Nonpolar selective emission (NPSE) of carbonyl-bridged rhodols

Polarity-responsive luminophores (PRLs), whose emission properties change in response to the polarity of the surrounding environment, are used for the fluorescence sensing of intracellular environments and various chemical compounds. Herein, we propose a concept called nonpolar selective emission (NPSE) for the development of a new PRL family. Unlike the conventional emission of PRLs, the NPSE luminophore can switch to a completely non-emissive state upon a slight increase in solvent polarity. The NPSE concept offers a new means of distinguishing between nonpolar and low-polarity environments. Moreover, the NPSE property is little affected by the viscosity of the surrounding medium. We demonstrate that NPSE dyes can be used as emission sensors for molecular gases. Furthermore, we discovered the potential use of NPSE dyes as a time-dependent security ink triggered by the volatilization of polar molecules.

Synthesis, Photophysical Properties, Theoretical Studies, and Living Cancer Cell Imaging Applications of New 7-(Diethylamino)quinolone Chalcones

In this article, three unsymmetrical 7-(diethylamino)quinolone chalcones with D-π-A-D and D-π-A-π-D type push-pull molecular arrangements were synthesized via a Claisen-Schmidt reaction. Using 7-(diethylamino)quinolone and vanillin as electron donor (D) moieties, these were linked together through the α,β-unsaturated carbonyl system acting as a linker and an electron acceptor (A). The photophysical properties were studied, revealing significant Stokes shifts and strong solvatofluorochromism caused by the ICT and TICT behavior produced by the push-pull effect. Moreover, quenching caused by the population of the TICT state in THF-H2O mixtures was observed, and the emission in the solid state evidenced a red shift compared to the emission in solution. These findings were corroborated by density functional theory (DFT) calculations employing the wb97xd/6-311G(d,p) method. The cytotoxic activity of the synthesized compounds was assessed on BHK-21, PC3, and LNCaP cell lines, revealing moderate activity across all compounds. Notably, compound 5b exhibited the highest activity against LNCaP cells, with an LC50 value of 10.89 μM. Furthermore, the compounds were evaluated for their potential as imaging agents in living prostate cells. The results demonstrated their favorable cell permeability and strong emission at 488 nm, positioning them as promising candidates for cancer cell imaging applications.

Dual role far red fluorescent molecular rotor for decoding the plasma membrane and mitochondrial viscosity

The dysfunctions in the mitochondria are associated with various pathological conditions like neurodegeneration, metabolic disorder, and cancer, leading to dysregulated cell death. Here, we have designed and synthesized a julolidine-based molecular rotor (JMT) to target mitochondria with far-red emission accounting for mitochondrial dysfunction. JMT showed viscosity sensitivity with 160-fold enhancement in fluorescence intensity. The origin of the dark state in a lower viscous environment was investigated through density functional calculations. We have employed JMT to monitor mitochondrial dysfunction induced by nystatin using confocal and fluorescence lifetime imaging microscopy. Further, we investigated mitochondrial abnormalities under inflammatory conditions triggered by lipopolysaccharide in live HeLa cells. The cellular uptake mechanisms of JMT were studied using various endocytosis inhibitors. Moreover, we reported tracking small fluorescent molecule switching from mitochondria to the plasma membrane upon introducing mitochondrial depolarizer in cells. On treating the mitochondria potential uncoupler, JMT relocates to the cell membrane and can be utilized for understanding the interplay between mitochondria and cell membranes. Moreover, JMT was applied to stain the RBC plasma membrane isolated from human blood.

Detection of breast cancer cells by a near-infrared fluorescent probe targeting mitochondrial viscosity

Monitoring abnormal viscosity in biological systems is important for basic research and clinical applications. Fluorescence imaging technology is adaptable for the visualization of tumor tissues due to its comprehensive features. However, fluorescence detection of intracellular viscosity in clinical samples remains challenging. We developed a promising near-infrared fluorescent probe, M556, for viscosity measurement. M556, which targets mitochondria, was successfully applied to monitor the mitochondrial viscosity in living cells. Furthermore, M556 was demonstrated to effectively discriminate tumors from normal tissues in a mouse tumor model and in clinical specimens from breast cancer patients, thus indicating the potential perioperative use of this probe by clinicians to assist with biopsy procedures.

In vivo biodistribution of kinetically stable Pt2L4 nanospheres that show anti-cancer activity

There is an increasing interest in the application of metal-organic cages (MOCs) in a biomedicinal context, as they can offer non-classical distribution in organisms compared to molecular substrates, while revealing novel cytotoxicity mechanisms. Unfortunately, many MOCs are not sufficiently stable under in vivo conditions, making it difficult to study their structure-activity relationships in living cells. As such, it is currently unclear whether MOC cytotoxicity stems from supramolecular features or their decomposition products. Herein, we describe the toxicity and photophysical properties of highly-stable rhodamine functionalized platinum-based Pt₂L₄ nanospheres as well as their building blocks under in vitro and in vivo conditions. We show that in both zebrafish and human cancer cell lines, the Pt₂L₄ nanospheres demonstrate reduced cytotoxicity and altered biodistribution within the body of zebrafish embryos compared to the building blocks. We anticipate that the composition-dependent biodistribution of Pt₂L₄ spheres together with their cytotoxic and photophysical properties provides the fundament for MOC application in cancer therapy.

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.

Design and synthesis of photostable triphenylamine based neutral AIE nano luminogens: specific and long-term tracking of mitochondria in cells

With the increasing dependence on fluorescence bioimaging, luminogens with aggregation-induced emission (AIE) properties have gained significant attention due to their excellent photostabilization, minimal photobleaching, high reliability, and superior biocompatibility. Since mitochondria are crucial subcellular organelles in eukaryotic cells with important biological functions, organelle-specific AIE emitters with distinct functions have been highly sought after, but with limited success using simple synthetic methods. Here, we describe a strategy for synthesizing two triphenylamine (TPA) based acrylonitriles, tethered to different donor groups, TPA and phenothiazine (PTZ), respectively, with superior AIE properties using Suzuki coupling. We conducted a systematic and detailed experimental analysis of the structural characteristics of both AIE luminogens, which exhibited excellent photostability, a large Stokes shift, and bright solid-state emission. A cell viability study carried out with F1 and F2 dyes revealed that both luminogens exhibited excellent biocompatibility. Based on fluorescence experiments, F2 displayed excellent AIE characteristics, permeability, biocompatibility, and photostability compared to rhodamine 123, allowing it to selectively stain and track mitochondria in cancer cells over an extended period of time. The Pearson correlation coefficient of F2 and rhodamine 123 was estimated to have an r-value of 0.99. Our findings are expected to provide insight into the synthesis of an extensive archive of AIE-based acrylonitriles with fascinating properties for mitochondrial staining.

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.

Triphenylamine-Modified Cinnamaldehyde Derivate as a Molecular Sensor for Viscosity Detection in Liquids

Liquid safety is considered a serious public health problem; a convenient and effective viscosity determination method has been regarded as one of the powerful means to detect liquid safety. Herein, one kind of triphenylamine-modified cinnamaldehyde-based fluorescent sensor (3-(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)acrylaldehyde (DPABA)) has been developed for sensing viscosity fluctuations in a liquid system, where a cinnamaldehyde derivative was extracted from one kind of natural plant cinnamon and acted as an acceptor, which has been combined with a triphenylamine derivate via the Suzuki coupling reaction within one facile step. Twisted intramolecular charge transfer (TICT) was observed, and the rotation could be restricted in the high-viscosity microenvironment; thus, the fluorescent signal was released at 548 nm. Featured with a larger Stokes shift (223.8 nm in water, 145.0 nm in glycerol), high adaptability, sensitivity, selectivity, and good photostability, the capability of high signal-to-noise ratio sensing was achieved. Importantly, this sensor DPABA has achieved noninvasively identifying thickening efficiency investigation, and viscosity fluctuations during the liquid deterioration program have been screened as well. We believed that this unique strategy can accelerate intelligent molecular platforms toward liquid quality and safety inspection.

Self-assembled nanoparticles based on cationic mono-/AIE tetra-nuclear Ir(III) complexes: long wavelength absorption/near-infrared emission photosensitizers for photodynamic therapy

Cyclometalated Ir(III) complexes as photosensitizers (PSs) have attracted widespread attention because of their good photostability and efficient ¹O₂ production ability. However, their strong absorption in the UV-vis region severely limits their applications in photodynamic therapy (PDT) because the short wavelength illuminating light can be easily absorbed by the skin and subcutaneous adipose tissue causing damage to the patient's normal tissue. Herein, mono- and tetra-nuclear Ir(III) complex-porphyrin conjugates are rationally designed and synthesized, especially [TPP-4Ir]4+ exhibits obvious aggregation-induced emission (AIE) characteristics. PSs comprising Ir(III) complex-porphyrin conjugates self-assembled as nanoparticles (NPs) are successfully achieved. The obtained [TPP-Ir]+ NPs and [TPP-4Ir]4+ NPs exhibit long wavelength absorption (500-700 nm) and near-infrared emission (635-750 nm), successfully overcoming the inherent defects of short wavelength absorption of traditional Ir(III) complexes. Moreover, [TPP-4Ir]4+ NPs exhibit good biocompatibility, high ¹O₂ generation ability, low half-maximal inhibitory concentration (IC₅₀) (0.47 × 10^-6 M), potent cytotoxicity toward cancer cells and superior cellular uptake under white light irradiation. This work extends the scope for transition metal complex PSs with promising clinical applications.

Sustainable natural chlorogenic acid as a functional molecular sensor toward viscosity detection in liquids

Liquids are perishable at ease during the long-term transportation and storage processes, non-invasive and in situ inspection method is urgent to be developed. In consideration of the important role of viscosity, one kind of sustainable natural product chlorogenic acid (CA) extracted from honeysuckle has been used as a versatile optical sensor for viscosity determination during the liquid spoilage process. The natural molecule was conducted by the O-diphenyl and carboxylic acid ester groups in coincidence, a typical twisted intramolecular charge transfer phenomenon was formed. This sensor features wide adaptability, high selectivity, good sensitivity, and excellent photo stability in various liquids. And CA displays a larger Stokes shift, high viscosity sensitive coefficient (0.62), and narrower energy band. The rotatable conjugate structure can be acted as the recognition site, and the bright fluorescent signal of CA is specifically activated when in the high viscous micro-environment. Inspired by this objective phenomenon, CA has been applied to detect the thickening efficiency of various food thickeners. More importantly, the viscosity fluctuations during the deterioration stage of liquids can be screened through non-invasive and in situ monitoring. We expected that more natural products can be developed as molecular tools for liquids safety investigation, and fluorescent analytical methods can be expanded toward interdisciplinary research.

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.

Activatable molecular rotor based on bithiophene quinolinium toward viscosity detection in liquids

The development of non-invasive and effective viscosity inspection methods during the liquid deterioration process is urgently needed since viscosity is one of the most important physical parameters of liquids. Methods featuring rapid detection, high sensitivity, cheap equipment, and fast result output are greatly desired. In this study, a viscosity-sensitive molecular rotor (BTPEQ) with a large Stokes shift (187 nm), and long emission wavelength (648 nm) has been developed. The rotor is comprised of a bithiophene donor and quinolinium acceptor, and displays a typical twisted intramolecular-charge transfer (TICT) feature, with good photostability, selectivity, and universality in various commercial liquids. With the aid of BTPEQ, the thickening effects of liquid thickeners can be determined. More importantly, BTPEQ was explored to visualize the viscosity variations in liquids at different metamorphic stages, and it was found that the viscosity level in microenvironments is highly dependent on the liquid food metamorphic period. It is worth noting that this approach can facilitate the continued perfection of fluorescent analytical methods for food quality and safety inspection.

An N-nitrosation reaction-based fluorescent probe for detecting nitric oxide in living cells and inflammatory zebrafish

Nitric oxide (NO), an essential biological messenger molecule, participates in various physiological and pathological processes. The sensitive and specific detection of NO is of great significance for understanding the biological function of NO. Here, we synthesized a fluorescent probe (Rho-NO) for highly selective detection of NO both in vitro and in vivo. The high selectivity of Rho-NO is attributed to the fact that NO is easily replaced by electron donor amino group to form N-nitrosation products, causing rhodamine spiro ring open and fluorescence emit. Rho-NO showed a good linear response to NO (0-100 µM) with a low detection limit (0.06 µM). Importantly, it exhibited excellent specificity for NO detection in human serum and was also applied for imaging NO in living cells and inflammatory model of zebrafish. This work proves the potential of Rho-NO in pathological research and disease diagnosis.

A novel mitochondria-targeted fluorescent probe for detecting viscosity in living cells and zebrafishes†

Based on the twisted intramolecular charge transfer (TICT) mechanism, a new mitochondria-targeted fluorescent probe CSS-1 for detection of viscosity variations was developed. The probe featured in a strong response to...

Triphenylamine indanedione as an AIE-based molecular sensor with one-step facile synthesis toward viscosity detection of liquids

AIE-based triphenylamine indanedione molecular sensors were synthesized in a one-step facile manner and designed for viscosity detection in liquids.

A biocompatible two-photon absorbing fluorescent mitochondrial probe for deep in vivo bioimaging

We reported a mitochondria-targeted two-photon fluorescent dye with an excellent two-photon absorption cross-section. With this dye, we reached an imaging depth of ca. 640 μm during mitochondrial imaging of cortical cells in live animals.

HydroFlipper membrane tension probes: imaging membrane hydration and mechanical compression simultaneously in living cells

HydroFlippers are introduced as the first fluorescent membrane tension probes that report simultaneously on membrane compression and hydration. The probe design is centered around a sensing cycle that couples the mechanical planarization of twisted push–pull fluorophores with the dynamic covalent hydration of their exocyclic acceptor. In FLIM images of living cells, tension-induced deplanarization is reported as a decrease in fluorescence lifetime of the dehydrated mechanophore. Membrane hydration is reported as the ratio of the photon counts associated to the hydrated and dehydrated mechanophores in reconvoluted lifetime frequency histograms. Trends for tension-induced decompression and hydration of cellular membranes of interest (MOIs) covering plasma membrane, lysosomes, mitochondria, ER, and Golgi are found not to be the same. Tension-induced changes in mechanical compression are rather independent of the nature of the MOI, while the responsiveness to changes in hydration are highly dependent on the intrinsic order of the MOI. These results confirm the mechanical planarization of push–pull probes in the ground state as most robust mechanism to routinely image membrane tension in living cells, while the availability of simultaneous information on membrane hydration will open new perspectives in mechanobiology.

HydroFlippers respond to membrane compression and hydration in the same fluorescence lifetime imaging microscopy histogram: the responses do not correlate.

Visual detection of viscosity through activatable molecular rotor with aggregation-induced emission

Food safety has become one of the urgent affairs in the global public health studies, and irregular viscosity is closely associated with the food spoilage extent. In this study, one kind of activatable molecular rotor (TPA-PBZ) based on triphenylamine derivates has been synthesized via the Schiff base condensation reaction. This rotor is comprised by donor-accepter conjugated structure, with aggregation induced-emission feature and a large Stokes shift of 160 nm in water. The rotation of aromatic rings in TPA-PBZ is restricted in high-viscosity microenvironment, with the gradually increasing fluorescence emission signal at 568 nm. Significantly, this rotor TPA-PBZ has successfully been applied not only in the determination of thickening effects of food gum, but also in the detection of viscosity enhancement during the liquid food spoilage process. This molecular rotor can be utilized as an intelligent monitor platform for food quality and safety inspection in viscosity-related conditions.

A bifunctional fluorescence probe for dual-channel detecting of mitochondrial viscosity and endogenous/exogenous peroxynitrite

The irregular viscosity in the mitochondrial can induce mitochondrial dysfunction. The content of peroxynitrite (ONOO^-) is related to various physiological and pathological processes. However, many mitochondrial probes only realized the detection of viscosity or ONOO^- in single channel, thus it is necessary to explore single fluorescence probe for dual-detecting mitochondrial viscosity and ONOO^-. In this work, we designed and synthesized a novel fluorescence probe (PV) for dual-detecting viscosity and ONOO^-, which was composed by intergrating a ONOO^-- responsive arlyboronate with a twisting intramolecular charge transfer (TICT) mechanism and possessed the mitochondria-targeting ability due to its pyridinium cation. PV exhibited a significant increase in viscosity with red emission at 582 nm and high sensitivity to ONOO^- levels with yellow emission at 507 nm. PV was also applied to living systems (including living cells and zebrafish) for viscosity and ONOO^- detection using two different channels. Moreover, the ability of PV to track mitophagy may make ONOO^- a powerful tool for its role in mitophagy.

Small molecule based fluorescent chemosensors for imaging the microenvironment within specific cellular regions

The microenvironment (local environment), including viscosity, temperature, polarity, hypoxia, and acidic-basic status (pH), plays indispensable roles in cellular processes. Significantly, organelles require an appropriate microenvironment to perform their specific physiological functions, and disruption of the microenvironmental homeostasis could lead to malfunctions of organelles, resulting in disorder and disease development. Consequently, monitoring the microenvironment within specific organelles is vital to understand organelle-related physiopathology. Over the past few years, many fluorescent probes have been developed to help reveal variations in the microenvironment within specific cellular regions. Given that a comprehensive understanding of the microenvironment in a particular cellular region is of great significance for further exploration of life events, a thorough summary of this topic is urgently required. However, there has not been a comprehensive and critical review published recently on small-molecule fluorescent chemosensors for the cellular microenvironment. With this review, we summarize the recent progress since 2015 towards small-molecule based fluorescent probes for imaging the microenvironment within specific cellular regions, including the mitochondria, lysosomes, lipid drops, endoplasmic reticulum, golgi, nucleus, cytoplasmic matrix and cell membrane. Further classifications at the suborganelle level, according to detection of microenvironmental factors by probes, including polarity, viscosity, temperature, pH and hypoxia, are presented. Notably, in each category, design principles, chemical synthesis, recognition mechanism, fluorescent signals, and bio-imaging applications are summarized and compared. In addition, the limitations of the current microenvironment-sensitive probes are analyzed and the prospects for future developments are outlined. In a nutshell, this review comprehensively summarizes and highlights recent progress towards small molecule based fluorescent probes for sensing and imaging the microenvironment within specific cellular regions since 2015. We anticipate that this summary will facilitate a deeper understanding of the topic and encourage research directed towards the development of probes for the detection of cellular microenvironments.

A coumarin-based TICT fluorescent probe for real-time fluorescence lifetime imaging of mitochondrial viscosity and systemic inflammation in vivo

Systemic inflammation, linked with abnormal mitochondrial viscosity, is reported to be associated with cerebro-cardiovascular disease and Alzheimer's disease. Therefore, it is of great significance to detect the mitochondrial viscosity to indicate the inflammatory signal in vivo. Considering the strategies of fluorescent molecular rotors (FMRs) and fluorescence lifetime imaging microscopy (FLIM), we have rationally designed a novel mitochondrial viscosity-specific fluorescent probe Mito-VCI, based on coumarin fluorophores with benzo[e]indolium as the rotor group. In a high viscosity solution system, the fluorescence lifetime of the probe Mito-VCI was prolonged due to the planarization and rigidity enhancement of the molecular rotor. Satisfactorily, the probe was only sensitive to viscosity, instead of non-viscosity factors such as pH and polarity. Furthermore, the probe sensitively targeted mitochondria in HeLa cells with a Pearson's correlation of 0.93, and specifically detected dynamics variation of mitochondrial viscosity with FLIM imaging in HeLa cells induced by LPS. Notably, significant fluorescence lifetime changes of Mito-VCI between normal and inflammatory tissues also occurred (for example, the fluorescence lifetime in the spleen changed from 1.128 to 1.432 ns). It can be inferred from the above observations that Mito-VCI could work as an effective and sensitive fluorescent molecular rotor for mitochondrial viscosity monitoring through FLIM imaging with a systemic inflammatory response, and provide potential applications for the diagnosis of systemic inflammation in pharmacology and toxicology studies.

Development of a one-step synthesized red emission fluorescent probe for sensitive detection of viscosity in vitro and in vivo

Diseases caused by metabolic abnormalities, such as inflammation and fatty liver, which are characterized by high viscosity, so it is necessary to detect the change of viscosity in vivo and in vitro. Due to the advantages of high sensitivity, noninvasive detection, high selectivity and real-time imaging, fluorescence imaging has become an effective means to detect biological parameters of biomolecules and life systems. Therefore, we have prepared a red emitting fluorescent probe NBI-V with easy synthesis which can ensure that the probe can be developed for the widely used to detection of viscosity changes in vivo and in vitro. The probe NBI-V has good stability, high response times, selectivity, and good biocompatibility. As the viscosity of a water-glycerol system increased from 1.29 cp to 937.48 cp, the fluorescence of NBI-V was increased by about 77 times. Biological experiments showed that the probe NBI-V can target mitochondria, and the Pearson correlation coefficient was as high as 0.89. What's more, it can distinguish normal liver from fatty liver, and can detect the viscosity changes caused by inflammation in mice.

A Xanthene Dye-based Sensor for Viscosity and Cell Imaging

A new xanthene dye, namely ImX, has been facilely prepared by reaction of 4-(1H-Imidazol-1-yl)benzaldehyde with N, N-diethyl-3-aminophenol in concentrated propionic acid, and then treated by p-chloranil. ImX presents the maximum absorption and emission band centered at 562 nm and 583 nm in water, respectively. Fluorescent spectra investigations demonstrate that ImX shows viscosity-selective fluorescent response and emission enhancement when the solvent viscosity increases from 1.1 cp. (water) to 1248 cp. (98 % glycerol). In addition, this viscosity-selective fluorescence response covers a wide pH range from 2.5 to 10.0. More significantly, ImX demonstrates low cytotoxicity and can be employed as tracer for the detection of Monensin-triggered viscosity enhancement by cell imaging.

The primary dipole of flipper probes

Despite their growing popularity in biology to image membrane tension, central design principles of flipper probes have never been validated. Here we report that upon deletion of their primary dipole, from electron-poor and electron-rich dithienothiophenes, absorptions blue-shift, lifetimes shorten dramatically, and mechanosensitivity in cells vanishes not partially, but completely.

Genetically Encoded Supramolecular Targeting of Fluorescent Membrane Tension Probes within Live Cells: Precisely Localized Controlled Release by External Chemical Stimulation

To image membrane tension in selected membranes of interest (MOI) inside living systems, the field of mechanobiology requires increasingly elaborated small-molecule chemical tools. We have recently introduced HaloFlipper, i.e., a mechanosensitive flipper probe that can localize in the MOI using HaloTag technology to report local membrane tension changes using fluorescence lifetime imaging microscopy. However, the linker tethering the probe to HaloTag hampers the lateral diffusion of the probe in all the lipid domains of the MOI. For a more global membrane tension measurement in any MOI, we present here a supramolecular chemistry strategy for selective localization and controlled release of flipper into the MOI, using a genetically encoded supramolecular tag. SupraFlippers, functionalized with a desthiobiotin ligand, can selectively accumulate in the organelle having expressed streptavidin. The addition of biotin as a biocompatible external stimulus with a higher affinity for Sav triggers the release of the probe, which spontaneously partitions into the MOI. Freed in the lumen of endoplasmic reticulum (ER), SupraFlippers report the membrane orders along the secretory pathway from the ER over the Golgi apparatus to the plasma membrane. Kinetics of the process are governed by both the probe release and the transport through lipid domains. The concentration of biotin can control the former, while the expression level of a transmembrane protein (Sec12) involved in the stimulation of the vesicular transport from ER to Golgi influences the latter. Finally, the generation of a cell-penetrating and fully functional Sav-flipper complex using cyclic oligochalcogenide (COC) transporters allows us to combine the SupraFlipper strategy and HaloTag technology.

Thermoresponsive Hemostatic Hydrogel with a Biomimetic Nanostructure Constructed from Aggregated Collagen Nanofibers

Uncontrollable bleeding poses considerable fatality risks by large-volume blood losses. Current emergency antibleeding handlings including either compression with gauze or "passive" blood transfusion are thus far from ideal, while most recently developed hemostatic agents still share common limitations without considering the subsequent tissue repairing and antibacterial activity after treatment. Herein, we introduce a novel bioinspired aggregated collagen nanofiber-based biocompatible and efficient hemostatic hydrogel material (TS-Gel-Ag-col) prepared by the integration of multifunctional compounds of muco-mimetic poloxamer, polyvinylpyrrolidone, and dencichine/chitosan dialdehyde synergistic crosslinked aggregated collagen nanofibers decorated with silver nanoparticles. Comprehensive material characterization and in vitro and in vivo studies of TS-Gel-Ag-col demonstrate that these materials possess effective antihemorrhagic and antibacterial wound protection effects. Moreover, TS-Gel-Ag-col can facilitate the tissue repairing of skin wounds by promoting revascularization. TS-Gel-Ag-col holds great promise for next-generation collagen-based absorbable hemostatic materials and for the development of smart artificial skins.

Construction of a novel GQD based ratiometric fluorescent composite probe for viscosity detection

Herein, a novel ratiometric fluorescent composite nanoprobe RV-1@GQDs-OH was developed based on OH-functionalized GQDs (GQDs-OH) and molecular probe (RV-1) viaπ-π stacking. Compared with the conventional "on-off" viscosity probes, RV-1@GQDs-OH can be successfully applied in living systems for the ratiometric detection of viscosity changes in the viscosity range of 0-600 cP.

All-in-one mitochondria-targeted NIR-II fluorophores for cancer therapy and imaging

Small-molecule subcellular organelle-targeting theranostic probes are crucial for early disease diagnosis and treatment. The imaging window of these molecules is mainly focused on the visible and near-infrared region (below ∼900 nm) which limits the tissue penetration depth and therapeutic effects. Herein, a novel NIR-II small-molecule probe H4–PEG-Glu with a thiopyrylium cation was synthesized. H4–PEG-Glu not only can quickly and effectively image mitochondria in acute myeloid leukemia (AML) cells, and induce G₀/G₁ phase arrest by the intrinsic mitochondrial apoptosis pathway w/o irradiation, but also exhibit moderate cytotoxicity against AML cancer cells in a dose dependent-manner without laser irradiation. The THP-1 cells treated with H4–PEG-Glu upon NIR laser irradiation showed enhanced chemo- and photothermal therapy (CPTT) with 93.07% ± 6.43 apoptosis by Annexin V staining. Meanwhile, H4–PEG-Glu displayed high synergistic CPTT effects in vivo, as well as specific NIR-II tumor imaging in AML patient derived PDX mouse models for the first time. Our work lays down a solid foundation for designing small-molecule NIR-II mitochondria-selective theranostic probes.

Small-molecule subcellular organelle-targeting theranostic probes are crucial for early disease diagnosis and treatment.

A fluoran-based viscosity probe with high-performance for lysosome-targeted fluorescence imaging

A new fluorescent probe Lyso-Fl has been facilely prepared by an esterification reaction of spironolactone fluoran dye Rdi with ethanol, which shows viscosity-selective response by fluorescence. The new probe delivers obvious fluorescence signal enhancement when environmental viscosity changes from 1.01 cP (water) to 1256 cP (98% glycerol). And, both the emission intensity (575 nm) and fluorescence lifetime of Lyso-Fl exhibit individually good linear relationships with the solution viscosity. Besides, Lyso-Fl gives a selective response to viscosity among various biological species and exhibits pH-independent (1-10) fluorescent signals towards viscosity. More importantly, Lyso-Fl shows low cytotoxicity and can be utilized for monitoring of dexamethasone-stimulated viscosity enhancement by cell imaging with excellent lysosome-targeted performance, promoting it a promising fluorescent probe for lysosomal viscosity detection.

Ester and amide derivatives of rhodamine B exert cytotoxic effects on different human tumor cell lines

Three esters of rhodamine B (1–3) differing in their alkyl chain lengths as well as several rhodamine B amides (4–9) were synthesized in good yields and tested for their cytotoxicity in SRB assays employing several human tumor cell lines. The rhodamine B esters were unselective but showed cytotoxicity of as low as EC50 = 0.15 ± 0.02 µM. The rhodamine B amides were slightly less cytotoxic but showed good selectivity against MCF-7 and A2780 tumor cell lines. Especially a morpholinyl derivative 4 was ~20 time more cytotoxic for MCF-7 than for nonmalignant NIH 3T3 cells.

A novel carbazolyl GFP chromophore analogue: synthesis strategy and acidic pH-activatable lysosomal probe for tracing endogenous viscosity changes

A novel, acidic pH-activatable carbazolyl GFP chromophore analogue was designed for tracing lysosomal viscosity changes.

A molecular rotor sensor for detecting mitochondrial viscosity in apoptotic cells by two-photon fluorescence lifetime imaging

A two-photon fluorescent probe was developed for detecting mitochondrial viscosity during apoptosis of living cells by two-photon microscopy (TPM) and fluorescence lifetime imaging microscopy (FLIM) with good selectivity and highly biocompatible.

A highly sensitive red-emitting probe for the detection of viscosity changes in living cells, zebrafish, and human blood samples

Intracellular viscosity can be measured to reflect the state of living cells. Fluorescent probes are powerful tools for viscosity detection in vivo.

Methyl Scanning for Mechanochemical Chalcogen-Bonding Cascade Switches

Chalcogen-bonding cascade switching was introduced recently to produce the chemistry tools needed to image physical forces in biological systems. In the original flipper probe, one methyl group appeared to possibly interfere with the cascade switch. In this report, this questionable methyl group is replaced by a hydrogen. The deletion of this methyl group in planarizable push-pull probes was not trivial because it required the synthesis of dithienothiophenes with four different substituents on the four available carbons. The mechanosensitivity of the resulting demethylated flipper probe was nearly identical to that of the original. Thus methyl groups in the switching region are irrelevant for function, whereas those in the twisting region are essential. This result supports the chalcogen-bonding cascade switching concept and, most importantly, removes significant synthetic demands from future probe development.

A Chalcogen-Bonding Cascade Switch for Planarizable Push-Pull Probes

Planarizable push-pull probes have been introduced to demonstrate physical forces in biology. However, the donors and acceptors needed to polarize mechanically planarized probes are incompatible with their twisted resting state. The objective of this study was to overcome this "flipper dilemma" with chalcogen-bonding cascade switches that turn on donors and acceptors only in response to mechanical planarization of the probe. This concept is explored by molecular dynamics simulations as well as chemical double-mutant cycle analysis. Cascade switched flipper probes turn out to excel with chemical stability, red shifts adding up to high significance, and focused mechanosensitivity. Most important, however, is the introduction of a new, general and fundamental concept that operates with non-trivial supramolecular chemistry, solves an important practical problem and opens a wide chemical space.

Feasibility Study of Tissue Transglutaminase for Self-Catalytic Cross-Linking of Self-Assembled Collagen Fibril Hydrogel and Its Promising Application in Wound Healing Promotion

Collagen-based bio-hydrogels are undoubtedly a hot spot in the development of biological dressings for wound healing promotion. Herein, glutamine transaminase (TGase), a biological nontoxic cross-linker with high specific activity and reaction rate under mild conditions, was utilized for the self-catalytic cross-linking of the regenerated collagen (COL) fibril hydrogel fabricated through a molecular self-assembly method. The results showed that the natural triple helical conformation of COL remained completely integrated after self-catalytic cross-linking TGase, which was definitively the fundamental for maintaining its superior bioactivity. It was worth noting that TGase could promote the self-assembly process of COL building blocks into a higher order D-period cross-striated structure. Also, the reconstructed TGase cross-linked COL fibrils exhibited a higher degree of interfiber entanglements with more straight and longer fibrils. Meanwhile, the thermal stability of COL was significantly improved after introducing TGase. Besides, the cytocompatibility analysis suggested that the regenerated COL fibril hydrogel showed excellent cell growth activity and proliferation ability when the dosage of TGase is less than 40 U/g. Further, animal experiments indicated that the targeted COL fibril hydrogel could significantly promote skin wound healing, exhibiting better capacity of skin tissue for regeneration than the COL hydrogel untreated as expected. Therefore, the reconstructed TGase cross-linked COL fibril hydrogel could serve as a novel soft material for wound healing promotion.

Mechanosensitive Fluorescent Probes to Image Membrane Tension in Mitochondria, Endoplasmic Reticulum, and Lysosomes

Measuring forces inside cells is particularly challenging. With the development of quantitative microscopy, fluorophores which allow the measurement of forces became highly desirable. We have previously introduced a mechanosensitive flipper probe, which responds to the change of plasma membrane tension by changing its fluorescence lifetime and thus allows tension imaging by FLIM. Herein, we describe the design, synthesis, and evaluation of flipper probes that selectively label intracellular organelles, i.e., lysosomes, mitochondria, and the endoplasmic reticulum. The probes respond uniformly to osmotic shocks applied extracellularly, thus confirming sensitivity toward changes in membrane tension. At rest, different lifetimes found for different organelles relate to known differences in membrane organization rather than membrane tension and allow colabeling in the same cells. At the organelle scale, lifetime heterogeneity provides unprecedented insights on ER tubules and sheets, and nuclear membranes. Examples on endosomal trafficking or increase of tension at mitochondrial constriction sites outline the potential of intracellularly targeted fluorescent tension probes to address essential questions that were previously beyond reach.