Facile fabrication of luminescent polymeric nanoparticles containing dynamic linkages via a one-pot multicomponent reaction: Synthesis, aggregation-induced emission and biological imaging

Facile preparation of luminescent cellulose nanocrystals with aggregation-induced emission feature through Ce(IV) redox polymerization

Cellulose nanocrystals (CNCs) are a novel type of natural nanomaterials that have attracted tremendous research interest for various applications especially in the biomedical fields owing to their natural origin, biodegradable potential, remarkable biocompatibility and massive reactive hydroxyl groups. In this work, a novel strategy has been developed for fabrication of luminescent CNCs with aggregation-induced emission (AIE) feature for the first time through a facile one-step Ce(IV) redox polymerization for direct surface grafting of AIE dye (PhE) and hydrophilic monomer Poly(ethylene glycol) monomethyl ether acrylate (PEGMA) on CNCs. Various characterization techniques would demonstrate the successful preparation of resultant CNC-PhE-PEGMA with uniform nanoscale size, remarkable fluorescent properties and extremely low cytotoxicity. Furthermore, compared with conventional modification strategy of CNCs, Ce(IV) redox polymerization only need moderate temperature and can operate in aqueous solution utilizing surface hydroxyl groups of CNCs as polymerization activity sites. More importantly, CNC-PhE-PEGMA show desirable fluorescent properties and can be used for cell dyeing, indicating their potential for biomedical applications.

Emulsion and miniemulsion techniques in preparation of polymer nanoparticles with versatile characteristics

In recent years, polymer nanoparticles (PNPs) have found their ways into numerous applications extending from electronics to photonics, conducting materials to sensors and medicine to biotechnology. Physical properties and surface morphology of PNPs are the most important parameters that significantly affect on their exploitations and can be controlled through the synthesis process. Emulsion and miniemulsion techniques are among the most efficient and wide-spread methods for preparation of PNPs. The objective of this review is to present and highlight the recent developments in the advanced PNPs with specific properties that are produced through emulsion and miniemulsion processes.

A fluorescent sensor based on aggregation-induced emission: highly sensitive detection of hydrazine and its application in living cell imaging

Aggregation-induced emission (AIE) molecules eliminate the aggregation-caused quenching (ACQ) phenomenon effectively and exhibit excellent properties of a fluorescent sensor in the aggregated state. In this paper, an allochroic fluorescent sensor based on AIE molecules with a diphenylacrylonitrile structure was prepared in high yield by a simple procedure. This molecule possessed good AIE properties and exhibited a sensitive sensor ability for aliphatic amines with an obvious color change from orange to blue-green. The detailed investigation on the detection of hydrazine suggested that the detection limit for hydrazine was 3.67 × 10-6 M, and the highly sensitive sensor for hydrazine was not influenced by other species. The sensor mechanism was confirmed by using 1H NMR and MS spectra. The sensor for hydrazine was successfully applied in a test paper, exhibiting good practical application potential for detecting hydrazine. The experiment of living cell imaging suggested that this sensor showed superior bioimaging performance and presented sensitive detection for hydrazine with an obvious color change from orange to blue-green.

A fluorescent sensor for thymine based on bis-BODIPY containing butanediamido bridges

A fluorescent sensor for thymine based on bis-BODIPY containing butanediamido bridges was prepared and applied in the sensitive detection of thymine in living cell imaging.

A novel AIE-active dye for fluorescent nanoparticles by one-pot combination of Hantzsch reaction and RAFT polymerization: synthesis, molecular structure and application in cell imaging

In recent years, amphiphilic AIE-active fluorescent organic materials with aggregation-induced emission (AIE) properties have been extensively investigated due to their excellent properties. This study describes the synthesis of a novel AIE-active dye of tetraphenylethylene diphenylaldehyde (TPDA). As compared with the reported fluorescent dye TPB, the fluorescence intensity of TPDA is significantly enhanced with the distinct red shift of emission wavelength. Subsequently, the corresponding novel polymers PEG-TPD were obtained through the one-pot combination of Hantzsch reaction and RAFT polymerization. The structure of PEG-TPD1 by the two-step process was similar with that of PEG-TPD2 by the one-pot method at the same feeding ratio of TPDA and PEGMA. The molecular weights (M_n) of the polymers PEG-TPD1 and PEG-TPD2 were respectively 52 000 and 28 000 with narrow polydispersity index (PDI), and their molar fractions of TPDA were respectively about 9.5% and 14.3%, indicating that the degree of Hantzsch reaction in the one-pot process was more complete. Subsequently, the effect of feed ratio of TPDA and PEGMA on polymer structure was further studied. It can be seen that the M_n of the polymers gradually increases as the proportion of TPDA increases. In aqueous solution, these amphiphilic PEG-TPD polymers tended to self-assemble into corresponding fluorescent polymer nanoparticles (FPNs). The diameter of PEG-TPD2 FPNs ranged from 200 to 300 nm, and their fluorescence emission spectra have maximum emission peak at 509 nm. The PEG-TPD FPNs have significant advantages such as good fluorescence intensity, high water dispersibility, good biocompatibility and easy absorption by cells, which can be attractively used in the field of bioimaging.

This work reported the fabrication of a novel AIE-active dye and its amphiphilic PEG-TPD fluorescent polymers via one-pot combination of RAFT polymerization and Hantzsch reaction, which showed potential applications in bioimaging.

AIE active piperazine appended naphthalimide-BODIPYs: photophysical properties and applications in live cell lysosomal tracking

Piperazine appended naphthalimide-BODIPYs (NPB1–NPB4) exhibiting solvatochromism, aggregation-induced emission, and high selectivity towards lysosomal pH in living cells have been described.

Defect-Induced Fluorescence of Silica Nanoparticles for Bioimaging Applications

With biocompatibility, biodegradability, and high functionality, silica nanoparticles (SNPs) have been widely investigated for various biomedical applications. However, lack of optical fluorescence has limited the application of SNPs as a degradable imaging agent. Here, we hydrothermally synthesized fluorescent SNPs by artificially generating optically active defect centers using tetraethyl orthosilicate and (3-aminopropyl)trimethoxysilane. The synthesized SNPs demonstrated strong blue photoluminescence originating from the dioxasilyrane (=Si(O₂)) and silylene (=Si:) defect centers with the aid of aminopropyl groups. Furthermore, phosphorescence was observed at 459 nm, indicating the presence of silylene in SNPs. Finally, these SNPs have been successfully utilized as a fluorescent probe for bioimaging of normal, cancer, and macrophage cells.

Photoactivation of Aggregation-Induced Emission Molecules for Fast and Efficient Synthesis of Highly Fluorescent Single-Chain Nanoparticles

Single-chain nanoparticles (SCNPs) are ultrasmall soft nanomaterials constructed via intrachain cross-linking of individual precursor polymer chains, with promising prospects for nanomedicine, catalysis, and sensing, among other different fields. SCNPs are versatile building blocks for the construction of new fluorescent probes with ultrasmall size, higher brightness, and better photostability than previous particle-based systems. Herein, we report on a new, fast, and efficient method to produce SCNPs with intense fluorescence emission in solution which is based on the photoactivation of appropriate aggregation-induced emission (AIE) cross-linking molecules containing azide functional groups. Remarkably, the presence of the azide moiety-that can be transformed to highly reactive nitrene species upon UV irradiation-was found to be essential for the SCNPs to display intense fluorescence emission. We attribute the fluorescence properties of the SCNPs to the immobilization of the initially nonfluorescent AIE molecules via intrachain cross-linking upon photoactivation. Such cross-linking-induced immobilization process activates the AIE mechanism and, hence, leads to fluorescent SCNPs in both solution and solid state.

Sericin-chitosan doped maleate gellan gum nanocomposites for effective cell damage in Mycobacterium tuberculosis

Polysaccharides are increasingly used as biodegradable nanocarrier to selectively deliver therapeutic agents to specific cells. In this study, maleate gellan gum (MA-GG) formed by addition of free radical polymerizable groups, which can be polymerized presence of acetone to design biodegradable three-dimensional networks, were synthesized by esterification. Natural silk sericin was grafted over the maleate gellan gum surface. Maleate Gellan Gum- Silk Sericin-Chitosan (MA-GG-SS-CS) nanocomposites loaded with rifampicin (RF) and pyrazinamide (PZA) to overcome the problems associated with Tuberculosis (TB) therapy. The pH responsive behavior of gellan gum nanocomposites was reposed by silk sericin and exhibited sustained release of 79% RF and 82% PZA for 120 h at pH 4.0. The designed formulations shows higher antimycobacterial activity and rapid delivery of drugs at TB infected macrophage. Nanomaterial effectively aggregated and internalized into the bacterial cells and MH-S cells. Dual drug release inside the cells makes damage in the cell membrane. Green nanocomposites studies pave the way for important use of macromolecules in pulmonary delivery TB drugs.

Construction of Functional Hyperbranched Poly(phenyltriazolylcarboxylate)s by Metal-Free Phenylpropiolate-Azide Polycycloaddition

The 1,3-dipolar cycloaddition of activated internal alkynes with azides has been developed into an efficient polymerization reaction for constructing functional linear 1,4,5-trisubstitued polytriazoles. However, it is rarely employed for the synthesis of hyperbranched polymers. In this work, metal-free polycycloadditions of tris(3-phenylpropiolate)s (1) and tetraphenylethene-containing diazides (2) are performed in dimethylformamide at 100 °C for 7 and 12 h, producing hyperbranched poly(phenyltriazolylcarboxylate)s (hb-PPTCs) with high molecular weights and satisfactory regioregularities in good yields. The hb-PPTCs have good solubility in common organic solvents and high thermal stability. They are non-emissive in solutions, but emit intensively upon aggregation, showing an aggregation-induced emission effect. Their aggregates can work as fluorescent sensors for explosive detection with high sensitivity. Furthermore, the polymers can be utilized for the fabrication of 2D fluorescent patterns with high resolution by UV irradiation through copper grid masks.

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin-Silica Nanoparticles Interface

The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin-filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m-3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin-filler interface.

Application of amphiphilic fluorophore-derived nanoparticles to provide contrast to human embryonic stem cells without affecting their pluripotency and to monitor their differentiation into neuron-like cells

Fluorogenic labeling is a potential technique in biology that allows for direct detection and tracking of cells undergoing various biological processes. Compared to traditional genetic modification approaches, labeling cells with nanoparticles has advantages, especially for the additional safety they provide by avoiding genomic integration. However, it remains a challenge to determine whether nanoparticles interfere with cell traits and provide long-lasting signals in living cells. We employed an amphiphilic fluorophore-derived nanoparticle (denoted by TPE-11) bearing a tetraphenylethene (TPE) moiety and two ionic heads; this nanoparticle has an aggregation-induced emission (AIE) effect and the ability to self-assemble. TPE-11 exhibited the property of higher or longer fluorescence intensities in cell imaging than the other two nanomaterials under the same conditions. We used this nanomaterial to label human embryonic stem (hES) cells and monitor their differentiation. Treatment with low concentrations of TPE-11 (8.0 μg/mL) resulted in high-intensity labeling of hES cells, and immunostaining analysis and teratoma formation assays showed that at this concentration, their pluripotency remained unaltered. TPE-11 nanoparticles allowed for long-term monitoring of hES cell differentiation into neuron-like cells; remarkably, strong nanoparticle signals were detected throughout the nearly 40-day differentiation process. Thus, these results demonstrate that the TPE-11 nanoparticle has excellent biocompatibility for hES cells and is a potential fluorogen for labeling and tracking the differentiation of human pluripotent stem cells.

STATEMENT OF SIGNIFICANCE

This study uses a nanoparticle-based approach to label human embryonic stem (hES) cells and monitor their differentiation. hES cells are distinguished by two distinctive properties: the state of their pluripotency and the potential to differentiate into various cell types. Thus, these cells will be useful as a source of cells for transplantation or tissue engineering applications. We noticed the effect of aggregation-induced emission, and the ability to self-assemble could enhance the persistence of signals. Treatment with low concentrations of TPE-11 nanoparticles showed high-intensity labeling of hES cells, and immunostaining analysis and teratoma formation assays showed that at this concentration, their pluripotency remained unaltered. Additionally, these nanoparticles allowed for long-term monitoring of hES cell differentiation into neuron-like cells lasting for 40 days.

Detecting live bacteria instantly utilizing AIE strategies

A new class of biosensor molecules evoking fluorescent emission by rotation-restricted binding with bacteria was examined for its applicability in detecting live bacteria instantly. The fluorogens possessed multiple tetraphenylethene (TPE)-cored boronic acids to oligomerize through complexation with cis-diols on bacterial surfaces, resulting in aggregation-induced emission (AIE). The fluorogen having two boronic acid units discriminated between live and dead bacteria by showing AIE activity only with the latter. Live bacteria were instantly detected by consequent treatment with reagents of three and four di-boronates (which showed AIE activity with both live and dead bacteria). This phenomenon may lead to a practical method for live bacteria detection.

One-pot ultrafast preparation of silica quantum dots and their utilization for fabrication of luminescent mesoporous silica nanoparticles

Silica quantum dots (SiQDs) and their luminescent composites have displayed great potential for biomedical applications owing to their chemical inert and low cost. In this work, we report a facile, cost-effective and ultrafast strategy to prepare a stable luminescent SiQDs using N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS) and salicylaldehyde as precursors for the first time. These luminescent SiQDs were further utilized for fabrication of luminescent mesoporous silica nanoparticles (MSNs) through direct encapsulation of SiQDs by MSNs. The novel synthetic and modified SiQDs uses commercial raw materials and the entire reaction can be completed within 30 s. The successful preparation of SiQDs and SiQDs@MSNs were characterized by various characterization equipments. The cell viability as well as cell uptake behavior of SiQDs@MSNs were also examined to evaluate their potential for biomedical applications. We demonstrated that these SiQDs@MSNs are low toxicity and of great potential for biological imaging. Based on the above results, we believe that these SiQDs@MSNs should be novel and promising candidates for biomedical applications owing to their intense fluorescence, biocompatibility and high specific surface areas.

A one-step ultrasonic irradiation assisted strategy for the preparation of polymer-functionalized carbon quantum dots and their biological imaging

Fluorescent carbon nanoparticles (FCNs) have gradually become the most promising alternative candidates to other traditional fluorescent nanomaterials for biological applications on account of their excellent fluorescence property and remarkable biocompatibility. Although many methods have reported on the preparation of FCNs, to date, no studies have reported the preparation of polymers of functionalized FCNs. A high-efficiency method was developed in this work to synthesize high-quality poly(ethylene oxide) (PEG)-functionalized FCNs from cigarette ash and thiol group-containing PEG via a facile one-pot ultrasonic irradiation treatment. A series of characterization techniques demonstrated the uniform nanoscale size, good fluorescence stability, high water dispersibility and remarkable biocompatibility of the generated FCNs. Furthermore, cell imaging was easily achieved at high resolution using the synthetic FCNs as probes, which validates their potential for bioimaging applications. In summary, an efficient one-pot strategy is reported for the first time on the preparation of PEG-functionalized FCNs with the assistance of ultrasonic irradiation. This method should be of great research interest for the fabrication of other polymer-functionalized FCNs with designable properties and functions.

Fluorescence probes based on AIE luminogen: application for sensing Hg2+ in aqueous media and cellular imaging

S1 and S2 could be applied for sensing Hg²⁺ in aqueous media and cellular imaging with remarkable AIEE.

A “Turn-On” fluorescent probe for sensitive and selective detection of fluoride ions based on aggregation-induced emission

Based on the fluorophore of 2-(2′-hydroxyphenyl)benzothiazole (HBT) with aggregation-induced emission (AIE) properties, a highly selective and sensitive fluorescent probe PBT towards F⁻ was investigated. “Turn-On” fluorescence type signaling was realized by employing fluoride-selective cleavage of the latent thiophosphinated probe in mixed aqueous media. The probe is designed in such a way that the excited state intramolecular proton transfer (ESIPT) of the HBT moiety becomes blocked. The chemodosimetric approach of F⁻ to the probe results in the recovery of the ESIPT by removal of a free AIE-active HBT moiety through a subsequent hydrolysis process. The F⁻ detection limit of the probe was 3.8 nM in the dynamic range of 0.5 μM to 10 μM. In addition, the proposed probe has been used to detect F⁻ in water samples and toothpaste samples with satisfying results.

A “Turn-On” fluorescent probe PBT for sensitive and selective detection of fluoride ions based on aggregation-induced emission.

A biomimetic fluorescent chemosensor for highly sensitive zinc(ii) detection and its application for cell imaging

To fabricate a novel biomimetic fluorescent chemosensor, PSaAEMA-co-PMPC was synthesized via atom transfer radical polymerization, and this copolymer could be used for the detection of zinc(ii) and cell imaging. A series tests with various metal ions verified the specific fluorescence response behavior. This novel biomimetic fluorescent chemosensor exhibits excellent selectivity for Zn²⁺ ions over a wide range of tested metal ions in an aqueous solution. Moreover, cytotoxicity and bio-imaging tests were conducted to study the potential bio-application of the chemosensor. Owing to the biomimetic portion (phosphorylcholine), this copolymer possesses outstanding biocompatibility and could clearly image cells. The results indicated that PSaAEMA-co-PMPC has great potential for application in zinc(ii) detection and cell imaging.

To fabricate a novel biomimetic fluorescent chemosensor, PSaAEMA-co-PMPC was synthesized via atom transfer radical polymerization, and this copolymer could be used for the detection of zinc(ii) and cell imaging.

Polysiloxane-based two-photon fluorescent elastomers with superior mechanical and self-healing properties and their application in bioimaging

The first report of the synthesis of novel self-healing elastomers possessing a dynamic dual cross-linked network and exhibiting a unique two-photon fluorescence, which show potential for application in bioimaging.

Halogen bond triggered aggregation induced emission in an iodinated cyanine dye for ultra sensitive detection of Ag nanoparticles in tap water and agricultural wastewater

Aggregation induced emission (AIE) has emerged as a powerful method for sensing applications. Based on AIE triggered by halogen bond (XB) formation, an ultrasensitive and selective sensor for picomolar detection of Ag nanoparticles (Ag NPs) is reported. The dye (CyI) has an iodine atom in its skeleton which functions as a halogen bond acceptor, and aggregates on the Ag NP plasmonic surfaces as a halogen bond donor or forms halogen bonds with the vacant π orbitals of silver ions (Ag⁺). Formation of XB leads to fluorescence enhancement, which forms the basis of the Ag NPs or Ag⁺ sensor. The sensor response is linearly dependent on the Ag NP concentration over the range 1.0–8.2 pM with an LOD of 6.21 pM (σ = 3), while for Ag⁺ it was linear over the 1.0–10 μM range (LOD = 2.36 μM). The sensor shows a remarkable sensitivity for Ag NPs (pM), compared to that for Ag⁺ (μM). The sensor did not show any interference from different metal ions with 10-fold higher concentrations. This result indicates that the proposed sensor is inexpensive, simple, sensitive, and selective for the detection of Ag NPs in both tap and wastewater samples.

Based on AIE triggered by halogen bond (XB) formation, we established an ultrasensitive and selective sensor for picomolar detection of Ag nanoparticles (Ag NPs).

Fabrication of multifunctional fluorescent organic nanoparticles with AIE feature through photo-initiated RAFT polymerization

Novel fluorescent organic nanoparticles with AIE feature have been fabricated through a catalyst-free photo-initiated RAFT polymerization.