Unraveling autoimmune and neurodegenerative diseases by amperometric serological detection of antibodies against aquaporin-4

•First amperometric magnetic beads-based biosensor for Aquaporin-4 antibody.•Amperometry of magnetic bioconjugates onto screen-printed carbon electrodes.•Linear range: 0.03–2.5 ng mL−1. Limit of detection: 8.8 pg mL−1.•Advantageous in terms of cost and point of care with respect to ELISA.•Application to sera from patients of Systemic Lupus Erythematosus and Alzheimer disease. This work reports the first electroanalytical bioplatform to date for the determination of antibodies against aquaporin-4 (AQP4-Abs), whose serum level is considered as relevant biomarker for certain autoimmune diseases. The bioplatform relies on the use of magnetic microparticles modified with the biotinylated protein for the capture of specific antibodies. The captured IgGs are enzymatically labelled with a secondary antibody conjugated to the horseradish peroxidase (HRP) enzyme. Amperometric transduction is performed using the H2O2/hydroquinone (HQ) system, which results in a cathodic current variation directly proportional to the concentration of the target antibodies. The evaluation of the analytical and operational characteristics of the developed bioplatform shows that it is competitive in terms of sensitivity with the only biosensor reported to date as well as with the commercially available ELISA kits. The achieved limit of detection value is 8.8 pg mL−1. In addition, compared to ELISA kits, the developed bioplatform is advantageous in terms of cost and point of care operation ability. The bioplatform was applied to the analysis of control serum samples with known AQP4-Abs contents as well as of sera from healthy individuals and patients diagnosed with Systemic Lupus Erythematosus (SLE) and Alzheimer (AD) diseases, providing results in agreement with the ELISA methodology.