Biocompatible Nanoparticles with Aggregation-Induced Emission Characteristics as Far-Red/Near-Infrared Fluorescent Bioprobes for In Vitro and In Vivo Imaging 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]-4-yl)amino)styryl)-4H-pyran-4-ylidene)malononitrile (TPE-TPA-DCM), is more emissive in the aggregate state, showing the 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 (H22)-tumor-bearing mouse model, respectively. The AIE-active fluorogen-loaded BSA NPs show an excellent cancer cell uptake and a prominent tumor-targeting ability in vivo due to the enhanced permeability and retention effect.