Nitrogen-doped graphene quantum dot for direct fluorescence detection of Al 3+ in aqueous media and living cells.

Graphene quantum dot (GQD) has been attractive in analytical science field due to its low toxicity, stable photoluminescence. Herein, nitrogen-doped GQD (N-GQD) was prepared by a facile solvothermal treatment of GO using dimethylformamide, and exhibited a green emission with 23.1% quantum yield. The N-GQD probe showed a selective and sensitive fluorescence enhancement response to Al ³⁺ , the mechanism might be the formation of a complex between Al ³⁺ and N-GQD constrained the photo-induced electron transfer (PET) process of N-GQD itself. With Benesi-Hildebrand equation, the binding constant and molar ratio between N-GQD and Al ³⁺ was calculated to be 4.6 × 10 ⁴ Lmol ^-1 and 1:1 respectively. The pK _a value of N-GQD was also determined to be 4.4 by capillary electrophoresis. In pH 4.0 PBS solution, there was a good linear relation between the fluorescence intensity and the logarithm of concentration of Al ³⁺ in the range of 2.5-75μmolL ^-1 , the limit of detection (3σ) was 1.3μmolL ^-1 . This "Off - On" fluorescence method had been applied to accurate quantification of aluminum in hydrotalcite tablets. What's more, the fluorescence switch property of N-GQD was explored by alternate addition of Al ³⁺ and EDTA. The probe was also utilized for detection Al ³⁺ in living cells due to its excellent biocompatibility.
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