BODIPY-Based Two-Photon Fluorescent Probe for Real-Time Monitoring of Lysosomal Viscosity with Fluorescence Lifetime Imaging Microscopy

Emerging fluorescent probes for bioimaging of drug-induced liver injury biomarkers: Recent advances

Drug-induced liver injury (DILI) has emerged as a significant concern in clinical settings, being one of the leading causes of acute liver failure. However, the specific pathogenesis of DILI remains unclear, and there is currently a lack of effective targeted therapies. Numerous studies have demonstrated that the occurrence and progression of DILI involve complex pathological processes, closely linked with various cellular substrates and microenvironments. Thus, developing non-invasive, highly sensitive, specific, and reliable methods to detect changes in biomarkers and microenvironments in situ would greatly aid in the precise diagnosis of DILI and help guide therapeutic interventions. Fortunately, fluorescence imaging technology has shown great promise in detecting biological species, microenvironments, and diagnosing DILI due to its superior detection capabilities. In this context, this review described the design strategies, working principles, and practical applications of small molecule fluorescent probes for monitoring biological species and microenvironments in DILI. Importantly, this review highlighted current limitations and future development directions, which may help uncover the underlying relationships between biological species, microenvironments, and DILI. This understanding could lead to potential diagnostic protocols and establish a platform for evaluating treatments and drug efficacy in DILI.

Development of multifunctional fluorescence-emitting potential theranostic agents for Alzheimer's disease

The cholinergic deficits and amyloid beta (Aβ) aggregation are the mainstream simultaneously observed pathologies during the progression of Alzheimer's disease (AD). Deposited Aβ plaques are considered to be the primary pathological hallmarks of AD and are contemplated as promising diagnostic biomarker. Herein, a series of novel theranostic agents were designed, synthesised and evaluated against cholinesterase (ChEs) enzymes and detection of Aβ species, which are major targets for development of therapeutics for AD. Among all the tested compounds against ChEs enzymes, compound/probe 39 & 43 exhibited potent inhibitory activities. Its excellent BBB permeability was anticipated in PAMPA assay. Measurement of fluorescent properties showed emission maxima (λemm) in between 530 and 550 nm in distinct organic solvent except in the most polar solvent i.e., PBS (10 % DMSO), where broad absorption (λabs of 440 nm) and emission spectrum (λemm of 640 nm) was observed. The relative fluorescence quantum yield of probe 39 in methanol was found to be 0.17. The increase in fluorescence intensity displayed by the probe 39 upon binding with Aβ aggregates in the in vitro assay, and produced high apparent binding constant. Further, it's binding affinity towards Aβ1-42 aggregates was validated on the basis of colocalization with thioflavin T (ThT). A significant enhancement in the fluorescence lifetime of probe 39 on binding with Aβ aggregates was observed in time-correlated single-photon counting (TCSPC) analysis (10.00 ± 1.12 ns) and fluorescence lifetime imaging microscopy (FLIM) imaging (11.53 ± 0.01 ns). Furthermore, acute oral toxicity studies signified the safety profile of lead probe 39. The in-vivo behavioural studies demonstrated a substantial improvement of cognitive and special memory impairment in the scopolamine-induced cognitive deficit in mice model on the administration of compound 39 at a dose of 20 mg/kg. The AChE inhibitory potential and antioxidant property of lead probe 39 were further accessed with ex vivo biochemical analysis. Together, our findings suggest Probe 39 as a promising theranostic agent for the AD.

Mechanistic study of tumor fluorescence response signals based on a near-infrared viscosity-sensitive probe

Viscosity is an important physiological parameter closely associated with various cellular processes and diseases. Several fluorescence probes responsive to viscosity have been developed, demonstrating high sensitivity specifically towards tumor tissues. However, the underlying core mechanism of this highly potential responsive signal has been a subject of debate, as highly sensitive probes encounter excessive environmental interferences in complex tumor tissues. Therefore, we have developed a viscosity-responsive fluorescence probe based on the classical TICT mechanism (twisted intramolecular charge transfer) as a research tool. This probe features an ultra-wide emission range of 700-1200 nm in the near-infrared spectrum, strong photostability, and simultaneous targeting of mitochondria and lysosomes. Through in-depth analysis, we have revealed the intrinsic mechanisms underlying its functionality, demonstrating that the major contributor to the fluorescence change of responsive probes during imaging is the inherent state of cells rather than the tumor microenvironment or the cell type. Our findings provide a theoretical foundation for the continued exploration and application of viscosity-responsive probes.

Measuring plasma membrane fluidity using confocal microscopy

Membrane fluidity is a crucial parameter for cellular physiology. Recent evidence suggests that fluidity varies between cell types and states and in diseases. As membrane fluidity has gradually become an important consideration in cell biology and biomedicine, it is essential to have reliable and quantitative ways to measure it in cells. In the past decade, there has been substantial progress both in chemical probes and in imaging tools to make membrane fluidity measurements easier and more reliable. We have recently established a robust pipeline, using confocal imaging and new environment-sensitive probes, that has been successfully used for several studies. Here we present our detailed protocol for membrane fluidity measurement, from labeling to imaging and image analysis. The protocol takes ~4 h and requires basic expertise in cell culture, wet lab and microscopy.

Optoelectronic Properties and Fluorescence Lifetime Imaging Application of Donor-Acceptor Dyads Derived From 2,6-DicarboxyBODIPY

Donor-acceptor BODIPY dyads, functionalized at the 2 and 6 positions with benzyl ester (BDP-DE) or carboxylic acid (BDP-DA) groups, were synthesized, and their optoelectronic properties were investigated. Carbonyl groups were found to increase the reduction potential of the BODIPY core by 0.15-0.4 eV compared to regular alkyl-substituted BODIPYs. These compounds exhibited efficient intramolecular charge separation and triplet state formation through the spin-orbit charge transfer intersystem crossing (SOCT-ISC) process, achieving singlet oxygen quantum yields of up to 92 %, depending on the solvent polarity. Notably, the fluorescence and singlet oxygen generation of BDP-DAs were found to depend on the ionization state of the carboxylic groups. Time-resolved fluorescence measurements revealed that complexation of BDP-DAs with bovine serum albumine (BSA) significantly extended their excited state lifetimes. Fluorescence lifetime imaging microscopy (FLIM) studies of human colorectal carcinoma (HCT116) cells and pig small intestinal organoids (enteroids) provided insights into subcellular localization. The diacid with 2,4-dimethoxyphenyl group at the meso-position (DA1) displayed longer lifetimes in lipid-droplet-like structures and shorter lifetimes in cytoplasmic regions. The diacid containing a meso-anthracenyl group (DA2) formed 'islands' in cell monolayers, exhibiting a distinct lifetime gradient from the periphery to the center. These results highlight the potential of donor-acceptor BODIPYs as fluorescent probes for biological imaging, particularly in revealing subtle differences in cellular environments.

Aggregation-induced emission-based fluorescent probes for cellular microenvironment detection

The cellular microenvironment exerts a pivotal regulatory influence on cell survival, function, and behavior. Dynamic analysis and detection of the cellular microenvironment can promptly elucidate changes in cellular microenvironmental information, uncover the pathogenesis of diseases associated with aberrant microenvironments, and aid in predicting disease risk and monitoring disease progression. Aggregation-induced emission (AIE) fluorescent molecules possess unique AIE characteristics and offer significant advantages in imaging and sensing cellular microenvironments. In this review, we present a profile of the remarkable progress achieved in utilizing AIE fluorescent molecules for detecting cellular microenvironments in recent years. We particularly focus on AIE fluorescent probes applied in imaging key parameters of the cellular microenvironment, including pH, viscosity, polarity, and temperature, as well as in analyzing critical biological components of the microenvironment, such as gas signal molecules, metal ions, redox state, and proteins. We underscore the design principles, detection mechanisms, sensing performance, and biological applications of these fluorescent probes. Furthermore, we address the current challenges confronting this field and provide prospects for the future development of AIE probes used for microenvironment detection. We trust that this review will inspire researchers to develop more precise and sensitive AIE fluorescent probes for the detection of cellular microenvironments.

The Molecular Mechanism of Fluorescence Lifetime of Fluorescent Probes in Cell Membranes

Fluorescence probes play crucial roles in unraveling the structure and dynamics of cell membranes including membrane fluidity, polarity, and lipid molecule ordering. The fluorescence lifetime of probes describes the average duration of time that a fluorescent molecule remains in an excited state before returning to the ground state, which is sensitive to environmental changes. However, the molecular mechanism and inherent properties to determine the fluorescence lifetimes remain unexplored and inadequately studied. Furthermore, the effects of the probe on the membrane are also unclear. In this study, we investigated the interactions between probes and lipids, as well as the structural properties of probes within the outer and inner membrane of Mycobacterium smegmatis (Msm) by combining molecular dynamics (MD) simulations, enhanced sampling methods, fluorescence lifetime imaging microscopy (FLIM), and time-correlated single photon counting (TCSPC). The results show that even though the probes have very little effect on the membrane lipids, different membrane environments significantly affect the fluorescence lifetime of the probes. The analysis based on the all-atom simulations shows a strong correlation between the probe's immersion depth within the membrane and its fluorescence lifetime. Specifically, probes buried in the membrane environment shielded from rapid water molecule collisions exhibit longer fluorescence lifetimes. The molecular basis of the fluorescence lifetime of probes in cell membranes revealed in this work would enhance the comprehension of fluorescence probes and facilitate the rational design of novel efficient probes.

Mitochondrial membrane potential-independent near-infrared fluorescent probes for viscosity-exclusive imaging

Elucidating the intrinsic relationship between disease and mitochondrial viscosity is crucial for early diagnosis. However, current mitochondrial viscosity fluorescent probes are highly dependent on mitochondrial membrane potential (MMP) and are sensitive to other mitochondrial microenvironment parameters. To address these issues, a mitochondria-targeting MMP-independent and viscosity exclusive near-infrared (NIR) fluorescent probe, ACR-DMA, was developed. ACR-DMA consists of thiophene acetonitrile as the skeleton and viscosity-sensitive unit, a pyridinium cation for the mitochondria-targeting group, and a benzyl bromide subunit for mitochondrial immobilization. It is very sensitive to viscosity and shows significant "turn-on" fluorescence behavior at 710 nm with a more than 150-fold fluorescence intensity increase. Furthermore, ACR-DMA can be firmly immobilized in mitochondria and can monitor viscosity changes induced by nystain, monensin, and lipopolysaccharide. Additionally, it was successfully used to visualize mitochondrial viscosity changes resulting from tumors, inflammation, and drug-induced acute kidney injury, revealing the relationship between viscosity and disease both in vitro and in vivo. ACR-DMA is expected to be a promising candidate for diagnosing mitochondrial viscosity-related diseases.

AIE-active large Stokes-shift BODIPY Functionalized with Carbazolyl for Lysosome-Targeted Imaging in Living Cells

A large number of studies have shown that lysosomal microcircumstances changes can affect many physiological and pathological processes at the cellular level. However, the visual detection of lysosomal microcircumstances is relatively difficult due to low pH (4.5-6.0) value in lysosomal that require the probe not only stable under acidic condition but also has a good localization effect to lysosomal. Obviously, novel fluorescent which possessed both acidic stability and lysosomal-target property together with lysosomal viscosity active is highly demanded. Herein, a novel BODIPY molecular CarBDP based on carbazole group was rationally designed and synthesized for the lysosomal imaging. CarBDP exhibited AIE feature with a large Stokes shift of up to 157 nm. More importantly, co-localization assay of the CarBDP-treated MCF-7 cells indicated that CarBDP has a good localization effect on lysosomal (Rr = 0.7109) due to the carbazole group while the normal BODIPY that without carbazole group (PhBDP) shows poor localization performance, this was the first time that a small molecule can locate lysosomes only based on carbazole group. CarBDP exhibits strong solid emission with long fluorescence decay lifetime (τ = 44.54 ns) and was stable under acid condition.The probe CarBDP assembled with carbazole group was successfully utilized for lysosomal localization and mapping lysosomal viscosity in live cells, which provides a novel candidate tool for the determination of lysosomal microcircumstances.

Xylan-based near-infrared fluorescent probes for monitoring viscosity abnormalities in living cells and zebrafish

Viscosity is a crucial indicator of the flow state of proteins, lipids, and polysaccharides in the cell microenvironment and plays a vital role in maintaining normal cellular activities. Abnormal viscosity in any part of the cell constituents can lead to various diseases in the organism. For instance, abnormal mitochondrial viscosity can lead to diseases, such as diabetes and Parkinson's disease. Therefore, real-time monitoring of changes in mitochondrial viscosity in both pathological and physiological environments is relevant. This study describes a water-soluble xylan-based near-infrared fluorescence probe that can detect changes in cellular viscosity. The designed mitochondria-targeting near-infrared fluorophores were introduced into modified xylan to form a viscosity-sensing fluorescent probe (NI-XylV). The fluorescence intensity of NI-XylV at 590 and 670 nm gradually increases with an increase in viscosity caused by environmental changes, enabling the sensitive detection of viscosity changes in mitochondria within living cells. NI-XylV exhibits good photostability, biocompatibility, excellent mitochondrial targeting, and broad application prospects as a bio-based fluorescence probe.

Unveiling intracellular phase separation: advances in optical imaging of biomolecular condensates

Intracellular biomolecular condensates, which form via phase separation, display a highly organized ultrastructure and complex properties. Recent advances in optical imaging techniques, including super-resolution microscopy and innovative microscopic methods that leverage the intrinsic properties of the molecules observed, have transcended the limitations of conventional microscopies. These advances facilitate the exploration of condensates at finer scales and in greater detail. The deployment of these emerging but sophisticated imaging tools allows for precise observations of the multiphasic organization and physicochemical properties of these condensates, shedding light on their functions in cellular processes. In this review, we highlight recent progress in methodological innovations and their profound implications for understanding the organization and dynamics of intracellular biomolecular condensates.

Glutathione and viscosity double-locked response fluorescent probe for imaging and surgical navigation of hepatocellular carcinoma

Early diagnosis and precise treatment of hepatocellular carcinoma (HCC) are crucial for human health. Therefore, addressing the potential markers of HCC, glutathione (GSH) and viscosity, we constructed a fluorescent probe (PG-V) activated cascadically by GSH/viscosity. PG-V possessed excellent photophysical properties and biocompatibility, and could specifically illuminate tumor tissue, achieving fluorescence imaging of HCC, and imaging-guided tumor resection.

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.

Construction of cationic meso-thiazolium-BODIPY AIE fluorescent probes for viscosity imaging in dual organelles

Two new cationic meso-thiazolium-BODIPY-based water-soluble and red-shifted fluorescent probes were constructed for the first time. They can monitor cellular viscosity in dual organelles and show aggregation-induced emission (AIE), which is ascribed to the efficient restricted rotation of meso-thiazolium in viscous or hindered systems. Probe 3 with an N-benzyl group shows better AIE as compared to probe 2 with an N-methyl group.

Dissecting lysosomal viscosity fluctuations in live cells and liver tissues with an ingenious NIR fluorescent probe

Viscosity is a pivotal component in the cell microenvironment, while lysosomal viscosity fluctuation is associated with various human diseases, such as tumors and liver diseases. Herein, a near-infrared fluorescent probe (BIMM) based on merocyanine dyes was designed and synthesized for detecting lysosomal viscosity in live cells and liver tissue. The increase in viscosity restricts the free rotation of single bonds, leading to enhanced fluorescence intensity. BIMM exhibits high sensitivity and good selectivity, and is applicable to a wide pH range. BIMM has near-infrared emission, and the fluorescent intensity shows an excellent linear relationship with viscosity. Furthermore, BIMM possessing excellent lysosomes-targeting ability, and can monitor viscosity changes in live cells stimulated by dexamethasone, lipopolysaccharide (LPS), and nigericin, and differentiate between cancer cells and normal cells. Noticeably, BIMM can accurately analyze viscosity changes in various liver disease models with HepG2 cells, and is successfully utilized to visualize variations in viscosity on APAP-induced liver injury. All the results demonstrated that BIMM is a powerful wash-free tool to monitor the viscosity fluctuations in living systems.

Exploration of Novel Meso-C═N-BODIPY-Based AIE Fluorescent Rotors with Large Stokes Shifts for Organelle-Viscosity Imaging

The research on fluorescent rotors for viscosity has attracted extensive interest to better comprehend the close relationships of microviscosity variations with related diseases. Although scientists have made great efforts, fluorescent probes for cellular viscosity with both aggregation-induced emissions (AIEs) and large Stokes shifts to improve sensing properties have rarely been reported. Herein, we first report four new meso-C═N-substituted BODIPY-based rotors with large Stokes shifts, investigate their viscosity/AIE characteristics, and perform cellular imaging of the viscosity in subcellular organelles. Interestingly, the meso-C═N-phenyl group-substituted probe 6 showed an obvious 594 nm fluorescence enhancement in glycerol and a moderate 650 nm red AIE emission in water. Further, on attaching CF3 to the phenyl group, a similar phenomenon was observed for 7 with red-shifted emissions, attributed to the introduction of a phenyl group, which plays a key role in the red AIE emissions and large Stokes shifts. Comparatively, for phenyl-group-free probes, both the meso-C═N-trifluoroethyl group and thiazole-substituted probes (8 and 9) exhibited good viscosity-responsive properties, while no AIE was observed due to the absence of phenyl groups. For cellular experiments, 6 and 9 showed good lysosomal and mitochondrial targeting properties, respectively, and were further successfully used for imaging viscosity through the preincubation of monensin and lipopolysaccharide (LPS), indicating that C═N polar groups potentially work as rotatable moieties and organelle-targeting groups, and the targeting difference might be ascribed to increased charges of thiazole. Therefore, in this study, we investigated the structural relationships of four meso-C═N BODIPY-based rotors with respect to their viscosity/AIE characteristics, subcellular-targeting ability, and cellular imaging for viscosity, potentially serving as AIE fluorescent probes with large Stokes shifts for subcellular viscosity imaging.

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.

Molecular Rotors: Fluorescent Sensors for Microviscosity and Conformation of Biomolecules

The viscosity and crowding of biological environment are considered vital for the correct cellular function, and alterations in these parameters are known to underly a number of pathologies including diabetes, malaria, cancer and neurodegenerative diseases, to name a few. Over the last decades, fluorescent molecular probes termed molecular rotors proved extremely useful for exploring viscosity, crowding, and underlying molecular interactions in biologically relevant settings. In this review, we will discuss the basic principles underpinning the functionality of these probes and will review advances in their use as sensors for lipid order, protein crowding and conformation, temperature and non-canonical nucleic acid structures in live cells and other relevant biological settings.

Fluorescent Probes Based on Charge and Proton Transfer for Probing Biomolecular Environment

Fluorescent probes for sensing fundamental properties of biomolecular environment, such as polarity and hydration, help to study assembly of lipids into biomembranes, sensing interactions of biomolecules and imaging physiological state of the cells. Here, we summarize major efforts in the development of probes based on two photophysical mechanisms: (i) an excited-state intramolecular charge transfer (ICT), which is represented by fluorescent solvatochromic dyes that shift their emission band maximum as a function of environment polarity and hydration; (ii) excited-state intramolecular proton transfer (ESIPT), with particular focus on 5-membered cyclic systems, represented by 3-hydroxyflavones, because they exhibit dual emission sensitive to the environment. For both ICT and ESIPT dyes, the design of the probes and their biological applications are summarized. Thus, dyes bearing amphiphilic anchors target lipid membranes and report their lipid organization, while targeting ligands direct them to specific organelles for sensing their local environment. The labels, amino acid and nucleic acid analogues inserted into biomolecules enable monitoring their interactions with membranes, proteins and nucleic acids. While ICT probes are relatively simple and robust environment-sensitive probes, ESIPT probes feature high information content due their dual emission. They constitute a powerful toolbox for addressing multitude of biological questions.

Simultaneous detection and removal of mercury (II) using multifunctional fluorescent materials

Environmental problems caused by mercury ions are increasing due to growing industrialization, poor enforcement, and inefficient pollutant treatment. Therefore, detecting and removing mercury from the ecological chain is of utmost significance. Currently, a wide range of small molecules and nanomaterials have made remarkable progress in the detection, detoxification, adsorption, and removal of mercury. In this review, we summarized the recent advances in the design and construction of multifunctional materials, detailed their sensing and removing mechanisms, and discussed with emphasis the advantages and disadvantages of different types of sensors. Finally, we elucidated the problems and challenges of current multifunctional materials and further pointed out the direction for the future development of related materials. This review is expected to provide a guideline for researchers to establish a robust strategy for the detection and removal of mercury ionsin the environment.

Visualization of Lysosomal Dynamics during Autophagy by Fluorescent Probe

Lysosomes are one of the important organelles within cells, and their dynamic movement processes are associated with many biological events. Therefore, real-time monitoring of lysosomal dynamics processes has far-reaching implications. A lysosome-targeted fluorescent probe N(CH2)3-BD-PZ is proposed for real-time monitoring of lysosomal kinetic motility. Using this probe, the dynamic process of lysosomes under starvation induction was successfully explored through fluorescence imaging. Importantly, we observed a new pattern of lysosomal dynamic movement, in which an irregular lysosome was slowly cleaved into two different-sized touching lysosomes and then fused to form a new round lysosome. This research provides a powerful fluorescence tool to understand the dynamic motility of intracellular lysosomes under fluorescence imaging.

Mitochondria-Targeting Multifunctional Fluorescent Probe toward Polarity, Viscosity, and ONOO- and Cell Imaging

Abnormal changes occurring in the mitochondrial microenvironment are important markers indicating mitochondrial and cell dysfunction. Herein, we designed and synthesized a multifunctional fluorescent probe DPB that responds to polarity, viscosity, and peroxynitrite (ONOO^-). DPB is composed of an electron donor (diethylamine group) and electron acceptor (coumarin, pyridine cations, and phenylboronic acid esters), in which the pyridine group with a positive charge is responsible for targeting to mitochondria. D-π-A structure with strong intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) properties give rise to respond to polarity and viscosity. The introduction of cyanogroup and phenylboronic acid esters increases the electrophilicity of the probe, which is prone to oxidation triggered by ONOO^-. The integrated architecture satisfies the multiple response requirements. As the polarity increases, the fluorescence intensity of probe DPB at 470 nm is quenched by 97%. At 658 nm, the fluorescence intensity of DPB increases with viscosity and decreases with the concentration of ONOO^-. Furthermore, the probe is not only successfully used to monitor mitochondrial polarity, viscosity, and endogenous/exogenous ONOO^- level fluctuations but also to distinguish cancer cells from normal cells by multiple parameters. Therefore, as-prepared probe provides a reliable tool for better understanding of the mitochondrial microenvironment and also a potential approach for the diagnosis of disease.

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.

Nuclear bodies protect phase separated proteins from degradation in stressed proteome

RNA-binding proteins (RBPs) containing intrinsically disordered domains undergo liquid-liquid phase separation to form nuclear bodies under stress conditions. This process is also connected to the misfolding and aggregation of RBPs, which are associated with a series of neurodegenerative diseases. However, it remains elusive how folding states of RBPs changes upon the formation and maturation of nuclear bodies. Here, we describe SNAP-tag based imaging methods to visualize the folding states of RBPs in live cells via time-resolved quantitative microscopic analyses of their micropolarity and microviscosity. Using these imaging methods in conjunction with immunofluorescence imaging, we demonstrate that RBPs, represented by TDP-43, initially enters the PML nuclear bodies in its native state upon transient proteostasis stress, albeit it begins to misfolded during prolonged stress. Furthermore, we show that heat shock protein 70 co-enters the PML nuclear bodies to prevent the degradation of TDP-43 from the proteotoxic stress, thus revealing a previously unappreciated protective role of the PML nuclear bodies in the prevention of stress-induced degradation of TDP-43. In summary, our imaging methods described in the manuscript, for the first time, reveal the folding states of RBPs, which were previously challenging to study with conventional methods in nuclear bodies of live cells. This study uncovers the mechanistic correlations between the folding states of a protein and functions of nuclear bodies, in particular PML bodies. We envision that the imaging methods can be generally applied to elucidating the structural aspects of other proteins that exhibit granular structures under biological stimulus.

GFP-based red-emissive fluorescent probes for dual imaging of β-amyloid plaques and mitochondrial viscosity

Alzheimer's disease (AD), with incurable neurodegenerative damage, has attracted growing interest in exploration of better AD biomarkers in its early diagnosis. Among various biomarkers, amyloid-β (Aβ) aggregates and mitochondrial viscosity are closely related to AD and their dual imaging might provide a potential and feasible strategy. In this work, five GFP-based red-emissive fluorescent probes were rationally designed and synthesized for selective detection of β-amyloid plaques and viscosity, among which C25e exhibited superior properties and could successfully image β-amyloid plaques and mitochondrial viscosity with different fluorescence wavelength signals "turn-on" at around 624 and 640 nm, respectively. Moreover, the staining of brain sections from a transgenic AD mouse showed that probe C25e showed higher selectivity and signal-to-noise ratio towards Aβ plaques than commercially-available Thio-S. In addition, the probe C25e was, for the first time, employed for monitoring amyloid-β induced mitochondrial viscosity changes. Therefore, this GFP-based red-emissive fluorescent probe C25e could serve as a dual-functional tool for imaging β-amyloid plaques and mitochondrial viscosity, which might provide a unique strategy for the early diagnosis of Alzheimer's disease.

Water-soluble fluorescent probes for differentiating cancer cells and normal cells by tracking lysosomal viscosity

Lysosomal viscosity is a significant parameter of lysosomes and closely related to various diseases. Herein, two fluorescent probes, Lyso-vis-A and Lyso-vis-B, were developed, which demonstrate diverse advantages, including great water solubility, lysosome targeting ability and viscosity sensitivity. In particular, Lyso-vis-A exclusively showed fluorescence response toward viscosity but was not influenced by pH changes, rendering it a selective lysosomal viscosity probe. Furthermore, Lyso-vis-A was successfully applied to monitor lysosomal viscosity variations in living cells and differentiate cancer cells and normal cells.

Dense and Acidic Organelle-Targeted Visualization in Living Cells: Application of Viscosity-Responsive Fluorescence Utilizing Restricted Access to Minimum Energy Conical Intersection

Cell-imaging methods with functional fluorescent probes are an indispensable technique to evaluate physical parameters in cellular microenvironments. In particular, molecular rotors, which take advantage of the twisted intramolecular charge transfer (TICT) process, have helped evaluate microviscosity. However, the involvement of charge-separated species in the fluorescence process potentially limits the quantitative evaluation of viscosity. Herein, we developed viscosity-responsive fluorescent probes for cell imaging that are not dependent on the TICT process. We synthesized AnP₂-H and AnP₂-OEG, both of which contain 9,10-di(piperazinyl)anthracene, based on 9,10-bis(N,N-dialkylamino)anthracene that adopts a nonflat geometry at minimum energy conical intersection. AnP₂-H and AnP₂-OEG exhibited enhanced fluorescence as the viscosity increased, with sensitivities comparable to those of conventional molecular rotors. In living cell systems, AnP₂-OEG showed low cytotoxicity and, reflecting its viscosity-responsive property, allowed specific visualization of dense and acidic organelles such as lysosomes, secretory granules, and melanosomes under washout-free conditions. These results provide a new direction for developing functional fluorescent probes targeting dense organelles.

Photo-Activated Ratiometric Fluorescent Indicator for Real-Time and Visual Detection of Plasma Membrane Homeostasis

Development of an activated ratiometric indicator that is specific to plasma membrane (PM) viscosity exhibits great application prospects in disease diagnosis and treatment but remains a great challenge. Herein, a photo-activated fluorescent probe (CQ-IC) was designed and prepared tactfully, which could analyze and real-time monitor the microenvironmental homeostasis of the PM based on a two-channel ratiometric imaging model. Interestingly, upon light irradiation, CQ-IC generates reactive oxygen species and thus increases the cellular viscosity, which increases two emission peaks at 480 and 610 nm. This work would propose a new strategy to sensor PM homeostasis and effectively guide the treatment of viscosity-related diseases among various physiological and pathological processes.

Two quinoline-based two-photon fluorescent probes for imaging of viscosity in subcellular organelles of living HeLa cells

Two viscosity-sensitive two-photon fluorescent probes (QL and QLS) were designed and synthesized, which can be localized in lysosome and mitochondria in living HeLa cells, respectively. As the increases of viscosity from 2.55 to 1150 cP, the fluorescence quantum yield (Φ) of QL and QLS was increased by 28-fold and 37-fold, respectively. At the same time, its effective two-photon absorption cross section (Φδ_TPA) was enhanced by 15-fold and 16-fold, respectively. Fluorescence lifetime imaging (FLIM) of living HeLa cells stained with QL and QLS, revealed that lysosomal viscosity ranged from 100.76 to 254.74 cP and mitochondrial viscosity ranged from 92.21 to 286.79 cP. This type of fluorescent probe is helpful in the design and application of materials for monitoring diseases associated with abnormal viscosity.

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.

PET- and ICT-Based Ratiometric Probe: An Unusual Phenomenon of Morpholine-Conjugated Fluorophore for Mitochondrial pH Mapping during Mitophagy

Mitochondrial functions are heavily influenced by acid-base homeostasis. Hence, elucidation of the mitochondrial pH is essential in living cells, and its alterations during pathologies is an interesting question to be addressed. Small molecular fluorescent probes are progressively applied to quantify the mitochondrial pH by fluorescence imaging. Herein, we designed a unique small molecular fluorescent probe, PM-Mor-OH, based on the lipophilic morpholine ligand-conjugated pyridinium derivative of "IndiFluors". The morpholine-conjugated fluorescent probe usually localized the lysosome. However, herein, we observed unusual phenomena of morpholine-tagged PM-Mor-OH that localized mitochondria explicitly. The morpholine ligand also plays a pivotal role in tuning optical properties via photoinduced electron transfer (PET) during internal pH alteration (ΔpHi). In the mitophagy process, lysosomes engulf damaged mitochondria, leading to ΔpHi, which can be monitored using our probe. It exhibited "ratiometric" emission at single wavelength excitation (ex. 488) and is suitable for monitoring and quantifying the ΔpHi using confocal microscope high-resolution image analysis during mitophagy. The bathochromic emission shifts due to intramolecular charge transfer (ICT) in basic pH were well explained by the time-dependent density functional theory (TD-DFT/PCM). Similarly, the change in the emission ratio (green/red) with pH variations was also validated by the PET process. In addition, PM-Mor-OH can quantify the pH change during oxidative stress induced by rapamycin, mutant A53T α-synuclein-mediated protein misfolding stress in mitochondria, and during starvation. Rapamycin-induced mitophagy was further elucidated by the translocation of mCherry Parkin to damaged mitochondria, which well correlates with our probe. Thus, PM-Mito-OH is a valuable probe for visualizing mitophagy and can act as a suitable tool for the diagnosis of mitochondrial diseases.

Simultaneous Monitoring of HOCl and Viscosity with Drug-Induced Pyroptosis in Live Cells and Acute Lung Injury

Pyroptosis is a newly identified form of cell death that is closely correlated with many diseases. Recent studies have indicated that the inflammation in pyroptosis would accelerate the generation of reactive oxygen species (ROS). In addition, intracellular viscosity is another key microenvironmental parameter that reflects many physiological and pathological states in the early stage, hypochlorous acid (HOCl), as an important ROS, also plays significant roles in a variety of pathologies. However, the fluctuation of viscosity and HOCl in the process of pyroptosis is still unknown. Herein, we present a dual-responsive fluorescent probe (Lyso-VH) for simultaneously detecting viscosity and HOCl. Lyso-VH was successfully used to image the fluctuation of HOCl and viscosity in the lysosome of three kinds of cells with dependent and independent channels. Moreover, Lyso-VH can be employed to investigate the changes of HOCl and viscosity during the process of pyroptosis in living cells and acute lung injury (ALI). Thus, this work can not only serve as a powerful tool to simultaneously visualize the fluctuation of HOCl and viscosity in lysosomes, but also provide a new insight into drug-induced pyroptosis in living cells and acute lung injury.

Lifetime-Based Responsive Probes: Design and Applications in Biological Analysis

With the development of modern biomedicine, biological analysis and detection are very important in disease diagnosis, detection of curative effect, prognosis and prediction of tumor recurrence. Compared with the currently widely used optical probes based on intensity signals, the lifetime signal does not depend on the influence of conditions such as the concentration of luminophore, tissue penetration depth and measurement method. Therefore, biological detection methods based on lifetime-based responsive probes have attracted great attention from the scientific community. Here, we briefly review the key advances in lifetime-based responsive probes in recent years (2017-2022). The review focuses on the design strategies of lifetime-based responsive probes and the research progress of their applications in the field of bioanalysis, and discusses the challenges they face. We hope it will further promote the development of lifetime-based responsive probes in the field of bioanalysis. With the development of modern biomedicine, biological analysis and detection are very important in disease diagnosis, detection of curative effect, prognosis and prediction of tumor recurrence. Compared with the currently widely used optical probes based on intensity signals, the lifetime signal does not depend on the influence of conditions such as the concentration of luminophore, tissue penetration depth and measurement method. Therefore, biological detection methods based on lifetime-based responsive probes have attracted great attention from the scientific community. Here, we briefly review the key advances in lifetime-based responsive probes in recent years (2017-2022). The review focuses on the design strategies of lifetime-based responsive probes and the research progress of their applications in the field of bioanalysis, and discusses the challenges they face. We hope it will further promote the development of lifetime-based responsive probes in the field of bioanalysis.

Intracellular Physical Properties with Small Organic Fluorescent Probes: Recent Advances and Future Perspectives

The intracellular physical parameters i. e., polarity, viscosity, fluidity, tension, potential, and temperature of a live cell are the hallmark of cellular health and have garnered immense interest over the past decade. In this context, small molecule organic fluorophores exhibit prominent useful properties including easy functionalizability, environmental sensitivity, biocompatibility, and fast yet efficient cellular uptakability which has made them a popular tool to understand intra-cellular micro-environmental properties. Throughout this discussion, we have outlined the basic design strategies of small molecules for specific organelle targeting and quantification of physical properties. The values of these parameters are indicative of cellular homeostasis and subtle alteration may be considered as the onset of disease. We believe this comprehensive review will facilitate the development of potential future probes for superior insight into the physical parameters that are yet to be quantified.

Precision Navigation of Hepatic Ischemia-Reperfusion Injury Guided by Lysosomal Viscosity-Activatable NIR-II Fluorescence

Hepatic ischemia-reperfusion injury (HIRI) is responsible for postoperative liver dysfunction and liver failure. Precise and rapid navigation of HIRI lesions is critical for early warning and timely development of pretreatment plans. Available methods for assaying liver injury fail to provide the exact location of lesions in real time intraoperatively. HIRI is intimately associated with oxidative stress which impairs lysosomal degradative function, leading to significant changes in lysosomal viscosity. Therefore, lysosomal viscosity is a potential biomarker for the precise targeting of HIRI. Hence, we developed a viscosity-activatable second near-infrared window fluorescent probe (NP-V) for the detection of lysosomal viscosity in hepatocytes and mice during HIRI. A reactive oxygen species-malondialdehyde-cathepsin B signaling pathway during HIRI was established. We further conducted high signal-to-background ratio NIR-II fluorescence imaging of HIRI mice. The contour and boundary of liver lesions were delineated, and as such the precise intraoperative resection of the lesion area was implemented. This research demonstrates the potential of NP-V as a dual-functional probe for the elucidation of HIRI pathogenesis and the direct navigation of HIRI lesions in clinical applications.

Coumarin-based fluorescent probes toward viscosity in mitochondrion/lysosome

Viscosity is an important microenvironmental indicator that plays an important role in the process of information transmission in various regions. Herein, two coumarin-based viscosity-sensitive fluorescent probes (CHB, CHN) were synthesized and the photophysical properties of the two probes were studied. The fluorescence quantum yields of CHB and CHN in glycerol can be as high as 25.2% and 18.3% respectively. The two probes can linearly detect viscosity in the viscosity logarithm range of 0.83-2.07, which is not interfered with pH, metal ions, anions and biomolecules. Fluorescent confocal cell experiments show CHB and CHN have good targeting ability to mitochondrion, lysosome, Endoplasmic reticulum and Golgi apparatus, and can be used to detect viscosity in mitochondrion/lysosome.

Coassembly of a New Insect Cuticular Protein and Chitosan via Liquid-Liquid Phase Separation

Insect cuticle is a fiber-reinforced composite material that consists of polysaccharide chitin fibers and a protein matrix. The molecular interactions between insect cuticle proteins and chitin that govern the assembly and evolution of cuticles are still not well understood. Herein, we report that Ostrinia furnacalis cuticular protein hypothetical-1 (OfCPH-1), a newly discovered and most abundant cuticular protein from Asian corn borer O. furnacalis, can form coacervates in the presence of chitosan. The OfCPH-1-chitosan coacervate microdroplets are initially liquid-like but become gel-like with increasing time or salt concentration. The liquid-to-gel transition is driven by hydrogen-bonding interactions, during which an induced β-sheet structure of OfCPH-1 is observed. Given the abundance of OfCPH-1 in the cuticle of O. furnacalis, this liquid-liquid phase separation process and its aging behavior could play critical roles in the formation of the cuticle.

Assessment of cancer cell migration using a viscosity-sensitive fluorescent probe

A novel viscosity probe (NV1) was developed for assessing cancer cell migration. NV1 can respond to changes of viscosity rapidly and exhibits high sensitivity in HepG2 cells treated with starvation, rotenone and nystatin. Importantly, NV1 was used for the first time to evaluate the relationship between intracellular viscosity changes and cancer cell migration and proved that increased intracellular viscosity inhibits cell migration while decreased intracellular viscosity promotes cell migration.

Fine Tuning of Multiphoton AIE Emission Behavior, Organelle Targeting, and Fluorescence Lifetime Imaging of Terpyridine Derivatives by Alkyl Chain Engineering

In this work, a series of multiphoton terpyridine agents (ZA, ZA-Mex, and ZA-Hex) for fluorescence lifetime imaging microscopy (FLIM) are designed and synthesized. The results from photophysical property research reveal that ZA-Hex, as an N-hexylated terpyridine salt, has stronger three-photon aggregation-induced emission (AIE) properties compared to ZA-Mex due to enhanced intramolecular charge transfer (ICT) performance. All three terpyridine derivatives possess suitable fluorescence intensities and stable fluorescence lifetimes under different pH conditions (pH = 4.0-8.0), thereby performing multiphoton fluorescence lifetime imaging. For biological imaging applications, it is found that ZA shows good lipid droplet (LD) turn-on fluorescence performance, and ZA-Hex could easily accumulate in mitochondria with high specificity. This is the first report of terpyridine salts as three-photon AIE probes used for multiphoton FLIM imaging.

D-π-A structure fluorophore: NIR emission, response to viscosity, detection cyanide and bioimaging of lipid droplets

Intracellular viscosity, an important microenvironment factor, is closely involved in various cell processes as well as diseases. On the other hand, cyanide is one of the most hazardous chemicals for human health and environments. However, a NIR fluorescent probe for both response to viscosity and detection of cyanide remains vacant. Herein, we reported a D-π-A structure fluorophore (named CTR) which exhibited NIR emission and fluorescent enhancement response to viscosity via the molecular rotor strategy. Furthermore, CTR displayed fluorescent and colorimetric response to cyanide. Notably, test strips stained with CTR were fabricated, which could serve as an efficient and suitable cyanide test kit. Moreover, CTR could selectively accumulate in lipid droplets and visualize the metabolism of lipid droplets in live cells. These findings would provide new avenue to design fluorescent probe for effective response to viscosity, detection of cyanide, and bioimaging of lipid droplets in live cells.

Novel cationic meso-CF3 BODIPY-based AIE fluorescent rotors for imaging viscosity in mitochondria

Two novel meso-CF₃ BODIPY-based fluorescent rotors have been rationally prepared and found to sensitively respond to viscosity in living cells with a fluorescence "turn-on" effect, attributed to the special restricted rotation of meso-CF₃ group in viscous environments. Interestingly, a monostyryl probe with one cationic group exhibits good mitochondrial localization and AIE property.

Novel lysosome-targeted fluorescent molecular rotors based on a cyanine-like modular system and their application in living cells

Two novel fluorescence molecular rotors DpIn and NaIn were designed and synthesized involving of indolium units linked with meta-diphenol or ortha-naphthalenediol moiety, respectively. They underwent intramolecular charge transfer to form a cyanine-like modular system at a physiological pH. In glycerol aqueous solutions, the probe DpIn exhibited NIR strong emission (3-fold) at ca. 700 nm, while the probe NaIn displayed a turn-on emission (8-fold) with a larger Stokes shift (⊿λ ≈ 97 nm). The HeLa cell imaging experiments indicated probe DpIn and NaIn both exhibited excellent selectivity for staining intracellular lysosomes instead of mitochondria. ¹H NMR spectra revealed that more electrons were accumulated around benzene ring of indolium groups, which could be the evidence for its basic character leading to the lysosomes targeted staining. Furthermore, the probe NaIn proved to be an ideal lysosome-targeting tracer for monitor the changes of viscosity caused by stimuli in living cells.

A bifunctional sensitive fluorescence probe based on pyrene for the detection of pH and viscosity in lysosome

Lysosome is one of the important organelles in intracellular transport. It plays a significant role in the physiological process. The lysosomal microenvironment affects the functions of lysosome. When the original acidic environment of lysozyme is destroyed or the fluid viscosity increases gradually, various diseases are easily induced. However, most fluorescent probes can only locate in cells. The fewer probes of subcellular organelles were found and their functions are often single. So, it is of great importance to design multifunctional fluorescent probes with the capable of localizing in lysosome. In this study, a novel lysosome probe, 4-(4-Pyren-1-yl-but-3-enyl)-morpholine (PIM), was synthesized using pyrene as a fluorescent group and morpholine as a target group. The introduction of morpholine group made PIM localize in lysosome with high selectivity. The fluorescence will be enhanced with the increased viscosity because of restricting the rotation of CC bond and CN in PIM, and the detecting linear range is from 4.05 cP to 393.48 cP, which qualified the requirement of the viscosity monitoring in body. Meanwhile, the fluorescence intensity of PIM declines with the decrease of pH because the Schiff base of PIM is hydrolyzed, which was affirmed by ¹H NMR, LC-MS and fluorescence spectra. Moreover, cell imaging and MTT experiments confirmed that PIM as a novel bifunctional probe can be used to detect pH and endogenous viscosity in lysosome.

Observation of macrophage autophagy in the healing of diabetic ulcers via a lysosome-targeting polarity-specific two-photon probe

As a disease with high incidence, mutilation, and fatality rates, diabetic ulcers (DUs) have become a difficult and complicated disease of widely concern in recent years due to the unclear healing mechanism. The main reason for the delayed healing in DU patients is the unduly long chronic inflammation window, and the polarization state of macrophages plays a key role in this process. Since autophagy is believed to be closely related to the polarization trend of macrophages, recent studies have shown that autophagy is closely related to the healing of DU. To this end, a lysosome-targeting polarity-sensitive probe, XZTU-VIS, was developed to monitor the changes in lysosomal polarity, thereby assessing the autophagy of macrophages in mice suffering from DU. The experimental results showed that under two-photon fluorescence microscopy, the green channel fluorescence signal of XZTU-VIS decreased significantly during autophagy. In the meantime, DU models established using BV-2 cells and mice showed a process that could cause inflammation and the release of ROS, thereby inducing autophagy.

A polarity-dependent two-photon fluorescent probe for evaluation of autophagy in the process of diabetic mouse skin ulcer-induced inflammation was constructed.

Benchmarking Density Functional Approximations for Excited-State Properties of Fluorescent Dyes

This study presents an extensive analysis of the predictive power of time-dependent density functional theory in determining the excited-state properties of two groups of important fluorescent dyes, difluoroboranes and hydroxyphenylimidazo[1,2-a]pyridine derivatives. To ensure statistically meaningful results, the data set is comprised of 85 molecules manifesting diverse photophysical properties. The vertical excitation energies and dipole moments (in the electronic ground and excited states) of the aforementioned dyes were determined using the RI-CC2 method (reference) and with 18 density functional approximations (DFA). The set encompasses DFAs with varying amounts of exact exchange energy (EEX): from 0% (e.g., SVWN, BLYP), through a medium (e.g., TPSSh, B3LYP), up to a major contribution of EEX (e.g., BMK, MN15). It also includes range-separated hybrids (CAM-B3LYP, LC-BLYP). Similar error profiles of vertical energy were obtained for both dye groups, although the errors related to hydroxyphenylimidazopiridines are significantly larger. Overall, functionals including 40-55% of EEX (SOGGA11-X, BMK, M06-2X) ensure satisfactory agreement with the reference vertical excitation energies obtained using the RI-CC2 method; however, MN15 significantly outperforms them, providing a mean absolute error of merely 0.04 eV together with a very high correlation coefficient (R2 = 0.98). Within the investigated set of functionals, there is no single functional that would equally accurately determine ground- and excited-state dipole moments of difluoroboranes and hydroxyphenylimidazopiridine derivatives. Depending on the chosen set of dyes, the most accurate μGS predictions were delivered by MN15 incorporating a major EEX contribution (difluoroboranes) and by PBE0 containing a minor EEX fraction (hydroxyphenylimidazopiridines). Reverse trends are observed for μES, i.e., for difluoroboranes the best results were obtained with functionals including a minor fraction of EEX, specifically PBE0, while in the case of hydroxyphenylimidazopiridines, much more accurate predictions were provided by functionals incorporating a major EEX contribution (BMK, MN15).