Template and catalytic effects of DNA in the construction of polypyrrole/DNA composite macro and microelectrodes

Electrochemical DNA hybridization-based sensors show great promise as portable and automated analytical devices for routine screening of pathogenic or foreign nucleic acid sequences in biological samples. However, current sensor technologies still exhibit some unresolved issues which hampers their direct application into everyday life. Conducting polymers, such as polypyrrole (PPy), are increasingly being adopted as suitable platforms for DNA probe immobilization and signal transduction. Immobilization of DNA probes during pyrrole electropolymerization is a simple and efficient strategy to build composite electrodes suitable for DNA sensing. However, the effects of the probe state and sequence on PPy growth kinetics have not been studied yet. Here, we show that growth of PPy is drastically affected by the presence of guanine in the DNA probes and whether DNA is present in its single-stranded or double-stranded form. We show that some immobilization protocols may provoke irreversible oxidation of guanine moieties in the probe and that this issue deserves careful investigation as it may interfere with hybridization processes. We have also explored new procedures to build microelectrode arrays bearing immobilized DNA molecules, which are known to show beneficial properties in stirred samples. Overall, we present new techniques and concerns regarding the development of DNA-containing PPy-based composite electrodes, which may be taken into consideration for increasing genosensor reproducibility, response and performance.