An AIEgen-based "turn-on" probe for sensing cancer cells and tiny tumors with high furin expression

Peptide-aggregation-induced emission (AIE) luminogen (AIEgen) conjugates are widely used in the bioimaging field for their good resistance to photobleaching, red and near-infrared light emission, good biocompatibility, etc. However, their peptides are mainly negatively charged and the positively charged peptide-AIEgen conjugates are rarely used in in vivo imaging due to their high non-specific interaction with protein to cause "false-positive" results and their potential risk of triggering hemolysis. Herein, we introduce a black hole quencher 3 (BHQ3) to RVRRGFF-AIE (FA) to build a "turn-on" probe, named BHQ3-RVRRGFF-AIE (BFA). Compared with FA, BFA has advantages in the anti-interference ability for different proteins and many solution environments. But, both BFA and FA have high risks of inducing hemolysis, which restricts their further application. Through co-assembly with poly-γ-glutamic acid (γ-PGA), molecular probes BFA and FA are formed into PGA-BFA and PGA-FA nanoparticles with high biocompatibility and suppressed phototoxicity. Cell studies show that PGA-BFA can discriminate cancer cells with high furin expression from low furin-expressed cancer cells and normal cells. In vivo studies show that PGA-BFA can light up tiny tumors in the abdominal cavity with a better tumor-to-intestine ratio (3.14) than that of PGA-FA (1.47), which is helpful for the accurate excision of tiny tumors. This study will advance the development of constructing good biosafety probes with a high signal-to-noise ratio for fluorescence image-guided cancer surgery.