Conjugated Polymer/Photochromophore Binary Nanococktails: Bistable Photoswitching of Near‐Infrared Fluorescence for In Vivo Imaging

In fl uorescence bioimaging, switchable signals have been exploited to overcome inherent limitations of the photon-based modality, such as interferences with light absorption, scattering and autofl uorescence from biological tissues. Fluorescence switching by specifi c physiological factors, such as pH, enzyme activity or other biologically relevant chemicals, has widely been studied to provide sensing/diagnostic information. [ 1 ] Switching by photostimulation is another possible way to improve the detectability as well as spatial resolution of fl uorescence imaging. [ 2 , 3 ] In an autofl uorescence-rich in vivo environment, probes whose signal modulation is synchronized with remote photoswitching can allow the dynamic signal to be distinguished from the static autofl uorescence background, to improve the capability of signal identifi cation. The in vivo utilization of such probes, however, is still in its infancy due to their low switching contrast and stability, limited emission brightness with greater tissue interference in the visible window, and complexity in probe synthesis and delivery formulation. Up to date, some conceptual examples have been demonstrated in small transparent animals such as caenorhabditis elegans or zebrafi sh. [ 3 ]