Amperometric aqueous sol-gel biosensor for low-potential stable choline detection at multi-wall carbon nanotube modified platinum electrode

A novel amperometric biosensor based on the determination of H₂O₂ liberated by the enzyme choline oxidase (ChOx) was fabricated by immobilization of ChOx into a sol-gel silicate film on the multi-wall carbon nanotubes (MWCNT) modified platinum electrode. Cyclic voltammetric results clearly showed that carbon nanotubes possess an excellent electrocatalytic activity towards the oxidation of H₂O₂ at a low potential (0.16 V versus Ag/AgCl). The remarkable catalytic property of MWCNT was further exploited as a selective determination scheme for choline in the presence of some electroactive compounds. Experimental parameters of the choline sensor, such as applied potential, pH, and temperature were studied. The performance of the sensor showed sensitive determination of choline with a linear range from 5 × 10^-6 to 1 × 10^-4 M and a response time of less than 8 s. The detection limit of choline was determined to be about 1 × 10^-7 M. This biosensor was used to detect choline released from Lecithin by phospholipase D (PLD) in serum samples.