Magnetic microparticles (MMPs) have been notably used as platforms in biosensing. Due to their magnetic behavior, they simplify purification and separation procedures, reducing time of analysis They also allow sample preconcentration, minimizing matrix effects, what is of key relevance for applications using real samples. Even though there is a great number of commercially available MMPs, their performance is not always reliable. In this work we propose the synthesis of novel polymeric MMPs for their use as electrochemical immunosensing platforms. Initially, magnetic nanoparticles of a diameter of 12 ± 2 nm and a saturation magnetization of 70 emu/g were synthesized and characterized. Then, they were encapsulated in a polymeric matrix of poly(lactic-co-glycolic) acid (PLGA), generating MMPs with a diameter of 90 ± 17 nm. Later, MMPs were functionalized with polyethyleneimine (PEI) as an intermediate step for the immobilization of affinity proteins or antibodies, necessary in electrochemical immunosensing. This would allow the obtaining of MMPs comparable to the commercially available ones but possessing higher saturation magnetization. The use of such MMPs could facilitate the detection of analytes of interest in diagnostics, among other applications.