Potentiometric study of quinohemoprotein alcohol dehydrogenase immobilized on the carbon rod electrode

Abstract

Enzymes, which exhibit redox properties and are able to directly exchange electrons with conducting materials, are currently of special interest in the fields of biosensorics and bioelectronics. The detection of new electronic properties makes them even more attractive for these growing fields. Quinohemoprotein alcohol dehydrogenase (QH-ADH) from Gluconobacter sp. 33 was demonstrated as ‘nano-sized electrical power generator’ able to separate the electrical charges and generate a measurable electrical potential. This phenomenon was investigated potentiometrically in electrochemical system where QH-ADH was applied as the catalyst oxidizing ethanol thereby converting the energy of this chemical reaction to an electrical potential. A basic immobilization technique based on cross-linking with glutaraldehyde was applied for the immobilization of QH-ADH onto a carbon rod. The maximal open circuit potential generated by QH-ADH immobilized on carbon rod electrode was −115 mV versus an inactivated QH-ADH-modified electrode (Inactiv-ADH/carbon). If 10 mM of redox mediator K 3[Fe(CN) 6] was added to the solution the potential rose to −190 mV versus Inactiv-ADH/carbon. The influence of concentration of Na acetate buffer, pH 6.0, on registered potential was approximately at the same level as the influence of KCl concentration (influence of ionic strength). This result implies that local pH changes do not play a significant role in the development of QH-ADH-modified carbon electrode potential. The potentiometric signal was more stable than amperometric signal based on the same QH-ADH-modified carbon electrode. The ability to directly generate electric potential opens new opportunities for the application of QH-ADH and other direct electron transfer exhibiting enzymes in the design of new potentiometric sensors, biofuel cells and self-powering bioelectronic devices.