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

Fluorescent Carbon Dioxide-Based Polycarbonates Probe for Rapid Detection of Aniline in the Environment and Its Biomarkers in Urine

Aniline compounds, as a class of widely used but highly toxic chemical raw materials, are increasingly being released and accumulated in the environment, posing serious threats to environmental safety and human health. Therefore, developing detection methods for aniline compounds is of particular significance. Herein, we synthesized the fluorescent third monomer cyano-stilbene epoxide M and ternary copolymerized it with carbon dioxide (CO2) and propylene oxide (PO) to synthesize carbon dioxide-based polycarbonate (PPCM) with fluorescence recognition functions, as well as excellent performance, for the first time. The results revealed that the PPCM fluorescent probe exhibited typical aggregation-induced luminescence properties and could be quenched by aniline compounds. The probe presented anti-interference-specific selectivity for aniline compounds, and the detection limit was 1.69 × 10-4 M. Moreover, it was found to be a highly sensitive aniline detection probe. At the same time, the aniline biomarker p-aminophenol in urine could also be detected, which could expand the potential applications of polymers in the fluorescence-sensing field.

Self-assembled super-small AIEgen nanoprobe for highly sensitive and selective detection of protamine and trypsin

Amphiphilic aggregation-induced emission (AIE) molecules show superior potential for fabricating novel ultrasmall nanoprobes. Here, an anionic dipyridyl tetraphenylethene (TPE) derivative is rationally designed and a super-small self-assembled AIEgen nanoprobe (TPE-2Py-SO₃NaNPs, ca. 2.48 nm) is thus conveniently constructed for the supersensitive detection of protamine and trypsin. In HEPES/DMSO solution (8 : 2, v/v, pH = 7.4), negatively charged TPE-2Py-SO₃NaNPs exhibited an AIE effect in the presence of positively charged protamine, presenting a fluorescence enhancement at 498 nm together with a large Stokes shift of 150 nm and a low detection limit of 8.0 ng mL^-1. In addition, the in situ formed TPE-2Py-SO₃Na/protamine nanocomposite can be dissociated by trypsin due to the highly selective degradation of protamine via enzymatic hydrolysis, achieving a detection limit for trypsin as low as 5.0 ng mL^-1.

Controllable Aggregation-Induced Emission and Förster Resonance Energy Transfer Behaviors of Bistable [c2] Daisy Chain Rotaxanes for White-Light Emission and Temperature-Sensing Applications

Bistable [c2] daisy chain rotaxanes with respective extended and contracted forms of [c2]A and [c2]B containing a blue-emissive anthracene (AN) donor and orange-emissive indandione-carbazole (IC) acceptor were successfully synthesized via click reaction. Tunable-emission bistable [c2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H₂O/THF) and FRET (with a compatible energy transfer of E_FRET = 33.2%) behaviors after the shuttling process (by adding base), the brightest white-light emission at CIE (0.31, 0.37) with a quantum yield of Φ = 15.64% was obtained in contracted [c2]B with good control of molecular shuttling to possess higher photoluminescence (PL) quantum yields and better energy transfer efficiencies (i.e., the manipulation of reduced PET and enhanced FRET processes) due to their intramolecular aggregations of blue AN donors and orange IC acceptors with a proper water content of 60% H₂O. Furthermore, dynamic light-scattering (DLS) and time-resolved photoluminescence (TRPL) measurements, along with theoretical calculations, were utilized to investigate and confirm AIE and FRET phenomena of bistable [c2] daisy chain rotaxanes. Especially, both bistable [c2] daisy chain rotaxanes [c2]A and [c2]B and noninterlocked monomer M could be exploited for the applications of ratiometric fluorescence temperature sensing due to the temperature effects on the AIE and FRET features. Based on these desirable bistable [c2] daisy chain rotaxane structures, this work provides a potential strategy for the future applications of tunable multicolor emission and ratiometric fluorescence temperature-sensing materials.

How sticky? How Tight? How Hot? Imaging probes for fluid viscosity, membrane tension and temperature measurements at the cellular level

We review the progress made in imaging probes for three important physical parameters: viscosity, membrane tension, and temperature, all of which play important roles in many cellular processes. Recent evidences showed that cell migration speed can be modulated by extracellular fluid viscosity; membrane tension contributes to the regulation of cell motility, exo-/endo-cytosis, and cell spread area; and temperature affects neural activity and adipocyte differentiation. We discuss the techniques implementing imaging-based probes to measure viscosity, membrane tension, and temperature at subcellular resolution dynamically. The merits and shortcomings of each technique are examined, and the future applications of the recently developed techniques are also explored.

Stimuli-Responsive Aggregation-Induced Emission (AIE)-Active Polymers for Biomedical Applications

At high concentration or in the aggregated state, most of the traditional luminophores suffer from the general aggregation-caused quenching (ACQ) effect, which significantly limits their biomedical applications. On the contrary, a few fluorophores exhibit an aggregation-induced emission (AIE) feature which is just the opposite of ACQ. The luminophores with aggregation-induced emission (AIEgens) have exhibited noteworthy advantages to get tunable emission, excellent photostability, and biocompatibility. Incorporating AIEgens into polymer design has yielded diversified polymer systems with fascinating photophysical characteristics. Again, stimuli-responsive polymers are capable of undergoing chemical and/or physical property changes on receiving signals from single or multiple stimuli. The combination of the AIE property and stimuli responses in a single polymer platform provides a feasible and effective strategy for the development of smart polymers with promising biomedical applications. Herein, the advancements in stimuli-responsive polymers with AIE characteristics for biomedical applications are summarized. AIE-active polymers are first categorized into conventional π-π conjugated and nonconventional fluorophore systems and then subdivided based on various stimuli, such as pH, redox, enzyme, reactive oxygen species (ROS), and temperature. In each section, the design strategies of the smart polymers and their biomedical applications, including bioimaging, cancer theranostics, gene delivery, and antimicrobial examples, are introduced. The current challenges and future perspectives of this field are also stated at the end of this review article.

Sustainable aggregation-induced emission material based on pectin-l-lysine: Potential antibacterial and monitoring in food spoilage

The demand of smart food detection system which in detecting food spoilage is increasing. In this work, a new type of aggregation-induced emission (AIE) compound was synthesized based on pectin (P) and l-lysine (Lys). P-Lys is an AIE active compound which has the advantages of simple synthesis, easy modification and processability, it also has good water solubility and biocompatibility. Moreover, P-Lys has potential application in detecting Fe³⁺ (oxidation from Fe²⁺) and bacterial in monitoring pork spoilage. In addition, P-Lys also has spectral antibacterial properties which can prevent pork spoilage. The research results shown that P-Lys, as a new type of food testing agent has a useful future in monitoring and protecting the freshness of food.

Upper Critical Solution Temperature Polyvalent Scaffolds Aggregate and Exterminate Bacteria

Specific recognition and strong affinities of bacteria receptors with the host cell glycoconjugates pave the way to control the bacteria aggregation and kill bacteria. Herein, using aggregation-induced emission (AIE) molecules decorated upper critical solution temperature (UCST) polyvalent scaffold (PATC-GlcN), an approach toward visualizing bacteria aggregation and controlling bacteria-polyvalent scaffolds affinities under temperature stimulus is described. Polyvalent scaffolds with diblocks, one UCST block PATC of polyacrylamides showing a sharp UCST transition and typical AIE behavior, the second bacteria recognition block GlcN of hydrophilic glucosamine modified polyacrylamide, are prepared through a reversible addition and fragmentation chain transfer polymerization. Aggregated chain conformation of polyvalent scaffolds at temperature below UCST induces the aggregation of E. coli ATCC8739, because of the high density of glucosamine moieties, whereas beyond UCST, the hydrophilic state of the scaffolds dissociates the bacteria aggregation. The sweet-talking of bacteria toward the polyvalent scaffolds can be visualized by the fluorescent imaging technique, simultaneously. Due to the specific recognition of polyvalent scaffolds with bacteria, the photothermal agent IR780 loaded PATC-GlcN shows the targeted killing ability toward E. coli ATCC8739 in vitro and in vivo under NIR radiation.

Well-defined polyacrylamides with AIE properties via rapid Cu-mediated living radical polymerization in aqueous solution: thermoresponsive nanoparticles for bioimaging

There is a requirement for the development of methods for the preparation of well-controlled polymers with aggregation-induced emission (AIE) properties.

Thermo-responsive poly(N-isopropylacrylamide)-hyaluronic acid nano-hydrogel and its multiple applications

It is a huge challenge to construct a nanoprobe that can convert temperature stimulation into monochromatic signal with "turn-on" function. Here, a drug delivery system of berberine (BBR)-loaded hyaluronic acid (HA)-modified-L-cysteine (Cys) grafted (N-isopropylacrylamide) (PNIPAM) was structured. HA-Cys-PN/BBR does not need to introduce other substances or external stimuli, by adjusting the temperature of this system, the fluorescence responsive intensity and reversible reciprocating control of the nanohydrogel with aggregation induced emission (AIE) performance can be realized. In addition, CD44-HA interaction can be used as targeting the delivery of cancer cells, thus, there is a great interest in development of targeting and imaging agents as payloads for tumor tissue therapy. Therefore, it can provide a side of the development with self-released drugs in the therapy of cancers or bacterial infections. Thus, HA-Cys-PN/BBR as AIE reversible nanogel has longer-term applications in biomedical applications.

Recent Advances in Aggregation-Induced Emission Active Materials for Sensing of Biologically Important Molecules and Drug Delivery System

The emergence and development of aggregation induced emission (AIE) have attracted worldwide attention due to its unique photophysical phenomenon and for removing the obstacle of aggregation-caused quenching (ACQ) which is the most detrimental process thereby making AIE an important and promising aspect in various fields of fluorescent material, sensing, bioimaging, optoelectronics, drug delivery system, and theranostics. In this review, we have discussed insights and explored recent advances that are being made in AIE active materials and their application in sensing, biological cell imaging, and drug delivery systems, and, furthermore, we explored AIE active fluorescent material as a building block in supramolecular chemistry. Herein, we focus on various AIE active molecules such as tetraphenylethylene, AIE-active polymer, quantum dots, AIE active metal-organic framework and triphenylamine, not only in terms of their synthetic routes but also we outline their applications. Finally, we summarize our view of the construction and application of AIE-active molecules, which thus inspiring young researchers to explore new ideas, innovations, and develop the field of supramolecular chemistry in years to come.

Recent Advances in Aggregation-Induced Emission Materials and Their Biomedical and Healthcare Applications

The emergence of the concept of aggregation-induced emission (AIE) has opened new opportunities in many research areas, such as biopsy analysis, biological processes monitoring, and elucidation of key physiological and pathological behaviors. As a new class of luminescent materials, AIE luminogens (AIEgens) possess many prominent advantages such as tunable molecular structures, high molar absorptivity, high brightness, large Stokes shift, excellent photostability, and good biocompatibility. The past two decades have witnessed a dramatic growth of research interest in AIE, and many AIE-based bioprobes with excellent performance have been widely explored in biomedical fields. This review summarizes some of the latest advancements of AIE molecular probes and AIE nanoparticles (NPs) with regards to biomedical and healthcare applications. According to the research areas, the review is divided into five sections, which are imaging and identification of cells and bacteria, photodynamic therapy, multimodal theranostics, deep tissue imaging, and fluorescence-guided surgery. The challenges and future opportunities of AIE materials in the advanced biomedical fields are briefly discussed. In perspective, the AIE-based bioprobes play vital roles in the exploration of advanced bioapplications for the ultimate goal of addressing more healthcare issues by integrating various cutting-edge modalities and techniques.

Aggregation-induced emission (AIE)-guided dynamic assembly for disease imaging and therapy

The phenomenon of aggregation-induced emission (AIE) is inseparable from molecular aggregation and self-assembly. Therefore, the combination of AIE and supramolecular self-assembly is well-matched. AIE-guided dynamic assembly (AGDA) could effectively respond to the endogenous stimuli (such as pH, enzymes, redox molecules) and exogenous stimuli (temperature, light, ultrasound) in the disease microenvironment, so as to achieve specific imaging and diagnosis of the disease lesions. Moreover, AGDA also dynamically adjust the intramolecular motions of AIE molecules, thereby adjusting the energy dissipation pathways and realizing the switch between photodynamic therapy and photothermal therapy for superior therapeutic effects. In this review, we aim to give an overview of the constructing strategies, stimuli-responsive imaging, regulation of intramolecular motion of AGDA in recent years, which is expected to grasp the research status and striving directions of AGDA for imaging and therapy.

Recent Progress in Polymeric AIE-Active Drug Delivery Systems: Design and Application

Aggregation-induced emission (AIE) provides a new opportunity to overcome the drawbacks of traditional aggregation-induced quenching of chromophores. The applications of AIE-active fluorophores have spread across various fields. In particular, the employment of AIEgens in drug delivery systems (DDSs) can achieve imaging-guided therapy and pharmacodynamic monitoring. As a result, polymeric AIE-active DDSs are attracting increasing attention due to their obvious advantages, including easy fabrication and tunable optical properties by molecular design. Additionally, the design of polymeric AIE-active DDSs is a promising method for cancer therapy, antibacterial treatment, and pharmacodynamic monitoring, which indeed helps improve the effectiveness of related disease treatments and confirms its potential social importance. Here, we summarize the current available polymeric AIE-active DDSs from design to applications. In the design section, we introduce synthetic strategies and structures of AIE-active polymers, as well as responsive strategies for specific drug delivery. In the application section, typical polymeric AIE-active DDSs used for cancer therapy, bacterial treatment, and drug delivery monitoring are summarized with selected examples to elaborate on their wide applications.

Temperature-sensitive poly(N-isopropylacrylamide)-chitosan hydrogel for fluorescence sensors in living cells and its antibacterial application

It is meaningful and challenging to design and develop a fluorescent probe for living cell temperature sensors since it should have good cell compatibility and high-resolution features. In this work, the temperature-sensitive polymer of PA-loaded cysteine (Cys) modified chitosan (Cs) grafted PNIPAM (Cs-Cys-PN/PA) with aggregation-induced emission enhancement (AIEE) properties that reversible hydrogel in an aqueous solution is synthesized. Here, we interpret the temperature stimulus as a monochromatic signal through the AIEE active reversible hydrogel of Cs-Cys-PN. In addition, the cytotoxicity test shown that Cs-Cys-PN has good biocompatibility. Cs-Cys-PN can be used to build antibacterial drugs carrier, thereby providing a new platform of self-released drugs for the treatment of bacterial infections.

Temperature and pH Responsive Light-Harvesting System Based on AIE-Active Microgel for Cell Imaging

A highly emissive microgel is synthesized by polymerizing tetraphenylethene (TPE) based comonomers, acrylic acid, NIPAM, and permanent crosslinker ethylenebisacrylamide (BIS) (named as TPE microgel), which exhibited temperature responsive fluorescence emission. Rhodamine B (RhB), a positively charged molecule, is then inserted onto the surface of fabricated microgels through electrostatic interaction. As a result, a novel artificial light harvesting system with high energy transfer efficiency is constructed (named as TPE microgel-RhB light harvesting system), which is the first light harvesting system based on TPE microgels presenting dual response to pH and temperature. MTT assay indicates the fabricated TPE microgel and TPE microgel-RhB light harvesting system has good cytocompatibility. The strong fluorescence and good cytocompatibility make them perfect candidates for cell imaging. The prepared emissive microgel and light-harvesting system with desirable fluorescent property not only provide a new strategy for the fabrication of tunable luminescent nanomaterials, but also expand potential applications in the fields of stomach recognition, temperature sensors, and drug delivery.

Functional Copolymers Married with Lanthanide(III) Ions: A Win-Win Pathway to Fabricate Rare Earth Fluorescent Materials with Multiple Applications

Lanthanide(III)-based luminescent materials have attracted great research interests due to their unique optical, electronic, and chemical characteristics. Up to now, how to extend these materials into large, broad application fields is still a great challenging task. In this contribution, we are intended to present a simple but facile strategy to enhance the luminescence from lanthanide ions and impart lanthanide(III)-based luminescent materials with more applicable properties, leading to meet the requirements from different purposes, such as being used as highly emissive powders, hydrogels, films, and sensitive probes under external stimuli. Herein, a water soluble, blue color emissive, temperature sensitive, and film-processable copolymer (Poly-ligand) was designed and synthesized. Upon complexing with Eu³⁺ and Tb³⁺ ions, the red color-emitting Poly-ligand-Eu and green color-emitting Poly-ligand-Tb were produced. After finely tuning the ratios between them, a standard white color emitting Poly-ligand-Eu₁:Tb₄ (CIE = 0.33 and 0.33) was obtained. Furthermore, the resulted materials not only possessed the emissive luminescent property but also inherited functions from the copolymer of Poly-ligand. Thus, these lanthanide(III)-based materials were used for fingerprint imaging, luminescent soft matters formation, colorful organic light-emitting diode device fabrication, and acid/alkali vapors detection.

Organic–inorganic nanohybrids based on an AIE luminogen-functional polymer and CdTe/ZnS QDs: morphologies, optical properties, and applications

Dual-emissive organic–inorganic nanohybrid self-assemblies were constructed by binding red-emitting CdTe/ZnS QDs to blue-emitting AIE-active polymeric micelles in water as a fluorescent probe for PA with interesting assembly behaviour.

Synthesis of poly(N-isopropylacrylamide) polymer crosslinked with an AIE-active azonaphthol for thermoreversible fluorescence

A fluorescent polymer was synthesized using N-isopropylacrylamide (NIPAM) crosslinked with a divinylazonaphthol monomer via radical emulsion polymerization. Because the crosslinked polymer contained an aggregation-induced emissive (AIE) azonaphthol-based crosslinker, a thermoreversible sol-gel transformation and gelation-induced reversible fluorescence alteration were successfully attained in an aqueous medium. Like typical PNIPAM, the size and transmittance of the polymer dramatically decreased near the lower critical solution temperature (LCST, 36 °C). Such gelation facilitated aggregation of the polymer chains, resulting in the close contact between azonaphthol groups producing fluorescence. The crosslinked polymer exhibited changes in dual properties: one is related to PNIPAM structural alteration, which corresponds to conventional swelling/shrinkage behavior; and the other is involved in the reversible fluorescence change in response to the swelling/shrinkage. Because the major backbone of the polymer was composed of NIPAM with an LCST at 36 °C, the resultant polymer is expected to have potential applications in biologically related fields.

TICT-Based Near-Infrared Ratiometric Organic Fluorescent Thermometer for Intracellular Temperature Sensing

Fluorescent thermometers with near-infrared (NIR) emission play an important role in visualizing the intracellular temperature with high resolution and investigating the cellular functions and biochemical activities. Herein, we designed and synthesized a donor-Π-acceptor luminogen, 2-([1,1'-biphenyl]-4-yl)-3-(4-((E)-4-(diphenylamino)styryl) phenyl) fumaronitrile (TBB) by Suzuki coupling reaction. TBB exhibited twisted intramolecular charge transfer-based NIR emission, aggregation-induced emission, and temperature-sensitive emission features. A ratiometric fluorescent thermometer was constructed by encapsulating thermosensitive NIR fluorophore TBB and Rhodamine 110 dye into an amphiphilic polymer matrix F127 to form TBB&R110@F127 nanoparticles (TRF NPs). TRF NPs showed a good temperature sensitivity of 2.37%·°C^-1, wide temperature response ranges from 25 to 65 °C, and excellent temperature-sensitive emission reversibility. Intracellular thermometry experiments indicated that TRF NPs could monitor the cellular temperature change from 25 to 53 °C for Hep-G2 cells under the photothermal therapy agent heating process, indicating the considerable potential applications of TRF NPs in the biological thermometry field.

Novel AIEgen-Functionalized Diselenide-Crosslinked Polymer Gels as Fluorescent Probes and Drug Release Carriers

Stimuli-responsive functional gels have shown significant potential for application in biosensing and drug release systems. In this study, aggregation-induced emission luminogen (AIEgen)-functionalized, diselenide-crosslinked polymer gels were synthesized via free radical copolymerization. A series of polymer gels with different crosslink densities or tetraphenylethylene (TPE) contents were synthesized. The diselenide crosslinker in the gels could be fragmented in the presence of H2O2 or dithiothreitol (DTT) due to its redox-responsive property. Thus, the TPE-containing polymer chains were released into the aqueous solution. As a result, the aqueous solution exhibited enhanced fluorescence emission due to the strong hydrophobicity of TPE. The degradation of polymer gels and fluorescence enhancement in an aqueous solution under different H2O2 or DTT concentrations were studied. Furthermore, the polymer gels could be used as drug carriers, suggesting a visual drug release process under the action of external redox agents. The AIEgen-functionalized, diselenide-crosslinked polymer gels hold great potential in the biomedical area for biosensing and controlled drug delivery.

A simple yet effective AIE-based fluorescent nano-thermometer for temperature mapping in living cells using fluorescence lifetime imaging microscopy

We designed and synthesized a novel nano-thermometer using aggregation-induced-emission (AIE) dye as the reporter and household butter as the matrix. This temperature nanosensor showed decreased fluorescence intensities (∼2%/°C) and shorter fluorescence lifetimes (∼0.11 ns/°C) upon increasing the environmental temperature in the physiological temperature range. Such fluorescence responses were reversible and independent of the environmental pH and ionic strength. The application of these nano-thermometers in temperature sensing in living cells using fluorescence lifetime imaging microscopy (FLIM) was also demonstrated. To the best of our knowledge, this is the first example of AIE-based nano-thermometer for temperature sensing in living cells. This work also provides us with a simple and low-cost method for rapid fabrication of an effective nanosensor based on AIE mechanism.

A lysosome specific, acidic-pH activated, near-infrared Bodipy fluorescent probe for noninvasive, long-term, in vivo tumor imaging

Long-term, in vivo, fluorescent cell tracking probes are useful for understanding complex cellular processes including tissue regeneration, communication, development, invasion, and cancer metastasis. A near-infrared fluorescent, water-soluble probe is particularly important for studying these biological events and processes. Herein, a lysosome specific, near-infrared Bodipy probe with increased fluorescent intensity in the acidic, lysosome environment is reported. This Bodipy probe is packaged in a nanoparticle using DSPE-PEG₂₀₀₀. The resulting nanoparticle is intravenously delivered to a tumor xenograft, where the fluorescent Bodipy becomes useful for non-invasive, long-term, in vivo fluorescent tumor imaging for periods greater than 36 days. These long-term, in vitro and in vitro tracking data indicate that the described Bodipy nanoparticles hold great potential for monitoring biological processes.

Synthesis of π-conjugated network polymers based on triphenylamine (TPA) and tetraphenylethylene (TPE) as building blocks via direct Pd-catalyzed reactions and their application in CO2 capture and explosive detection

In this study, we report the synthesis of π-conjugated network polymers via palladium-catalyzed direct arylation polycondensation of triphenylamine (TPA) and tetraphenylethylene (TPE) with different active substrates. Moreover, six conjugated porous polymers were obtained (named as TPA-TPA-MA, TPA-PB-MA, TPA-TFB-MA, TPA-TPE-MA, TPE-PB-MA, and TPE-TFB-MA). Then, the fluorescence properties in the solid and dispersed states, the corresponding microporous structures, and the Brunauer–Emmett–Teller (BET) surface areas of all polymers were well studied. Among the obtained materials, TPA-PB-MA possessed not only largest BET surface area (686 m² g⁻¹) and largest pore volume (0.716 cm³ g⁻¹), but also the smallest pore size of 0.823 nm. These properties are very beneficial for the application of TPA-PB-MA in CO₂ storage and PA sensing. At 1 bar, TPA-PB-MA demonstrated the significant CO₂ uptake of 2.70 and 1.35 mmol g⁻¹ at 273 and 298 K, respectively. Furthermore, TPA-PB-MA was most sensitive and selective towards PA recognition. The K_SV constant was measured as 4.0 × 10⁴ M⁻¹.

In this study, we report the synthesis of π-conjugated network polymers via palladium-catalyzed direct arylation polycondensation of triphenylamine (TPA) and tetraphenylethylene (TPE) with different active substrates.

Self-Assembled Fluorescent Organic Nanomaterials for Biomedical Imaging

Fluorescent nanomaterials, self-assembled from building blocks through multiple intermolecular interactions show diversified structures and functionalities, and are potential fluorescence contrast agents/probes for high-performance biomedical imaging. Self-assembled nanomaterials exhibit high stability, long circulation time, and targeted biological distribution. This review summarizes recent advances of self-assembled nanomaterials as fluorescence contrast agents/probes for biomedical imaging. The self-assembled nanomaterials are classified into two groups, i.e., ex situ and in situ construction of self-assembled nanomaterials. The advantages of ex situ as well as in situ constructed nanomaterials for biomedical applications are discussed thoroughly. The directions of future developments for self-assembled nanomaterials are provided.

Positively Charged Hyperbranched Polymers with Tunable Fluorescence and Cell Imaging Application

Fluorescence-tunable materials are becoming increasingly attractive because of their potential applications in optics, electronics, and biomedical technology. Herein, a multicolor molecular pixel system is realized using a simple copolymerization method. Bleeding of two complementary colors from blue and yellow fluorescence segments reproduced serious multicolor fluorescence materials. Interestingly, the emission colors of the polymers can be fine-tuned in the solid state, solution phase, and in hydrogel state. More importantly, the positive fluorescent polymers exhibited cell-membrane permeable ability and were found to accumulate on the cell nucleus, exhibiting remarkable selectivity to give bright fluorescence. The DNA/RNA selectivity experiments in vitro and in vivo verified that [tris(4-(pyridin-4-yl)phenyl)amine]-[1,8-dibromooctane] has prominent selectivity to DNA over RNA inside cells.

Progress and Trends in AIE-Based Bioprobes: A Brief Overview

Luminescent bioprobes are powerful analytical means for biosensing and optical imaging. Luminogens featured with aggregation-induced emission (AIE) attributes have emerged as ideal building blocks for high-performance bioprobes. Bioprobes constructed with AIE luminogens have been identified to be a novel class of FL light-up probing tools. In contrast to conventional bioprobes based on the luminophores with aggregation-caused quenching (ACQ) effect, the AIE-based bioprobes enjoy diverse superiorities, such as lower background, higher signal-to-noise ratio and sensitivity, better accuracy, and more outstanding resistance to photobleaching. AIE-based bioprobes have been tailored for a vast variety of purposes ranging from biospecies sensing to bioimaging to theranostics (i.e., image-guided therapies). In this review, recent five years' advances in AIE-based bioprobes are briefly overviewed in a perspective distinct from other reviews, focusing on the most appealing trends and progresses in this flourishing research field. There are altogether 11 trends outlined, which have been classified into four aspects: the probe composition and form (bioconjugtes, nanoprobes), the output signal of probe (far-red/near-infrared luminescence, two/three-photon excited fluorescence, phosphorescence), the modality and functionality of probing system (dual-modality, dual/multifunctionality), the probing object and application outlet (specific organelles, cancer cells, bacteria, real samples). Typical examples of each trend are presented and specifically demonstrated. Some important prospects and challenges are pointed out as well in the hope of intriguing more interests from researchers working in diverse areas into this exciting research field.

Thermo-Responsive Fluorescent Polymers with Diverse LCSTs for Ratiometric Temperature Sensing through FRET

Temperature is a significant parameter to regulate biological reactions and functions inside cells. Sensing the intracellular temperature with a competent method is necessary to understand life science. In this work, an energy-transfer polymeric thermometer was designed for temperature sensing. The thermometer was prepared from two thermo-responsive polymers with different lower critical solution temperatures (LCSTs) of 31.1 °C and 48.6 °C, coupling with blue and red fluorescent molecules, respectively, developed for ratiometric temperature sensing based on the Förster resonance energy transfer (FRET) mechanism. The polymers were synthesized from two monomers, N-isopropylacrylamide (NIPA) and N-isopropylmethacrylamide (NIPmA), which provided different temperature responses. The fluorescent intensity of each polymer (peaked at 436 and 628 nm, respectively) decreased upon the heating of the polymer aqueous solution. While these two polymer aqueous solutions were mixed, the fluorescent intensity decrease at 436 nm and substantial fluorescence enhancement at 628 nm was observed with the increasing temperature due to FRET effect. The cell imaging of HeLa cells by these thermo-responsive polymers was explored. The difference of LCSTs resulting in ratiometric fluorescence change would have a potential impact on the various biomedical applications.

Spermine-directed supramolecular self-assembly of water-soluble AIE-active tetraphenylethylene: nanobelt, nanosheet, globular and nanotubular structures

Tetrasulfonate-tetraphenylethylene (Su-TPE) is non-emissive in water and upon addition of a good solvent such as THF (f_THF = 95%) it displays strong fluorescence emission with a quantum yield of 6.33%.

Real-time imaging of cancer cell generations and monitoring tumor growth using a nucleus-targeted red fluorescent probe

A red nucleus-targeted fluorescent probe was reported and used for tracing cancer cell generations and monitoring tumor growth.

Multiple cation-doped linear polymers toward ATP sensing and a cell imaging application

A set of multiple cation-doped linear polymers (abbreviated as OPY-1,2-BE, OPY-1,4-BB, OPY-1,8-BO, OPY-1,4-OBB) synthesized from a dipyridine derivative (OPY) and dibrominated compounds were employed as fluorescent probes for adenosine triphosphate (ATP) sensing.

Novel Hydrogen-Bonding Cross-Linking Aggregation-Induced Emission: Water as a Fluorescent "Ribbon" Detected in a Wide Range

The development of efficient sensors for detection of the water content in a wide detection range is highly desirable for balance in many industrial processes and products. Presented herein are six novel different substituted Schiff base Zn(II) complexes, which exhibit the remarkable capability to detect traces of water in a wide linear range (most can reach 0-94%, v/v), low detection limit of 0.2% (v/v), and rapid response time of 8 s in various organic solvents by virtue of an unusual water-activated hydrogen-bonding cross-linking AIE (WHCAIE) mechanism. As a proof-of-concept, the WHCAIE mechanism is explained well by single X-ray diffraction, absorption spectra, fluorescence spectra, dynamic light scattering, ¹H NMR spectra, and theoretical calculations. In addition, the molecules demonstrated their application for the detection of humidity (42-80%). These Schiff base Zn(II) complexes become one of the most powerful water sensors known due to their extraordinary sensitivity, fast response, and wide detection range for water.

BSA-coated fluorescent organic–inorganic hybrid silica nanoparticles: preparation and drug delivery

A novel BSA-coated inorganic–organic hybrid nano-material with drug delivery ability under stimulation by temperature changes is reported.

A direct crossed polymerization of triphenylamines and cyclohexanones via CC bond formation: the method and its bioimaging application

Fluorescent polymers synthesized by ACC reactions with interesting optical performances and the potential cell imaging 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.

Zwitterionic Phosphorylcholine-TPE Conjugate for pH-Responsive Drug Delivery and AIE Active Imaging

Polymeric micelles have emerged as a promising nanoplatform for cancer theranostics. Herein, we developed doxorubicin (DOX) encapsulated pH-responsive polymeric micelles for combined aggregation induced emission (AIE) imaging and chemotherapy. The novel zwitterionic copolymer poly(2-methacryloyloxyethylphosphorylcholine-co-2-(4-formylphenoxy)ethyl methacrylate) (poly(MPC-co-FPEMA)) was synthesized via RAFT polymerization and further converted to PMPC-hyd-TPE after conjugation of tetraphenylethene (TPE, a typical AIE chromophore) via acid-cleavable hydrazone bonds. The AIE activatable copolymer PMPC-hyd-TPE could self-assemble into spherical PC-hyd-TPE micelles, and DOX could be loaded through hydrophobic interactions. The zwitterionic micelles exhibited excellent physiological stability and low protein adsorption due to the stealthy phosphorylcholine (PC) shell. In addition, the cleavage of hydrophobic TPE molecules under acidic conditions could induce swelling of micelles, which was verified by size changes with time at pH 5.0. The in vitro DOX release profile also exhibited accelerated release rate with pH value decreasing from 7.4 to 5.0. Fluorescent microscopy and flow cytometry studies further demonstrated fast internalization and accumulation of drug loaded PC-hyd-TPE-DOX micelles in HepG2 cells, resulting in considerable time/dose-dependent cytotoxicity. Meanwhile, high-quality AIE imaging of PC-hyd-TPE micelles was confirmed in HepG2 cells. Notably, ex vivo imaging study exhibited efficient accumulation and drug release of PC-hyd-TPE-DOX micelles in the tumor tissue. Consequently, the multifunctional micelles with combined nonfouling surface, AIE active imaging, and pH-responsive drug delivery showed great potential as novel nanoplatforms for a new generation of cancer theranostics.