Ultrahigh peroxidase-like catalytic performance of Cu-N4 and Cu-N4S active sites-containing reduced graphene oxide for sensitive electrochemical biosensing

Carbon-based nanozymes possessing peroxidase-like activity have attracted significant interest because of their potential to replace native peroxidases in biotechnology. Although various carbon-based nanozymes have been developed, their relatively low catalytic efficiency needs to be overcome to realize their practical utilization. Here, inspired by the elemental uniqueness of Cu and the doped elements N and S, as well as the active site structure of Cu-centered oxidoreductases, we developed a new carbon-based peroxidase-mimicking nanozyme, single-atom Cu-centered N- and S-codoped reduced graphene oxide (Cu-NS-rGO), which preserved many Cu-N4 and Cu-N4S active sites and showed dramatically high peroxidase-like activity without any oxidase-like activity, yielding up to 2500-fold higher catalytic efficiency (kcat/Km) than that of pristine rGO. The high catalytic activity of Cu-NS-rGO might be attributed to the acceleration of electron transfer from Cu single atom as well as synergistic effects from both Cu-N4 and Cu-N4S active sites, which was theoretically confirmed by Gibbs free energy calculations using density functional theory. The prepared Cu-NS-rGO was then used to construct an electrochemical bioassay system for detecting choline and acetylcholine by coupling with the corresponding oxidases. Using this system, both target molecules were selectively determined with high sensitivity that was sufficient to clinically determine their levels in physiological fluids. Overall, this study will facilitate the development of nanocarbon-based nanozymes and their electrochemical biosensing applications, which can be extended to the development of miniaturized devices in point-of-care testing environments.

Elevated prolidase activity in keloids: correlation with type I collagen turnover

BACKGROUND

Keloid pathogenesis involves an altered balance of extracellular matrix metabolism, mainly accumulation of type I collagen. This could be due to excessive synthesis or decreased degradation of matrix, or a combination of both processes. Prolidase, an imidodipeptide-cleaving cytosolic enzyme, plays an important role in the collagen catabolic process by recycling proline for collagen synthesis. Collagen accumulation in keloids is due to an imbalance in the steady state of collagen turnover.

OBJECTIVES

To investigate prolidase activity and its role in the steady state of collagen turnover between normal skin and keloid tissue and their derived fibroblasts.

METHODS

Ten sets of keloid and normal skin tissues and their derived fibroblasts were employed. Measurements were made of tissue prolidase activity, free proline level, and concentrations of the collagen synthesis product aminoterminal propeptide of type I procollagen (PINP) and the collagen degradative product carboxyterminal telopeptide of type I collagen (ICTP). Also, synthesis of collagens type I and III and matrix metalloproteinases 1 and 2 was investigated using Western blot analysis.

RESULTS

Keloid tissues had a significant increase in prolidase activity, up to fourfold that in normal skin. The elevated prolidase activity was accompanied by an increase in tissue PINP and ICTP concentrations in keloid; in addition, the collagen turnover index (PINP/ICTP) was higher in keloids.

CONCLUSIONS

The combination of elevated prolidase activity and associated higher collagen synthesis to degradation ratio in keloids suggests a possible metabolic process for the excessive accumulation of type I collagen in keloids.