Cellulose-based carbon dots with fluorescence and oxidase-like activities: A tunable and sustainable substitute for natural enzymes to detect nitrite

Abstract

The currently reported carbon dots with oxidase-like activity, as substitutes for natural enzymes, are generally prepared using organics with small molecules as carbon precursors. However, renewable cellulose as a feedstock is more conducive to the sustainable production of carbon dots. Herein, the Mn and N elements doped carbon dots with oxidase-like activity were prepared from carboxymethylcellulose, ethylenediamine, and MnCl₂, and the effects of these three elements on the structure of the carbon dots were comprehensively studied and verified by advanced techniques. Moreover, the increase of ethylenediamine dosage and the prolongation of hydrothermal time promoted the coordination of O-based and N-based groups to Mn ions. The enhancement of the Mn-N and Mn-O bond content strengthened the oxidation-like activity of the carbon dots. The maximum reaction velocity and the Michaelis constant for 3, 3′, 5, 5′-tetramethylbenzidine were 19.8 × 10^-5 mM s⁻¹ and 0.159 mM, respectively. Finally, a platform for the dual-mode detection of nitrite was established based on the catalytic ability of the carbon dots for 3, 3′, 5, 5′-tetramethylbenzidine and the diazotization reaction of 3, 3′, 5, 5′-tetramethylbenzidine with nitrite. The response ranges of ratiometric colorimetric and fluorescence detection for nitrite were 0–200 μM and 0–100 μM, respectively. This work verified the feasibility of constructing carbon dots with oxidase-like activity and fluorescence property from carboxymethylcellulose, which can stimulate more efforts to explore the application of biomass-based carbon dots with oxidase-like activity in the field of nitrite detection.