When　excited　at　435 nm,　tetra-sulfonate　zinc　phthalocyanine　(ZnPcS4)　emitted　dual　fluorescence　at　495　and　702 nm.　The　abnormal　fluorescence　at　495 nm　was　experimentally　studied　and　analyzed　in　detail　for　the　first　time.　The　abnormal　fluorescence　at　495 nm　was　deduced　to　originate　from　triplet–triplet　(T–T)　energy　transfer　of　excited　phthalocyanine　(3*ZnPcS4).　Furthermore,　graphene　quantum　dots　(GQDs)　enhanced　the　495 nm　fluorescence　quantum　yield　(Q)　of　ZnPcS4.　The　fluorescence　properties　of　ZnPcS4–GQDs　conjugate　were　retained　in　a　cellular　environment.　Based　on　the　fluorescence　of　ZnPcS4–GQDs　conjugate,　we　designed　and　prepared　an　Apt29/thrombin/Apt15　sandwich　thrombin　sensor　with　high　specificity　and　affinity.　This　cost-saving,　simple　operational　sensing　strategy　can　be　extended　to　use　in　sensing/imaging　of　other　biomolecules.　Copyright　©　2016　John　Wiley　&　Sons,　Ltd.