Cytophilic fluorescent bioprobes for long-term cell tracking

Fluorescent Polymer Nanoparticles for Cell Barcoding In Vitro and In Vivo

Fluorescent polymer nanoparticles for long-term labeling and tracking of living cells with any desired color code are developed. They are built from biodegradable poly(lactic-co-glycolic acid) polymer loaded with cyanine dyes (DiO, DiI, and DiD) with the help of bulky fluorinated counterions, which minimize aggregation-caused quenching. At the single particle level, these particles are ≈20-fold brighter than quantum dots of similar color. Due to their identical 40 nm size and surface properties, these nanoparticles are endocytosed equally well by living cells. Mixing nanoparticles of three colors in different proportions generates a homogeneous RGB (red, green, and blue) barcode in cells, which is transmitted through many cell generations. Cell barcoding is validated on 7 cell lines (HeLa, KB, embryonic kidney (293T), Chinese hamster ovary, rat basophilic leucemia, U97, and D2A1), 13 color codes, and it enables simultaneous tracking of co-cultured barcoded cell populations for >2 weeks. It is also applied to studying competition among drug-treated cell populations. This technology enabled six-color imaging in vivo for (1) tracking xenografted cancer cells and (2) monitoring morphogenesis after microinjection in zebrafish embryos. In addition to a robust method of multicolor cell labeling and tracking, this work suggests that multiple functions can be co-localized inside cells by combining structurally close nanoparticles carrying different functions.

Fabrication of Stable and Luminescent Copper Nanocluster-Based AIE Particles and Their Application in β-Galactosidase Activity Assay

Thiolated copper nanoclusters (CuNCs) with aggregation-induced emission characteristic are becoming a novel luminescent material, but it is still a challenging task to retain its bright luminescence in a neutral solution. In this work, we report a new copper nanocluster with aggregation-induced emission (AIE) enhancement property using a hydrophobic molecule as the protecting ligand, and brightly luminescent AIE particles of copper nanocluster were prepared via hydrophobic interaction. These CuNCs AIE particles possess uniform rod-like shapes, with sizes in hundreds of nanometer, and an intense luminescence; more importantly, its luminescence remains stable in neutral and alkaline solutions. It is found that 4-nitrophenol is able to effectively quench the luminescence of CuNC AIE particles through strong hydrophobic interaction and electron transfer between them. This strong quenching effect was adopted to develop a luminescent assay for β-galactosidase at physiological condition. This work presents a demonstration of preparing CuNC AIE particles with bright luminescence at neutral condition and gives an example of the use of AIE particles in monitoring the enzyme activity.

Dual-targeted peptide-conjugated multifunctional fluorescent probe with AIEgen for efficient nucleus-specific imaging and long-term tracing of cancer cells

Precisely targeted transportation of a long-term tracing regent to a nucleus with low toxicity is one of the most challenging concerns in revealing cancer cell behaviors. Here, we report a dual-targeted peptide-conjugated multifunctional fluorescent probe (cNGR-CPP-NLS-RGD-PyTPE, TCNTP) with aggregation-induced emission (AIE) characteristic, for efficient nucleus-specific imaging and long-term and low-toxicity tracing of cancer cells. TCNTP mainly consists of two components: one is a functionalized combinatorial peptide (TCNT) containing two targeted peptides (cNGR and RGD), a cell-penetrating peptide (CPP) and a nuclear localization signal (NLS), which can specifically bind to a cell surface and effectively enter into the nucleus; the other one is an AIE-active tetraphenylethene derivative (PyTPE, a typical AIEgen) as fluorescence imaging reagent. In the presence of aminopeptidase N (CD13) and integrin αvβ3, TCNTP can specifically bind to both of them using cNGR and RGD, respectively, lighting up its yellow fluorescence. Because it contains CPP, TCNTP can be effectively integrated into the cytoplasm, and then be delivered into the nucleus with the help of NLS. TCNTP exhibited strong fluorescence in the nucleus of CD13 and integrin αvβ3 overexpression cells due to the specific targeting ability, efficient transport capacity and AIE characteristic in a more crowded space. Furthermore, TCNTP can be applied for long-term tracing in living cells, scarcely affecting normal cells with negligible toxicity in more than ten passages.

Preparation and Fluorescence Properties of Perylenediimide Nanodispersions Having a One-Dimensional π-Stacked Structure

We prepared stable nanodispersions of a fluorescent perylenediimide (PDI) derivative having long alkyl chains by nanosecond laser fragmentation of its microcrystalline powder in acetonitrile (ACN). The nanoparticles had cube-like or rod shapes with a mean size of 100 nm, and they dispersed stably for longer than 1 month. The prepared nanobricks exhibited absorption and fluorescence spectra characteristic of one-dimensional aggregates with cofacial stacking of PDI planes. Single-particle fluorescence measurements demonstrated that nanobricks had a well-aligned structure of one-dimensional columns of PDI. The aqueous dispersions were also fabricated by redispersing the prepared nanobricks, utilizing lipophilic interactions of surfactants having long alkyl chains. We examined the fluorescence properties of nanoparticles dispersed in ACN and in water, and observed amplified fluorescence quenching by the surface-adsorbed dye.

Long wavelength excitable near-infrared fluorescent nanoparticles with aggregation-induced emission characteristics for image-guided tumor resection

Near infrared (NIR) fluorescence imaging (700-900 nm) is a promising technology in preclinical and clinical tumor diagnosis and therapy. The availability of excellent NIR fluorescent contrast agents is still the main barrier to implementing this technology. Herein, we report the design and synthesis of two series of NIR fluorescent molecules with long wavelength excitation and aggregation-induced emission (AIE) characteristics by fine-tuning their molecular structures and substituents. Further self-assembly between an amphiphilic block co-polymer and the obtained AIE molecules leads to AIE nanoparticles (AIE NPs), which have absorption maxima at 635 nm and emission maxima between 800 and 815 nm with quantum yields of up to 4.8% in aggregated states. In vitro and in vivo toxicity results demonstrate that the synthesized AIE NPs are biocompatible. Finally, the synthesized AIE NPs have been successfully used for image-guided tumor resection with a high tumor-to-normal tissue signal ratio of 7.2.

Label-Free Automated Cell Tracking: Analysis of the Role of E-cadherin Expression in Collective Electrotaxis

Collective cell migration plays an important role in wound healing, organogenesis, and the progression of metastatic disease. Analysis of collective migration typically involves laborious and time-consuming manual tracking of individual cells within cell clusters over several dozen or hundreds of frames. Herein, we develop a label-free, automated algorithm to identify and track individual epithelial cells within a free-moving cluster. We use this algorithm to analyze the effects of partial E-cadherin knockdown on collective migration of MCF-10A breast epithelial cells directed by an electric field. Our data show that E-cadherin knockdown in free-moving cell clusters diminishes electrotactic potential, with empty vector MCF-10A cells showing 16% higher directedness than cells with E-cadherin knockdown. Decreased electrotaxis is also observed in isolated cells at intermediate electric fields, suggesting an adhesion-independent role of E-cadherin in regulating electrotaxis. In additional support of an adhesion-independent role of E-cadherin, isolated cells with reduced E-cadherin expression reoriented within an applied electric field 60% more quickly than control. These results have implications for the role of E-cadherin expression in electrotaxis and demonstrate proof-of-concept of an automated algorithm that is broadly applicable to the analysis of collective migration in a wide range of physiological and pathophysiological contexts.

The HOF structures of nitrotetraphenylethene derivatives provide new insights into the nature of AIE and a way to design mechanoluminescent materials

This study probes the effect of intramolecular rotations on aggregation-induced emission (AIE) and leads to a kind of supramolecular mechanoluminescent material. Two hydrogen-bonded organic frameworks (HOFs), namely HOFTPE3N and HOFTPE4N, have been constructed from nitro-substituted tetraphenylethene (TPE) building blocks, namely tris(4-nitrophenyl)phenylethene (TPE3N) and tetrakis(4-nitrophenyl)ethene (TPE4N). Using single-crystal X-ray diffraction analysis, two types of pores are observed in the HOFTPE4N supramolecular structure. The pore sizes are 5.855 Å × 5.855 Å (α pores) and 7.218 Å × 7.218 Å (β pores). Powder X-ray diffraction and differential scanning calorimetry studies further reveal that the α pores, which contain nitrophenyl rings, quench the emission of HOFTPE4N. This emission can be turned on by breaking the α pores in the HOFs by grinding the sample. Temperature-dependent emission studies demonstrate that the emission quenching of HOFTPE4N is attributed to the intramolecular rotations of nitro-substituted phenyl units within the space of the α pores. These results clearly reveal AIE by controlling the intramolecular rotations, which can serve as a basis for developing mechanoluminescent materials.

AIEgen-functionalised mesoporous silica nanoparticles as a FRET donor for monitoring drug delivery

AIEgen-functionalised mesoporous silica nanoparticles can be used for cell imaging and monitoring the drug release process by different emission colours based on the FRET mechanism.

A self-assembled fluorescent organic nanoprobe and its application for sulfite detection in food samples and living systems

An AIEE-based nanoprobe has been rationally developed for detection of sulfite in food samples and living systems with excellent selectivity and an extremely low detection limit.

Synthesis of a Tetraphenylethene-Substituted Tetrapyridinium Salt with Multifunctionality: Mechanochromism, Cancer Cell Imaging, and DNA Marking

The development of functional materials is a crucial step in the development of newer and better technologies. The development of efficient luminescent materials, whose potential lie in applications in fields such as electronics, optics, data storage, and biological sciences, through simple synthetic procedures is therefore of interest. Herein, we report the synthesis of a tetrapyridinium-tetraphenylethylene (TPy-TPE) luminogen with multiple functionalities. TPy-TPE displayed characteristic features of an aggregation-induced emission material being weakly emissive in solution, but strongly emissive when aggregated and in the solid state. The solid-state emission of TPy-TPE can be reversibly switched between green and yellow by grinding–fuming/heating processes with a high contrast due to a transformation from a crystalline to an amorphous state and vice versa. TPy-TPE also works as a good fluorescent visualiser for specific staining for cellular imaging and as a DNA marker.

One bioprobe: a fluorescent and AIE-active macromolecule; two targets: nucleolus and mitochondria with long term tracking

The novel macromolecule fluorescent probe TPPA–DBO was developed with highly specific nucleolus-targeting and long term cell tracking ability.

Ultra long-term cellular tracing by a fluorescent AIE bioconjugate with good water solubility over a wide pH range

TPE-NSCS, which displayed an AIE effect, could be solubilized in water over a wide pH range, and used in cell tracing for 30 passages.

Emergence through delicate balance between the steric factor and molecular orientation: a highly bright and photostable DNA marker for real-time monitoring of cell growth dynamics

A bright and biostable molecular fluorogenic material for real-time monitoring of in vitro cellular growth dynamics.

Conjugates of Benzoxazole and GFP Chromophore with Aggregation-Induced Enhanced Emission: Influence of the Chain Length on the Formation of Particles and on the Dye Uptake by Living Cells

Six conjugates of benzoxazole and green fluorescent protein chromophore that differ by the length of their alkyl chain (from C1 to C16) are investigated. They exhibit rigidofluorochromism and clear aggregation-induced emission enhancement (AIEE) behavior with emission in the orange-red that is specific to the solid state. A preparation method based on solvent exchange is used to prepare particles. The self-association properties of these molecules depend on the length of the alkyl chain. Microfibers, platelets, and rounded microparticles are successively obtained by increasing the chain length. The same method is used to prepare nanoparticles (NPs) that are fully characterized. In particular, homogeneous populations of stable NPs measuring around 70 nm are obtained with the analogs whose chains contain four to eight carbon atoms. The behavior with respect to living cells is also influenced by the nature of the compounds. Only the dyes with intermediate hydrophobicity are efficiently uptaken by both normal and tumor cells, and fluorescence only originates from dispersed dye molecules. There is no evidence for incorporation of NPs into cells. This work shows that small variations of the chemical structure must be taken into account for making the best use of AIEE compounds in view of precise applications.

Organic Dots Based on AIEgens for Two-Photon Fluorescence Bioimaging

Two-photon fluorescence imaging technique is a powerful bioanalytical approach in terms of high photostability, low photodamage, high spatiotemporal resolution. Recently, fluorescent organic dots comprised of organic emissive cores and a polymeric matrix are emerging as promising contrast reagents for two-photon fluorescence imaging, owing to their numerous merits of high and tunable fluorescence, good biocompatibility, strong photobleaching resistance, and multiple surface functionality. The emissive core is crucial for organic dots to get high brightness but many conventional chromophores often encounter a severe problem of fluorescence quenching when they form aggregates. To solve this problem, fluorogens featuring aggregation-induced emission (AIE) can fluoresce strongly in aggregates, and thus become ideal candidates for fluorescent organic dots. In addition, two-photon absorption property of the dots can be readily improved by just increase loading contents of AIE fluorogen (AIEgen). Hence, organic dots based on AIEgens have exhibited excellent performances in two-photon fluorescence in vitro cellular imaging, and in vivo vascular architecture visualization of mouse skin, muscle, brain and skull bone. In view of the rapid advances in this important research field, here, we highlight representative fluorescent organic dots with an emissive core of AIEgen aggregate, and discuss their great potential in bioimaging applications.

Aggregation-Induced Emission: Lighting up Cells, Revealing Life!

Understanding metabolism and dynamic biological events in cells, as well as physiological functions and pathological changes in organisms, is the major goal of biological investigations. It will improve our capability to diagnose and treat diseases, and will enhance personalized medicine. Fluorescence imaging is a powerful tool that plays an essential role in acquiring the comprehensive knowledge necessary to help reach this goal. Fluorescent molecules are crucial factors for obtaining high quality images. In contrast to conventional fluorogens with aggregation-caused quenching (ACQ) effect, molecules that show aggregation-induced emission (AIE) effect open up new avenues for fluorescence imaging. So far, a large variety of AIE probes have been developed and applied to bioimaging because of their outstanding characteristics, such as high fluorescence efficiency, excellent photostability and high signal-to-noise ratio (SNR). In this review, recent advances in AIE-based probes for biomedical imaging of intracellular microenvironments, natural macromolecules, subcellular organelles, intracellular processes, living tissues, and diagnosis and therapeutic evaluation of diseases in vivo are summarized. It is hoped that this review generates great research enthusiasm for AIE-based bioimaging, in order to promote the development of promising AIE probes and guide us to a better understanding of the biological essence of life.

Ratiometric Detection of β-Amyloid and Discrimination from Lectins by a Supramolecular AIE Glyconanoparticle

While the development of AIE (aggregation-induced-emission) based fluorimetric probes for biological applications has been an active research area, probes with a ratiometric signal for biomolecular recognition have been rare. Here, a ratiometric AIE glyconanoparticle formed by the supramolecular assembly between a silole-based AIEgen and fluorescent glycoprobes for the detection of amyloid β (Aβ) peptides and fibrils, which are a signature of neurological disorders such as the Alzheimer's disease, is shown. Complexation of glycoprobes with the AIEgen produces an intensive fluorescence emission of the former because of a Förster resonance energy transfer between the two molecules. Subsequently, the presence of Aβ dissembles the particle, producing a fluorescence emission of the AIEgen. Interestingly, the addition of lectins that selectively recognize the glycoprobes results in a different ratiometric response of the particle, thereby enabling a discrimination from Aβ detection. This research offers insight into the simple construction of multifunctional ratiometric probes based on the supramolecular hybridization of a wide variety of AIEgens with fluorescent molecular probes.

Multifunctional Nanoparticles Self-Assembled from Small Organic Building Blocks for Biomedicine

Supramolecular self-assembly shows significant potential to construct responsive materials. By tailoring the structural parameters of organic building blocks, nanosystems can be fabricated, whose performance in catalysis, energy storage and conversion, and biomedicine has been explored. Since small organic building blocks are structurally simple, easily modified, and reproducible, they are frequently employed in supramolecular self-assembly and materials science. The dynamic and adaptive nature of self-assembled nanoarchitectures affords an enhanced sensitivity to the changes in environmental conditions, favoring their applications in controllable drug release and bioimaging. Here, recent significant research advancements of small-organic-molecule self-assembled nanoarchitectures toward biomedical applications are highlighted. Functionalized assemblies, mainly including vesicles, nanoparticles, and micelles are categorized according to their topological morphologies and functions. These nanoarchitectures with different topologies possess distinguishing advantages in biological applications, well incarnating the structure-property relationship. By presenting some important discoveries, three domains of these nanoarchitectures in biomedical research are covered, including biosensors, bioimaging, and controlled release/therapy. The strategies regarding how to design and characterize organic assemblies to exhibit biomedical applications are also discussed. Up-to-date research developments in the field are provided and research challenges to be overcome in future studies are revealed.

Long-Term Tracking of the Osteogenic Differentiation of Mouse BMSCs by Aggregation-Induced Emission Nanoparticles

Bone marrow-derived mesenchymal stem cells (BMSCs) have shown great potential for bone repair due to their strong proliferation ability and osteogenic capacity. To evaluate and improve the stem cell-based therapy, long-term tracking of stem cell differentiation into bone-forming osteoblasts is required. However, conventional fluorescent trackers such as fluorescent proteins, quantum dots, and fluorophores with aggregation-caused quenching (ACQ) characteristics have intrinsic limitations of possible interference with stem cell differentiation, heavy metal cytotoxicity, and self-quenching at a high labeling intensity. Herein, we developed aggregation-induced emission nanoparticles decorated with the Tat peptide (AIE-Tat NPs) for long-term tracking of the osteogenic differentiation of mouse BMSCs without interference of cell viability and differentiation ability. Compared with the ability of the commercial Qtracker 655 for tracking of only 6 passages of mouse BMSCs, AIE-Tat NPs have shown a much superior performance in long-term tracking for over 12 passages. Moreover, long-term tracking of the osteogenic differentiation process of mouse BMSCs was successfully conducted on the biocompatible hydroxyapatite scaffold, which is widely used in bone tissue engineering. Thus, AIE-Tat NPs have promising applications in tracking stem cell fate for bone repair.

Aggregation induced enhanced emission of 2-(2'-hydroxyphenyl)benzimidazole

In this study, the aggregation induced emission enhancement (AIEE) of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) is reported. To investigate the AIEE process of HPBI, absorption/fluorescence spectroscopy, fluorescence imaging and field emission scanning electron microscopy were employed. A comparative study with 2-phenylbenzimidazole (PBI) divulges the significance of the hydroxyl group in the AIEE process. Further, molecular dynamics simulations have been carried out with explicit solvent molecules to follow the aggregation process of HPBI with time. The obtained molecular dynamics simulation results not only predicted the formation of aggregates but also provided detailed insight and information on the molecular interactions. The cellular studies showed aggregates yield higher fluorescence in the visible region inside HeLa cells in comparison to monomeric compounds which failed to exhibit any visible fluorescence inside the cell. The obtained aggregates were further found to be biocompatible and therefore can be used for bio-imaging applications.

Subcellular Behaviour Evaluation of Nanopharmaceuticals with Aggregation-Induced Emission Molecules

Nanopharmaceuticals possess a myriad of advantages for disease treatment, not only in delivering therapeutic agents, but also in deciphering their innate intracellular or subcellular behaviours, providing detailed diagnostic and prognostic information, quantifying treatment efficacy and designing better therapeutics. To evaluate the subcellular behaviour of nanopharmaceuticals, colourful fluorescence is the most potential technique, because it is capable of painting the subcellular detail in three dimensions with high resolution. Furthermore, the fluorescence is switchable, and thus the subcellular details can be lightened specifically without the undesirable background. However, most nanopharmaceuticals lack a fluorescent report group, and its introduction requires extra steps. Moreover, the introduced fluorescent groups can suffer from concentration quenching or aggregation-caused quenching (ACQ) when they are embedded in nanopharmaceuticals at a high concentration. The unique aggregation-induced emission (AIE) effect provides a straightforward solution. The aromatic cores of AIE molecules are always hydrophobic and do not undergo the ACQ effect even at high concentrations. Hence, AIE molecules can be directly introduced as building blocks to provide the driving force for the self-assembly of nanopharmaceuticals and can allow us to develop label-free, ACQ-free and luminescent nanopharmaceuticals that can simultaneously implement drug delivery and subcellular behaviour evaluation. This review presents different types of AIE molecules-based nanopharmaceuticals and their biological properties and applications for imaging subcellular behaviours, including the drug releasing process, metabolism of nanopharmaceuticals, subcellular distributions of drug and carriers, and therapeutic effect. With detailed acquaintance of these subcellular behaviours, we anticipate that the research we discuss in this review can inspire other scientists to develop next generation nanopharmaceuticals that can be guided by fluorescence imaging and thus can realize concisely controllable drug delivery.

Green light-emitting polyepinephrine-based fluorescent organic dots and its application in intracellular metal ions sensing

In this paper, we present a class of bio-dots, polyepinephrine (PEP)-based fluorescent organic dots (PEP-FODs) for selective and sensitive detection of Fe(2+), Fe(3+), and Cu(2+). The PEP-FODs were derived from epinephrine via self-polymerization at relatively low temperature down to 60°C with low cytotoxicity and relative long lifetime (7.24ns). The surface morphology and optical properties of the synthesized PEP-FODs were characterized. We found that the diameters of PEP-FODs were mainly distributed in the narrow range of 2-4nm with an average diameter of 2.9nm. An optimal emission peak located at 490nm was observed when the green light-emitting PEP-FODs were excited at 400nm. It is discovered that Fe(2+), Fe(3+), and Cu(2+)can strongly quench the fluorescence of PEP-FODs through the nonradiative electron-transfer. The detection limit of 0.16, 0.67, and 0.15μM was obtained for Fe(2+), Fe(3+), and Cu(2+), respectively. The independent sensing platform of Fe(2+), Fe(3+), and Cu(2+)could be established by using NaF as a complexing agent and by regulating the reaction time between NaF and metal ions. Cell viability studies reveal that the as-prepared PEP-FODs possess good solubility and biocompatibility, making it as excellent imaging nanoprobes for intracellular Fe(2+), Fe(3+), and Cu(2+)sensing. The developed PEP-FODs might hold great promise to broaden applications in nanotechnology and bioanalysis.

AIE-Active Tetraphenylethylene Cross-Linked N-Isopropylacrylamide Polymer: A Long-Term Fluorescent Cellular Tracker

There is a great demand to understand cell transplantation, migration, division, fusion, and lysis. Correspondingly, illuminant object-labeled bioprobes have been employed as long-term cellular tracers, which could provide valuable insights into detecting these biological processes. In this work, we designed and synthesized a fluorescent polymer, which was comprised of hydrophilic N-isopropylacrylamide polymers as matrix and a hydrophobic tetraphenylethene (TPE) unit as AIE-active cross-linkers (DDBV). It was found that when the feed molar ratio of N-isopropylacrylamides to cross-linkers was 22:1, the produced polymers demonstrated the desirable LCST at 37.5 °C. And also, the temperature sensitivity of polymers could induce phase transfer within a narrow window (32-38 °C). Meanwhile, phase transfer was able to lead the florescent response. And thus, we concluded that two responses occur when one stimulus is input. Therefore, the new cross-linker of DDBV rendered a new performance from PNIPAm and a new chance to create new materials. Moreover, the resulted polymers demonstrated very good biocompatibility with living A549 human lung adenocarcinoma cells and L929 mouse fibroblast cells, respectively. Both of these cells retained very active viabilities in the concentration range of 7.8-125 μL/mg of polymers. Notably, P[(NIPAm)22-(DDBV)1] (P6) could be readily internalized by living cells with a noninvasive manner. The cellular staining by the fluorescent polymer is so indelible that it enables cell tracing for at least 10 passages.

Fluorescent Polymer Nanoparticles Based on Dyes: Seeking Brighter Tools for Bioimaging

Speed, resolution and sensitivity of today's fluorescence bioimaging can be drastically improved by fluorescent nanoparticles (NPs) that are many-fold brighter than organic dyes and fluorescent proteins. While the field is currently dominated by inorganic NPs, notably quantum dots (QDs), fluorescent polymer NPs encapsulating large quantities of dyes (dye-loaded NPs) have emerged recently as an attractive alternative. These new nanomaterials, inspired from the fields of polymeric drug delivery vehicles and advanced fluorophores, can combine superior brightness with biodegradability and low toxicity. Here, we describe the strategies for synthesis of dye-loaded polymer NPs by emulsion polymerization and assembly of pre-formed polymers. Superior brightness requires strong dye loading without aggregation-caused quenching (ACQ). Only recently several strategies of dye design were proposed to overcome ACQ in polymer NPs: aggregation induced emission (AIE), dye modification with bulky side groups and use of bulky hydrophobic counterions. The resulting NPs now surpass the brightness of QDs by ≈10-fold for a comparable size, and have started reaching the level of the brightest conjugated polymer NPs. Other properties, notably photostability, color, blinking, as well as particle size and surface chemistry are also systematically analyzed. Finally, major and emerging applications of dye-loaded NPs for in vitro and in vivo imaging are reviewed.

Silole-Based Red Fluorescent Organic Dots for Bright Two-Photon Fluorescence In vitro Cell and In vivo Blood Vessel Imaging

Robust luminescent dyes with efficient two-photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation-caused quenching. In this work, a red fluorescent silole, 2,5-bis[5-(dimesitylboranyl)thiophen-2-yl]-1-methyl-1,3,4-triphenylsilole ((MesB)2 DTTPS), is synthesized and characterized. (MesB)2 DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation-enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2 DTTPS within lipid-PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two-photon absorption cross section of 3.43 × 10(5) GM, which yields a two-photon action cross section of 1.09 × 10(5) GM. These (MesB)2 DTTPS dots show good biocompatibility and are successfully applied to one-photon and two-photon fluorescence imaging of MCF-7 cells and two-photon in vivo visualization of the blood vascular of mouse muscle in a high-contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network.

Multi-color solid-state emission of β-iminoenolate boron complexes tuned by methoxyl groups: aggregation-induced emission and mechanofluorochromism

New β-iminoenolate boron complexes bearing benzoxazole were synthesized, and they exhibited strong luminescence in solid states.

Aggregation-induced emission enhancement and living cell imaging of novel diarylanthracene conjugated dyes

Diarylanthracene conjugated dyes with good aggregation-induced emission enhancement (AIEE) properties were synthesized and their BSA nanoparticles were successfully used in HeLa cell imaging.

A sensitive AIEE probe for amphiphilic compounds

AIEE active α-cyanostilbene as a probe for surfactants.

Fabrication of amphiphilic fluorescent nanoparticles with an AIE feature via a one-pot clickable mercaptoacetic acid locking imine reaction: synthesis, self-assembly and bioimaging

Water dispersible and non-toxic AIE active fluorescent organic nanoparticles were fabricatedviaa one-pot clickable mercaptoacetic acid locking imine reaction.

Fabrication of hybridized nanoparticles with aggregation-induced emission characteristics and application for cell imaging

More TPE-CS/HA nanoparticles are endocytosed by culture for a long time, resulting in a much stronger fluorescence emission.

AIE Based Coumarin Chromophore - Evaluation and Correlation Between Solvatochromism and Solvent Polarity Parameters

A new class of red emitting extensively conjugated donor-π-acceptor type dyes bearing coumarin units have been synthesized by condensation of 7-(diethylamino)-2-oxo-2 H-chromene-3-carbaldehyde with different active methylenes. All the dyes are characterized by (1)H NMR, (13)C NMR and HRMS spectroscopy. The photophysical behaviour and the relation between structure and properties of the coumarin "push-pull" derivatives were investigated experimentally. The dyes exhibited positive solvatochromism and solvatofluorism in solution of varying polarity. These coumarin dyes show aggregation induced emission properties with red emitting fluorescence. They show absorption in the range of 501-528 and emission in the range of 547-630 nm. We evaluated photophysical properties of coumarin dyes using solvotochromism and solvent dependent shift in the emission wavelength. All the synthesized coumarin dyes COS1-COS4 are showing very good solvatochromic properties.

Aggregation-induced emission of siloles

Aggregation-induced emission (AIE) is a unique and significant photophysical phenomenon that differs greatly from the commonly acknowledged aggregation-caused emission quenching observed for many π-conjugated planar chromophores. The mechanistic decipherment of the AIE phenomenon is of high importance for the advance of new AIE systems and exploitation of their potential applications. Propeller-like 2,3,4,5-tetraphenylsiloles are archetypal AIE-active luminogens, and have been adopted as a core part in the design of numerous luminescent materials with diverse functionalities. In this review article, we elucidate the impacts of substituents on the AIE activity and shed light on the structure-property relationship of siloles, with the aim of promoting the judicious design of AIE-active functional materials in the future. Recent representative advances of new silole-based functional materials and their potential applications are reviewed as well.

Intracellular pH-induced fluorescence used to track nanoparticles in cells

A nanoparticle with pH-induced fluorescence was reported for intracellular tracking. The fluorescence was evoked by the isomerization of the ring-closed form spiropyran (SP) to the ring-open form merocyanine (MC) in the weak acidic environment of cells. The SP-MC switch accelerated the dissociation of nanoparticles to trigger the release of trapped paclitaxel.

Polymeric AIE-based nanoprobes for biomedical applications: recent advances and perspectives

The development of polymeric luminescent nanomaterials for biomedical applications has recently attracted a large amount of attention due to the remarkable advantages of these materials compared with small organic dyes and fluorescent inorganic nanomaterials. Among these polymeric luminescent nanomaterials, polymeric luminescent nanomaterials based on dyes with aggregation-induced emission (AIE) properties should be of great research interest due to their unique AIE properties, the designability of polymers and their multifunctional potential. In this review, the recent advances in the design and biomedical applications of polymeric luminescent nanomaterials based on AIE dyes is summarized. Various design strategies for incorporation of these AIE dyes into polymeric systems are included. The potential biomedical applications such as biological imaging, and use in biological sensors and theranostic systems of these polymeric AIE-based nanomaterials have also been highlighted. We trust this review will attract significant interest from scientists from different research fields in chemistry, materials, biology and interdisciplinary areas.

Highly Emissive Nanoparticles Based on AIE-Active Molecule and PAMAM Dendritic "Molecular Glue"

The highly emissive nanoparticles Gn-TCMPE (n = 0-4) were prepared by using PAMAM dendrimers as "molecular glue" to adhere an AIE-active molecule tetra(4-(carboxymethoxy)phenyl)ethylene (TCMPE). The electrostatic interaction of ammonium-carboxylate ion pairs provides a driving force between TCMPE and PAMAM dendrimers to form the nanoparticles Gn-TCMPE (n = 0-4), which is validated by the FTIR and (1)H NMR spectra. The formation of nanoparticles dramatically blocks the nonradiative pathway and enhances the fluorescence of TCMPE. The quantum yields of Gn-TCMPE gradually boost at first and then reach to a plateau with increasing the generation of PAMAM dendrimers, and the highest absolute quantum yields are obtained to be 0.42 and 0.64 for Gn-TCMPE (n = 2-4) in methanol dispersion and solid phases, respectively. The fluorescence of the nanoparticles can be tuned by addition of trifluoroacetic acid (TFA). Furthermore, the G4-TCMPE has been successfully applied to selectively image cytoplasm of Hela cells with excellent photostability and low cytotoxicity. This study provides a novel noncovalent strategy for developing highly emissive and robust organic materials fitting for cell fluorescence imaging.