Electrochemical investigation of amino acids Parkia seeds using the composite electrode based on Copper/Carbon nanotube/Nanodiamond

Abstract An electrochemical biosensor comprising copper, nano-diamond (ND) and carbon nanotube (CNT) has been fabricated to detect the amino acids of Parkia speciosa (PS) seeds. Parkia speciosa (stink bean), a Southeast Asian legume, is composed of medicinal chemicals which exhibit biological activities. The electro-catalytic activity of three electrodes Cu/CNT/ND, Zn/CNT/ND and NiO/CNT/ND was studied using 5 mM potassium ferrocyanide in 0.1 MKCl. The Zn/CNT/ND electrode exhibited irreversible reaction free oxidation with reduction peaks at −1 V, whereas, a pair redox peaks was observed for Cu/CNT/ND electrode. The immobilization of l -amino acid oxidase on the Cu/CNT/ND electrode was carried out to catalyze the amino acids detection. It was observed that the anodic and cathodic peak currents increased linearly with both the square root of the scan rate (ν 1/2 ) and scan rate (ν) over the studied scan range of 0.01–0.1 V/s with high correlation coefficients and following both the adsorption and the diffusion-controlled mechanisms. The developed biosensor displayed a very good electro-catalytic activity toward the oxidation of the amino acid to release H 2 O 2 and NH 3 as a result of the reaction between the active sites and the Parkia speciosa component. This was also confirmed by a drop in the pH value from 6.8 to 6.5 and a change in the color of the solution from green to yellow (releasing H 2 S). The impedance results indicated an inductance behavior due to the co-formation of the hydrogen peroxide (H 2 O 2 ) and the water via the adsorption on the electrode surface.