Highly sensitive d-alanine electrochemical biosensor based on functionalized multi-walled carbon nanotubes and d-amino acid oxidase

•PTCA-MWCNTs achieved signal amplification and exhibited good dispersibility.•Large immobilization amount of DAAO has been achieved by PTCA-MWCNTs.•The designed sensor achieved high selectivity and sensitivity of d-alanine.

With an excellent electron-transfer ability of 3,4,9,10-perylene tetracarboxylic acid functionalized multi-walled carbon nanotubes (PTCA-MWCNTs), and successful maintenance of d-amino acid oxidase (DAAO) activity by the protection of bovine serum albumin (BSA) and glycerol, a signal amplification biosensor for chiral recognition of d-alanine (d-Ala) has been designed. PTCA worked as redox probe due to its self-derived redox activity. The proposed biosensor was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). After the biosensor interacting with d-alanine and l-alanine respectively, a larger current response was obtained from d-alanine. The linear range of the biosensor under the optimum working conditions was investigated by current-time response in successive addition of d-Ala from 1.0 × 10−8 to 1.0 × 10−3 M with a lower detection limit of 3.3 × 10−9 M (S/N = 3). Possible explanations for substrate specificity of the biosensor were discussed. This method showed high sensitivity and selectivity for chiral recognition of d-alanine. It also exhibited good stability, repeatability and reproducibility. The proposed biosensor was applied for real sample measurement.

Graphical abstractIllustration of the proposed electrochemical biosensor based on the 3,4,9,10-perylene tetracarboxylic acid functionalized multi-walled carbon nanotubes and d-amino acid oxidase for chiral recognition of d-alanine.Figure optionsDownload full-size imageDownload as PowerPoint slide