Ricin is a highly toxic protein largely existing in castor beans, which could be used as a warfare agent due to its unique properties. As a deadenylase, inactivation of ricin means a loss of its toxic threat. Therefore, developing simple, accurate, and sensitive on-site detection of biologically active ricin in wide types of complex matrices is most valuable. Here, antifouling polymer brush modified magnetic beads were prepared first and post modified with ricin monoclonal antibody (the MB@P(C-H)-mAbricin) to efficiently capture ricin from various foods and biological matrices. Active ricin obtained in this manner were sequentially determined by a new designed AuNP/QDs nanoassembly. In this double strand oligodeoxynucleotides (dsODN) linked core-satellite nanoprobe, the fluorescence of satellite QDs was extensively quenched by AuNPs due to the dipole-metal interaction. Active ricin can react with its specific depurination substrates which had been inserted in the dsODN linkers. This reaction would trigger the separation of QDs from Au cores by cutting multiple adenines, and then result in the restoration of QDs fluorescence. By coupling with the magnetic enrichment, this AuNP/QDs nanoprobe provided a qualitative result for active ricin in the range from 10.0 to 100.0 ng mL-1 with the limit of detection as low as 7.46 ng mL-1. Compared with previously proposed methods, this on-site detection strategy offered an easy to handle on-site test for trace amounts of active ricin in a wide range of complex matrices.