[en] Highlights: •Electrochemical characteristics on nanoparticles and nanocomposites were compared. •The reasons for superior electrochemical activity of Fe₃O₄@Pt were discussed. •We report an excellent nitrite biosensor based on Fe₃O₄@Pt. •Electro-analytical parameters of nitrite at Fe₃O₄@Pt were evaluated in detail. -- Abstract: The electrochemical differences (such as charge transfer resistivity, electroactive surface, standard electron transfer rate constant, adsorption amount and analytical performance of nitrite sensor) between Fe₃O₄@Pt nanocomposites with two elements and core–shell structure and NPs (Fe₃O₄ nanoparticles and Pt nanoparticles) with single component and simple structure were investigated in detail. Above those investigations, it is believed that for the Fe₃O₄@Pt core–shell nanocomposites, Pt shell could provide more electro-catalytic activity while magnetic Fe₃O₄ core could provide larger surface area and facilitate the purification of nanocomposites. After that, Fe₃O₄@Pt nanocomposites modified GCE served as a nitrite sensor. Electrochemical parameters of nitrite at Fe₃O₄@Pt nanocomposites such as electron transfer number, electron transfer coefficient, standard heterogeneous rate constant and electron diffusion coefficient were evaluated. With the proposed electrochemical sensors, nitrite in tap water and orange juice could be detected. This investigation suggested that core–shell nanocomposites were superior for the fabrication of electrochemical sensors