A disposable electrochemical immunosensor for the determination of leptin in serum and breast milk

The preparation of a disposable electrochemical immunosensor for the quantification of the hormone leptin is described in this work. The preparation approach involved immobilization of a specific biotinylated anti-leptin antibody on the surface of streptavidin-functionalized magnetic beads (Strept-MBs) and a sandwich-type immunoassay involving the target analyte, monoclonal anti-leptin, and IgG labeled with alkaline phosphatase (AP-IgG). The electrochemical transduction step was accomplished by trapping the MBs bearing the immunoconjugates onto screen-printed carbon electrodes (SPCEs) by means of an Nd magnet and measuring the electrochemical oxidation of the 1-naphthol generated in the AP enzyme reaction upon 1-naphthyl phosphate (1-NPP) additions by differential pulse voltammetry (DPV). A calibration plot with a linear range between 5 and 100 pg mL−1 as well as a detection limit of 0.5 pg mL−1 (3sb/m) were achieved. This value is more than 27 times lower than that reported in the only voltammetric immunosensor for leptin described in the literature until now. The usefulness of the immunosensor was demonstrated by analyzing different types of real samples: human serum, infant powdered milk, and breast milk from a nursing mother with two months of breastfeeding.