Simultaneous Increase in Brightness and Singlet Oxygen Generation of an Organic Photosensitizer by Nanocrystallization

Abstract

Efficient organic photosensitizers are attractive for cancer cell ablation in photodynamic therapy. Bright fluorescent photosensitizers are highly desirable for simultaneous imaging and therapy. However, due to fundamental competition between emission and singlet oxygen generation, design attempts to increase singlet oxygen generation almost always leads to the loss of fluorescence. Herein, it is shown for the first time that nanocrystallization enables a simultaneous and significant increase in the brightness and singlet oxygen generation of an organic photosensitizer. Spectroscopic studies show simultaneous enhancement in the visible light absorption and fluorescence after nanocrystallization. The enhanced absorption of visible light in nanocrystals is found to translate directly to the enhanced singlet oxygen production, which shows a higher ability to kill HeLa cells as compared to their amorphous counterpart.

Aggregation‐Induced Emission: New Vistas at the Aggregate Level

“…Notably, the aggregation process can also enhance the emission of PSs. Liu's group demonstrated that nanoparticles prepared by nanocrystallization increased the generation of singlet oxygen by a photosensitizer by 50 % and at the same time the fluorescence quantum yield more than doubled . The nanocrystals have been applied directly for HeLa cell ablation, and are found to be considerably more effective than their amorphous counterparts.…”

Aggregation‐enhanced theranostics: AIE sparkles in biomedical field

“…Additionally, crystallization is also regarded as an effective strategy to further elevate the fluorescence brightness and ROS generation efficiency of many AIEgens, as the packing degree of molecules increases to the maximum through crystallization, which remarkably minimizes the intramolecular motions. [ 74,75 ] Liu's group reported that the singlet oxygen ( 1 O 2 ) generation efficiency and fluorescence quantum yield (QY) of a PS could be elevated by 50% and over twofold at the same time after being fabricated into NPs through nanocrystallization method [76] . In addition, as a general and simple method to realize closer and ordered molecular packing, crystallization could also contribute to enhance the molar extinction coefficients with red‐shifted absorption maxima for some AIEgens [75] …”

Aggregationsinduzierte Emission: Einblicke auf Aggregatebene

“…Es ist dabei erwähnenswert, dass durch Aggregation auch die Emission von PS gesteigert werden kann. Die Gruppe um Liu demonstrierte, dass in Nanopartikeln, die durch Nanokristallisation erhalten wurden, die Erzeugung von Singulett‐Sauerstoff durch einen Photosensibilisator um 50 % gesteigert und zugleich auch die Quantenausbeute um mehr als das Doppelte erhöht wurde . Diese Nanokristalle wurden auch direkt zur Ablation von HeLa‐Zellen genutzt und erwiesen sich dabei als effektiver als die entsprechenden amorphen Materialien.…”