An electrochemical immunosensor based on the screen-printed carbon working electrode with an onboard carbon counter, and silver-silver chloride pseudo-reference electrode for tungro disease, is described in this chapter. A direct competitive enzyme-linked immunosorbent assay format was first developed and optimized on the surface of a carbon screen-printed working electrode by immobilizing the capture antibody (polyclonal) using an electro-deposition of gold nanoparticles conjugated with polyclonal antitetracycline antibodies. The detection reagent, tetracycline-horseradish peroxidase conjugate, was used as an enzyme label. Electrochemical detection was then carried out using 3,3',5,5'-tetramethylbenzidine dihydrochloride/H2O2 as the enzyme mediator/substrate system, and conducted using chronoamperometry at 300 mV versus an onboard screen-printed Ag-AgCl pseudo-reference electrode. It also showed very high sensitivity using the amplification strategy applied with the use of gold nano-particles. This makes the developed sensor a potential tool for rapid, simple, and sensitive detection of Tungro disease in paddy plantations.
