Amperometric immunosensor for Schistosoma japonicum antigen using antibodies loaded on a nano-Au monolayer modified chitosan-entrapped carbon paste electrode

A new strategy to construct amperometric immunosensor for Schistosoma japonicum antigen (SjAg) assay based on nano-size particulate gold (nano-Au) monolayer as sensing platform has been described. The nano-Au monolayer was obtained through chitosan-entrapped carbon paste electrode (CCPE). The high affinity of chitosan entrapped in CCPE for nano-Au associated with its amino groups facilitated the formation of nano-Au monolayer on the surface of CCPE. A sequential competitive immunoassay format was performed on the nano-Au monolayer supported by CCPE using S. japonicum antibody (SjAb) and SjAg as a model system. The assay comprised first loading of SjAb on nano-Au monolayer, then blocking in BSA solution, followed by a competitive incubation in the buffer containing the SjAg (analyte) and SjAg labeled with horseradish peroxidase (HRP) and finally the amperometric detection with hydroquinone as an enzymatic substrate. The dynamic concentration range for SjAg assay is 0.11–22.4 μg ml−1 with a detection limit of 0.06 μg ml−1. The feasibility of regenerating nano-Au monolayer for consecutive assays was demonstrated by a simple chemical treatment after each determination. The simple manipulations of construction of nano-Au monolayer, low-cost and improved sensitivity are main features of proposed immunosensing method.