Abstract: Nitrogen doped carbon dots (N-CDs) with an average size of 3.88 nm were prepared via a one-pot hydrothermal method by using neutral red and formamide as the carbon precursors. The as-synthesized N-CDs exhibit excellent water dispersibility as well as good photostability. Moreover, on the basis of ratiometric fluorescence emission characteristics by the interaction between N-CDs and Ag⁺, a new analytic method has been developed, and the effects of ionic strength and pH on N-CDs are estimated. Under the optimized condition, a good linearity is presented between the Ag⁺ concentration in the range of 0~12 μmol/L and the fluorescence intensity ratio at 520 and 580 nm (520/580 nm). The detection limit is 0.14 μmol/L. The interference research shows that N-CDs have high sensitivity and selectivity for Ag⁺, which could be attributed to the amino groups on the surface of the N-CDs that could bind to Ag⁺ and form the complex of N -CDs-Ag⁺. In addition, the test results based on different water samples (tap water, spring water and river water) for Ag⁺ detection show that the recoveries are within 98.5%~104.2%.

Key words: Carbon dots, Ratio fluorescent detection, Ag⁺