Nanozyme colorimetric sensing of L-cysteine and copper ions based on PtCo nanoparticles@multi-walled carbon nanotubes

In this work, PtCo bimetallic nanoparticles supported on multi-walled carbon nanotubes (PtCo@MWCNTs) nanohybrid was prepared simply and used for the first time as a novel nanozyme in the colorimetric sensing of L-cysteine (L-Cys) and Cu²⁺. Due to its strong enzyme-like catalytic activity, the prepared PtCo@MWCNTs nanohybrid can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to form ox-TMB without H₂O₂. Interestingly, the oxidase-like active of PtCo@MWCNTs was effectively suppressed by L-Cys, which could reduce ox-TMB to colorless TMB and lead to a pronounced blue fading, and the absorbance at 652 nm gradually decreased with increasing L-Cys concentration. On the other hand, the nanozyme activity of PtCo@MWCNTs can be recovered due to the complexation between L-Cys and Cu²⁺. Therefore, a colorimetric method based on PtCo@MWCNTs nanozyme was established to detect L-Cys and Cu²⁺. The results show that the assay platform has simple, rapid, sensitive performance and good selectivity. The detection limits for L-Cys and Cu²⁺ are 0.041 μM and 0.056 μM, respectively, coupled with the linearities of 0.01 ~ 60.0 μM and 0.05 ~ 80.0 μM. The successful first application of PtCo bimetal-based nanozyme in colorimetric sensing herein opens a new direction for nanozyme and colorimetric analysis, showing great potential applications.