Promising Applications of AIEgens in Animal Models

Abstract

organisms cannot be achieved from these static findings. Therefore, gaining in-depth insights into biological and physiological functions at the in vivo level is of great significance, and various imaging techniques have been explored for this purpose. [1] In addition to the clinically available magnetic resonance imaging (MRI), ultrasonic imaging, computed tomography (CT), positron emission tomography (PET), and single-photon emission computed tomography, fluorescence imaging (another distinct type of optical imaging [1c] from bioluminescence imaging [2] ) has attracted increasing attention, owing to its advantages of high temporal-spatial resolution and sensitivity, noninvasive, and real-time applications, and the ability to provide dynamic information for basic research and (pre-)clinical settings at cellular and subcellular levels. [3] Fluorescent probes or contrast agents are essential for fluorescence imaging. Compared with fluorescent proteins, [4] inorganic nanoparticles (NPs), [5] such as quantum dots, [6] upconversion NPs, [7] and metallic NPs, [8] and organic dyes [9] (e.g., U.S. Food and Drug Administration (FDA)-approved 5-ALA, indocyanine green (ICG), and methylene blue), organic NPs [10] have obvious advantages, such as easy preparation and good biocompatibility. However, many organic NPs show weak fluorescence because they are made with conventional organic dyes, which suffer from the aggregation-caused quenching (ACQ) effect, i.e., their fluorescence is partially or completely quenched in the aggregated state.The advent of the aggregation-induced emission (AIE) concept offers a new strategy to deal with ACQ. [11] AIE refers to the interesting photophysical phenomenon that luminogens are weakly fluorescent or nonfluorescent in solution but show greatly enhanced emission in the aggregated state, primarily because of restricted intramolecular motion. [12] The past 19 years have witnessed spectacular advances of AIEgens, [13] due to their advantages of structural variety, easy functionalization, strong luminescence, large Stokes shift, high photobleaching-resistance, and so on. In particular, various AIE bioprobes have been designed: [14] (i) water-soluble AIEgens, which are comprised of a hydrophobic AIE core and hydrophilic units (e.g., ionic groups, peptides, carbohydrates, DNA, aptamers, antibodies, and poly(ethylene glycol) (PEG)); (ii) bare AIEgen dots (nanoaggregates); iii) AIEgen/biopolymer dots, which can be obtained by loading AIEgens onto biopolymer matrixes covalently (e.g., chitosan, dextran, and starch) or noncovalently (e.g., bovine serum albumin, human serum albumin (HSA), and fetal bovine serum (FBS)); (iv)In vivo investigations using small animal models are of great significance for the comprehensive understanding of biological and physiological functions-seeing is believing. Fluorescence imaging can provide real-time and dynamic information of living systems. During the past few years, aggregation-induced emission luminogens (AIEgens) are widely and rapidly developed for biolog...

Recent advances in stimuli‐responsive theranostic systems with aggregation‐induced emission characteristics

“…[ 13 ] Physical encapsulating or covalent conjugating fluorescent agents is a straight strategy to construct fluorescent imaging‐guided therapeutic systems. [ 14 ] These systems offer an opportunity to real‐time, in situ, and noninvasive monitor biological processes in cells or organisms, such as tracking drug release, tracing the processes of translocation, monitoring the excretion of therapeutic agents, and predicting treatment responses. [ 15–17 ] However, conventional organic fluorescent molecules may suffer from obvious photobleaching and severe background interference.…”

Aggregation‐enhanced theranostics: AIE sparkles in biomedical field

“…[112] On basis of this fact, several ROS-responsive turn-on systems based on AIEgens have been developed for lesion-specific theranostics. [20] Abnormal level of H 2 O 2 production has proven to be closely associated with inflammation, neurodegeneration disease, diabetes, and cancer. Xia et al developed a H 2 O 2responsive theranostic turn-on probe (TT) to implement detection and treatment methods for inflammatory cells (Figure 11).…”

“…It has been reported that the expression levels of ROS, such as hydrogen peroxide (H 2 O 2 ), hydroxyl radical ( • OH), superoxide radical ( • O 2− ), hypochlorous acid (HOCl), 1 O 2 and peroxynitrite (ONOO − ), are usually much higher in pathological cells or tissues [112] . On basis of this fact, several ROS‐responsive turn‐on systems based on AIEgens have been developed for lesion‐specific theranostics [20] …”

Gathering brings strength: How organic aggregates boost disease phototheranostics

“…AIEgens have been used in many areas including optoelectronic devices, process and environment monitoring, chemical sensing, and biological imaging 58–65 . Thanks to the intrinsic merits of large Stokes shift, high brightness, good stability and biocompatibility, and turn‐on property from solution to aggregate, AIEgens have also shown great promise in the field of biomedical applications 66–73 …”