Bimetallic nanoparticles with enhanced peroxidase-like activity and enantioselectivity for colorimetric discrimination of D,L-tryptophan

Chiral recognition by monometallic nanozymes has received extensive attention. However, determining the basis of the chiral identification properties of bimetallic nanozymes is critical and poses challenges. Herein, by leveraging L-tryptophan (LW), L-histidine (LH), L-proline, L-tyrosine and L-dipeptide (LWLH) as chiral ligands, four kinds of bimetallic nanozymes were fabricated based on gold nanoparticles (AuNPs) modified onto the surface of copper nanoparticles (LWLH@CuNPs) . The substrate 3,3′,5,5′-tetramethylbenzidine (TMB) was efficiently oxidized to yield blue oxTMB in these nanozymes-H₂O₂ systems, verifying their peroxidase-like activity that resulted from the synergistic effect of the bimetallic nanozymes. Notably, in the presence of D,L-tryptophan (D,L-Trp), the visible absorbance of oxTMB at 650 nm in the LW@AuNPs-LWLH@CuNPs-TMB-H₂O₂ system was significantly altered, in the contrast with the other three bimetallic nanozymes and monometallic LWLH@CuNPs. The mechanism underpinning the enhanced chiral discrimination ability of LW@AuNPs-LWLH@CuNPs was based on hydrogen-bonding and electron transfer. Furthermore, the proposed LW@AuNPs-LWLH@CuNPs nanozymes were applied to measure L-Trp in saliva samples. This study deepens understanding of the advantages of incorporating AuNPs onto CuNPs, specifically, improving the peroxidase-like activity of bimetallic nanozymes and highlighting their potential for colorimetric chiral recognition of D,L-amino acids.