A Highly Sensitive Electrochemical Immunosensor Based on Core–Shell SiO2-PEI@Ag NPs Nanocomposites for MPA Detection

In recent years, food safety concerns associated with veterinary drug residues have aroused significant public attention, highlighting the critical need for continuous monitoring in both animal-derived foods and the environment to safeguard public health. Medroxyprogesterone acetate (MPA), a major anabolic steroid widely used in animal husbandry, poses potential human health risks according to recent studies. Although conventional analytical techniques based on chromatography and immunological assays are effective, they often suffer from complex operations, the need for skilled personnel, high cost, and time consumption. To overcome these limitations, electrochemical immunosensors modified with advanced nanomaterials offer a promising alternative. Herein, a highly sensitive electrochemical immunosensor was developed for trace MPA detection utilizing core–shell SiO2-PEI@Ag nanoparticles as the sensing matrix. In this nanocomposite, the structural synergy between the SiO2 core and outer Ag NPs shell not only provides a high-density platform for specific antibody immobilization, but also drastically expands the electroactive surface area and accelerates electron transfer to maximize signal amplification. Benefiting from these synergistic advantages, the constructed immunosensor exhibited a limit of detection (LOD) of 0.014 ng/mL and a wide linear range of 0.03–100 ng/mL. Furthermore, the recovery rates in pork and milk samples were 91.32–97.29% and 95.14–102.54%, respectively. In addition, negligible cross-reaction was observed toward structurally related steroid hormones related to MPA and common antibiotics. The immunosensor shows good stability, reproducibility, and accuracy, demonstrating great potential as a promising candidate to complement conventional tools for future MPA residue screening.