Aggregation-induced Emission Probe Research Articles

Paper-based fluorescent materials containing on-demand nanostructured brain-cells-inspired AIE self-assembles for real-time visual monitoring of seafood spoilage

Biogenic amines containing NH3 are important indicators for conducting full-scale appraisal of food spoilage and disease diagnosis. However, the currently-used detection methods of NH3 have several limitations such as time-consuming high cost, and inability to provide visual real-time monitoring. Therefore, researchers have attempted to explore strategies for quantitative real-time monitoring of NH3 for food spoilage has attracted widespread attentions. Herein, we developed sustainable, fast response, hypersensitized, user-friendly and molecular-level light-emitting biomass-based materials (AFP-FP) containing on-demand nanostructured brain-cells-inspired aggregation-induced-emission (AIE) self-assembles for real-time visual monitoring of seafood spoilage. The 2-hydroxy-5-methyl-isophthalaldehyde-based AIE probe (AFP) was synthesized using a simple “one-step” route. AFP-FP exhibited high selectivity, sensitivity, repeatable and quantitative recognition (y = 7.292×103x + 7.621×104, R = 0.990) of NH3 with a low detection limit (246 ppb) and fast response (<1 s). Furthermore, we integrated AFP-FP into a user-friendly smartphone color recognition app, enabling its practical application in visual, real-time daylight monitoring of food spoilage.

A near-infrared aggregation-induced emission probe for imaging lipid droplet and in vivo visualization of diabetes-related viscosity variations

As a pivotal parameter of microenvironment, viscosity is closely related to many diseases and dysfunction in vivo. Lipid droplets, as organelles that store and metabolize lipids, are involved in various physiological processes related to metabolism in cells. Diabetes is one of the metabolic diseases that may lead to dysfunction of organs, which is associated with abnormal viscosity changes. It is of great significance for the study of related diseases to clarify the relationship between viscosity variations in vivo and monitor the changes of lipid droplets. Here, a near-infrared fluorescent probe DPX ((E)− 6-(dimethylamino)− 4-(4-(diphenylamino)benzylidene)− 9-methyl-1,2,3,4-tetrahydroxanthylium) with AIE characteristics was designed, which shows an “off-on” fluorescence response to viscosity based on twisting intramolecular charge transfer (TICT) mechanism. The probe DPX features excellent mitochondria and lipid droplets targeting, and sensitively monitor accumulation of LDs induced by oleic acid and mitochondrial viscosity variations in HeLa cells. More importantly, DPX has been successfully applied to visualize viscosity changes of diabetic liver injury in vivo, which may be benefit for development of diabetes related clinical research.

A colormetric and ratiometric AIE probe for imaging endogenous and exogenous hypochlorite

Herein, we designed a potent ClO− probe named ETMC, which exhibited aggregation-induced emission (AIE) characteristic in solid state and water/EtOH binary solvent. Probe ETMC exhibited an colormetric from yellow to blue and ratiometric response to ClO− with high selectivity and sensitivity, and a low detection limit of 3.66 × 10−7 M. Moreover, probe ETMC could be applied to visibly and quantitatively detect the different concentraction of ClO− in test paper. Importantly, probe ETMC could effectively detect endogenous and exogenous ClO− in living A549 cells by an outstanding ratio signal change. Also, the sensing mechanism of probe ETMC for ClO− was confirmed by FT-IR, 1H NMR, HRMS, DLS, TEM and DFT calculation.

Aggregation-Induced Near-Infrared Emission and Electrochemiluminescence of an Iridium(III) Complex for Ampicillin Sodium Sensing.

A new iridium(III) complex was synthesized and characterized. Its photophysical properties and aggregation-induced emission and electrochemiluminescence in the near-infrared range were studied. The large conjugated cyclometallic ligand 1,2-phenylbenzoquinoline (pbq) was selected to form the Ir-C bond with the metal iridium(III) center and provide near-infrared emission of the complex. The auxiliary ligand 4,4'-diamino-2,2'-bipyridine (dabpy) can form hydrogen bonds, which was beneficial for the generation of aggregation-induced emission. The complex was aggregated into small spherical nanoparticles in 80% water and fascinating nanorings in 90% water. The sensing of ampicillin sodium (AMP) antibiotic by the iridium(III) complex were also investigated by photoluminescent and electrochemiluminescent methods. The complex showed a good selectivity toward AMP antibiotic compared to sodium phenylacetate and other eight antibiotics. The detection limits for AMP antibiotic was 0.76 μg/mL. This work provided a new strategy for the design of iridium(III) complex-based aggregation-induced emission and electrochemiluminescence probes for the sensing application.

Viscosity-responsive NIR-II fluorescent probe with aggregation-induced emission features for early diagnosis of liver injury

As the primary organ for drug metabolism and detoxification, the liver is susceptible to damage and seriously impaired function. In situ diagnosing and real-time monitoring of liver damage are thus of great significance but remain limited owing to the lack of reliable in vivo visualization protocols with minimal invasion. Herein, we reported for the first time an aggregation-induced emission (AIE) probe, namely DPXBI, emitting light in the second near-infrared window (NIR-II) for early diagnosis liver injury. DPXBI featured by strong intramolecular rotations, excellent aqueous solubility and robust chemical stability, is powerfully sensitive to viscosity alteration affording rapid response and high selectivity, through NIR-Ⅱ fluorescence intensity changes. The prominent viscosity-responsive performance enables DPXBI to accurately monitor both drug-induced liver injury (DILI) and hepatic ischemia-reperfusion injury (HIRI) with excellent image contrast to the background. By using the presented strategy, the detection of liver injury in mouse model can be achieved at least several hours earlier than typical clinical assays. Moreover, DPXBI is able to dynamically track the liver improvement process in vivo in the case of DILI when the hepatotoxicity is alleviated by using hepatoprotective medication. All these results demonstrate that DPXBI is a promising probe for investigating viscosity-associated pathological and physiological processes.

Improving the sensitivity of protein fluorescent probes by molecular structural fine-tuning based on aggregation-induced emission mechanism

Three 1,3-butadiene derivatives were synthesized to investigate the effect of small structural changes on the detection sensitivity with bovine serum albumin (BSA). The compound 2-MFDNa with methyl group added to the 5-furan ring showed a 132-fold fluorescent enhancement response to BSA, while 3-FDNa with no methyl group on the 5-furan ring showed a 52-fold fluorescent enhancement response to BSA. Compared with the detection limits of 3-FDNa 0.19 μg/mL and 2-FDNa 0.17 μg/mL, that of 2-MFDNa was reduced to 0.01 μg/mL. 2-MFDNa achieved a higher selective and sensitive detection to BSA. Molecular docking analysis revealed that the improved detection sensitivity was due to the enhanced restriction of intramolecular motion, with more C–H···π interactions limiting the rotation of the rotor of the probe molecule, leading to enhanced fluorescence. These results provide a simple and effective strategy for the molecular design of aggregation-induced emission probes for the detection of proteins with higher sensitivity.

Direct self-assembly of AIE-active tetraphenylethene derivative with cucurbit[7]uril as a fluorescence probe for metformin detection

A fast, simple, sensitive and stable “turn-on” fluorescent probe method by the self-assembly of aggregation-induced emission luminogen 1,1,2,2-tetra(biphenyl-4-yl)ethene and cucurbit[7]uril was developed for selective determination of metformin. Simultaneously the host–guest complex can improve the poor water solubility of traditional aggregation-induced emission material. The response mechanism of the supramolecular probe to metformin was studied by UV–visible absorption spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, dynamic light scattering technology, scanning electron microscope. The proposed method showed good sensitivity and accuracy for the detection of metformin. The relative fluorescence intensity was linearly correlated with the concentration of metformin in the range of 5 to 100 µM, with a detection limit of 1.5 µM. In addition, the aggregation-induced emission probe was successfully utilized to determine the metformin concentration in serum samples, and the recovery ranged from 90.80% to 104.0% with satisfactory results. Therefore, the established fluorescence assay provides a promising pathway for metformin analysis in biomedicine.

Interactions of Amino Group Functionalized Tetraphenylvinyl and DNA: A Label-Free “On-Off-On” Fluorescent Aptamer Sensor toward Ampicillin

As a type of aggregation-induced emission (AIE) fluorescent probe, tetraphenylvinyl (TPE) or its derivatives are widely used in chemical imaging, biosensing and medical diagnosis. However, most studies have focused on molecular modification and functionalization of AIE to enhance the fluorescence emission intensity. There are few studies on the interaction between aggregation-induced emission luminogens (AIEgens) and nucleic acids, which was investigated in this paper. Experimental results showed the formation of a complex of AIE/DNA, leading to the quenching of the fluorescence of AIE molecules. Fluorescent test experiments with different temperatures proved that the quenching type was static quenching. The quenching constants, binding constants and thermodynamic parameters demonstrated that electrostatic and hydrophobic interactions promoted the binding process. Then, a label-free "on-off-on" fluorescent aptamer sensor for the detection of ampicillin (AMP) was constructed based on the interaction between the AIE probe and the aptamer of AMP. Linear range of the sensor is 0.2-10 nM with a limit of detection 0.06 nM. This fluorescent sensor was applied to detect AMP in real samples.

An Alkaline Phosphatase-Responsive Aggregation-Induced Emission Photosensitizer for Selective Imaging and Photodynamic Therapy of Cancer Cells.

Fluorescence-guided photodynamic therapy (PDT) has been considered as an emerging strategy for precise cancer treatment by making use of photosensitizers (PSs) with reactive oxygen species (ROS) generation. Some efficient PSs have been reported in recent years, but multifunctional PSs that are responsive to cancer-specific biomarkers are rarely reported. In this study, we introduced a phosphate group as a cancer-specific biomarker of alkaline phosphatase (ALP) on a PS with the features of aggregation-induced emission (AIE) for cancer cell imaging and therapy. In cancer cells with high ALP expression, the phosphate group on the AIE probe is selectively hydrolyzed by ALP. Consequently, the hydrophobic probe residue is aggregated in aqueous media and gives a "turn on" fluorescent response. Moreover, fluorescence-guided PDT was realized by the aggregates of probe residue with strong ROS generation efficiency under white light irradiation. Overall, this work presents a strategy of applying ALP-responsive AIE PS for specific imaging cancer cells and succeeding with specific PDT upon the cancer biomarker stimulated responsive reactions.

A versatile AIE probe with mitochondria targeting for dual-channel detection of superoxide anion and viscosity

Abnormal viscosity and excessive superoxide anion (O2•-) levels in living cells often cause a series of biological dysfunction and oxidative damage. However, a great challenge remains in quickly and conveniently detecting the viscosity and O2•- levels in living cells. Herein, we fabricated a versatile aggregation-induced emission (AIE) probe with mitochondria targeting, DTPB, for dual-imaging of viscosity and O2•- level in living cells with two different channels. The obtained DTPB contained a diphenyl phosphinic acid unit responsive to O2•-, a unit with twisted intramolecular charge trans (TICT) function responsive to viscosity, and a pyridine cation unit with mitochondria targeting. The results showed that DTPB exhibited a remarkable response to viscosity with a near-infrared emission peak at 671 nm and was highly sensitive to O2•- levels with an emission peak at 587 nm. The dual-channel probe has great application prospects in the visual diagnosis of cancer and related diseases.

Quinoline-Malononitrile-Based Aggregation-Induced Emission Probe for Monoamine Oxidase Detection in Living Cells.

A quinoline-malononitrile (QM)-based aggregation-induced emission probe was developed to detect MAOs in cells through an enzymatic reaction followed by β-elimination. After being incubated at 37 °C, QM-NH2 responded to the MAO enzymes with great specificity and within just 5 min. This 5 min responsive mechanism was fast, with the limit of detection (LOD) at 5.49 and 4.76 µg mL-1 for MAO-A and MAO-B, respectively. Moreover, QM-NH2 displayed high enzyme specificity even in the presence of high concentrations of biological interferences, such as oxidizing and reducing agents, biothiols, amino acids, and glucose. Furthermore, QM-NH2 demonstrated biocompatibility as the cells retained more than 70% viability when exposed to QM-NH2 at concentrations of up to 20 µM. As a result, QM-NH2 was used to detect MAO-A and MAO-B in SH-SY5Y and HepG2 cells, respectively. After 1h incubation with QM-NH2, the cells exhibited enhanced fluorescence by about 20-fold. Moreover, the signal from cells was reduced when MAO inhibitors were applied prior to incubating with QM-NH2. Therefore, our research recommends using a QM probe as a generic method for producing recognition moieties for fluorogenic enzyme probes.

A ratiometric hypochlorite-specific nanoprobe constructed by rationally designed AIE luminogen for fluorescence imaging of alcoholic liver disease

There is a lack of effective and friendly diagnostic technique for alcoholic liver disease (ALD). Fluorescence imaging, which has been widely applied in disease diagnostic ascribed to the merits of high sensitivity, excellent temporal resolution and minimal invasiveness, is probably a good candidate for ALD studying. Herein, by precise molecular optimization, an aggregation-induced emission (AIE) probe of TCPQ was designed to show bright near-infrared (NIR) emission centered at 680 nm, and selective response towards ClO− for ALD diagnosis. In comparison with PNQ, the started fluorophore constructed with ClO− oxidizable donor phenothiazine (PZ) and AIE active acceptor quinoline-malononitrile (QM), the emission wavelength and fluorescence quantum yield of TCPQ were 63 nm red-shifted and 2.3-fold enhanced after structural optimization. Once exposed to ClO−, the S atom in PZ donor of TCPQ could be oxidized to sulfoxide, leading to blue-shifted emission, which made TCPQ be suitable for ratiometirc imaging with high accuracy, while the such weak emissions of the other probes here in presence of ClO− made the ratiometric imaging impossible. After forming nanoparticles (NPs) with amphiphilic F-127, TCPQ NPs have successfully imaged the exogenous and endogenous ClO− fluctuations through the ratio between brightness of green channel and red channel, and have been further utilized to quantitatively evaluate the ClO− levels in four types of cells. The possibility of ClO− as a biomarker for ALD was confirmed in the cellular ALD model. Subsequently, TCPQ NPs were further applied in ALD diagnosis and pharmacodynamic evaluation of an anti-ALD drug in the mouse model.

Mitochondria Targeted AIE Probes for Cancer Phototherapy.

In recent years, mitochondrion (powerhouse of the cells) gained lots of interest as one of the unorthodox targets for futuristic cancer therapy. As a result, novel small molecules were developed to damage and image mitochondria in cancer models. In this context, aggregation-induced emission probes (AIEgens) received immense attention due to their applications in mitochondria-targeted biosensing, imaging, and biomedical theranostics. On the other hand, phototherapy (photodynamic and photothermal) has emerged as a powerful alternative to manage cancer due to its less invasive nature. However, merging these two areas to engineer mitochondria-targeted phototherapeutic probes for cancer diagnosis and treatment has remained a major challenge. In this mini-review, we will outline the development of novel mitochondria-targeted small molecule AIEgens as imaging agents and photosensitizers for photodynamic therapy along with dual photodymanic-phototheramal therapy and chemo-photodynamic therapy. We will also highlight the current challenges in developing mitochondria-targeted photothermal therapy probes for future biomedical theranostic applications to manage cancer.

Nanoarchitectonics of the aggregation-induced emission luminescent molecule Tetraphenylethylene-COOH (TPE-COOH): Fluorescence imaging of targeted cancer microsphere cells

Cancer microspheres are an ideal cellular model for studying cancer stem cells. However, the lack of effective and rapid fluorescent imaging reagents for cancer microspheres has severely hampered cytological studies associated with cancer microspheres. Here, we have identified an aggregation-induced emission (AIE) probe, TPE-COOH, to bind to a targeting cyclic heptapeptide molecule to form a new TPE-Peptide probe. This probe has been employed for fluorescence imaging of normal, cancer and cancer microsphere cells. A novel analogue of TPAPy-1 was synthesized to verify the cell-specific targeting. For the first time, the fluorescence imaging of cancer microspheres was achieved and microspheres were imaged due to changes in viscosity, thereby providing a means to visualize and identify cancer microspheres.

Real-time tracking of endogenous CYP2J2 by red-emitting aggregation-induced emission probe with large Stokes shift

The abnormal expression of cytochrome P450 2J2 (CYP2J2) is closely related to the proliferation of human cancer cells. In this study, a red-emitting probe with an aggregation-induced emission (AIE) effect for the quantification of CYP2J2 was developed by modifying the typical AIE fluorescent group tetraphenylethylene (TPE) through two-step synthesis. Upon addition of CYP2J2, the probe underwent O-demethylation and spontaneously 1,6-elimination reactions of p-hydroxybenzyl that allowed it to alter its photophysical properties, thus realizing light-up detection of CYP2J2 with extremely large Stokes shift (236 nm), excellent sensitivity and selectivity, low detection limit (1.09 nM). Moreover, this new AIE-active probe with good biocompatibility was admirably employed to tracking endogenous CYP2J2 in living cells.

A novel red-emitting aggregation-induced emission probe for determination of β-glucosidase activity

β-Glucosidase (β-Glu) is a ubiquitous enzyme which has multiple roles in medical diagnosis, food production, agriculture, etc. Existing β-Glu assays have limitations such as complex operation, long running time, and high background noise. Here we report a red-emissive probe TBPG for measuring the activity of β-Glu. The probe was synthesized through conjugating a β-Glu targeting glucoside to an aggregation-induced emission (AIE) fluorophore. In the presence of β-Glu, TBPG was hydrolyzed and exhibited a fluorescence turn-on process. The detection conditions including time, temperature, pH value, buffer, and probe concentration were optimized systematically. Afterwards, fluorescence titration was conducted showing an excellent linearity (R2 = 0.998), a wide linear dynamic range (0–5.0 U/mL), and a limit of detection as low as 0.6 U/L. The detection specificity and ion interference were evaluated by adding various biological species and ions to probe without or with β-Glu. Next, we demonstrate the applicability of probe TBPG in determining the β-Glu activity in living cells using confocal microscopy and flow cytometry. Finally, this newly established assay was applied to real soil samples. Comparable results were obtained as the commercial assay, manifesting its great potential in soil enzyme analysis.

De novo design of a novel AIE fluorescent probe tailored to autophagy visualization via pH manipulation

BackgroundMacroautophagy is an essential cellular self-protection mechanism, and defective autophagy has been considered to contribute to a variety of diseases. During the process, cytoplasmic components are transported via autophagosomes to acidic lysosomes for metabolism and recycling, which represents application niches for lysosome-targeted fluorescent probes. Additionally, in view of the complexity of the autophagy pathway, it entails more stringent requirements for probes suitable for monitoring autophagy. Meanwhile, aggregation-induced emission (AIE) fluorescent probes have been impressively demonstrated in the biomedical field, which bring fascinating possibilities to the autophagy visualization.MethodsWe reported a generalizable de novo design of a novel pH-sensitive AIE probe ASMP-AP tailored to lysosome targeting for the interpretation of autophagy. Firstly, the theoretical calculation was carried out followed by the investigation of optical properties. Then, the performance of ASMP-AP in visualizing autophagy was corroborated by starvation or drugs treatments. Furthermore, the capability of ASMP-AP to monitor autophagy was demonstrated in ex vivo liver tissue and zebrafish in vivo.ResultsASMP-AP displays a large stokes shift, great cell permeability and good biocompatibility. More importantly, ASMP-AP enables a good linear response to pH, which derives from the fact that its aggregation state can be manipulated by the acidity. It was successfully applied for imaging autophagy in living cells and was proved capable of monitoring mitophagy. Moreover, this novel molecular tool was validated by ex vivo visualization of activated autophagy in drug-induced liver injury model. Interestingly, it provided a meaningful pharmacological insight that the melanin inhibitor 1-phenyl-2-thiourea (PTU)-induced autophagy was clearly presented in wild-type zebrafish.ConclusionsASMP-AP offers a simple yet effective tool for studying lysosome and autophagy. This is the first instance to visualize autophagy in zebrafish using a small-molecule probe with AIE characters, accurate lysosome targeting and simultaneous pH sensitivity. Ultimately, this novel fluorescent system has great potential for in vivo translation to fuel autophagy research.Graphical

Nanospheres of Near-Infrared Aggregation-Induced Emission Probes to Target Mitochondria to Ablate Tumors with Reactive Oxygen Species Generation under Hypoxia

Severe aggregation-caused quenching and the lack of special organelle targeting in conventional photosensitizers (PSs) have limited their advantages in terms of their accurate spatial–temporal control and noninvasive features. Furthermore, severe tumor hypoxia equally diminished the effectiveness of treatment. Herein, a series of aggregation-induced emission (AIE) PSs with precise targeting of organelles are synthesized by simply regulating the molecular structure. The rotation of the donor in the molecule was optimized by altering the tail chain of the triphenylamine derivative, which inhibited nonradiative internal conversion and promoted intersystem crossing to facilitate the free radical generation, and the production efficiency of the type I reactive oxygen species exceeds that of the commercial indicator rose bengal (3-fold). The optimal AIE PS named BETTP can specifically target mitochondria and recognize cancer cells. Simultaneously, live/dead cell costaining assays and flow cytometry validated that BETTP nanoparticles (NPs) have the ability to efficaciously ablate cancer cells in hypoxic conditions after encapsulating BETTP into carriers as nanoparticles. In addition, BETTP NPs also manifest superior performance during near-infrared imaging-guided type I photodynamic therapy in solid tumors. Such BETTP NPs demonstrate the critical feasibility of achieving precise delivery of drugs and targeting of organelles for precise therapy in hypoxic environments, providing a reliable reference for tumor hypoxia challenges.

Enrichment of Aggregation-Induced Emission Aggregates Using Acoustic Streaming Tweezers in Microfluidics for Trace Human Serum Albumin Detection.

Aggregation-dependent brightness (ADB) indirectly limits the in vitro performance of a pure aggregation-induced emission (AIE) probe in many ways; thus, controlling the aggregation state of the AIE probe is helpful for detecting an object of interest. Many studies are focused on the molecule design of the AIE probes, while less efforts have been made for the control of the aggregation of the AIEs. Here, an acoustic streaming tweezer (AST) generated using a gigahertz bulk acoustic wave resonator was applied to manipulate the aggregation status of the AIE probe and further enhance their performance for human serum albumin (HSA) detection. As the trapping size of the AST matches the working size of the AIE probe, the streaming can enrich and accumulate AIE nanoparticles, which then further trigger larger aggregates. Due to the ADB effect, the fluorescence intensity strongly increased, and thus, the detection limit of HSA was reduced to 0.5 μg/mL, which is low enough for kidney disease detection. Such an AST-assisted ADB strategy is potentially applicable to other AIE probes and can work as a portable choice for the biomedical detection.

Novel AIE Probe for In Situ Imaging of Protein Sulfonation to Assess Cigarette Smoke-Induced Inflammatory Damage.

Cysteine sulfonic acid, a product of protein oxidative damage, is an important sign by which the body and cells sense oxidative stress. Cigarette smoke (CS) can trigger inflammatory reactions in humans that lead to higher levels of oxidative stress and reactive oxygen species (ROS) in the body. Available evidence indicates a possible relationship between protein oxidative damage and cigarette smoke, which is poorly understood due to the limitations of analytical techniques. Herein, we developed a donor-acceptor structured aggregation-induced emission (AIE) fluorescence probe H-1, which exhibited excellent optical properties for the highly sensitive and specific detection of sulfonic acid biomacromolecules. The probe could be easily synthesized by click chemistry conjugating triazole heterocycles onto a triphenylamine fluorophore, followed by a cationization reaction. Due to low cytotoxity, the probe was successfully applied for in situ imaging of intracellular protein sulfonation, achieving visualization of protein sulfonation in cigarette smoke stimulation-induced inflammatory RAW264.7 cell models. Moreover, an immunofluorescence study of the aorta and lung revealed that significant blue fluorescence signals could be observed only in CS-stimulated vascular. It indicated that CS-stimulated vascular sulfonation injury can be monitored using H-1. This study will provide an efficient method for revealing CS-induced oxidative damage-relevant diseases.