Construction of an amperometric d-amino acid biosensor based on d-amino acid oxidase/carboxylated mutliwalled carbon nanotube/copper nanoparticles/polyalinine modified gold electrode

An improved d-amino acid biosensor was constructed based on covalent immobilization of d-amino acid oxidase onto carboxylated mutliwalled carbon nanotube/copper nanoparticles/polyalinine hybrid film electrodeposited on gold electrode. The biosensor exhibited an optimal response within 2 s at pH 8.0 and 30 °C when polarized at 0.09 V. There was a linear relationship between biosensor response (μA) and d-alanine concentration ranging from 0.001 to 0.7 mM. The sensitivity of the biosensor was 54.85 μA cm−2 mM−1 with a lower limit of detection of 0.2 μM (signal/noise = 3). The enzyme electrode was used 150 times over a period of 4 months. The biosensor measured the d-amino acid level in fruit juices.