Fluorescent carbon dots (CDs) are inspiring intensive research interests because of their high chemical stability, low toxicity and customizable surface functionalization. However, there are still some limitations such as low quantum yield, less active sites and so on. As research continues, nitrogen-doped carbon dots (N-CDs) have recently become of great interest because it addresses the above problems of CDs to achieve promising applications for them in biochemical sensing, environmental detection and other fields. In the past five years, doping CDs with nitrogen as a principle way to tune the intrinsic properties of CDs has been considered as an effective strategy, and the procedures for preparing N-CDs have become increasingly green and facile. But the formation mechanism of N-CDs is still not clarified. To easily understand the mechanism and expand its application fields, we reviewed the discovery history, preparation methods and optical properties of N-CDs, especially in latest developments of analytical and bioanalytical applications in quantitative analysis. We also give perspectives on future opportunities and promising applications, which would provide the reference for the development of N-CDs in analytical chemistry.

Contents
1 Introduction
2 Preparation and properties of nitrogen-doped carbon dots
2.1 Preparation of nitrogen-doped carbon dots
2.2 Properties of nitrogen-doped carbon dots
3 Applications in Quantitative analysis of nitrogen-doped carbon dots
3.1 Detection of ions
3.2 Detection of molecules
4 Conclusion and outlook