Ochratoxin A (OTA) is one of the most toxic food contaminant mycotoxin, which can cause nephrotoxicity, teratogenicity, and carcinogenicity activity. Here an ultrasensitive electrochemical aptasensor for OTA was successfully fabricated. This aptasensor was constructed by combining nanocomposites of gold nanoparticles (AuNPs) functionalized silica-coated iron oxide magnetic nanoparticles (mSiO(2)@Au) and cadmium telluride quantum dots (CdTe QDs) modified graphene/AuNPs nanocomposites (GAu/CdTe). The as-prepared aptasensor exhibited a wide linear range (0.2 pg mL(-1) -4 ng mL(-1)), and an extremely low detection limit of 0.07 pg m(L-1) (S/N = 3). This work provides a novel strategy for the ultrasensitive detection of various target molecules and would have great potential in food safety monitoring and clinical diagnosis. (C) 2016 Elsevier B.V. All rights reserved.