A sensitive electrochemical immunosensor for HBsAg detection was constructed based on hemin/G-quadruplex conjugated Fe304-Au nanocomposites. G-quadruplex DNAzyme, which is composed of hemin and guanine-rich nucleic acid, is an effective signal amplified tool for its prominent peroxidase activity [1,2]. Fe3Q4-Au nanocomposites with a large surface area and pseudobienzyme activity are suitable for the immobilization of hemin/G-quadruplex to form hemin/G-quadruplex conjugated f e304-Au nanocomposites [3]. The target protein was sandwiched between the primary antibody immobilized on the graphene oxide and second antibody immobilized on the f e3Q4-Au nanocomposites. Glutaraldehyde was used as linking agent for the immobilization of primary antibody on the surface of graphene oxide. the Fe3Q4 cores of Fe3Q4-Au nanocomposites and hemin/G-quadruplex can cooperative to electrocatalyze the reduction of H202 with the help of methylene blue. The proposed electrochemical immunosensor had a wide dynamic linear range of 0.1 pM to 300 pM with a detection limit of 0.06 pM, which provided a promising method for a sensitive assay for the detection of proteins in electrochemical immunosensor.
