Novel "on-off" fluorescence sensing for rapid and accurate determination of Cr3+ based on g-CNQDs

Abstract

Cr³⁺ is one of the most essential trace elements in living organisms and plays a vital role in human metabolism. However, both deficiency and excess intake of Cr³⁺ can be harmful to the human body. Therefore, the quantitative determination of Cr³⁺ is of great significance in the field of life science. Based on this, in this study, a g-CNQDs@p-acetaminophenol fluorescence sensing system was developed for the quantitative detection of Cr³⁺ in actual complex samples. G-CNQDs were synthesized with sodium citrate and urea as precursors. The fluorescence signal was enhanced by the synergistic effect between p-acetaminophenol (APAP) and g-CNQDs. The fluorescence quenching phenomenon can be produced when Cr³⁺ is introduced into the fluorescence-enhanced g-CNQDs@p-acetaminophenol system. An "on-off" fluorescence sensing system was constructed based on g-CNQDs@p-acetaminophenol for the quantitative detection of Cr³⁺. The experimental data showed a wide linear region in the concentration range of 0.64-63.0 μM, and the detection limit was as low as 0.23 μM. The construction of the sensor system broadens the research field for the practical application of Cr³⁺.

Fig. 1. Research scheme of Cr³⁺ sensing of g-CNQDs@p-acetaminophenol system.

Fig. 2. (A) TEM images, (B) HR-TEM images, (C) particle size distribution histogram, and (D) XRD of the prepared g-CNQDs.

Fig. 3. (A) FT-IR spectra of g-CNQDs (g-CNQDs is the red line, sodium citrate is the black line, and urea is the blue line), XPS full spectra (B), and high-resolution XPS spectra of C 1s (C) and N 1s (D) of the prepared g-CNQDs.

Fig. 4. (A) UV-Vis absorption spectra (black line) and emission spectra (blue line) of g-CNQDs, inset: photographs of g-CNQDs solution under visible light (left) and 365 nm UV light (right). (B) CIE colour coordinates of g-CNQDs. (C) Fluorescence emission spectra of g-CNQDs under different excitation wavelengths. (D) Normalized fluorescence spectra of g-CNQDs.

Fig. 5. Construction of the “on–off” fluorescence sensing system.

Fig. 6. Fluorescence response of g-CNQDs in the presence of various mental ions.

Fig. 7. (A) Fluorescence spectrum of g-CNQDs@p-acetaminophenol with the addition of various concentrations of Cr³⁺ (0.64 μM to 63.0 μM); (B) linear relationship between fluorescence intensity and different concentrations of Cr³⁺.

Fig. 8. UV-visible absorption spectra of the multiple substances.