A simple electrochemical immunosensor for determination of Streptococcus suis serotype 2 (SS2) is presented. Nickel hexacyanoferrate nanoparticles (NiHCFNPs) and gold nanocages (AuNCs) were combined together through complexation between the cyanide (CN−) and gold ions, and acted as a carrier for immobilization of the detection antibody (Ab2). The capture antibody (Ab1) was combined by a protein A (PA) and gold nanoparticle (AuNP) modified electrode. In a sandwich-type immunoassay mode, ascorbic acid (AA) was added to the base solution and its oxidation was catalyzed by the AuNCs–NiHCFNPs complex to greatly amplify the response signal. The resulting immunosensor exhibited excellent selectivity and sensitivity, with a linear concentration range of 0.0005–80 ng mL−1 and a detection limit of 0.15 pg mL−1.
