GUCY2C and colorectal carcinoma: In this study, an efficient cytotoxic oxygen generating hydrophilic tetra sulphonated metal-based PS (Zinc Phthalocyanine Tetrasulfonic Acid, ZnPcS4), was bound onto the surface of heterobifunctional pegylated amine stabilized AuNPs, which were conjugated to CRC-specific targeting antibodies (Anti-Guanylate Cyclase Ab: Anti-GCC), to enhance the active PS uptake in CRC cells and so improve the primary PDT treatment of CRC.