Light-up bioprobe with aggregation-induced emission characteristics for real-time apoptosis imaging in target cancer cells

Specific bioprobes that are capable of real-time and targeted monitoring and imaging of cancer cell apoptosis are highly desirable for cancer diagnosis and the evaluation of cancer therapy efficacy. In this work, an asymmetric fluorescent light-up bioprobe with aggregation-induced emission (AIE) characteristics was designed and synthesized by the conjugation of two different hydrophilic peptides, caspase-specific Asp-Glu-Val-Asp (DEVD) and cyclic Arg-Gly-Asp (cRGD), onto a typical AIE luminogen of a tetraphenylsilole (TPS) unit. The asymmetric probe is almost non-emissive in aqueous solution and its fluorescence is significantly switched on in the presence of caspase-3. The fluorescence turn-on is due to the cleavage of the DEVD moiety by caspase-3, and the aggregation of released TPS-cRGD residues, which restricts the intramolecular rotations of TPS phenyl rings and populates the radiative decay channels. Application of the asymmetric light-up probe for real-time targeted imaging of cancer cell apoptosis is successfully demonstrated using integrin α_vβ₃ receptor overexpressing U87MG human glioblastoma cells as an example. The probe shows specific targeting capability to U87MG cancer cells by virtue of the efficient binding between cRGD and integrin α_vβ₃ receptors and is able to real-time monitor and image cancer cell apoptosis in a specific and sensitive manner.