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In order to alleviate oil consumption, biomass energy is being developed to produce petroleum derivatives. The thermal-catalytic oxidation of 5-hydroxymethyl furfural (HMF) into 2,5-furandicarboxaldehyde (DFF) seems to be an effective strategy for synthesizing the intermediates of valuable petroleum derivatives. The breakage of the O–H bond and αH–C in the hydroxyl group and the protection of the aldehyde group are the key points for the selective production of DFF. In order to summarize the common rule of promoting HMF conversion and selectivity of DFF, the modification methods for various types of catalysts and the current challenges have been sorted and described in this review according to the correlation and logic between different reports. The basic reaction pathway (the redox mechanism of Mars-van Krevelen) suitable for composite metal oxides and the "oxoammonium" mechanism for (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) catalysts are also introduced. Besides, the solvent system, as a crucial part of synergetic catalysis, has been introduced in detail. [ABSTRACT FROM AUTHOR]

Although metal–organic frameworks (MOFs) with intriguing physiochemical properties have recently attracted increasing attention of researchers, MOFs have not adequately achieved various applications due to their instability and unsatisfactory processability. Hence, MOF-based composites as well as structurally novel MOFs have been established to solve this challenge. Recently, some efforts have been made for the development of MOF-based hydrogels. They exhibit excellent properties compared to initial MOFs in many ways (e.g., mechanical strength, absorption capacity and total pore volume). In this review, the up-to-date research progress of MOF-based hydrogels will be briefly summarized. We mainly focus on expounding the classification of MOF-based hydrogels and their related synergistic effects. As to details, we will provide a conspectus of laconic and latest approaches for the synthesis of MOF-based hydrogels, focusing on composite systems, mechanism research, and stability. In addition, the applications of MOF-based hydrogels have been widely discussed, particularly in the environmental, energy and medical aspects. It is hoped that the detailed description of this review can help researchers working on MOF-based hydrogels to develop more novel composite materials and investigate their wider application. [ABSTRACT FROM AUTHOR]

Herein, a viscosity-sensitive and hepatic-targeted NIR fluorescent probe has been developed for early diagnosis of hepatic fibrosis. Importantly, we observed increased liver viscosity upon CCl4-induced hepatotoxicity and decreased liver viscosity after metformin treatment, which confirmed its high clinical application prospects. [ABSTRACT FROM AUTHOR]

Strong excitonic effects are the major constraints hindering free charge carrier generation for conducting photocatalysis in polymeric semiconductors, which is usually inhibited by Frenkel excitons with intrinsically strong Coulomb interactions, severely limiting the photocatalytic activity of organic semiconductors. Minimizing the potential Coulomb interaction of Frenkel excitons is ideal for reducing energy loss and thus boosting the generation of charge carriers. Nonetheless, this has been long neglected and its development is still in its infancy in covalent triazine frameworks (CTFs). Herein, a series of CTFs were developed to promote exciton dissociation via a built-in dipole control strategy. Thiophene-rich CTFs deliver a reduction of exciton binding energy down to 97.5 meV to enable exciton dissociation. Thus, the facilitated generation and separation of photogenerated charge carriers over CTFs of thiophene-rich structures enabled the Ugi reaction and functionalization of thiophenols with higher yields than the benzyl analogue Ph-CTF, where boosting superoxide radical (O2˙−) and singlet oxygen (1O2) photogeneration via electron and energy transfer processes was facilitated, respectively. This architecture not only establishes a comprehensive understanding of regulating the exciton effect of polymeric semiconductors but also furnishes a feasible avenue for the rational design of polymer-based photocatalysts with highly efficient electron–hole separation from the exciton aspect. [ABSTRACT FROM AUTHOR]

Fabricating S-scheme photocatalysts to optimize their ability of using sunlight has gained great attention in environmental remediation. Herein, we designed a soluble hybrid, titanium oxide cluster–perylene diimide–polyhedral oligomeric silsesquioxane (TOC–PDI–POSS). Through π–π stacking interaction with the most commonly applied graphitic carbon nitride (g-C3N4), a new S-scheme heterostructure was successfully constructed. The combination of the near full visible light responsive TOC–PDI–POSS and g-C3N4 enhanced the utilization of sunlight to achieve highly efficient charge-carrier separation. More importantly, the photo-Fenton reaction can be achieved without an extra oxidant. Owing to the enhanced oxidation capacity of holes, the obtained TOC–PDI–POSS/g-C3N4 heterostructure displayed efficient photocatalytic degradation for phenol under an air atmosphere and the reaction rate constant reaches 5.6 h−1 in five cycles under simulated sunlight. [ABSTRACT FROM AUTHOR]

Adenosine triphosphate (ATP) is a direct energy source in cells and the core of the biochemical system, and is closely related to various metabolic activities in living organisms. Therefore, designing a simple and rapid ATP detection method is significant to study its physiological function. Herein, a dual-channel fluorescent probe RhB-NA for the in situ imaging of ATP in living cells was designed and synthesized. When ATP bound to RhB-NA , the spirolactam in rhodamine B was induced to open, resulting in a new fluorescence response at 589 nm. Notably, in cell imaging, the treatment of HeLa cells with exogenous H2O2 and H2S, which have certain effects on the mitochondria, confirmed that RhB-NA could detect fluctuations in ATP levels after the mitochondrial state was affected. We believe that RhB-NA has far-reaching significance for studying certain physiological diseases caused by abnormal ATP levels. [ABSTRACT FROM AUTHOR]

Herein, a NIR fluorescent probe has been developed for visualization of the roles of SO2/SO32− in mitochondrial viscosity. The results showed that SO32− would increase mitochondrial viscosity and decrease mitochondrial membrane potential (MMP). However, increasing SO2 stimulation decreased mitochondrial viscosity and caused inconspicuous MMP changes. [ABSTRACT FROM AUTHOR]

We have developed a novel approach for the construction of 2-((2-arylquinolin-4-yl)oxy)ethan-1-ol derivatives by an NH4I-catalyzed radical-mediated tandem cyclization of three components including aromatic aldehydes, arylamines and 1,4-dioxane. This strategy involves the breakage (C–H, N–H, C＝O, and C–O bonds) and formation (C–C, C–N and O–H bonds) of multiple types of bonds. This transformation could involve a radical-mediated tandem cyclization reaction instead of the typical [4+2] cycloaddition reaction of imines with olefins. 1,4-Dioxane was used as a C4/O2 synthon to provide a 2-(vinyloxy)ethan-1-ol group. [ABSTRACT FROM AUTHOR]

Reactive sulfur species (RSS) play pivotal roles in various pathological and physiological processes. There exists an intricate relevance in generation and metabolism among these substances. Although they are nucleophilic, there are still some differences in their reactivity. There are many methods to detect them by using reactive fluorescent probes, but the systematic study of their reactivity is still lacking. In our study, we designed a multiple reaction site fluorescent probe based on benzene conjugated benzopyrylium and NBD. The study revealed that besides both biothiols and hydrogen sulfide, sulfur dioxide (SO2) can cleave the ether bond. There are two reaction forms for GSH with low reactivity: cutting the ether bond and adding the conjugated double bond of benzopyrylium. Nevertheless, Cys/Hcy with higher activity can further rearrange with NBD after cutting the ether bond. In addition, SO2 can not only cleave the ether bond, but also continue to add the conjugated double bond of benzopyrylium. The above processes lead to multicolor emission of the probe, thus realizing the characteristic analysis of different sulfides. Thus the probe can be used for the detection of sulfide in mitochondria, and further for the imaging of sulfide in cells and zebrafish. This effective analysis method will provide a broad application prospect for practical applications. [ABSTRACT FROM AUTHOR]

Conjugated porous polymers with rapid separation of photogenerated charges and multiple catalytic pathways remain a great challenge. Herein, two ferrocene-based polymers (Fc-CPPs) with high charge separation efficiency and unique dual catalytic routes for Cr(VI) reduction were developed. They exhibited an excellent efficiency, with almost 99% of Cr(VI) readily converted to Cr(III) under 15 min of visible light illumination (λ > 420 nm). [ABSTRACT FROM AUTHOR]

A new ratiometric fluorescent probe, namely TPE-RNS, has been developed for detecting intracellular HClO/ClO− in living cells and discriminating cancer cells from normal cells. Based on the ratiometric fluorescence properties conferred by the AIE and DTBET effects, this probe has excellent sensitivity and specificity for the HCIO response. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite solar cells (PSCs) are attracting considerable attention due to their excellent thermal stability. However, their unsatisfactory power-conversion efficiency and moisture instability lead to challenges for practical commercialization. Here, a facile but effective strategy is demonstrated to stabilize/passivate the cubic phase of CsPbI3 by inhibiting the moisture invasion using 18-crown-6 ether (Crown). The strong interaction between Crown and surface Cs+ ion not only effectively improved the moisture tolerance, but also simultaneously reduced surface defects and related migrations, thus accordingly improving the phase and operation stability of the CsPbI3 films and devices. Based on the obtained high-quality CsPbI3–Crown films, PSCs with up to 16.9% efficiency were fabricated. The devices readily maintained ∼91% of the initial PCE for more than 1000 h (85 °C, N2) and even ∼90% for up to 2000 h (relative humidity 20%) without encapsulation. More importantly, the developed strategy has been successfully used to fabricate large-area CsPbI3 modules, showing an efficiency of up to 11.8% with the 16 cm2 total area. A stability performance that can retain ∼95% of the original value for over 500 h (operating conditions, relative humidity 60%) with encapsulation has also been achieved in the first PSC module based on the CsPbI3 system. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO2), as an important anti-oxidant and gaseous signaling molecule, plays fundamental roles in the regulation of intracellular signaling and cell death cellular bioenergetics. The accurate determination of the SO2 levels in an organism is a critical step in establishing its biological functions. Therefore, there is a high demand for developing efficient analytical methods for monitoring the wide range of concentration changes of SO2 in living systems. Herein, for the first time, we have successfully constructed a dual-site functionalized NIR fluorescent material (NIR-SP), which is capable of monitoring low concentrations of SO2 with red fluorescence responses and high concentrations of SO2 with blue fluorescence enhancements. Further studies absolutely confirmed that the discriminative response was due to the fact that the reactivity of the unsaturated C=C double bond (site I) in NIR-SP was superior to that of the aldehyde group (site II). Furthermore, detection in a concentration-dependent manner was demonstrated by fluorescent imaging in cells and mice. We envision that this strategy would lead to insights into SO2 concentration-dependent biological effects and cell signals. [ABSTRACT FROM AUTHOR]

The recovery of lithium from salt lake brines with a high Mg/Li ratio continues to be a challenge due to the very similar ionic properties of Li+ and Mg2+ in aqueous solutions. Here we develop a novel strategy to extract Li+ based on a sensitive photochromic crowned spiropyran probe with the control of UV light. The probe presents high selectivity for Li+ complexation even in solutions with a high Mg/Li ratio up to 1000. On this basis, a high-stability “spiropyran-crown ether” polymer composite membrane material for the visualization and efficient extraction of trace lithium ions in the complicated system of salt lake brines with high ionic strengths will be constructed in the future. [ABSTRACT FROM AUTHOR]

Hydrazine (N2H4) has been widely applied in most of the chemical industry; however, it is now believed that it can cause serious damage to protein and nucleic acid upon ingestion. Herein we introduced a specially designed molecular probe 1, with an electron deficient lactone group as a specially designed reactive site and a naphthalimide fluorophore that is easily modified owing to lactone involvement. The free probe 1 exhibited blue fluorescence in neutral buffer owing to the low favorability of ICT (intramolecular charge transfer), while the specially designed lactone group could potentially undergo a ring-opening reaction with hydrazine, resulting in a favoured ICT effect and bathochromically shifted (125 nm) fluorescence response. The ratiometric fluorescence signal enabled quantitative determination of hydrazine using probe 1 in complex applications. Besides, probe 1 features a rapid signal response time (within 5 min) and low detection limit (36 nM) for hydrazine. Utilizing these excellent properties, probe 1 was further applied in hydrazine vapor detection and bio-imaging. Conceptually, we now present a new approach for the detection of hydrazine, and the enhanced performances of probe 1 will promote its applications in living systems and the environment. [ABSTRACT FROM AUTHOR]

Fluorescence imaging is advancing quickly through the discovery of new fluorescent molecules and the invention of various strategies that can optimize and detect the fluorescence of various fluorophores. Dicyano-based fluorescent materials, including DCM (dicyanomethylene-4Hpyran) and DCO (dicyanoisophorone), have attracted great attention in recent years due to their excellent photophysical properties, outstanding biocompatibility, and low toxicity to living systems. In this review, we describe the principal strategies to create dicyano-based chemosensors through synthetic methods and the current photophysical understanding of these compounds. Then, we discuss efforts to target small-molecule compounds for imaging cellular events and studying biological processes. Additionally, dicyan-based materials applied to diagnostic tools, drug delivery and potential therapeutics have been described in detail. Finally, we conclude by discussing the opportunities and challenges of this class of materials, which may act as precision tools in the areas of biology and medicine. [ABSTRACT FROM AUTHOR]

The morphology of plasma membrane is dynamic and keeps changing in order to maintain its homeostasis. Abnormality in cell membrane shape could be viewed as a sign of unhealthy cells. A lipophilic cyanostilbene derivative (AS2CP-TPA) composed of a hydrophilic pyridinium salt and a hydrophobic triphenylamino group was designed for staining the cell membrane and monitoring membrane morphology under different conditions. Due to strong donor–acceptor interaction and aggregation-induced emission property, AS2CP-TPA emits weak emission in aqueous solution, but it lights up the plasma membrance of HeLa cells with near infrared fluorescence under an excitation wavelength of 460 nm. With merits of high photostability and high specificity to plasma membrane, AS2CP-TPA is capable of long-term monitoring of the morphological changes of cell membrane during Hg2+ and trypsin treatments. [ABSTRACT FROM AUTHOR]

In this study, we synthesize a modified polyethersulfone membrane through surface-initiated electrochemical atom transfer radical polymerization of glucose allyl amide and cyclodextrin acrylic acid to construct block copolymer brushes on the membrane surface. NMR is used to characterize the synthetic monomers; X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy are employed to characterize the chemical compositions, morphologies, and roughness of the membranes. The results of static water contact angle testing show that the modified membranes with a polysaccharide surface have good hydrophilicity. In addition, filtration experiments fed with pure water and BSA show that both the permeation and anti-fouling properties of the fabricated membranes are improved compared with pristine polyethersulfone. These results show that the efficient approach of surface-initiated electrochemical atom transfer radical polymerization of saccharide monomer can be used for the surface design and fabrication of a polymer membrane, which can be employed for practical applications in separation and purification fields. [ABSTRACT FROM AUTHOR]

A novel Schiff (Mo) base complex supported on GO surface was successfully prepared, which was further combined with graphitic carbon nitride (g-C3N4) polymer (Mo-GO/g-C3N4) to make it photo-active. The photocatalytic activity of the resulting nano-composite was tested under simulated sunlight (AM 1.5) for the epoxidation of various olefin substrates. In addition, surface photovoltage (SPV) measurements were applied to explore the electron acceleration effect caused by GO and molybdenum. It was demonstrated that both GO and the metal active centers can efficiently accelerate electron transfer, which would finally contribute to the superior catalytic performance. [ABSTRACT FROM AUTHOR]

Most of the existing tissue-engineered scaffolds for the regeneration of anterior cruciate ligament (ACL) are unable to recapitulate the structural/compositional/mechanical gradients at native ACL–bone interface. Herein, we present a unique electrospinning strategy to fabricate microfiber-reinforced nanofibrous scaffolds with structure and composition gradients. The orientations of the electrospun nanofibers gradually change from random to highly aligned, and the contents of nano-hydroxyapatite (nHA) and bone morphogenesis protein (BMP-2) encapsulated into the nanofibers exhibit gradient variation. The gradient nanofibrous scaffolds were found to regulate cellular morphology and zonal bone-specific differentiation in vitro. The incorporation of microfibers significantly improved the mechanical property of the gradient nanofibrous scaffolds, which was similar to native ACL–bone fixation after implantation in vivo. Histological observations revealed that the gradient scaffolds facilitated the formation of fibrocartilage transitional zone at graft and bone attachments that are similar to native ligament-to-bone interface. We envision that the presented method might provide biomimetic physical/chemical/mechanical microenvironments for enhanced multitissue regeneration particularly at the soft-hard tissue interface. [ABSTRACT FROM AUTHOR]

In this study, we report the preparation, characterization and properties of a polyethersulfone membrane modified by surface-initiated electrochemically atom transfer radical polymerization. Three kinds of copolymer brushes of the homopolymer, block copolymer, and random variety are covalently grafted onto the surface of the polyethersulfone membrane. X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and a mercury intrusion porosimeter are applied to characterize the chemical composition, morphologies, roughnesses, and pore structure of membranes. A static water contact angle experiment shows that the hydrophilicity of modified membranes is largely enhanced due to the hydrophilic polymer brush; and filtration experiments fed with water and BSA show that both the permeation and anti-fouling properties of fabricated membranes are improved significantly. Moreover, the membrane modified by random copolymers shows the best resistance to protein adsorption compared to those of the block copolymer and homopolymer brushes. [ABSTRACT FROM AUTHOR]

Porous materials are important in established processes, such as catalysis and molecular separations, and in emerging technologies for energy and health. Porous organic polymers (POPs), a class of highly crosslinked, amorphous polymers possessing nanopores, have recently emerged as a versatile platform for potential applications. As an emerging material, POPs offer high flexibility for the molecular design and post-synthetic modification of their conjugated skeletons and nanopores. They have shown great potential for challenging energy and environmental issues, as exemplified by their excellent performance in gas storage/separation, catalysis, environmental remediation, and sensing. This review article summarizes the recent frontiers of functional exploration and potential applications of porous organic polymers. [ABSTRACT FROM AUTHOR]

Dynamic visualization of the morphology of membrane-bound organelles offers useful insights for studying various intracellular activities. Fluorescent probes with superior specificity and photostability are desirable for long-term tracking of these processes. In this work, we present the design and synthesis of an α-cyanostilbene derivative, abbreviated as ASCP, with the aggregation-induced emission (AIE) characteristic, and its application in cell imaging. ASCP can simultaneously label mitochondria and nucleolus in live cells with distinct fluorescence, which is demonstrative of a single molecule with dual-colour organelle imaging. [ABSTRACT FROM AUTHOR]

An isothiocyanate-functionalized tetraphenylethene is synthesized and used as a fluorescent bioprobe for mitochondrion imaging with high specificity and photostability. The covalent conjugation of the bioprobe to mitochondrial proteins endows it with high resistance to microenvironmental changes, enabling it for real-time monitoring of mitophagy. [ABSTRACT FROM AUTHOR]

Retraction of ‘Potential applications of functional porous organic polymer materials’ by Weijie Zhang et al., J. Mater. Chem. A, 2017, 5, 8795–8824. [ABSTRACT FROM AUTHOR]

Drug delivery systems based on nanoparticles still face challenges of low efficacy and an inability to track treatment effects in tumor therapy due to biological barriers. This limitation hinders clinicians' ability to determine treatment effects and proper drug dosages, thus, ultimately impeding the further application and transformation of nanoplatforms. To address this challenge, an all-in-one nanoplatform for therapy and imaging is proposed. The nanoplatform is constructed by using nanoparticles through the co-encapsulation of the photothermal therapeutic agent IR780, the passively targeted drug OA@Fe 3 O 4 , and the chemotherapeutic drug paclitaxel. Under the guidance of magnetic navigation, the nanoparticles can enhance local enrichment of the drug, while the luminescence properties of IR780 enable drug tracking at the same time. Remarkably, the nanoparticles exhibit improved photothermal-chemotherapy synergy under magnetic targeting guidance, demonstrating antitumor effects in both in vitro and in vivo experiments. It is demonstrated that the use of these polymeric nanoparticles has significant potential for future biomedical applications and clinical decisions., Competing Interests: The authors have declared that no competing interest exists., (This journal is © The Royal Society of Chemistry.)

Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo 2 C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo 2 C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo-O surface layer, thus producing intimate O-Mo-C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O-Mo-C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo 2 C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O-Mo-C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo 2 C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Sulfur dioxide (SO 2 ), as an important anti-oxidant and gaseous signaling molecule, plays fundamental roles in the regulation of intracellular signaling and cell death cellular bioenergetics. The accurate determination of the SO 2 levels in an organism is a critical step in establishing its biological functions. Therefore, there is a high demand for developing efficient analytical methods for monitoring the wide range of concentration changes of SO 2 in living systems. Herein, for the first time, we have successfully constructed a dual-site functionalized NIR fluorescent material (NIR-SP), which is capable of monitoring low concentrations of SO 2 with red fluorescence responses and high concentrations of SO 2 with blue fluorescence enhancements. Further studies absolutely confirmed that the discriminative response was due to the fact that the reactivity of the unsaturated C[double bond, length as m-dash]C double bond (site I) in NIR-SP was superior to that of the aldehyde group (site II). Furthermore, detection in a concentration-dependent manner was demonstrated by fluorescent imaging in cells and mice. We envision that this strategy would lead to insights into SO 2 concentration-dependent biological effects and cell signals.

A novel dark through-bond energy transfer (DTBET) strategy is proposed and applied as the design strategy to develop ratiometric Hg 2+ sensors with high performance. Tetraphenylethene ( TPE ) derivatives with aggregation-induced emission (AIE) characteristics are selected as dark donors to eliminate emission leakage from the donors. The TBET mechanism has been adopted since it experiences less influence from spectral overlapping than Förster resonance energy transfer (FRET), making it more flexible for developing cassettes with large pseudo-Stokes shifts. In this work, energy transfer from the TPE derivatives (dark donor) to a rhodamine moiety (acceptor) was illustrated through photophysical spectroscopic studies and the energy transfer efficiency (ETE) was found to be up to 99%. In the solution state, no emission from the donors was observed and large pseudo-Stokes shifts were achieved (>280 nm), which are beneficial for biological imaging. Theoretical calculations were performed to gain a deeper mechanistic insight into the DTBET process and the structure-property relationship of the DTBET cassettes. Ratiometric Hg 2+ sensors were rationally constructed based on the DTBET mechanism by taking advantage of the intense emission of TPE aggregates. The Hg 2+ sensors exhibited well resolved emission peaks. >6000-fold ratiometric fluorescent enhancement is also achieved and the detection limit was found to be as low as 0.3 ppb. This newly proposed DTBET mechanism could be used to develop novel ratiometric sensors for various analytes and AIEgens with DTBET characteristics will have great potential in various areas including light harvesting materials, environmental science, chemical sensing, biological imaging and diagnostics.

Biotin-decorated fluorescent silica nanoparticles (FSNPs) were successfully fabricated by a sol-gel reaction of silole-functionalized siloxane followed by a sequential reaction with tetraethoxysilane, (3-aminopropyl)triethoxysilane and biotin. The FSNPs were uniformly sized, spherical in shape and monodispersed. While their silole precursor was non-emissive in solution, the suspension of the FSNPs emitted strong green light upon photoexcitation due to the aggregation-induced emission characteristics of the silole aggregates in the hybrid nanoparticles. Morphology study and cell viability, trypan blue exclusion, Annexin V-FITC/PI apoptosis and ROS generation assays showed that the FSNPs showed low toxicity to living cells. The FSNPs worked as fluorescent visualizers for selective imaging of the cytoplasm of tumor cells with over-expressed biotin receptors. The fluorescent nanoparticles were lastingly retained inside the living cells, thus enabling long-term tumor cell tracking over multiple passages and quantitative analysis of tumor cell migration.