Unity Makes Strength: How Aggregation‐Induced Emission Luminogens Advance the Biomedical Field

Abstract

research fields to provide new opportunities for precise and personalized medical treatment of patients. [16][17][18][19][20][21][22][23][24][25][26][27] An ideal fluorescent agent should have low toxicity, high brightness, excellent stability, good selectivity, and versatile functionality. To date, a vast variety of synthetic fluorescent materials, including organic dyes, [28][29][30] fluorescent proteins, [31,32] inorganic quantum dots (QDs), [33,34] conjugated polymer nanoparticles (NPs), [35][36][37][38][39][40] metallic nanoclusters, [41] as well as upconversion NPs, [42][43][44] have been explored and demonstrated for biological applications.Among the above-mentioned fluorescent materials, synthetic organic dyes and dye-loaded fluorescent NPs have attracted special attention due to the good biocompatibility and easy availability. However, a considerable number of organic dyes are hydrophobic, which often form aggregation through π-π stacking in aqueous solutions and buffers even though different strategies have been applied to improve their water solubility. The serious π-π stacking interactions among dye molecules facilitate nonradiative pathways to relax the exciton energy, leading to partially or completely quenched fluorescence. This phenomenon is well known as aggregation-caused quenching (ACQ) effect, [45] which is the main obstacle of construction of highly emissive fluorescence bioprobes in complicated biological microenvironments. Although great efforts have been made from various aspects to overcome the notorious undesired ACQ effect, [46] it remains a major challenge for the significant improvement of traditional fluorescent bioprobes in biomedicine and life sciences.In 2001, Tang and co-workers discovered a novel fluorescent phenomenon that is opposite to the ACQ effect: the organic Figure 4. Confocal images of Hela cancer cells after incubation with A-D) A6-A9 (5 × 10 −6 m) for 15 min, respectively. Adapted with permission. [104]

Organic/polymer photothermal nanoagents for photoacoustic imaging and photothermal therapy in vivo

“…Based on the above results, Tang, Ding and co-workers thus put forward a concept of "intramolecular motion-induced photothermy (iMIPT)" as a new molecular guideline to develop advanced photothermal agents. Contrary to the "aggregation-induced emission" (AIE) process, which suppresses active intramolecular motion to emit bright light in the aggregates [93][94][95][96][97][98][99][100], iMIPT process favors the active excited-state intramolecular motion to generate heat in aggregates ( Fig. 9).…”

High‐Fidelity Trapping of Spatial–Temporal Mitochondria with Rational Design of Aggregation‐Induced Emission Probes

“…To attain this goal, taking the strategy of aggregation‐induced emission (AIE) is preferential to design organelle‐specific “ light‐up ” fluorescent probes . Particularly, in light of accumulating 100–1000 folds of cations in mitochondrial membrane matrix with respect to extracellular medium, the feature of AIE luminogen (AIEgen) is well suited for high‐fidelity trapping of mitochondria, which can emit strong fluorescence during the process of concentration enrichment in mitochondria .…”

An NIR‐II Fluorescence/Dual Bioluminescence Multiplexed Imaging for In Vivo Visualizing the Location, Survival, and Differentiation of Transplanted Stem Cells

“…Herein, we developed an NIR‐II fluorescence/dual bioluminescence multiplexed imaging method spectrally ranging from 400 to 1700 nm to in situ track the location, survival, and osteogenic differentiation of transplanted human mesenchymal stem cells (hMSCs), which integrates the advantages of exogenous fluorescence imaging in the second near‐infrared window (NIR‐II) and endogenous bioluminescence imaging (BLI). Due to the deep penetration and high spatiotemporal resolution of the NIR‐II imaging, the NIR‐II imaging can be an ideal method for tracking the dynamic location of transplanted hMSCs . With the powerful capability of BLI to specifically report the viability and cellular processes of cells, the BLI is a promising method for imaging the survival and osteogenic differentiation of transplanted hMSCs.…”