Portugaliae Electrochimica Acta 21 (2003) 361-370 PORTUGALIAE ELECTROCHIMICA ACTA Oligonucleotide Immobilisation on Polytyramine-Modified Electrodes Suitable for Electrochemical DNA Biosensors A. Tenreiro a)* , C.M. Cordas b) , L.M. Abrantes b) a) Laboratório de Bioelectroquímica, ICAT, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749 - 016 Lisboa, Portugal b) Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749 - 016 Lisboa, Portugal Received 31 January 2003; accepted in revised form 31 October 2003 Abstract The surface of platinum electrodes was modified by electrochemical polymerisation of tyramine to provide binding sites for covalent specific immobilisation of the nucleotide deoxyguanosine triphosphate (dGTP). The EQCM has been used to monitor the growth of polymeric films, which is clearly demonstrated by the decrease in the frequency, corresponding to a continuous mass increase. The carbodiimide coupling reaction was used to bind the terminal 5’ phosphate groups of the dGTP to the available primary amine functions on the polymer surface. The biomolecule immobilisation process was followed by measuring simultaneously the evolution of QC-frequency and open circuit potential. Intrinsic redox signal of guanine base residues provides evidence of the dGTP grafting. Keywords: Polytyramine; electrochemical polymerisation; EQCM; covalent immobilisation; DNA biosensor. Introduction In recent years, there has been considerable interest in the development of DNA biosensors due to their numerous potential applications that range from health care, medicine, food industries and environmental monitoring [1-6]. An important effort has been devoted to develop techniques for immobilising oligonucleotides on suitable supports. In this context, modified electrodes prepared by electropolymerisation of different monomers aiming the immobilisation of oligonucleotides have had many advances during last decade * Corresponding author. E-mail address: amtenreiro@fc.ul.pt