoring the effects of anticholinergic drugs on the central nervous system.

Recent Progress of Activity-Based Fluorescent Probes for Imaging Leucine Aminopeptidase

Leucine aminopeptidase (LAP) is an important protease that can specifically hydrolyze Leucine residues. LAP occurs in microorganisms, plants, animals, and humans and is involved in a variety of physiological processes in the human body. In the physiological system, abnormal levels of LAP are associated with a variety of diseases and pathological processes, such as cancer and drug-induced liver injury; thus, LAP was chosen as the early biochemical marker for many physiological processes, including cancer. Considering the importance of LAP in physiological and pathological processes, it is critical that high-efficiency and dependable technology be developed to monitor LAP levels. Herein, we summarize the organic small molecule fluorescence/chemiluminescence probes used for LAP detection in recent years, which can image LAP in cancer, drug-induced liver injury (DILI), and bacteria. It can also reveal the role of LAP in tumors and differentiate the serum of cirrhotic, drug-induced liver injury and normal models.

A review: Small organic molecule dual/multi-organelle-targeted fluorescent probes

In recent years, the dual/multi-organelle-targeted fluorescent probe based on small organic molecules has good biocompatibility and can visualize the interaction between different organelles, which has attracted much attention. In addition, these probes can also be used to detect small molecules in the organelle environment, such as active sulfur species (RSS), reactive oxygen species (ROS), pH, viscosity and so on. However, the review of dual/multi-organelle-targeted fluorescent probe for small organic molecules lacks a systematic summary, which may hinder the development of this field. In this review, we will focus on the design strategies and bioimaging applications of dual/multi-organelle-targeted fluorescent probe, and classify them into six classes according to different organelles targeted. The first class probe targeted mitochondria and lysosome. The second class probe targeted endoplasmic reticulum and lysosome. The third class probe targeted mitochondria and lipid droplets. The fourth class probe targeted endoplasmic reticulum and lipid droplets. The fifth class probe targeted lysosome and lipid droplets. The sixth class multi-targeted probe. The mechanism of these probes targeting organelles and the visualization of the interaction between different organelles are emphasized, and the prospect and future development direction of this research field are prospected. This will provide a systematic idea for the development and functional research of dual/multi-organelle-targeted fluorescent probe, and promote its research in related physiological and pathological medicine field in the future.

NIR Mitochondrial Fluorescent Probe for Visualizing SO2/Polarity in Drug Induced Inflammatory Mice

SO₂ and polarity are important microenvironmental parameters in cells, which are closely related to physiological activities in organisms. The intracellular levels of SO₂ and polarity are abnormal in inflammatory models. To this end, a novel near-infrared fluorescent probe BTHP that can simultaneously detect SO₂ and polarity was studied. BTHP can sensitively detect polarity change with emission peak change from 677 to 818 nm. BTHP can also detect SO₂ with fluorescence change from red to green. After addition of SO₂, the fluorescence emission intensity ratio I₅₁₇/I₇₆₈ of the probe increased by about 33.6 times. BTHP can determine bisulfite in single crystal rock sugar with high recovery rate (99.2%-101.7%). Fluorescence imaging of cells showed that BTHP could better target mitochondria and monitor exogenous SO₂ in A549 cells. More importantly, BTHP has been successfully used for dual channel monitoring SO₂ and polarity in drug-induced inflammatory cells and mice. In particular, the probe showed increased green fluorescence with the generation of SO₂ and increased red fluorescence with the decrease of polarity in inflammatory cells and mice.