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

• The THi–GR nanocomposite acted as a biocompatible matrix for ds-DNA and a mediator.
• The nano-bionic interface was applied in chiral sensing for Tryptophan enantiomers.
• The recognition mechanism relied on stereoselectivity of ds-DNA to Cu(II) complex.
• This chiral biosensor is expected to provide a novel model for chiral sensing.

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 2.5 mM with a low limit of detection of 0.17 μM (S/N = 3). The binding constant was calculated to be 2.97 × 103 M− 1 for [Cu(II)(l-Trp)2] and 2.50 × 102 M− 1 for [Cu(II)(d-Trp)2].

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