Facile preparation of highly fluorescent nitrogen-doped graphene quantum dots for sensitive Fe3+ detection

Abstract

Nitrogen-doped graphene quantum dots (N-GQDs) were synthesized by the hydrothermal method. The results of the transmission electron microscope and atomic force microscopy indicated that the average diameter and height of the homogeneously distributed N-GQDs were approximately 5 nm and less than 10 nm, respectively. The results of the X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirmed the successful incorporation of the N element into GQDs. The aqueous solution of N-GQDs dispersed in water remained stable and homogeneous at room temperature for 3 months. N-GQDs had a higher fluorescence intensity than GQDs and presented low toxicity and the survival rate of cells (3T3-Swiss albino) was more than 85% in the cytotoxicity test. To better understand the luminescence mechanism, the band gaps of GQDs and N-GQDs were calculated using the density functional theory (DFT). The effect of the pH value on the fluorescence intensity of N-GQDs before and after the addition of Fe3+ ions was investigated. N-GQDs were applied to selectively detect Fe3+ ions, and the results exhibited a wide linear correlation between the fluorescence intensity and the Fe3+ concentration of 0–100 uM with a detection limit of 0.74 uM. This study provided a simple and efficient synthesis method and proved the ultra-high Fe3+ detection selectivity and sensitivity of N-GQDs, offering the experimental and theoretical basis for N-GQDs’ applications in biosensing, bioimaging, environmental monitoring, etc.