A Molecularly Imprinted Chiral Sensor for Colorimetric Resolution of Cysteine Enantiomers Utilizing Oxidase Mimicking of Mn₂O₃ and Reducing Capacity of Cysteine

A surface molecularly imprinted chiral sensor is designed for colorimetric resolution of cysteine (Cys) enantiomers by utilizing oxidase mimicking of Mn₂O₃ and reducing capacity of Cys. As the templates, l-Cys is anchored to the Mn₂O₃ nanozymes through Mn-S bonds, and the resultant Mn₂O₃-l-Cys is coated by the rigid silicon dioxide (SiO₂) imprinting layer. After the l-Cys templates are removed by calcination, molecularly imprinted SiO₂@Mn₂O₃ (MI-SiO₂@Mn₂O₃) is obtained. Owing to the oxidase mimicking of Mn₂O₃, colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be converted into blue oxidized TMB (oxTMB) by the MI-SiO₂@Mn₂O₃; while the blue colored oxTMB can be reduced to colorless TMB by the reductive Cys. Due to the higher affinity of MI-SiO₂@Mn₂O₃ for l-Cys, more d-Cys is left in the solution after the Cys enantiomers are respectively incubated with the MI-SiO₂@Mn₂O₃, which can make the fading of oxTMB easier. Therefore, colorimetric resolution of the Cys enantiomers can be achieved by the developed molecularly imprinted chiral sensor.