Synergistically enhanced peroxidase-like activity of Pd nanoparticles dispersed on CeO.sub.2 nanotubes and their application in colorimetric sensing of sulfhydryl compounds

In this work, we proposed a new hybrid of Pd nanoparticles dispersed on CeO.sub.2 nanotubes (Pd NPs/CeO.sub.2 NTs) with synergistically enhanced peroxidase-like activity for the visual detection of sulfhydryl compounds. In comparison with individual Pd NPs and CeO.sub.2 NTs, the Pd NPs/CeO.sub.2 NTs hybrid exhibited a synergy effect to trigger the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to its blue product TMBox mediated by H.sub.2O.sub.2. It was further demonstrated that the improved activity observed in Pd NPs/CeO.sub.2 NTs originated from the strong interplays between Pd NPs and CeO.sub.2 NTs, which could significantly increase the Ce.sup.3+/Ce.sup.4+ ratio. Besides, sulfhydryl compounds were found to have the capacity to suppress the color reaction of TMB + H.sub.2O.sub.2 catalyzed by the Pd NPs/CeO.sub.2 NTs nanozyme at a low level. Based on this principle, mercaptoacetic acid in the concentration range of 66-400 nM could be linearly determined. Similarly, sulfhydryl-containing amino acid (cysteine) and its derivative (glutathione) in the linear scope of 6-40 nM were also detected, providing a detection limit down to 2.9 and 11.3 nM, respectively.