Extending the tissue penetration capability of conventional photosensitisers: a carbon quantum dot–protoporphyrin IX conjugate for use in two-photon excited photodynamic therapy

A carbon quantum dot (CQD)–protoporphyrin (IX) sensitisier conjugate was designed to exploit the large two-photon absorption cross section of CQDs and enable the indirect excitation of the sensitiser with 800 nm irradiation via FRET.