Dual-reporter fluorescent probe for precise identification of liver cancer by sequentially responding to carboxylesterase and polarity

Early treatment significantly improves the survival rate of liver cancer patients, so the development of early diagnostic methods for liver cancer is urgent. Liver cancer can develop from viral hepatitis, alcoholic liver, and fatty liver, thus making the above diseases share common features such as elevated viscosity, reactive oxygen species, and reactive nitrogen species. Therefore, accurate differentiation between other liver diseases and liver cancer is both a paramount practical need and challenging. Numerous fluorescent probes have been reported for the diagnosis of liver cancer by detecting a single biomarker, but these probes lack specificity for liver cancer in complex biological systems. Obviously, using multiple liver cancer biomarkers as the basis for judgment can dramatically improve diagnostic accuracy. Herein, we report the first fluorescent probe, LD-TCE, that sequentially detects carboxylesterase (CE) and lipid droplet polarity in liver cancer cells with high sensitivity and selectivity, with linear detection of CE in the range of 0-6 U/mL and a 65-fold fluorescence enhancement in response to polarity. The probe first reacts with CE and releases weak fluorescence, which is then dramatically enhanced due to the decrease in lipid droplet polarity in liver cancer cells. This approach allows the probe to enable specific imaging of liver cancer with higher contrast and accuracy. The probe successfully achieved the screening of liver cancer cells and the precise identification of liver cancer in mice. More importantly, it is not disturbed by liver fibrosis, which is a common pathological feature of many liver diseases. We believe that the LD-TCE is expected to be a powerful tool for early diagnosis of liver cancer.

Design of a prodrug photocage for cancer cells detection and anticancer drug release

Developing probes for simultaneous diagnosis and killing of cancer cells is crucial, yet challenging. This article presents the design and synthesis of a novel Rhodamine B fluorescence probe. The design strategy involves utilizing an anticancer drug (Melphalan) to bind with a fluorescent group (HRhod-OH), forming HRhod-MeL, which is non-fluorescent. However, when exposed to the high levels of reactive oxygen species (ROS) of cancer cells, HRhod-MeL transforms into a red-emitting Photocage (Rhod-MeL), and selectively accumulates in the mitochondria of cancer cells, where, when activated with green light (556 nm), anti-cancer drugs released. The Photocage improve the efficacy of anti-cancer drugs and enables the precise diagnosis and killing of cancer cells. Therefore, the prepared Photocage can detect cancer cells and release anticancer drugs in situ, which provides a new method for the development of prodrugs.

A highly selective probe engineered to detect polarity and distinguish normal cells and tumor cells in tissue sections

Early diagnostics and therapies for diseases such as cancer are limited by the fact that the inducing factors for the development of cytopathies are not clear. The stable polarity of lipid droplets is a potential biomarker for tumor cells; however, the complex intracellular biological environment poses great difficulties for specific detection of the polarity. Therefore, to meet this pressing challenge, we designed a highly selective fluorescent probe, DCI-Cou-polar, which used the ICT mechanism to differentiate normal cells and tumor cells in tissue sections by detecting changes in the polarities of intracellular lipid droplets. The introduction of a cyclic amine at the 7-position of coumarin (benzoquinolizine coumarin) reduced its ability to donate electrons compared with the diethylamino group, which increased the probe selectivity while retaining the sensitivity to polarity. With NIR emission and large Stokes shifts, DCI-Cou-polar has high sensitivity to polarity, excellent photostability, and biocompatibility, and it tracks lipid droplets with high fidelity. Therefore, we believe that this polarity-sensitive probe provides information on the connection between the polarity of lipid droplets and tumors while improving the development of highly selective polarity probes.

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

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

Ketocyanine-Based Fluorescent Probe Revealing the Polarity Heterogeneity of Lipid Droplets and Enabling Accurate Diagnosis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) has gradually become a pronoun for terrifying death owing to its high mortality rate. With the progression of HCC, lipid droplets (LDs) in HCC cells exhibit specific variations such as increased LDs number and decreased polarity, which can serve as the diagnostic target. However, developing an effective method to achieve HCC diagnosis and reveal LDs polarity heterogeneity is still a crucial challenge. Herein, the first high-performance LDs-targeting probe (1) is reported based on ketocyanine strategy with ultrasensitive polarity-responding ability and near-infrared emission. Probe 1 shows excellent sensitivity to polarity parameter Δf (0.027-0.290) with 808-fold fluorescence enhancement and the emission wavelength red-shifts 91 nm. In HCC cells, probe 1 shows a 2.5- to 5.9-fold fluorescence enhancement compared with normal and other cancer cells which exceeds clinical threshold of 2.0, indicating probe 1 can distinguish HCC cells. The LDs polarity heterogeneity is revealed and it displays a sequence, HCC cells < other cancer cells < normal cells, which may provide useful insight to engineer LDs-targeting probes for HCC cell discrimination. Finally, probe 1 realizes accurate HCC diagnosis on the cellular, organ, and in vivo levels, providing a satisfying tool for clinical HCC diagnosis and surgical navigation.

A golgi-targeting and polarity-specific fluorescent probe for the diagnosis of cancer and fatty liver in living cells and tissues

Elucidating the intrinsic relationship between diseases and Golgi apparatus polarity remains a great challenge owing to the lack of the Golgi-specific fluorescent probe for polarity. Until now, the visualization of abnormal Golgi apparatus polarity in clinical cancer patient samples has not been achieved. To meet this urgent challenge, we facilely synthesized a robust Golgi-targeting and polarity-specific fluorescent probe (GCSP), which consists of an electron-acceptor solvatochromic coumarin 343 and an electron-donor Golgi-targeting group phenylsulfonamide. Owing to the typical D-π-A molecular configuration with unique intramolecular charge transfer effect, GCSP exhibits high sensitivity to polarity change in different solvents. Moreover, we revealed that GCSP possessed a satisfactory ability to sensitively monitor Golgi apparatus polarity changes in living cells. Using GCSP, we have successfully shown that Golgi apparatus polarity may serve as an ubiquitous marker for cancer and fatty liver detection. Surprisingly, the visualization of Golgi polarity has been achieved not only at the cellular levels, but also in clinical tissue samples from cancer patients, thus holding great potential in the clinical diagnosis of human cancer. All these features render GCSP an effective tool for the accurate diagnosis of Golgi apparatus related diseases.

Liquid core fluorescent organic nanoprobes: Long-term stability and highly selective lipid droplets bio-imaging

Lipid droplets (LDs) are important subcellular organelles that play a huge role in cell metabolism and growth. In this study, we synthesized two LDs fluorescent probes with benzothiadiazole (BTH) as electron acceptor and triphenylamine (TPA) as electron donor, which named as TPA-BTH1 and TPA-BTH2, respectively. Meanwhile, we introduced long alkyl chain to the probe as a shielding group and LDs targeting enhancement group. The results showed that the two probes were too sensitive to solvents' polarity because of the D-A structures possessed twisted intramolecular charge-transfer (TICT) effect. Furthermore, we prepared the two probes into nanoprobes by nanoprecipitation, which named as TPA-BTH1-20 and TPA-BTH2-20, respectively. The nanoprobes also had excellent fluorescence emission abilities and biocompatibility, as well as high photostability and accurately target LDs ability, which could be successfully applied in cell fluorescence imaging experiments.

Photoactivable AIEgen-based Lipid-Droplet-Specific Drug Delivery Model for Live Cell Imaging and Two-Photon Light-Triggered Anticancer Drug Delivery

Lipid droplets (LDs) are dynamic complex organelles involved in various physiological processes, and their number and activity are linked to multiple diseases, including cancer. In this study, we have developed LD-specific near-infrared (NIR) light-responsive nano-drug delivery systems (DDSs) based on chalcone derivatives for cancer treatment. The reported nano-DDSs localized inside the cancer microenvironment of LDs, and upon exposure to light, they delivered the anticancer drug valproic acid in a spatiotemporally controlled manner. The developed systems, namely, 2'-hydroxyacetophenone-dimethylaminobenzaldehyde-valproic (HA-DAB-VPA) and 2'-hydroxyacetophenone-diphenylaminobenzaldehyde-valproic (HA-DPB-VPA) ester conjugates, required only two simple synthetic steps. Our reported DDSs exhibited interesting properties such as excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) phenomena, which provided advantages such as AIE-initiated photorelease and ESIPT-enhanced rate of photorelease upon exposure to one- or two-photon light. Further, colocalization studies of the nano-DDSs by employing two cancerous cell lines (MCF-7 cell line and CT-26 cell line) and one normal cell line (HEK cell line) revealed LD concentration-dependent enhanced fluorescence intensity. Furthermore, systematic investigations of both the nano-DDSs in the presence and absence of oleic acid inside the cells revealed that nano-DDS HA-DPB-VPA accumulated more selectively in the LDs. This unique selectivity by the nano-DDS HA-DPB-VPA toward the LDs is due to the hydrophobic nature of the diphenylaminobenzaldehyde (mimicking the LD core), which significantly leads to the aggregation and ESIPT (at 90% volume of fw, ΦF = 20.4% and in oleic acid ΦF = 24.6%), respectively. Significantly, we used this as a light-triggered anticancer drug delivery model to take advantage of the high selectivity and accumulation of the nano-DDS HA-DPB-VPA inside the LDs. Hence, these findings give a prototype for designing drug delivery models for monitoring LD-related intracellular activities and significantly triggering the release of LD-specific drugs in the biological field.

Two Polarity-Sensitive Fluorescent Probes Based on Curcumin Analogs for Visualizing Polarity Changes in Lipid Droplets

As a class of highly dynamic organelles, lipid droplets (LDs) are involved in numerous physiological functions, and the changes in polarity of LDs are closely related to a variety of diseases. In this work, we developed two polarity-sensitive fluorescent probes (CC-CH and CC-Cl) based on curcumin analogs. CC-CH and CC-Cl with a donor-acceptor-donor (D-A-D) structure exhibited the property of intramolecular charge transfer (ICT); thus, their fluorescence emissions were significantly attenuated with increasing ambient polarity. Cell experiments indicated that CC-CH and CC-Cl showed excellent photostability, a low cytotoxicity, and a superior targeting ability regarding LDs. After treatment with oleic acid (OA) and methyl-β-cyclodextrin (M-β-CD), the polarity changes of LDs in living cells could be visualized by using CC-CH and CC-Cl. In addition, CC-CH and CC-Cl could monitor polarity changes of LDs in different pathological processes, including inflammatory responses, nutrient deprivation, and H2O2-induced oxidative stress. Therefore, CC-CH and CC-Cl are promising potential fluorescent probes for tracking intracellular LD polarity changes.

A fluorescent probe for lipid droplet polarity imaging with low viscosity crosstalk

Monitoring the variations of lipid droplet (LD) polarity is of great significance for the investigation of LD-related cellular metabolism and function. We hereby report a lipophilic fluorescent probe (BTHO) with the feature of intramolecular charge transfer (ICT) for imaging the LD polarity in living cells. BTHO exhibits an obvious attenuation of fluorescence emission in response to the increase of environmental polarity. The linear response range of BTHO to polarity (ε, the dielectric constant of solvents) is derived to be 2.21-24.40, and the fluorescence of BTHO in glyceryl trioleate falls in this range. Furthermore, BTHO has high molecular brightness, which may effectively improve the signal to noise ratio, along with the decrease of phototoxicity. BTHO exhibits excellent photostability and targeting capability to LDs with low cytotoxicity, which is satisfactory in long-term imaging in live cells. The probe was successfully applied for imaging LD polarity variation in live cells caused by oleic acid (OA), methyl-β-cyclodextrin (MβCD), H₂O₂, starvation, lipopolysaccharide (LPS), nystatin, and erastin. The low crosstalk caused by viscosity to BTHO measuring the LD polarity was confirmed from a calculation result.

Synthesis of a Red-Emitting Polarity-Sensitive Fluorescent Probe Based on ICT and Visualization for Lipid Droplet Dynamic Processes

Abnormal lipid droplets (LDs) have been recognized as critical factors in many diseases because they are metabolically active and dynamic organelles. Visualization for LD dynamic processes is fundamental for elucidating the relationship of LDs and related diseases. Herein, a red-emitting polarity-sensitive fluorescent probe (TPA-CYP) based on intramolecular charge transfer (ICT) was proposed, which was constructed by employing triphenylamine (TPA) and 2-(5,5-dimethyl-2-cyclohex-1-ylidene)propanedinitrile (CYP) as electron donor and acceptor moiety, respectively. The spectra results underlined the excellent characteristics of TPA-CYP, such as high polarity sensitivity (Δf = 0.209 to 0.312), strong solvatochromic effect (λ_em 595-699 nm), and the large Stokes shifts (174 nm). Moreover, TPA-CYP exhibited a specific ability to target LDs and effectively differentiated cancer cells and normal cells. Surprisingly, TPA-CYP had been successfully applied to dynamic tracking of LDs, not only in inflammation induced by lipopolysaccharide (LPS), the process of oxidative stress, but also in live zebrafish. We believe that TPA-CYP could serve as a powerful tool to gain insight into the dynamics of LDs and to understand and diagnose LD-associated diseases.

Thiopurines Analogues with Additional Ring: Synthesis, Spectroscopic Properties, and Anticancer Potency

Purine scaffolds constitute a starting point for the synthesis of numerous chemotherapeutics used in treating cancer, viruses, parasites, as well as bacterial and fungal infections. In this work, we synthesized a group of guanosine analogues containing an additional five-membered ring and a sulfur atom at the C-9 position. The spectral, photophysical, and biological properties of the synthesized compounds were investigated. The spectroscopic studies revealed that a combination of the thiocarbonyl chromophore and the tricyclic structure of guanine analogues shifts the absorption region above 350 nm, allowing for selective excitation when present in biological systems. Unfortunately, due to the low fluorescence quantum yield, this process cannot be used to monitor the presence of these compounds in cells. The synthesized compounds were evaluated for their effect on the viability of human cervical carcinoma (HeLa) and mouse fibroblast (NIH/3T3) cells. It was found that all of them display anticancer activity. In vitro studies were preceded by in silico ADME and PASS analyses, which confirmed that the designed compounds are promising candidates for anticancer agents.

Rational design of water-soluble mitochondrial-targeting near-infrared fluorescent probes with large Stokes shift for distinguishing cancerous cells and bioimaging

In the paper, two new near-infrared fluorescent probes (TTHPs) with D-π-A structure were successfully synthesized. TTHPs exhibited polarity and viscosity sensitivity and mitochondrial targeting under physiological conditions. The emission spectra of TTHPs showed strong polarity/viscosity dependence with more than a large Stokes shift of 200 nm. Based on their unique merits, TTHPs were used to distinguish cancerous and normal cells, which could be new tools for cancer diagnosis. Moreover, TTHPs were the first to achieve biological imaging of Caenorhabditis elegans, which could be labeling probes to apply in multicellular organisms.

Monitoring Cell Plasma Membrane Polarity by a NIR Fluorescence Probe with Unexpected Cell Plasma Membrane-Targeting Ability

The cell plasma membrane, the natural barrier of a cell, plays critical roles in a mass of cell physiological and pathological processes. Therefore, revealing and monitoring the local status of the cell plasma membrane are of great significance. Herein, using a near-infrared (NIR) fluorescence probe BTCy, microenvironmental polarity in the cell plasma membrane was in situ monitored. BTCy showed sensitive and selective fluorescence decrease response at 706 nm with the increase of polarity as its polarity-responsive D-π-A structure. Most importantly, BTCy showed unexpected cell plasma membrane-targeting ability, probably due to its amphiphilic structure. With BTCy, the distinguishing imaging of cancer and normal cells was done, in which cancer cells exhibited significantly stronger signals due to their lower cell plasma membrane polarity. In addition, with the imaging of BTCy, the ferroptosis process was revealed with no significant cell plasma membrane polarity variation for the first time. Furthermore, BTCy was employed for in vivo imaging of tumor tissue in the 4T1-tumor-bearing mice. The polarity-responsive and cell plasma membrane-targeting properties of BTCy make it a useful tool for monitoring cell plasma membrane polarity variation, providing an efficient and simple method for tumor diagnosis.

Preparation of oxime compound lipid droplet-specifically labeled fluorescent probe and its application in cell imaging

Fluorescent probes can facilitate our further comprehension of the functional and physiological roles of LDs and thus promote the development of effective therapeutic approaches. Oxime compounds are widely used due to their good crystallinity and high reactivity. However, the majority oximes fluorescent probes are usually employed for the detection of HCIO, and the application of oximes in fluorescently labeled LD_S is poorly reported. In this paper, three kinds of LDs fluorescent probes (NAP-a, NAP-b and NAP-c) with D-π-A structure were synthesized by simple synthesis method with 1,8-naphthalimide as fluorescent matrix and oxime group as electron donor. These probes were highly sensitive to polarity, and possessed good photostability and low cytotoxicity. Co-staining experiments showed that these probes could target LDs and the fluorescence image was green. These probes NAP-a, NAP-b and NAP-c possessed high Pearson coefficient (HeLa cells: 0.91, 0.95, 0.86) and Manders coefficient (HeLa cells: 0.91, 0.96, 0.86) with Nile Red. Interestingly, the dynamic variations in their size, shape and distribution could be clearly observed in the oleic acid-treated cell model of LDs. Imaging of zebrafish was performed and green fluorescence was collected in zebrafish. These excellent properties make oxime compound fluorescent probes a promising fluorescent probes for studying LDs and metabolic diseases. This study opens up a new way for the preparation of LDs fluorescent probe.

Rational Design of Novel Lipophilic Aggregation-Induced Emission Probes for Revealing the Dynamics of Lipid Droplets during Lipophagy and Ferroptosis

Lipid droplets (LDs), as crucial organelles, play a significant role in some physiological processes. Monitoring the concentration of LDs and dynamic behaviors between LDs and other organelles during some physiological processes is important for studying their biological function and medical diagnosis. Herein, we report a series of aggregation-induced emission (AIE) probes AIE-Cbz-LD-C_n (n = 1, 3, 5, 7, OMe) based on the conjugation of quinoline-malononitrile (QM) and carbazole for tracking the dynamic changes of LDs and studying the association between LDs and lysosome/endoplasmic reticulum (ER). To our great delight, AIE-Cbz-LD-C₃, AIE-Cbz-LD-C₅, and AIE-Cbz-LD-C₇ could aggregate in LDs accurately and light up the LDs with good photostability. Among them, AIE-Cbz-LD-C₇ was used to visualize the interplay between LDs and lysosomes during lipophagy due to the excellent LD-specificity. We also succeeded in tracking the number of newborn LDs generated near the endoplasmic reticulum regions revealing that the number increased considerably during ferroptosis by using AIE-Cbz-LD-C₇, which supplies useful evidence for the hypothesis that LDs generate from the ER. We expect the probe AIE-Cbz-LD-C₇ would be a practical tool for tracking the physiological and pathological processes contacted with LDs.

Design of a ratiometric near-infrared fluorescent probe with double excitation for hydrazine detection in vitro and in vivo

Hydrazine has a wide range of industrial applications, but it is also a toxic and explosive chemical substance, which brings potential risks to human health and environmental safety. Therefore, rapid and sensitive monitoring of hydrazine is of great importance in environmental sciences and biological systems. In this work, a new near-infrared (NIR) ratiometric fluorescent probe (Ac-HY) was designed to detect hydrazine under double excitation and emission mode. Ac-HY exhibited large stokes shift (130 nm), high selectivity and sensitivity to hydrazine detection. The applications of Ac-HY probe for detecting hydrazine in vapor and imaging hydrazine in lipid droplets and zebrafish. Therefore, Ac-HY can be used to monitor the distribution of exogenous hydrazine in vitro and in vivo.

Highly Efficient Red/NIR-Emissive Fluorescent Probe with Polarity-Sensitive Character for Visualizing Cellular Lipid Droplets and Determining Their Polarity

Lipid droplets (LDs), which are ubiquitous organelles existing in almost all eukaryotic cells, have attracted a lot of attention in the field of cell biology over the last decade. For the biological study of LDs via fluorescence imaging, the superior LD fluorescent probes with environmental polarity-sensitive character are highly desired and powerful but are very scarce. Herein, we have newly developed such a kind of fluorescent probe named LDs-Red which enables us to visualize LDs and to further reveal their polarity information. This fluorescent probe displays the advantages of intense red/near-infrared emission, high LD staining specificity, and good photostability; thus, it would be very useful for LD fluorescence imaging application. As a result, the three-dimensional confocal imaging to visualize spatial distribution of LDs and the multicolor confocal imaging to simultaneously observe LDs and other cellular organelles have been realized using this new LD fluorescent probe. Furthermore, the polarity-sensitive emission character of this probe enables us to quantitatively determine the LD polarity via spectral scan imaging. Consequently, the cancer cells (HepG2, HeLa, and Panc02) displaying lower polarity of LDs than the normal cells (L929, U251, and HT22) have been systematically demonstrated. In addition, this polarity-sensitive probe displaying shorter fluorescence wavelengths in cancer cells than in normal cells has an important and potential ability to distinguish them.

Polarity-Sensitive Cell Membrane Probe Reveals Lower Polarity of Tumor Cell Membrane and Its Application for Tumor Diagnosis

Cancer is a health threat worldwide, and it is urgent to develop more sensitive cancer detection methods. Herein, a polarity-sensitive cell membrane probe (named COP) was developed for detecting cancer cells and tumors sensitively and selectively at the cell membrane level. The probe shows a strong polarity-dependent fluorescence and excellent cell membrane targeting ability to visualize cell membrane with red fluorescence with a non-washing process. Notably, COP can selectively light up the tumor cell membranes, which reveals that cancer cell membranes have lower polarity than normal cell membranes. The giant unilamellar vesicle model and cell imaging studies proved this. Moreover, COP can effectively and selectively light up tumors. Overall, this work demonstrates that the polarity of the tumor cell membrane is quite different to normal cell membranes, and based on this, sensitive membrane probes can be developed to selectively visualize cancer cells and tumors, which opens up a new way for tumor diagnosis at the cellular level.

Engineering BODIPY-based near-infrared nanoparticles with large Stokes shifts and aggregation-induced emission characteristics for organelle specific bioimaging

Lipid droplets (LDs) and lysosomes, as two important subcellular organelles, play specific and indispensable roles in various cellular processes. The development of efficient LD- and lysosome-specific fluorescent bio-probes is of great importance. However, current commercial lipid droplet- (LD) and lysosome-specific fluorescent specific bio-probes often suffer from the aggregation-caused quenching (ACQ) effect, short absorption and emission wavelengths, poor photostability and low specificity. Herein, a typical ACQ luminogen BODIPY was directly conjugated to strong electron donating triarylamine units at its α-positions, giving near-infrared (NIR) fluorescent materials TPAB and 2TPAB with aggregation-induced emission (AIE). Both TPAB and 2TPAB nanoparticles were obtained by self-assembly, and showed NIR emissions, large Stokes shifts, good photostability and two-photon absorption. These nanoparticles presented remarkable bioimaging performances and were shown to specifically localize in LDs or lysosomes, respectively, depending on the number of triarylamine units attached. They have been successfully used to detect endogenous LD overproduction, and monitor abnormal activities of LDs/lysosomes, as well as real-time track the lipophagy process in cells. Their far NIR emission and two-photon excitation further supported their promising bioimaging application for lipid droplet tracking in liver tissue and live zebrafish larvae. Our work here enriches BODIPY based NIR AIE dyes and provides organelle specific bio-probes which are superior to currently used commercial ones.

Natural flavylium-inspired far-red to NIR-II dyes and their applications as fluorescent probes for biomedical sensing

Fluorescent probes that emit in the far-red (600-700 nm), first near-infrared (NIR-I, 700-900 nm), and second NIR (NIR-II, 900-1700 nm) regions possess unique advantages, including low photodamage and deep penetration into biological samples. Notably, NIR-II optical imaging can achieve tissue penetration as deep as 5-20 mm, which is critical for biomedical sensing and clinical applications. Much research has focused on developing far-red to NIR-II dyes to meet the needs of modern biomedicine. Flavylium compounds are natural colorants found in many flowers and fruits. Flavylium-inspired dyes are ideal platforms for constructing fluorescent probes because of their far-red to NIR emissions, high quantum yields, high molar extinction coefficients, and good water solubilities. The synthetic and structural diversities of flavylium dyes also enable NIR-II probe development, which markedly advance the field of NIR-II in vivo imaging. In the last decade, there have been huge developments in flavylium-inspired dyes and their applications as far-red to NIR fluorescent probes for biomedical applications. In this review, we highlight the optical properties of representative flavylium dyes, design strategies, sensing mechanisms, and applications as fluorescent probes for detecting and visualizing important biomedical species and events. This review will prompt further research not only on flavylium dyes, but also into all far-red to NIR fluorophores and fluorescent probes. Moreover, this interest will hopefully spillover into applications related to complex biological systems and clinical treatments, ranging in focus from the sub-organelle to whole-animal levels.

Advances in the Structural Strategies of the Self-Assembly of Photoresponsive Supramolecular Systems

Photosensitive supramolecular systems have garnered attention due to their potential to catalyze highly specific tasks through structural changes triggered by a light stimulus. The tunability of their chemical structure and charge transfer properties provides opportunities for designing and developing smart materials for multidisciplinary applications. This review focuses on the approaches reported in the literature for tailoring properties of the photosensitive supramolecular systems, including MOFs, MOPs, and HOFs. We discuss relevant aspects regarding their chemical structure, action mechanisms, design principles, applications, and future perspectives.

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.

Lipid Droplet-Specific Dual-Response Fluorescent Probe for the Detection of Polarity and H2O2 and Its Application in Living Cells

H₂O₂ and polarity are quite important in many physiological and pathological processes, and their relationship is complicated and obscure for researchers. Thus, it is vital and challenging to achieve simultaneous detection of H₂O₂ and polarity in vivo. Herein, the first naphthalimide-triphenylamine-based dual-site fluorescent probe NATPA is developed for simultaneously imaging intracellular H₂O₂ and polarity fluctuations. It exhibits excellent sensitivity (LOD = 44 nM), selectivity, and fast response (15 min) to H₂O₂ and a superior capacity for detecting polarity upon the intramolecular charge transfer (ICT) effect. Besides, the probe displays low cytotoxicity and lipid droplet targeting and is further applied in imaging H₂O₂ and polarity fluctuations in HepG2 and L-02 cells, so that NATPA is qualified to distinguish cancer cells from normal cells. This research contributes a new design principle for the construction of dual-site fluorescent probes for simultaneously detecting active molecules and polarity.

Development of a fluorescent nanoprobe based on an amphiphilic single-benzene-based fluorophore for lipid droplet detection and its practical applications

Lipid droplets (LDs) are crucial biological organelles connected with metabolic pathways in biological systems and diseases. To monitor the locations and accumulation of LDs in lipid-related diseases, the development of a visualization tool for LDs has gained importance. In particular, LD visualization using fluorescent probes has gained attention. Herein, a new fluorescent nanoprobe, BMeS-Ali, is developed that can sense LDs based on an amphiphilic single benzene-based fluorophore (SBBF). BMeS-Ali consists of hydrophilic (-NH₂) and hydrophobic (-C₁₂H₂₅) moieties and exists as a micelle nanostructure in aqueous media. BMeS-Ali has a weak fluorescence, but its emission was dramatically enhanced upon exposure to the LD components such as oleic acids (OA) by reassembling its nano-formulation. BMeS-Ali showed a selective LD staining ability and great biocompatibility in cells (cancer cells and stem cells). It also showed a practical sensing ability towards biologically derived lipids and can be applied to the visualization of human fingerprints. We found that the nanoprobe BMeS-Ali has significant potential to serve as a practical dye and sensor for lipids, especially for LD imaging in the biomedical research area and broader industrial applications.

A lipid droplet-targetable and biothiol-sensitive fluorescent probe for the diagnosis of cancer cells/tissues

Lipid droplets (LDs) have recently been reported as an attractive target for cancer diagnosis and treatment, owing to their special structure or microenvironment changes in cancer development and resistance. However, the relationship between the biothiol level of LDs and cancer is still poorly understood, partially owing to the absence of effective molecular tools. Herein, we developed a LD-targetable and biothiol-sensitive fluorescent probe, BTDA-RSS, by introducing 2,4-dinitrobenzenesulfonyl (DNBS) as the biothiol reaction group into a benzothiazolyl derivative. BTDA-RSS displayed a marked and rapid fluorescence turn-on response toward biothiols, due to the biothiol-triggered cleavage of DNBS to yield the highly fluorescent benzothiazolyl iminocoumarin BTDA. In addition, the probe shows significant LD-targetable ability, and has been applied for imaging endogenous/exogenous biothiol changes in LDs. Importantly, BTDA-RSS has successfully been utilized to distinguish cancerous cells/tissues from normal cells/tissues with excellent contrast. Surprisingly, we demonstrated for the first time the visualization of LD biothiols in surgical specimens from cancer patients, thereby holding great potential for the application of BTDA-RSS in the clinical diagnosis of human cancers.

A Near-Infrared Probe for Specific Imaging of Lipid Droplets in Living Cells

Lipid droplets (LDs) are involved in various physiological processes and associated with cancer development, and are regarded as a potential tumor marker for cancer diagnosis. Monitoring LDs is of prior importance to understand their involvement in biological mechanisms and the early detection of cancers. Highly sensitive and specific noninvasive fluorescent probes are particularly desirable for imaging LDs and cancer diagnosis. Herein, according to the high-viscosity and low-polarity microenvironment in LDs, we developed four easily prepared LDs-specific probes based on noncharged merocyanines. Among them, LD-1 absorbs and emits in the near-infrared (NIR) region with a large Stokes shift. Importantly, LD-1 displayed high sensitivity to high viscosity and low polarity, which allowed it to show high LDs-targeting ability. In cell imaging, LD-1 successfully probed the changes in LDs in the presence of oleic acid or during ferroptosis and was used to distinguish cancer cells from normal cells.

BF2 group chelated AIE fluorescent probe for polarity mapping of lipid droplets in cells and in vivo

Lipid droplets (LDs), are multi-functional organelles with the storage of neutral lipids and proteins, participating in various of physiological processes. However, abnormal of LDs in morphology and numbers always lead to multiple diseases, including cancer, viral infection, obesity, inflammation. To better understand the physiological function of LDs in living cells, we designed two new fluorescent probes LDs-CA and LDs-BCA based on the triphenylamine and coumarin fluorophores to monitor LDs polarity and numbers variation in this work. The one-step strategy for the regulation of BF₂ group realized a gratifying in emission wavelengths from orange fluorescence of LDs-CA to the red fluorescence of LDs-BCA, surprisingly. The two novel probes showed strong positive solvatochromism effect in different solvents and exhibited the aggregation-induced emission (AIE) effect. Based on the above excellent optical properties, LDs-CA and LDs-BCA were applied for imaging of the LDs with high overlap coefficient when co-stained with commercial dyes, respectively. The probes of LDs-CA and LDs-BCA provided an intuitive method to visualize the dynamic changes of LDs in morphology, size, and numbers under nutritionalstimulation, affording a powerful tool for fluorescence visualization of LDs related biological processes. Notably, the near-infrared emissive probe LDs-BCA successfully imaged the gastric fat in living obese mouse, which may provide a new idea for medical diagnostics.

A rhodol-based fluorescent probe with a pair of hydrophilic and rotatable wings for sensitively monitoring intracellular polarity

Cell polarity, as a vital intracellular microenvironment characteristic, has immense effects on numerous pathological and biological processes. Therefore, the tracking of polarity variations is highly essential to explore the role and mechanism of the polarity in pathophysiological processes. Herein, we designed and synthesized a novel rhodol-based fluorescent probe RDS sensitive to polarity by introducing a bis(2-hydroxyethylthio)methyl group, like a pair of hydrophilic and rotatable wings, into the rhodol skeleton. This unique design makes RDS adopt the colorless and non-fluorescent spirocyclic form in low polarity medium while the colored and fluorescent ring-open form in high polarity system, resulting in a positive-correlation response of fluorescence intension to polarity. Importantly, RDS was successfully applied to monitor the polarity changes in living cells including cancer cells, healthy cells and senescent healthy cells, visualizing that the polarity of cancer cells is lower than that of healthy cells in which the more senescent ones have higher polarity.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Synthesis of a new environment-sensitive fluorescent probe based on TICT and application for detection of human serum albumin and specific lipid droplets imaging

Environment-sensitive fluorescent probes have always been as forceful tools to understand the pathophysiological processes of relevant diseases. In this work, a new fluorescent probe with typical D-π-A structure was designed and showed high sensitivity to polarity and viscosity changes. DPAR could selectively detect human serum albumin (HSA) with turn-on orange emission in aqueous PBS buffer (pH 7.4), which showed advantages such as rapid response (4 min), high sensitivity (LOD 0.98 μg/mL). Therefore, it was successfully used for achieving HSA levels in urine samples and HSA imaging in HeLa cells. DPAR also exhibited the capability to recognize the cancer cells over the normal cells by lower polarity guided lipid droplets (LDs) imaging (in green emission channel). The detection mechanism for HSA and cancer diagnosis was convinced that DPAR encountered the lower-polarity and higher-viscosity microenvironment, resulting in the confinement of the TICT process and intramolecular rotation. These facts showed that DPAR had good application prospects in environment-related biomedical research and clinical diagnosis.

Two Water-Soluble and Wash-Free Fluorogenic Probes for Specific Lighting Up Cancer Cell Membranes and Tumors

The construction of microenvironment-sensitive probes with good cell membrane-targetability can reveal the fundamental properties of cell membranes. Herein, two polarity-sensitive probes, termed MEMs were reported for the first time to specifically light up cancer cell membranes. Both probes were designed with tetrahydroquinoxaline coumarin amide as the fluorophore, and quaternary ammonium groups were appended to increase water solubility and target cell membranes. In vitro studies showed that the fluorescence of both probes displayed strong polarity dependence and had a wide linear range to polarity (Δf). MEMs also displayed excellent cell membrane targeting ability and could long-term light up cell membranes with red fluorescence and a wash-free process. More excitingly, MEMs could specifically light up cancer cell membranes, revealing that cancer cells might have lower cell membrane polarity than normal cells. In vivo studies showed that MEMs could also effectively distinguish tumors from normal tissues. Overall, this work has not only developed two polarity-sensitive probes with good cell membrane targetability, but also provided new insights and methods for an in-depth understanding of cancer cells and cancer diagnosis.

Fluorescent probes based on acridine derivatives and their application in dynamic monitoring of cell polarity variation

Dynamic monitoring of the polarity of lipid droplets or lysosomes in HeLa cells.

TICT-Based Microenvironment-Sensitive Probe with Turn-on Red Emission for Human Serum Albumin Detection and for Targeting Lipid Droplet Imaging

Fluorescent probes sensitive to microenvironment have always been fascinating due to their tremendous advantages in tracking changes in the pathophysiological microenvironment and potential application in the early diagnosis of related diseases. In this study, a fluorescent luminogen, triphenylamine-thiophene-rhodanine (TPA-TRDN), with high sensitivity to changes in polarity and viscosity was designed and could be applied to detecting human serum albumin (HSA) in actual urine, as well as lipid droplets (LDs) in cells and in vivo with turn-on red emission. TPA-TRDN could selectively detect HSA with fast response (10 min), superior sensitivity (LOD 0.34 μg/mL, about 60-fold fluorescence enhancement), and wide detection range (0.00-0.30 mg/mL). The detection mechanism was demonstrated: TPA-TRDN encountered the hydrophobic IB domain of HSA, leading to the inhibition of the twisted intramolecular charge transfer (TICT) phenomenon and intramolecular rotation. Moreover, TPA-TRDN demonstrated satisfactory ability to identify cancer cells and noncancer cells by microenvironment-guided specific LD bioimaging. This evidence indicated that TPA-TRDN has promising application in the microenvironment-related biomedical field and clinical diagnosis.

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.

Dynamic Excimer (DYNEX) Imaging of Lipid Droplets

Unraveling cellular physiological processes via luminescent probes that target specific cellular microenvironments is quite challenging due to the uneven distribution of probes. Herein, we designed a new dynamic excimer (DYNEX) imaging method that involves the sensitive detection of nanosecond-scale dynamic molecular contacts of a fluorescent acridone derivative and reveals the cell microenvironment polarity. Using our method, we specifically tracked cell lipid droplets in fibroblast colon carcinoma cells. These organelles play a central role in metabolic pathways, acting as energy reservoirs in regulatory processes. DYNEX imaging provides the inner polarity of cell lipid droplets, which can be related to lipid contents and metabolic dysfunctions. This new methodology will inspire development of novel multidimensional fluorescent sensors that are able to provide target-specific and orthogonal information at the nanosecond scale.

Luminescent Neutral Cyclometalated Iridium(III) Complexes Featuring a Cubic Polyhedral Oligomeric Silsesquioxane for Lipid Droplet Imaging and Photocytotoxic Applications

New neutral iridium(III) complexes featuring a cubic polyhedral oligomeric silsesquioxane (POSS) unit, [Ir(N^∧C)₂(L1-POSS)] [HN^∧C = 2-phenylpyridine (Hppy; 1), 2-phenylbenzothioazole (Hbt; 2), and 2-(1-naphthyl)benzothiazole (Hbsn; 3); L1-POSS = (E)-4-[(2-hydroxybenzylidene)amino]benzyl 3-heptakis(isobutyl)POSS-propyl carbamate], were designed and synthesized. Their POSS-free counterparts, [Ir(N^∧C)₂(L1)] [L1 = (E)-N-(4-hydroxymethylphenyl)-1-(2-hydroxyphenyl)methanimine; HN^∧C = Hppy (1a), Hbt (2a), and Hbsn (3a)], and the poly(ethylene glycol) (PEG) derivatives [Ir(N^∧C)₂(L1-PEG)] [L1-PEG = (E)-4-[(2-hydroxybenzylidene)amino]benzyl 3-[2-[ω-methoxypoly(1-oxapropyl)]ethyl]carbamate; HN^∧C = Hppy (1b), Hbt (2b), and Hbsn (3b)] were also prepared. The photophysical, photochemical, and biological properties of the POSS complexes were compared with those of their POSS-free and PEG-modified counterparts. Upon irradiation, all of these complexes displayed orange-to-red emission and long emission lifetimes under ambient conditions. The bsn complexes 3, 3a, and 3b exhibited the highest singlet oxygen (¹O₂) generation quantum yields (Φ_Δ = 0.85-0.86) in aerated CH₃CN. Laser-scanning confocal microscopy images revealed that complexes 1-3 and 1a-3a showed exclusive lipid-droplet staining upon cellular uptake, while the PEG derivatives 1b-3b displayed lysosomal localization. Complex 3 was utilized to study various lipid-droplet-related biological events including lipid-droplet accumulation under oleic acid stimulation, the movement of lipid droplets, and preadipocyte differentiation. Notably, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays indicated that the ppy complexes 1 and 1b and the bt complexes 2 and 2b were noncytotoxic both in the dark and upon irradiation at 450 nm for 5 min (IC₅₀ > 200 μM), while the bsn complexes 3, 3a, and 3b showed low dark cytotoxicity (IC₅₀ = 52.9 to >200 μM) and high photocytotoxicity (IC₅₀ = 1.1-5.3 μM). The cellular uptake, internalization mechanisms, and cell death pathways of these complexes were also investigated. This work not only offers promising luminescent probes for lipid droplets through the structural modification of iridium(III) complexes but also paves the way to the construction of new reagents for theranostics.

Fluorescence imaging of pathophysiological microenvironments

Abnormal microenvironments (viscosity, polarity, pH, etc.) have been verified to be closely associated with numerous pathophysiological processes such as inflammation, neurodegenerative diseases, and cancer. As a result, deep insights into these pathophysiological microenvironments are particularly beneficial for clinical diagnosis and treatment. However, the monitoring of pathophysiological microenvironments is unattainable by the traditional clinical diagnostic techniques such as magnetic resonance imaging, computed tomography, and positron emission tomography. Recently, fluorescence imaging has shown tremendous advantages and potential in the tracing of pathophysiological microenvironment variations. In this context, a general discussion is provided on the state-of-the-art progress of fluorescent probes for visualizing pathophysiological microenvironments (viscosity, pH, and polarity), since 2016, as well as the future perspectives in this challenging field.

Nanozyme Sensor Array Plus Solvent-Mediated Signal Amplification Strategy for Ultrasensitive Ratiometric Fluorescence Detection of Exosomal Proteins and Cancer Identification

Tumor exosomes with molecular marker-proteins inherited from their parent cells have emerged as a promising liquid biopsy biomarker for cancer diagnosis. However, facile, robust, and sensitive detection of exosomal proteins remains challenging. Therefore, a nanozyme sensor array is constructed by using aptamer-modified C₃N₄ nanosheets (Apt/C₃N₄ NSs) together with a solvent-mediated signal amplification strategy for ratiometric fluorescence detection of exosomal proteins. Three aptamers specific to exosomal proteins are selected to construct Apt/C₃N₄ NSs for high specific recognition of exosomal proteins. The adsorption of aptamers enhances the catalytic activity of C₃N₄ NSs as a nanozyme for oxidation of o-phenylenediamine (oPD) to 2,3-diaminophenazine (DAP). In the presence of target exosomes, the strong affinity between aptamer and exosome leads to the disintegration of Apt/C₃N₄ NSs, resulting in a decrease of catalytic activity, thereby reducing the production of DAP. The ratiometric fluorescence signal based on a photoinduced electron transfer (PET) effect between DAP and C₃N₄ NSs is dependent on the concentration of DAP generated, thus achieving highly facile and robust detection of exosomal proteins. Remarkably, the addition of organic solvent-1,4-dioxane can sensitize the luminescence of DAP without affecting the intrinsic fluorescence of C₃N₄ NSs, achieving the amplification of the aptamer-exosome recognition events. The detection limit for exosome is 2.5 × 10³ particles/mL. In addition, the accurate identification of cancer can be achieved by machine learning algorithms to analyze the difference of exosomal proteins from different patients' blood. We hope that this facile, robust, sensitive, and versatile nanozyme sensor array would become a promising tool in the field of cancer diagnosis.

Lipid Droplet-Specific Fluorescent Probe for In Vivo Visualization of Polarity in Fatty Liver, Inflammation, and Cancer Models

Elucidating the intrinsic relationship between diseases and lipid droplet (LD) polarity remains a great challenge owing to the lack of the research on multiple disease models. Until now, the visualization of abnormal LD polarity in models of inflammation and clinical cancer patient samples has not been achieved. To meet the urgent challenge, we facilely synthesized a robust LD-specific and polarity-sensitive fluorescent probe (LD-TTP), which consists of a triphenylamine segment as an electron-donor group (D) and a pyridinium as an electron-acceptor moiety (A), forming a typical D-π-A molecular configuration. Owing to the unique intramolecular charge transfer effect, LD-TTP exhibits high sensitivity to polarity change in the linear range from Δf = 0.258 to 0.312, with over 278-fold fluorescence enhancement. Moreover, we revealed that LD-TTP possessed satisfactory ability for sensitively monitoring LD-polarity changes in living cells. Using LD-TTP, we first demonstrated the detection of LD-polarity changes in fatty liver tissues and inflammatory living mice via confocal laser scanning fluorescence imaging. Surprisingly, the visualization of LD polarity has been achieved not only at the cellular levels and living organs but also in surgical specimens from cancer patients, thus holding great potential in the clinical diagnosis of human cancer. All these features render LD-TTP an effective tool for medical diagnosis of LD polarity-related diseases.

Charge-Dependent Strategy Enables a Single Fluorescent Probe to Study the Interaction Relationship between Mitochondria and Lipid Droplets

Cooperation between organelles is essential to maintain the normal operation of the cell. A lipid droplet (LD), a dynamic organelle, is specialized in lipid storage and can interact physically with mitochondria in several cell types. However, an appropriate method for in situ studying the interaction relationships of mitochondria-LDs is still lacking. Herein, a charge-dependent strategy is proposed for the first time by considering adequately the charge difference between mitochondria and LDs. According to the novel strategy, we have developed a unique fluorescent probe Mito-LD based on the cyclization and ring-opening conversion. Mito-LD could simultaneously stain mitochondria and LDs and emit a red and green fluorescence, respectively. More importantly, with the probe Mito-LD, the in situ interaction relationships of mitochondria-LDs were investigated in detail from LD accumulation, mitochondrial dysfunction, lower environmental temperatures, and four aspects of apoptosis. The experimental results showed that mitochondria played an important role in LD accumulation, and the numbers and size of LDs would increase after mitochondrial dysfunction that may be due to excess liposomes. In addition, as an energy storage organelle, LDs played an important role in helping to coordinate mitochondrial energy supply in response to cold. In addition, the Mito-LD revealed that the polarity of mitochondria was higher than that of LDs. In a word, the probe Mito-LD could serve as a potential tool for further exploring mitochondria-LD interaction mechanisms, and importantly, the charge-dependent strategy is valuable for designing robust new probes in imaging multiple organelles.

Detecting lipid droplets polarity: Silicone-based unique fluorescent probe for cancer diagnosis in living cells

Fluorescent probes for monitoring polarity of lipid droplets (LDs) are essential tools in pathological research, especially cancer related. Herein, we have designed a biocompatible and novel fluorescent probe (TDCQ) with intramolecular charge transfer mechanism, which consists of a naphthalimide moiety accepting electron and a triphenylamine fragment providing electron. In view of polarity-sensitivity and AIE characteristic, TDCQ specially aggregates on the LDs in cells by remarkable green dots fluorescent. Due to the variation of LDs numbers in normal cells and cancer cells, the probe emits stronger green fluorescence in cancer cells but weaker in normal cells. Moreover, TDCQ has outstanding photostability and low toxicity, permitting green fluorescence to persist for a valid time in cells. This article demonstrates that the capacity of TDCQ for facilitating the in-depth study of LDs and applying to the identification of cancer cells.

One-Step Synthesis of Carbon Nanoparticles Capable of Long-Term Tracking Lipid Droplet for Real-Time Monitoring of Lipid Catabolism and Pharmacodynamic Evaluation of Lipid-Lowering Drugs

Lipid droplets (LDs) are intracellular lipid-rich organelles, which not only serve as neutral lipid reservoirs but also involve in many physiological processes and are associated with a variety of metabolic diseases and cancers. Long-term tracking of the state and behavior of LDs is of great significance but challenging. The difficulty is largely due to the lack of low cytotoxicity, high photobleaching resistance, and long intracellular retention probes that are capable of long-term tracking LDs. Herein, we report the discovery of two amphiphilic LD-targeting carbon nanoparticles (CNPs, i.e., CPDs and CDs) prepared by one-step room-temperature and hydrothermal methods. Their high lipid-water partition coefficient (log P > 2.13) and strong positive solvatochromism property ensure the quality of LD imaging. Especially, CDs exhibit favorable biocompatibility (2 mg mL^-1, cell viability >90%), excellent photostability (after continuous laser irradiation on a confocal microscope for 2 h, relative FL intensity >85%), and superior intracellular retention ability, thereby enabling long-term tracking of LDs in hepatocytes for up to six passages. Based on the excellent long-term tracking ability, CDs are successfully applied to observe autophagy in a typical catabolic process and to evaluate the effect of a commonly used lipid-lowering drug atorvastatin on hepatocyte lipid uptake.

Aggregation-induced Emission Properties of Triphenylamine Chalcone Compounds

Two triphenylamine chalcone derivatives 1 and 2 were synthesized through the Vilsmeier-Haack reaction and Claisen-Schmidt condensation reaction. Through ultraviolet absorption spectroscopy and fluorescence emission spectroscopy experiments, it was confirmed that these two compounds exhibited good aggregation-induced emission (AIE) behavior in ethanol/water mixtures. The solvent effect test showed with the increase of the orientation polarizability of the solvent, the Stokes shift in the solvent of compound 1 and compound 2 shows a linear change trend. Through solid state fluorescence test and universal density function theory (DFT), the existence of π-π stacking interaction in the solid state of the compound has been studied, resulting in weak fluorescence emission. pH has no effect on the fluorescence intensity of the aggregate state of excited state intramolecular proton transfer (ESIPT) molecules in an acidic environment, but greatly weakens its fluorescence intensity in an alkaline environment. Cyclic voltammetry (CV) test shows that compound 1 was more prone to oxidation reaction than compound 2. The results of thermal stability test show that the thermal stability of compound 1 was better than that of compound 2, indicating that triphenylamine chalcone derivatives can improve the thermal stability of compounds by increasing the number of branches.

An Enumerated Outlook of Intracellular Micropolarity Using Solvatochromic Organic Fluorescent Probes

The spatiotemporal distribution of intracellular physical parameters of a live cell is heterogeneous and complex. Measuring physical properties inside given cellular compartments (organelles) is challenging and important for therapy and diagnostics. The tiny volume of a single cell and even tinier organelles are not accessible by classical measuring devices. The microenvironment inside an organelle vastly controls the outcome of any biochemical and biophysical processes taking place inside it, which is crucial for the overall cellular health. Therefore, it is very important to understand the microenvironmental physical properties inside cellular organelles. Moreover, specific alterations of such microenvironmental properties were observed in the disease condition, making them a diagnostic hallmark. With this high demand, small-molecule organic fluorophores are emerging as the most successful tool due to their small relative size, bioavailability, and ease of functionalization. In this mini-review, the development of micropolarity-sensitive small organic fluorophore with the capability of targeting a specific cellular organelle has been discussed. Here, we have highlighted the strategies of targeting a specific organelle, the micropolarity, and the challenges and prospects of the field.