Because of the extreme toxicity of cyanide anions, the development of colorimetric and fluorescent sensors for the cyanide anion (CN^-) has received considerable attention. Among numerous CN^- sensors, the colorimetric or fluorescent sensors received more and more attention because these kinds of sensors possess a lot of advantages such as high sensitivity, does not require expensive equipment and easy to operate. This review article highlights advances in the research of colorimetric or fluorescent sensors for the cyanide anion after 2006. According to recognition mechanisms of these sensors, we grouped them into six categories, including hydrogen bond based CN^- sensors, deprotonation based CN^- sensors, addition reaction based CN^- sensors, coordination based sensors, nano-material based CN^- sensors, and the sensors based on other recognition mechanism. This review summarizes the main design principles, CN^- recognition abilities of the sensors. The developing orientation for further research is presented.

Contents
1 Introduction
2 Design principles of colorimetric and fluorescent CN-sensors
3 Hydrogen bond based CN-sensors
4 Deprotonation based CN-sensors
5 Addition reaction based CN-sensors
5.1 Addition of CN-to alkene
5.2 Addition of CN-to boride
5.3 Addition of CN-to Schiff base
5.4 Addition of CN-to spiro-compound
5.5 Addition of CN-to carbonyl group
6 Coordination based CN-sensors
6.1 Direct coordination
6.2 Competitive coordination
7 Nano-material based CN-sensors
8 Sensors based on other recognition mechanism
9 Conclusion and outlook