Biocompatible aggregation-induced emission nanoparticles with red emission for in vivo three-photon brain vascular imaging.

Three-photon luminescence (3PL) imaging with near-infrared (NIR) excitation is quite promising for its deep penetration, high resolution, and good signal-to-noise ratio (SNR). In this report, a type of red emissive fluorophore TPEPT with aggregation-induced emission (AIE) properties was synthesized, and it was found to possess a large three-photon absorption (3PA) cross-section of 6.33 × 10 cm s under 1550 nm femtosecond laser excitation. TPEPT was then encapsulated with mPEG-DSPE to form AIE nanoparticles, and the chemical stability, optical properties and toxicity were studied afterwards. TPEPT nanoparticles were then applied for 3PL in vivo vascular imaging of mouse brain under 1550 nm fs laser excitation, and a fine three-dimensional (3D) reconstruction with a depth of 500 μm was achieved.