Analytical and Bioanalytical Chemistry

, Volume 411, Issue 12, pp 2619–2633 | Cite as

Efficient dual-mode colorimetric/fluorometric sensor for the detection of copper ions and vitamin C based on pH-sensitive amino-terminated nitrogen-doped carbon quantum dots: effect of reactive oxygen species and antioxidants

  • Gopi Kalaiyarasan
  • James JosephEmail author
Research Paper


We present a facile strategy for highly sensitive and selective determination of copper(II) ions and vitamin C (ascorbic acid, AA) using new amino-terminated nitrogen-doped carbon quantum dots (CQDs) synthesized from melamine as the carbon and nitrogen source by the hydrothermal method. The CQDs have superior optical features, including a pH-sensitive photoinduced electron transfer process. The CQDs form a complex with Cu2+ ions, leading to the development of naked-eye, colorimetric, and fluorometric determination. AA reduces the Cu2+ ions to Cu+ ions, which cannot form the complex. Thus the absorbance and fluorescence of the CQDs are recovered by addition of AA because of dissociation of the complex into Cu+ and CQD. The in situ generation of reactive oxygen species when AA is added to Cu–CQD complexes in the presence of dissolved oxygen leads to the sensitive determination of AA, proposed on CQDs for the first time. The in situ generation of reactive oxygen species was confirmed by a fluorescence method using a hydroxyl radical indicator (i.e., coumarin). This novel “turn-off/turn-on” sensing approach using amine-functionalized CQDs is potentially applicable to determining the concentration of Cu2+ ions and AA in the areas of materials chemistry, nanobiomedicine, nanobiotechnology, and bioengineering because of its high sensitivity, high selectivity, low cost, simple naked-eye readout, and good linearity.

Graphical abstract


Reactive oxygen species Antioxidants Biosensors Naked-eye detection Fluorescence Quantum dots 



GK thanks joint CSIR-UGC, India, for the award of a senior research fellowship.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no competing interests.

Ethics approval

The study was approved by the ethics committee of the CSIR Central Electrochemical Research Institute health center and was performed in accordance with ethical standards. Informed consent was obtained from all individual participants included in the study.

Supplementary material

216_2019_1710_MOESM1_ESM.pdf (801 kb)
ESM 1 (PDF 801 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Academy of Scientific and Innovative ResearchCSIR Central Electrochemical Research Institute CampusKaraikudiIndia
  2. 2.Electrodics and Electrocatalysis DivisionCSIR Central Electrochemical Research InstituteKaraikudiIndia

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