This study investigates a sandwich-type electrochemical immunosensor for the determination of Hepatitis B Virus Surface Antigen (HBsAg) as the biological target. Capture antibody (Ab1) was immobilized on the synthesized magnetic nanoparticles coated with silica and APTES (MNP@SiO2@APTES). A reporter antibody (Ab2) was assembled on gold nanoparticle-Thionine (GNP), which made use of Th as a redox probe for electrochemical detection. Each gold nanoparticle holds a lot of thionine molecules on its surface. Therefore, after the formation of a sandwich-type probe a magnified electrical signal is achieved. On the other hand, a magnet has been implemented in the electrode. Thus, Magnetic nanoparticle (MNP) acts as the probe collector and fixator component on the electrode's surface, assuring a strong and prolonged interaction of the ultimate sandwich-type probe with the electrode. Under optimal conditions, the current signal increased with the increment of HBsAg concentration in the linear dynamic range of 0.001 fg/ml-2 ng/ml with a detection limit (LOD) of 0.3ag/ml (S/N = 3). Furthermore, the assembled immunosensor successfully quantified the HBsAg concentration in serum. The successful results imply the high potential of the proposed immunosensor in developing ultrasensitive and rapid diagnostic platforms.
