Nanozyme based on CoFeO modified with MoS for colorimetric determination of cysteine and glutathione.

A nanozyme based on CoFeO modified with MoS was constructed for colorimetric determination of cysteine (Cys) and glutathione (GSH). Firstly, ferrite CoFeO is synthesized, and it is then modified by MoS to form a flower-like polymer (MoS@CoFeO). In the presence of HO, a redox interaction takes place, and the resulting hydroxyl promoted a colorimetric conversion from colorless to blue in the presence of 3,3',5,5'-tetramethylbenzidine (TMB). However, once Cys or GSH is added, they are capable to compete with the interaction of the hydroxyl with TMB, resulting in an inhibition of the colorimetric conversion. The colorimetric distinction is sensitive to the amount of target. The results obtained proved that the catalytic efficiency of MoS@CoFeO is 4.4-fold and 1.8-fold to that of MoS and CoFeO. Meanwhile, the K values to TMB and HO are 0.067 and 0.048 mM, respectively, which are 6.5-fold and 77-fold, respectively smaller than those of natural peroxidase such as HPR. This indicates that the MoS@CoFeO possesses a favorable interaction affinity. Additionally, the colorimetric distinction caused by the competition between TMB and cysteine or glutathione is obvious. The signal responses to cysteine and glutathione are linear in the range 0.515 μM and 0.535 μM, and the LODs are 0.10 and 0.21 μM, respectively. In practical assay of Cys in serum, the RSD of the sample tests is 4.6%, and the recoveries for the spiked assays are 95.3% and 96.0% with the RSD of 2.1% and 4.2%, respectively.