Immunosensor for the determination of the herbicide simazine based on an ion-selective field-effect transistor

An immunosensor based on the ion-selective field effect transistor (ISFET) was developed for the express determination of herbicide simazine. Polyclonal antibodies against simazine were attached to the ISFET gate via staphylococcal protein A. Two methods of simazine detection were used - (i) competitive immune assay when native (detected) and peroxidase-labelled simazine molecules competed for binding with antibodies on the ISFET surface, and (ii) sequential saturation of antibodies, left unbound after their exposure to native simazine in investigated sample, with labelled simazine. The catalytic activity of bound peroxidase was measured in the presence of ascorbic acid and H2O2 The limit of simazine detection by competitive immune assay was 1.25 ng ml(-1), the linearity was observed in the range of 5-175 ng ml(-1). Sequential saturation of the antibodies led to the growth of the assay sensitivity up to 0.65 ng ml(-1). Acidic treatment of the ISFETs allowed using them several times without loss of the signal amplitude. The analysis had rapid kinetics; its overall time including duration of all preparation stages was around 50 min. (C) 2000 Elsevier Science B.V. All rights reserved.