Nitrogen doping can effectly adjust the compositions and structures of carbon dots and hence enhance their fluorescence. In this work, we report a fast and low-cost route for synthesis of nitrogen-doped carbon dots (N-CDs) by microwave pyrolysis of citric acid and ammonium within 7 min. The as-prepared N-CDs contain plentiful oxygen and nitrogen functional groups, and dispaly intense fluorescence with high quantum yield of ca. 44.3% and have an average size of 1.8 nm. The obtained N-CDs exhibit highly stable against photobleaching, ionic strengths, and can be used for selective and sensitive detection of Fe(III). It is postulated that the Fe³⁺-mediated fluorescence quenching is attributed to the charge transfer between N-CDs and Fe³⁺. In particular, the emission peaks from blue to red region can be tuned by interparticle distance of N-CDs, simply by increasing the concentration of N-CDs in aqueous solution, which indicates its potential applications as a promising optical image probe in multicolor cellular imaging.

氮掺杂可以有效地调节碳点的组成和结构，从而增强其荧光。在这项工作中，我们报告了通过微波热解柠檬酸和铵在7分钟内合成氮掺杂碳点（N-CDs）的快速且低成本的途径。所制备的N-CD含有大量的氧和氮官能团，并且显示出强烈的荧光，且具有约90的高量子产率。44.3％，平均大小为1.8 nm。所获得的N-CD表现出对光漂白和离子强度的高度稳定性，可用于Fe（III）的选择性和灵敏检测。据推测，Fe ³⁺介导的荧光猝灭归因于N-CD与Fe ³⁺之间的电荷转移。特别是，仅通过增加水溶液中N-CD的浓度即可通过N-CD的粒子间距离来调节从蓝色到红色区域的发射峰，这表明其在多色细胞成像中作为有希望的光学图像探针的潜在应用。