CoO/Co-graphene quantum dots as an oxidative mimetic nanozyme for the colorimetric detection of L-cysteine

• Published in: Analytical methods 2024-04, Vol.16 (14), p.2044-2050
• Main Authors: Xu, Dan, Tu, Qingbo, San, Xin, Zhu, Anhong, Li, Xinru
• Format: Article
• Language: English
• Subjects: Benzidines; Cobalt; Cobalt - chemistry; Colorimetry; Colorimetry - methods; Cysteine; Cysteine - metabolism; Detection; Graphene; Graphite - chemistry; Nanoparticles; Oxidase; Oxidation; Oxidative Stress; Oxidoreductases - chemistry; Oxidoreductases - metabolism; Quantum dots; Quantum Dots - chemistry; Thermal reduction; Tryptophan
• ISSN: 1759-9660; 1759-9679; 1759-9679
• DOI: 10.1039/d4ay00086b

The preparation of cobalt-based nanozymes with high oxidase-like activity still needs more efforts. In this paper, we report the synthesis of a CoO/Co-tryptophan-functional graphene quantum dot hybrid (CoO/Co-Try-GQD). Firstly, cobalt ions coordinate with the indole nitrogen on Try-GQD to form a complex, followed by thermal reduction and oxidation. The resulting hybrid presents a three-dimensional network structure, and CoO/Co nanoparticles are uniformly dispersed on the graphene sheet with an average size of 10 ± 0.24 nm. This unique structure improved the oxidase-like activity of the hybrid, enabling it to catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to rapidly produce deep blue ox-TMB with a strong absorbance at 652 nm ( ). A colorimetric method was developed for the highly sensitive determination of L-cysteine (L-cys) based on the inhibition of the hybrid's oxidase-like activity and low caused by the binding of L-cys with Co atoms on CoO/Co the Co-S bond. The linearly decreased with increasing L-cys concentration in the range of 0.05-2 μM, and the detection limit was 0.032 μM. Further, the established method has been successfully applied to the determination of L-cys in milk.