The application of thionine-graphene nanocomposite in chiral sensing for Tryptophan enantiomers.

The thionine-graphene (THi-GR, positively charged) nanocomposite was successfully synthesized as a good biocompatible matrix for ds-DNA which acted as a chiral selector to construct an electrochemical chiral biosensor for Tryptophan (Trp) enantiomers sensing with the assistance of Cu(II). The nano-bionic interface was constructed as follows: Firstly, the nanocomposite was dropped on the surface of glassy carbon electrode (GCE), and then ds-DNA (negatively charged) was immobilized onto the nanocomposite film via the opposite-charged adsorption techniques. This biofunctionalized nanocomposite was characterized with scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectrometry and cyclic voltammetry (CV). The chiral biosensor was employed to study the recognition effect between ds-DNA and Trp enantiomers by CV. The results show that larger electrochemical response was obtained from l-Trp when Cu(II) was present, indicating this strategy could be employed to enantioselectively recognize Trp enantiomers. Under optimum conditions, the chiral biosensor exhibited a good linear response to Trp enantiomers in the range of the concentration of [Cu(II)(Trp)2] from 5.0 × 10(-4) to 2.5mM with a low limit of detection of 0.17 μM (S/N=3). The binding constant was calculated to be 2.97 × 10(3)M(-1) for [Cu(II)(l-Trp)2] and 2.50 × 10(2)M(-1) for [Cu(II)(d-Trp)2].