Maleimide-NOTA is a chelate. Maleimide-NOTA can be site-specifically coupled to the hPD-L1 nanobody bearing the Cys-tag. Maleimide-NOTA can specifically conjugate to A20FMDV2 (HY-P1654). The [68Ga]Ac-CG6 formed by the conjugation of 68Ga radiolabeled Maleimide-NOTA with A20FMDV2 can be used for PET imaging of alphavbeta6 integrin-positive pancreatic ductal adenocarcinoma[1][2].