Background: Cyanide is an immensely poisonous chemical that is exceedingly noxious to the human body.
Methods: Considering this issue, we present a Rectangular core photonic crystal fiber (RPCF) to detect the cyanide. Zeonex is chosen as base material and the investigation is accomplished in the terahertz (THz) frequency region. Results: The RPCF model proffers high sensitivity, enlarged effective area, and insignificant confinement loss. Conclusion: It is very worthy to note that the proposed model structure can be fabricated by applying the existing fabrication techniques.Keywords: Optical sensor, PCF, relative sensitivity, cyanide, zeonex, electromagnetic spectrum.