The determination of polyphenols is important due to their biological importance as plant secondary metabolite, their ecological role in the antioxidant capacity, physiological effects, employment as markers in taxonomic studies, and their properties to food quality control. Therefore, a biosensor based on horseradish peroxidase (HRP) and DNA immobilized onto silica-titanium is presented, and its application for measuring the polyphenols compounds in vegetables samples was studied. Various analytical parameters influencing the biosensor performance have been studied as function of the chlorogenic acid (CGA) polyphenol compound, parameters such as working potential, type and concentration of the buffer, pH, response time and response with other compounds were investigated. In the optimized conditions, the biosensor presented a linear response range for CGA from 1 to 50 mumol l(-1), applying a potential of -50 mV versus Ag/AgCl, with a sensitivity of 181 mumol(-1) 1 nA cm(-2) and a detection limit of 0.7 mumol l(-1). The biosensor was tested in the polyphenols determination in vegetables extract and the results were compared with the Folin-Ciocalteau traditional method and the biosensor showed suitability to the quantification of the total polyphenol in the tested samples. (C) 2003 Elsevier B.V. All rights reserved.963636645