Recent advances in super-resolution optical imaging based on aggregation-induced emission.

Super-resolution imaging has rapidly emerged as an optical microscopy technique, offering advantages of high optical resolution over the past two decades; achieving improved imaging resolution requires significant efforts in developing super-resolution imaging agents characterized by high brightness, high contrast and high sensitivity to fluorescence switching. Apart from technical requirements in optical systems and algorithms, super-resolution imaging relies on fluorescent dyes with special photophysical or photochemical properties. The concept of aggregation-induced emission (AIE) was proposed in 2001, coinciding with unprecedented advancements and innovations in super-resolution imaging technology. AIE probes offer many advantages, including high brightness in the aggregated state, low background signal, a larger Stokes shift, ultra-high photostability, and excellent biocompatibility, making them highly promising for applications in super-resolution imaging. In this review, we summarize the progress in implementation methods and provide insights into the mechanism of AIE-based super-resolution imaging, including fluorescence switching resulting from photochemically-converted aggregation-induced emission, electrostatically controlled aggregation-induced emission and specific binding-regulated aggregation-induced emission. Particularly, the aggregation-induced emission principle has been proposed to achieve spontaneous fluorescence switching, expanding the selection and application scenarios of super-resolution imaging probes. By combining the aggregation-induced emission principle and specific molecular design, we offer some comprehensive insights to facilitate the applications of AIEgens (AIE-active molecules) in super-resolution imaging.

Cationic Conjugated Polyelectrolytes with Aggregation-Induced Ratiometric Fluorescence.

The molecular diversity of aggregation-induced emission remains a challenge due to the limitation of conventional synthesis methods. Here, a series of novel neutral and cationic conjugated polymers composed of various ratios of tetraarylethylene (TAE) containing a bridged oxygen (O) and fluorene (F) units is designed and synthesized via the geminal cross-coupling (GCC) of 1,1-dibromoolefins. The incorporation of TAE segments into the conjugated backbone of polyfluorene produces pronounced aggregation-induced ratiometric fluorescence, i.e., aggregation-induced emission (AIE) at 520-600 nm and grows synergistically with aggregations-caused quenching (ACQ) at 400-450 nm. The content of fluorene unit in the polymer backbones determines the intensity of the initial fluorescence in the blue light region. The huge distinction (about 150 nm) in dual emission wavelengths caused by the environment change makes these conjugated polyelectrolytes particularly suitable for ratiometric fluorescence sensing. Based on electrostatic interaction mechanism, the gradual addition of heparin into the cationic conjugated polymers aqueous solutions can induce dual-color fluorescence changes with a detection limit of 9 × 10-9 m. This work exhibits the great facility of using GCC reaction to synthesis the conjugated TAE polymers with superior AIE properties and special functions.