A novel electrochemical sensing platform based on Fe3O4-antibody conjugate was developed for the rapid and sensitive determination of Salmonella typhimurium antigen in model suspensions. The conjugates Fe3O4-antibody were synthesized via carbodiimide cross-linking and characterized by infrared spectroscopy and cyclic voltammetry. The electrochemical properties of Fe3O4 magnetic nanoparticles in water were investigated; the possible mechanism of direct electrochemical reduction was proposed and justified as an analytical signal. The design of an electrochemical sensing platform with magnetically controlled flows has been proposed. Under the most appropriate conditions, the developed portable device was provided the linear response as I (µA) = (7.20 ± 0.35) × (–lg CAg) − (23.77 ± 1.95) in the concentration range 1 × 10−7–1 × 10−4mg/mL. The detection limit was 390 ng/mL and was comparable to other works.