Detection of Ethanol by Alcohol Dehydrogenase Modified Electrode with Anthraquinone and Carboxylated Multiwalled Carbon Nanotubes

The detection of ethanol is based on the signal produced by nicotinamide adenine dinucleotide NAD, the product of the enzymatic reaction. Anthraquinone 2-carboxylic acid AQ as electron shuttling mediator was attached to NAD of alcohol dehydrogenase ADH to facilitate the electron transferring. Also, multiwalled carbon nanotubes MWCNTs for the high electrical conductivity, MWCNTs capability for functionalization and large surface were used as carriers for protein immobilization. Based on, MWCNTs at first were functionalized with carboxyl groups by oxidation with nitric acid 65 and ultrasonic dispersion. FTIR and SEM studies confirm the formation of carboxylic acid functionalized MWCNTs. The electrocatalytic activities of AQ and MWCNT improve towards the reduction of NAD. Covalent attachment of carboxylic acid of anthraquinone molecules and carboxylic acid functionalized MWCNTs to the amine group of NAD established. The CNT/AQ-NAD/ADH electrode was applied for amperommetric sensing of ethanol in the linear concentration range from 3.34 up to 22.8 µM at optimum conditions and specifically, the attached ADH on NAD-AQ/CNT/GC electrode showed quasi-reversible cyclic voltammogram with the formal potential of -0.562 and -0.488V. The CNT/AQ-NAD electrode represents a general approach to the development of dehydrogenases-based electrochemical biosensors.