Amperometric immunoassay for the obesity biomarker amylin using a screen printed carbon electrode functionalized with an electropolymerized carboxylated polypyrrole.

Amylin (the islet amyloid polypeptide) is a hormone related to adiposity, hunger and satiety. It is co-secreted with insulin from pancreatic B-cells. An amperometric immunosensor is presented here for the determination of amylin. It is making use of a screen printed carbon electrode (SPCE) functionalized with electropolymerized poly(pyrrole propionic acid) (pPPA) with abundant carboxyl groups that facilitate covalent binding of antibody against amylin. A competitive immunoassay was implemented using biotinylated amylin and streptavidin labeled with horse radish peroxidase (HRP-Strept) as the enzymatic tracer. The amperometric detection of H2O2 mediated by hydroquinone was employed as an electrochemical probe to monitor the affinity reaction. The variables involved in the preparation and function of the immunosensor were optimized and the electrodes were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The calibration graph for amylin, obtained by amperometry at -200 mV vs Ag pseudo-reference electrode, showed a range of linearity extending from 1.0 fg∙mL-1 to 50 pg∙mL-1, with a detection limit of 0.92 fg∙mL-1. This is approximately 7000 times lower than the minimum detectable concentration reported for the ELISA immunoassays available for amylin. The assay has excellent reproducibility and good selectivity over potential interferents. Graphical abstract Schematic of an amperometric competitive immunoassay for the obesity biomarker amylin using a poly(pyrrole propionic acid)-modified screen-printed electrode. The detection limit is 0.92 fg∙mL-1 amylin. The method provides excellent reproducibility for the measurements, good selectivity and successful applicability to human urine and serum samples.