An Intracellular H2 O2 -Responsive AIEgen for the Peroxidase-Mediated Selective Imaging and Inhibition of Inflammatory Cells

Modular Peptide Probe for Protein Analysis

The analysis and regulation of proteins are of great significance for the development of disease diagnosis and treatment. However, complicated analytical environment and complex protein structure severely limit the accuracy of their analysis results. Nowadays, ascribing to the editability and bioactivity of peptides, peptide-based probes could meet the requirements of good selectivity and high affinity to overcome the challenges. In this review, we summarize the advances in the use of modular peptide probes for proteins analysis. It focuses on how to design and optimize the structure of probes, as well as their performance. Then, the strategies and application to improve the analysis result of modular peptide probes are introduced. Finally, we also discuss current challenge and provide some ideas for the future direction for modular peptide probes, hoping to accelerate their clinical transformation.

Spatial Order of Functional Modules Enabling Diverse Intracellular Performance of Fluorescent Probes

To overcome a series of challenges in tumor therapy, modular-agent probes (MAPs) comprised of various functional modules have been proposed. Researchers have tried to optimize the MAPs by exploiting the new modules or increasing the numbers of module, while neglecting the configuration of various modules. Here, we focus on the different spatial arrangements of existing modules. By utilizing a tetraphenylethylene (TPE) derivative with stereochemical structure and dual modifiable end-group sites as small molecule scaffold, two MAPs with same modular agents (module T for enhancing the internalization of MAPs by tumor cells and module M for causing mitochondrial dysfunction) but different spatial arrangements (on the one side, TM-AIE, and two sides, T-AIE-M, of the molecule scaffold) are designed. T-AIE-M with larger RGD binding angle performed higher specificity, while TM-AIE characterizing longer α-helix structure displayed superior toxicity.

Cancer-Cell-Activated in situ Synthesis of Mitochondria-Targeting AIE Photosensitizer for Precise Photodynamic Therapy

Maximization of phototoxic damage on tumor with minimized side effect on normal tissue is essential for effective anticancer photodynamic therapy (PDT). This requires highly cancer-cell-specific or even cancer-cell-organelle-specific synthesis or delivery of efficient photosensitizers (PSs) in vitro and in vivo, which is difficult to achieve. Herein, we report a strategy of cancer-cell-activated PS synthesis, by which an efficient mitochondria-targeting photosensitizer with aggregation-induced-emission (AIE) feature can be selectively synthesized as an efficient image-guided PDT agent inside cancer cells. MOF-199, a Cu^II -based metal-organic framework, was selected as an inert carrier to load the PS precursors for efficient delivery and served as a Cu^I catalyst source for in situ click reaction to form PSs exclusively in cancer cells. The in situ synthesized PS showed mitochondria-targeting capability, allowing potent cancer-cell-specific ablation under light irradiation. The high specificity of PSs produced in cancer cells also makes it safer post-treatment.

Aggregation-Induced Emission: New Vistas at the Aggregate Level

Aggregation-induced emission (AIE) describes a photophysical phenomenon in which molecular aggregates exhibit stronger emission than the single molecules. Over the course of the last 20 years, AIE research has made great strides in material development, mechanistic study and high-tech applications. The achievements of AIE research demonstrate that molecular aggregates show many properties and functions that are absent in molecular species. In this review, we summarize the advances in the field of AIE and its related areas. We specifically focus on the new properties of materials attained by molecular aggregates beyond the microscopic molecular level. We hope this review will inspire more research into molecular ensembles at and beyond the meso level and lead to the significant progress in material and biological science.

Single AIEgen for multiple tasks: Imaging of dual organelles and evaluation of cell viability

Fully understanding the complicated interplays among various chemical species and organelles is greatly important to unravel the mystery of life. However, fluorescent probes capable of visualizing multiple targets discriminatively are severely deficient, which extremely limit the investigation on intracellular interplays among various species. Towards this end and in consideration of the unique advantages of aggregation-induced emission luminogens (AIEgens), here we rationally designed and presented a single AIEgen, named TVQE, bearing lipophilic, cationic and hydrolyzable moieties, and this AIEgen was capable of illuminating mitochondria and lipid droplets with red and blue emission, respectively. In addition, TVQE was successfully used for evaluating cell viability due to its distinct two-color emission changes tuned by esterase-mediated hydrolysis. Of particular importance is that TVQE can selectively differentiate live, early apoptotic, late apoptotic, and dead cells by confocal microscopy and quantify cell viability statistically by flow cytometry.

AIEgens/Nucleic Acid Nanostructures for Bioanalytical Applications

DNA occupies significant roles in life processes, which include encoding the sequences of proteins and accurately transferring genetic information from generation to generation. Recent discoveries have demonstrated that a variety of biological functions are correlated with DNA's conformational transitions. The non-B form has attained great attention among the diverse forms of DNA over the past several years. The main reason for this is that a large number of studies have shown that the non-B form of DNA is associated with gross deletions, inversions, duplications, translocations as well as simple repeating sequences, which therefore causes human diseases. Consequently, the conformational transition of DNA between the B-form and the non-B form is important for biology. Conventional fluorescence probes based on the conformational transitions of DNA usually need a fluorophore and a quencher group, which suffers from the complex design of the structure and tedious synthetic procedures. Moreover, conventional fluorescence probes are subject to the aggregation-caused quenching (ACQ) effect, which limits their application toward imaging and analyte detection. Fluorogens exhibiting aggregation-induced emission (AIE) have attracted tremendous attention over the past decade. By taking advantage of this unique behavior, plenty of fluorescent switch-on probes without the incorporation of fluorescent quenchers/fluorophore pairs have been widely developed as biosensors for imaging a variety of analytes. Herein, the recent progress in bioanalytical applications on the basis of aggregation-induced emission luminogens (AIEgens)/nucleic acid nanostructures are presented and discussed.

In Vivo and in Situ Activated Aggregation-Induced Emission Probes for Sensitive Tumor Imaging Using Tetraphenylethene-Functionalized Trimethincyanines-Encapsulated Liposomes

The design and exploration of fluorescent probes with high-sensitivity and low-background are essential for noninvasive optical molecular imaging. The in vivo and in situ activated aggregation-induced emission (AIE) probes were found to be ideal for achieving higher signal-to-background ratios for tumor detections. We herein developed novel tetraphenylethene-encapsulated liposomes (TPE-LPs) constructed by loading TPE-trimethincyanine into liposomes for the first time, and the probes were applied to tumor bioimaging in vivo. TPE-functionalized trimethincyanines were synthesized with a new and efficient one-pot reaction. In TPE-LPs, TPE-functionalized bicarboxylic acids benzoindole trimethinecyanine (TPE-BICOOH) fluorophores were found to be well dispersed in lipid bilayers (with non-restricted rotation) during the blood circulation, and then aggregated (with restriction of intramolecular rotation) upon liposome rupture in the tumor tissue, achieving a low-background and high-target signal for tumor imaging. The in situ activated AIE probes not only had great accumulation at the tumor site after intravenous injection in 4T1 tumor-bearing mice but also demonstrated excellent signal-to-background ratios, as well as low cytotoxicity and excellent biocompatibility. The proposed strategy is believed to be a simple and powerful tool for the sensitive detection of tumors.

Hybridized Polyoxometalate-Based Metal-Organic Framework with Ketjenblack for the Nonenzymatic Detection of H2 O2

The rational design and development of efficient and affordable enzyme-free electrocatalysts for electrochemical detection are of great significance for the large-scale applications of sensor materials, and have aroused increasing research interest. Herein, we report that a typical polyoxometalate (POM)-based metal-organic framework (NENU5) that was hybridized with ketjenblack (KB) was a highly efficient electrochemical catalyst that could be used for the highly sensitive nonenzymatic detection of H2 O2 . The composite catalyst exhibited superb electrochemical detection performance towards H2 O2 , including a broad linear range from 10-50 mm, a low detection limit of 1.03 μm, and a high sensitivity of 33.77 μA mm-1 , as well as excellent selectivity and stability. These excellent electrocatalytic properties should be attributed to the unique redox activity of the POM, the high specific surface area of the metal-organic framework (MOF), the strong conductivity of KB, and the synergistic effects of the multiple components in the composites during the electrolysis of H2 O2 . This work provides a new pathway for the exploration of nonenzymatic electrochemical sensors.