A colorimetric and photothermal dual-mode chiral sensor based on CuS-L-histidine for optical resolution of aspartic acid isomers.

As the chiral source, L-histidine (L-His) is used for the decoration of copper sulfide nanoparticles (CuS NPs), which is further utilized to fabricate a colorimetric and photothermal dual-mode chiral sensor for the optical resolution of aspartic acid (Asp) isomers. Since the optical activity of L-His is consistent with L-Asp, the CuS-L-His shows higher affinity for L-Asp than D-Asp, and thus more 3,3',5,5'-tetramethylbenzidine (TMB) is captured by CuS-L-His/L-Asp through electrostatic attractions compared with CuS-L-His/D-Asp. Owing to the superior peroxidase-like activity of CuS NPs, the captured TMB can be catalyzed to blue oxidized TMB (oxTMB) in the presence of HO, and thus the optical resolution of the Asp isomers can be realized by the colorimetric mode. In addition, the nanosized CuS has outstanding photothermal conversion ability, and the combination with Asp isomers may lead to the decrease in temperature. Since the decrease in the temperature of CuS-L-His/L-Asp is more pronounced than that of CuS-L-His/D-Asp, the Asp isomers can also be optically resolved by the photothermal mode. The proposed dual-mode chiral sensor is more attractive than conventional single-mode chiral sensors, since it can provide higher accuracy for the optical resolution.