Construction of cyclodextrin functionalized nitrogen-doped graphene quantum dot electrochemical sensing interface for recognition of tryptophan isomers

Amino acids are the most common class of enantiomers, and they are also an indispensable component of life. Nitrogen-doped graphene quantum dots (NGQDs) were prepared by a top-down method. And then amide reaction was used to covalently graft aminated β-cyclodextrin (NH2-β-CD) to the edge of NGQDs. By preparing β-cyclodextrin (β-CD) functionalized nitrogen-doped graphene quantum dots (β-CD-NGQDs) and applying them to the glassy carbon electrode to construct an electrochemical sensing interface, enantiomers of tryptophan can be effectively identified. NGQDs can effectively improve the conductivity of β-CD. When chiral selectors interact with enantiomers, NGQDs can provide additional interactions, such as hydrophobic, hydrogen bonding, and electrostatic interactions to indirectly enhancing chiral recognition capabilities. β-Cyclodextrin has the ability to combine with a variety of guest molecules to form composite materials, including some amino acid molecules with different configurations. The microscopic morphology of the material was characterized by a transmission electron microscope, and it was found that the β-CD-NGQDs chiral composite material has good film-forming properties, which is beneficial to the formation of a sensing interface. At the same time, its composition and structure were also identified by X-ray powder diffraction, infrared spectroscopy, Raman spectroscopy, ultraviolet spectroscopy, and X-ray photoelectron spectroscopy. The β-CD-NGQDs was drip-coated on the glassy carbon electrode to form a working electrode. The tested differential pulse voltammetry curves of different configurations of tryptophan showed that the chiral composite material can recognize l-tryptophan.