Immobilization of 6-O-α-maltosyl-β-cyclodextrin on the surface of black phosphorus nanosheets for selective chiral recognition of tyrosine enantiomers.

A novel chiral sensing platform, 6-O-α-maltosyl-β-cyclodextrin (Mal-βCD)-based film, is proposed for selective electrochemical recognition of tyrosine (Tyr) enantiomers. Black phosphorus nanosheets (BP NSs) and Mal-βCD modified glassy carbon electrode (Mal-βCD/BP NSs/GCE) were prepared by a layer-to-layer drop-casting method, and the platform was easy to fabricate and facile to operate. It is proposed that the amino and hydroxyl groups of the Tyr enantiomers and the chiral hydroxyl groups of Mal-βCD selectively form intermolecular hydrogen bonds to dominate effective chiral recognition. Two linear equations of Ip (μA) = 11.40 C (mM) + 0.28 (R = 0.99147) and Ip (μA) = 7.96 C (mM) + 0.22 (R = 0.99583) in the concentration range 0.01-1.00 mM have been obtained. The limits of detection (S/N=3) for L-Tyr and D-Tyr were 4.81 and 6.89 µM, respectively. An interesting phenomenon was that the value of I/I (1.51) in this work was slightly higher than the value of I/I (1.49) reported in our previous study, where tryptophan (Trp) enantiomers were electrochemically recognized by Nafion (NF)-stabilized BPNSs-G2-β-CD composite. The two similar sensors fabricated by different methods showed different recognition ability toward either Tyr or Trp enantiomers, and the underlying mechanism was discussed in detail. More importantly, the proposed chiral sensor enables prediction of the percentages of D-Tyr in racemic Tyr mixtures. The chiral sensor may provide a novel approach for the fabrication of novel chiral platforms in the practical detection of L- or D-enantiomer in racemic Tyr mixtures.Graphical abstract.