One-step Synthesis of Specific pH-responsive Carbon Quantum Dots and Their Luminescence Mechanism

doi:10.15541/jim20190089

Abstract

Abstract:

Nitrogen-doped carbon quantum dots (CDs) were synthesized via a facile one-step solvothermal reaction using citric acid, formamide and water. Subsequent characterizations indicate that the nitrogen-doped CDs are featured by good water solubility, bright blue emission and typical excitation-dependent emission. However, unlike from conventional pH response of most CDs, the as-prepared CDs possess unique pH response. Apart from that fluorescence intensity varies with the pH value, the prepared CDs can generate excitation-independent red emission in alkaline conditions. Through scientific research towards fluorescent property of prepared CDs in different alkaline environments as well as solution with different hydroxyl content, combined with chemical composition and surface states based on Raman spectrum, FT-IR and XPS, the fluorescent mechanism of the unique pH response are attributed to a large number of hydroxyl groups in strong alkaline environment bonded to the surface of CDs, thus changing the surface states of CDs, further forming a new stable luminescence center. Finally, cytotoxicity tests and cell imaging experiments showed that the prepared CDs have low cytotoxicity, and can be used as fluorescent probe for cell imaging, indicating their potential application in the field of biological imaging.

Key words: carbon quantum dots, specific pH-response, red emission, luminescence mechanism, cell labeling

CLC Number:

TQ174

GAO Dong, ZHANG Yu-Liang, SUN Jing, FAN Hong-Jun. One-step Synthesis of Specific pH-responsive Carbon Quantum Dots and Their Luminescence Mechanism[J]. Journal of Inorganic Materials, 2019, 34(12): 1309-1315.

Figures/Tables 7

Fig. 1 TEM image (a), HRTEM image (b), XRD pattern (c), and Raman spectrum (d) of the prepared CDs with inset in (a) showing diameter distribution

Fig. 2 (a) FT-IR spectrum of prepared CDs, high-resolution XPS spectra of C1s (b), N1s (c) and O1s (d) of prepared CDs

Fig. 3 UV-Vis absorption spectrum of prepared CDs with insets showing optical images of prepared CDs under UV lamp (365 nm) (a) and ?uorescent spectra under various excitation wavelengths (b)

Fig. 4 Fluorescent spectra of as-prepared CDs with different pH values under various excitation wavelengths (a-g), fluorescent intensity at different pH under excitation of 360 nm (h) and optical images of prepared CDs with different pH under UV lamp (365 nm) (i)

Fig. 5 Fluorescent spectra of prepared CDs in methanol (a) and ethanol (b) under various excitation wavelengths

Fig. 6 Fluorescent spectra of prepared CDs in the mixed solution of methanol and water at methanol concentration of 75% (a), 50% (b) and 25% (c) under various excitation wavelengths, and their optical images under UV lamp excitation (365 nm) (d)

Fig. 7 Cell viability (a) and fluorescence images of MG-63 cells excited by UV (b), blue (c), and green light (d)

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