Schistosoma japonicum antibody assay by immunosensing with fluorescence detection using 3,3',5,5'-tetramethylbenzidine as substrate.

An immunosensing system for Schistosoma Japonicum antibody (SjAb) assay has been developed which is useful for the diagnosis of schistosomaisis. To circumvent the difficulty of regeneration of the immunosensing device, the sol-gel technique is used which results in a considerable retention of the activity of the encapsulated antigen (SjAb) and easily diffusing into the pores of the polymeric silica matrix. The surface of the immunosensing device prepared can easily be renewed by simply polishing. The regenerated surface serves as a platform for the competitive immuno-reaction of HRP-SjAb and SjAb with SjAg bound at the surface. By using 3, 3', 5, 5'-tetramethylbenzidine (TMB) as the substrate, the amount of HRP-SjAb bound is quantitated fluorimetrically, which is in turn related with the SjAb content. An amplification effect is obtained by using the enzymatic reaction, and an improved detection limit of 4.5 ng ml(-1) is thus realized. The optimum analytical conditions such as pH, amount of the labeled antibody and flow rates of substrate carrier solution were established. The immunosensing procedure shows a pseudo linear response range from 4.5 to 55 ng ml(-1). The proposed procedure has been employed to determine SjAb in serum samples.