Aggregation-Induced Emission (AIE) Dots: Emerging Theranostic Nanolights

Abstract

Theranostic nanolights refer to luminescent nanoparticles possessing both imaging and therapeutic functions. Their shape, size, surface functions, and optical properties can be precisely manipulated through integrated efforts of chemistry, materials, and nanotechnology for customized applications. When localized photons are used to activate both imaging and therapeutic functions such as photodynamic or photothermal therapy, these theranostic nanolights increase treatment efficacy with minimized damage to surrounding healthy tissues, which represents a promising noninvasive nanomedicine as compared to conventional theranostic approaches. As one of the most promising theranostic nanolights, organic dots with aggregation-induced emission (AIE dots) are biocompatible nanoparticles with a dense core of AIE fluorogens (AIEgens) and protective shells, whose sizes are in the range of a few to tens of nanometers. Different from conventional fluorophores that suffer from aggregation-caused quenching (ACQ) due to π-π stacking interaction in the aggregate state, AIEgens emit strongly as nanoaggregates due to the restriction of intramolecular motions. Through precise molecular engineering, AIEgens could also be designed to show efficient photosensitizing or photothermal abilities in the aggregate state. Different from ACQ dyes, AIEgens allow high loading in nanoparticles without compromised performance, which makes them the ideal cores for theranostic nanolights to offer high brightness for imaging and strong photoactivities for theranostic applications. In this Account, we summarize the recent advance of AIE dots and highlight their great potential as theranostic nanolights in biomedical applications. Starting from the design of AIEgens, the fabrication of AIE dots and their bioimaging applications are discussed. The exceptional advantages of superbrightness, high resistance to photobleaching, lack of emission intermittency, and excellent biocompatibility have made them reliable cross platform contrast agents for different imaging techniques such as confocal microscopy, multiphoton fluorescence microscopy, super-resolution nanoscopy, and light-sheet ultramicroscopy, which have been successfully applied for cell tracking, vascular disease diagnosis, and image-guided surgery. The integration of therapeutic functions with customized AIEgens has further empowered AIE dots as an excellent theranostic platform for image-guided phototherapy. Of particular interest is AIE photosensitizer dots, which simultaneously show bright fluorescence and high photosensitization, yielding superior performance to commercial photosensitizer nanoparticles in image-guided therapy. Further development in multiphoton excited photodynamic therapy has offered precise treatment with up to 5 μm resolution at 200 μm depth, while chemiexcited photodynamic therapy has completely eliminated the limitation of penetration depth to realize power-free imaging and therapy. With this Account, we hope to stimulate more collaborative research interests from different...

Selective Fluorescence Turn‐On Sensing of Phosphate Anion in Water by Tetraphenylethylene Dimethylformamidine

“…Some of them show valuable application prospect in monitoring, analysis, imaging of ions . However, research work on anion sensors based on AIE effect was relatively little.…”

Aggregation‐Induced Emission Properties of Copper Iodide Clusters

“…In recenty ears, the great development of AIE compounds is relatedtomultiple potential applications, including luminescent probes for biomedical imaging and sensing applications, which are under intensive development. [9][10][11][12][13][14][15][16][17][18] Because of their twisted conformations, AIE-active organic molecules usually aggregate into al oosely( defective) packed solid state that facilitates their transformation between differ-ent molecular arrangements. This characteristicc onfers an enhanced sensitivity to externals timuli and, in particular, to mechanical forces onto thesec ompounds.…”

“Turn‐On” Activatable AIE Dots for Tumor Hypoxia Imaging

“…For example, the tightly packed AIEgens in the core of AIE nanoparticles yields high fluorescence brightness, which can be 10–40 times brighter than that of quantum dots . Additionally, AIE aggregates show an excellently linear concentration‐dependent increase in brightness and high resistance to photobleaching . Moreover, due to the large two‐photon absorption cross‐sections, AIE aggregates are especially suitable for two‐photon fluorescence imaging .…”

“…Therefore, AIE fluorogens have recently become appealing fluorescence agents for bioimaging. Among them, AIE dots are nanoparticles with an AIE fluorogen (AIEgens) core and biocompatible materials as the shell . Due to the high brightness and biocompatibility, the AIE dots have been used with great success in bioimaging.…”