Immobilisation and bioelectrochemisry of proteins on nanoporous TiO_2 and ZnO films

摘要

In this paper we compare the use of nanoporous TiO_2 and ZnO films as substrates for portein immobilisation and as electrodes for electrocemical reduction of the absorbed protein.These two metal oxides are of particular interest as at physiological pH values their surface charges are counterpoised,their isoelectric points being 6 and 9.5 for TiO_2 and ZnO,respectivley.We find that protein immobilisation on both films may be readily achieved from pH 7 aqueous solutions at 4 degC with a high binding stability and no detectable protein denaturation.However,consistent with the difference in surface charge of the two metal oxides fluorescence protein bidns optimally to the ZnO film.We conclude that,ZnO films may be particularlyattractive for the immobilisation of low IEP proteins.Cyclic voltammetry and spectroelectrochemistry are employee to investigate reduction of immobilised Cyt-c on both metal oxides.Control studies in te absence of adsorbed protein indicate the ZnO film to be more conductive at moderate applied potentials than the TiO_2 film.Studies with adsorbed Cyt-c indicate that the direct reduction of cyt-c is possible on both films without the addition of electron transfer promoters or mediators and that all the proteinon both films is electroactive.However,consistent with the difference in conductivity of the two films,Cyt-c reductionis obsewrved at less negative potentials for the ZnO films relative to TiO_2.This observation suggests that the use of ZnO films may be advantageous for the developemnt of nanoporous biosensors employing reductive electrochemistry.