Electrochemical recognition of tryptophan enantiomers using a multi-walled carbon nanotube@polydopamine composite loaded with copper(II)

The work describes a voltammetric method for the recognition of tryptophan (Trp) enantiomers. A glassy carbon electrode (GCE) was modified with polydopamine-coated multiwalled carbon nanotubes and subsequently loaded with copper(II) ions. The morphology and structure of the material were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and electrochemical methods. The recognition of Trp enantiomers by the modified GCE was investigated by differential pulse voltammetry. Under optimum conditions, the sensor revealed a linear range from 1.0 to 100.0 μM with the limit of detection values of 0.15 μM and 0.20 μM for D-Trp and L-Trp, respectively. The recognition efficiency for the Trp enantiomers (with a chiral separation factor of 5.4 for L-Trp over D-Trp) is much higher than that of other electrodes. This is assumed to be due to the unique features of MWCNTs, PDA and Cu(II). After optimizing various experimental conditions, the method was successfully applied to chiral sensing of Trp isomers in a racemic mixture. The potential application to chiral separation of the amino acids phenylalanine and tyrosine was also evaluated, with a chiral separation factor of 2.14 and 1.33 for L−/D-phenylalanine and L−/D-tyrosine, respectively. Graphical abstract Schematic presentation of the synthesis of a multi-walled carbon nanotubes@polydopamine composite loaded with copper(II), and its application in electrochemical enantiorecognition of tryptophan enantiomers.