Sensors and Actuators B 122 (2007) 253–258 An electrogenerated polyterthiophene for binding and sensing polyadenosine-functionalised oligonucleotides Simon J. Higgins a,∗ , Fouzi Mouffouk a , Stewart J. Brown a , Daryl R. Williams b , Andrew R. Cossins b a Donnan and Robert Robinson Laboratories, Department of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, UK b The Laboratory for Environmental Gene Regulation (LEGR), School of Biological Sciences of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK Received 3 April 2006; received in revised form 11 May 2006; accepted 22 May 2006 Available online 3 July 2006 Abstract The isolation of mRNA from other cellular RNA is a key step in isolating genetic information. Since most mRNA has a polythymine ‘tail’ at the 3 ′ end, this is usually done by hybridisation with polyadenosine oligonucleotides anchored to magnetic particles. In this paper, we describe an electrochemical method for binding and reporting mRNA. A terthiophene bearing an activated ester-terminated side-chain has been electro- chemically polymerised using a 2 mm diameter disk electrode, and to this polymer has been grafted an aminoalkyl-terminated polyadenosine oligonucleotide. The cyclic voltammogram of the polymer showed distinctive changes upon the binding of polythymine. Attempts to adopt the method for microelectrodes to boost sensitivity are also described. © 2006 Elsevier B.V. All rights reserved. Keywords: Electrochemical detection; Polythiophene; Conjugated polymer; DNA sensor 1. Introduction DNA biosensor technologies are of immense potential sci- entific and commercial importance, since they are promise a rapid, cheap and sensitive means of diagnosing infectious agents. At present, most DNA tests, such as those involving microar- rays, use fluorescence detection, which is limited by signal/noise and dynamic range considerations. Sensitivity is increased by the polymerase chain reaction (PCR) which amplifies the very small samples involved, but nevertheless, such methods require time, extensive sample preparation and expensive reagents. Electrochemical methods incorporating ‘label-free’ oligonu- cleotide detection are therefore of great interest [1,2]. Here, the main challenges are sensitivity and selectivity. Early methods involved the electrochemical oxidation of nucleobases, but this has obvious drawbacks. A better route is to anchor the oligonu- cleotide in (or on) a conducting polymer matrix, and monitor changes in the electrochemical properties of the polymer on ∗ Corresponding author. E-mail address: shiggins@liv.ac.uk (S.J. Higgins). hybridisation. This may be done by simply electropolymerising a pyrrole in the presence of the oligonucleotide, which, being negatively charged, is entrapped as charge-balancing anion on polymer formation [3]. More elegantly, the DNA can be cova- lently coupled to the polymer backbone [2]. For example, the covalent attachment of amine-terminated single-strand DNA oli- gos on electrogenerated poly(pyrrole-3-acetic acid) has been described [2]. The cyclic voltammetry of these films underwent significant changes on hybridisation [2]. However, there were problems with polypyrrole instability, and sensitivity was low. These problems were addressed in later work by anchoring fer- rocene groups to the polymer in addition to the oligonucleotides; a change in the redox potential of the ferrocenes on hybridisa- tion served as the transduction mechanism, and the polypyrrole simply served to anchor the redox groups and oligonucleotides to the electrode, and mediate electron transfer [4]. The synthetic chemistry of 3-substituted thiophenes is rather more straightforward than that of 3-substituted pyrroles. More- over, polythiophenes are more robust, in both their neutral and p-doped forms. A drawback with electropolymerised polythio- phenes is that their monomer oxidation potentials are very pos- itive, but this can be ameliorated by the use of oligothiophenes 0925-4005/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2006.05.031