Prussian Blue Nanoparticles as labels in a Sandwich-type Nanostructured Immunosensor to detect Immunoglobulin G

The need for small, portable, accurate, and simple-to-use analytical devices for biomedical applications has drawn the scientific community attention to electrochemical biosensors. In this work, a sandwich-type electrochemical immunosensor based on Gold Nanowires (GNWs) was developed for Human Immunoglobulin G (H-IgG) detection. H-IgG was selected as model analyte because of its physical, chemical, and biological features similar to many other protein biomarkers. The sensor substrate was a GNW electrode. GNWs were obtained through electrochemical template deposition into a nanoporous polycarbonate membrane. To achieve the best morphology, various deposition conditions were analyzed such as the time of deposition, and Au salt concentration in the deposition bath solution. The best deposition conditions that ensure the formation of mechanically stable nanowires were selected. Prussian blue (PB) is a transition metal hexacyanometalate with the formula of Fe4III[FeII(CN)6]3. This compost drew a lot of attention because Prussian White, a reduced form of PB, can catalyze the electrochemical reduction of hydrogen peroxide. For this reason, PB Nanoparticles (PBNPs) were fabricated to serve as secondary antibody catalytic label. Figure 1b shows the PBNPs with a typical cubic shape. A sandwich-type immunosensor consists of a primary antibody covalently attached to the electrode surface, the antigen (H-IgG) selectively bound by the primary antibody, and a secondary PBNP-labelled antibody. The fabrication process requires several incubation steps, which are summarized in Figure 2. Since PBNPs act as catalysts for H2O2 reduction, chronoamperometry in an H2O2 probe solution can detect H-IgG. This is due to the fact that the amount of PB catalyst on the electrode increases with analyte concentration. Therefore, the electrode was used to measure H2O2 reduction current density, which is indirectly related to the concentration of H-IgG. In this way, the calibration curve was constructed obtaining a linear range of 1-1000 ng mL-1 and high sensitivity.