An　ion-selective　electrode　(ISE)-based　immunoassay　has　been　innovatively　designed　for　the　sensitive　detection　of　liver　cancer　biomarker　(alpha-fetoprotein,　AFP),　using　metal　sulfide　quantum　dot　(QD)-based　nano　labels.　CdS　QDs-aggregated　PAMAM　dendrimer　(QD-DE)　was　first　synthesized　and　functionalized　with　polyclonal　rabbit　anti-human　AFP　antibodies.　Thereafter,　a　sandwich　immunoreaction　was　implemented　on　monoclonal　mouse　anti-human　AFP　antibody-coated　microplate　by　using　antibody-functionalized　QD-DE　as　the　secondary　antibody.　Accompanying　the　immunocomplex,　subsequent　potentiometric　detection　of　cadmium　ion　dissolved　from　the　QD-DE　under　acidic　condition　was　conducted　on　a　portable　cadmium　ion-selective　electrode　(Cd-ISE).　Results　revealed　that　the　electrode　potential　of　the　Cd-ISE　increased　with　the　increment　of　AFP　concentration　from　0.1　to　100　ng　mL−1　at　a　detection　limit　(LOD)　of　68　pg　mL−1.　The　relative　standard　deviations　(RSD)　were　below　9.09%　and　10.54%　for　the　intra-　and　inter-assay,　respectively.　Additionally,　six　human　serum　specimens　were　determined　on　Cd-　ISE-based　immunosensor　by　using　commercial　human　AFP　ELISA　kit　as　the　reference,　and　gave　good　relationship　between　two　methods.　Importantly,　Cd-ISE-based　immunoassay　offers　the　promise　for　simple　and　cost-effective　screening　of　disease-related　biomarkers.　©　2018,　Science　China　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.