Co, N-doped carbon dot nanozymes with acid pH-independence and substrate selectivity for biosensing and bioimaging

Nanozymes are more stable, economical, and easier to produce than natural enzymes; however, their low activity in non-acidic environments and lack of substrate selectivity severely limit the applications of nanozymes. In this study, we developed Co- and N-doped carbon dot nanozymes (CoNCDs) that specifically exhibited peroxidaselike activity toward o-phenylenediamine in a non-acidic environment. Based on the peroxidase-like activity and fluorescence property of CoNCDs in a neutral environment, a one-pot multi-mode sensing platform (colorimetric and ratiometric fluorescence imaging) was developed to detect cholesterol and xanthine in solution and human serum samples. This platform was simple to operate, and the CoNCDs demonstrated a reduced detection time and an improved analytical performance compared to most of the reported nanozymes. Moreover, the improved peroxidase activity at neutral pH, good biocompatibility, and photostability of CoNCDs facilitated their use for monitoring endogenous H2O2 levels in vivo. This study not only provides a novel approach for developing an acid pH-independent and substrate selectivity nanozyme but also demonstrates the application of ratiometric fluorescence imaging using the developed CoNCDs both in vitro and in vivo.

Automated summary

Nanozymes offer stability and cost-effectiveness, but often lack substrate selectivity and activity in non-acidic environments. The study introduced CoNCDs with peroxidase-like activity, leading to a efficient multi-mode sensing platform for detecting analytes in solution and serum samples. The CoNCDs demonstrated improved performance, biocompatibility, and photostability, making them suitable for in vivo monitoring of H2O2 levels.