Lysine enhances the photoresponsive oxidase-like activity of twin CdZnS for direct colorimetric detection of lysine.

Background: Lysine (Lys) is one of the eight essential amino acids for the human body, which can't be synthesized by the body and must be obtained from external sources. And the detection of Lys is of significance for disease monitoring. The construction of photoresponsive nanozymes based analytical methods have received increasing attention and have been successfully achieved for the detection of metal ions, small molecules and natural enzymes. However, the exploration of photoresponsive nanozyme in amino acids detection has not been tapped.

Results: This study presents an innovative method based on surface passivation by Lys to stimulate the photoresponsive nanozyme activity of twin CdZnS nanomaterials. Specifically, Lys can bind with twin CdZnS, which filled the dangling bonds on the surface of CdZnS and caused passivation of the surface state, resulting in the promotion of the separation efficiency of electrons and holes, along with the facilitation of the production of active intermediates. Therefore, the CdZnS in the presence of Lys showed a high catalytic oxidation ability for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB). This new kind of photoresponsive oxidase-like activity could be regulated by switching visible light sources and showed the specificity of being only affected by Lys without influenced by other amino acids, thus achieved direct colorimetric detection of Lys. The linear range for Lys detection was 1-100 μM, with a detection limit of 0.18 μM (S/N = 3).

Significance: This study developed a new nanozyme of twin CdZnS, whose activity leverages on Lys as a stimulator. Moreover, the Lys detection method proposed by us had the characteristics of high sensitivity, good selectivity, fast detection speed, and low cost. Therefore, it holds significant potential application value, making it a promising candidate in the field of Lys detection and related research areas.