Colorimetric Picomolar-Level Determination of L-Cysteine with Fabricated N, Fe-Codoped Carbon Dots as a Peroxidase Mimic

Abstract

Novel nitrogen/iron-codoped carbon dots (N/Fe-CDs) were prepared from citric acid, ethylenediamine, and ferric chloride by a facile one-step solvothermal method and their peroxidase-like activity was evaluated. The structure and composition of the obtained carbon dots were characterized by several methods, including electron microscopy, X-ray diffraction, and spectral techniques. The presence of dopants in the particles was confirmed by X-ray photoelectron spectroscopy and inductively coupled plasma – mass spectrometry (ICP-MS). The obtained N/Fe-CDs displayed excellent peroxidase-like activity and efficiently catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of H₂O₂, leading to a rapid change in the solution color from colorless to blue. Based on this reaction, H₂O₂ was determined from 0 to 40 μM under optimal conditions with a detection limit of 9.0 nM. In addition, L-cysteine was shown to cause the blue color to fade. Considering this feature, a highly sensitive, fast, and specific colorimetric method was developed for L-cysteine with a detection limit of 15.8 pM, which is lower than observed in similar studies. Further, this colorimetric method was applied for the determination of L-cysteine in real samples, and the results of recovery and relative standard deviation were satisfactory. The reported catalyst can be prepared conveniently using readily available raw materials and is inexpensive, which is advantageous for its widespread application.

Keywords:

• Colorimetric analysis
• L-cysteine
• nitrogen/iron-codoped carbon dots
• peroxidase mimic
• solvothermal synthesis

Disclosure statement

No potential conflicts of interest are reported by the authors.

Ethical approval

This article does not contain work with human participants or animals.

Additional information

Funding

Authors are highly thankful to Natural Science Foundation of Fujian Province of China (grants 2020Y0054 and 2019S0031), Project of Education Department of Fujian Province (grant JAT200340), and the College Students' Innovative and Entrepreneurial Training Program (grant 202010402023).