Far-Red/Near-Infrared Fluorescent Bioprobes Based on Biocompatible Nanoparticles with Aggregation-Induced Emission Characteristics for Bioimaging Applications

Light emission of 2-(2,6-bis((E)-4-(diphenylamino) styryl]-4H-pyran-4-ylidene} malononitrile (TPA-DCM) is weakened by aggregate formation. Attaching tetraphenylethene (TPE) units as terminals to TPA-DCM dramatically changes its emission behavior: the resulting fluorogen 2-(2,6-bis((E)-4-(phenyl(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4yl ) amino) styryl)-4H-pyran-4-ylidene) malononitrile (TPE-TPA-DCM) is more emissive in the aggregate state, showing a novel phenomenon of aggregation-induced emission (AIE). Formulation of TPE-TPA-DCM using bovine serum albumin (BSA) as the polymer matrix yields uniformly sized protein nanoparticles (NPs) with high brightness and low cytotoxicity. Applications of the fluorogen-loaded BSA NPs for in vitro and in vivo far-red/near-infrared (FR/NIR) bioimaging are successfully demonstrated using MCF-7 breast cancer cells and a murine hepatoma-22 (H-22) tumor-bearing mice model, respectively. The AIE-active fluorogen-loaded BSA NPs show excellent cancer cell uptake and prominent tumor targeting ability in vivo due to the enhanced permeability and retention effect