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Electrochemical immunoassay involving two magnetic steps-separation of unbound nanoparticles from bacteria/antigen-Fe3O4 nanoparticles conjugates and concentrating of the conjugates on solid substrate is proposed. Carbon screen printed electrodes covered antibodies specific to Salmonella typhimurium (strain SL 7207) serves as the mentioned substrate. Immunocomplex formed is being solved in the mixture of acids (0.36 M H2SO4 and 0.28 M HNO3) is analyzed for Fe3+ concentration. The last is determined by stripping voltammetric method. It provides information on quantity of conjugates localized on the substrate and the last one is proportional to the pathogen concentration in the analyte. Detection limit is for Salmonella typhimurium 8.18 CFU/ml and for antigen Salmonella typhimurium 1.51 × 10-7 mg/ml (1.51 CFU/ml).