Highly emissive and stable polyphosphazene nanospheres by tetraphenylethylene for super-resolution imaging and cancer therapy

Polyphosphazene nanospheres play significant roles in biomedical applications, but their multifunctional theranostics with high brightness and stability are still urgently needed. Particularly, in situ visualization of their formation and drug delivery has not been investigated yet. Herein, by using the commercially available aggregation-induced emission (AIE)-active molecules and HCCP, the cross-linked and highly emissive polyphosphazene nanospheres are prepared (2OH-HCCP and 4OH-HCCP). It is observed that much higher fluorescence intensity in 2OH-HCCP and 4OH-HCCP can be obtained than the corresponding AIEgens in solids, where their photoluminescence quantum yields are determined to be 29.35% and 17.72%, respectively. It is noted that ultra-high photostability is also achieved in these nanospheres. Subsequently, real-time and in situ monitoring of their formation can be realized by fluorescence spectroscopy. Then, ultra-high resolution imaging by structural illumination microscopy is conducted by using 2OH-HCCP, leading to a much better imaging resolution. In addition, 2OH-HCCP-DOX is also prepared by cross-linking HCCP with 2OH-TPE and doxorubicin through a fluorescence resonance energy transfer strategy, resulting in efficient cancer therapy in vitro and in vivo. The work here provides a facile but efficient strategy to design the nanosystems with high brightness and stability, giving clues in preparation of high-performance nanomedicine in cancer therapy.