<p>In this paper, a photonic crystal fiber sensor is designed and proposed based on the laws of light propagation in the fiber and random holes in its center. The optimization algorithm governing the geometrical parameters of the fiber is the Nelder–Mead optimization algorithm, based on which the radius of the air holes and the thickness of the plasmonic layer are at their best value. This optimization results in a better coupling of the core mode and the plasmonic mode, and the highest peak resonance occurs, followed by the highest sensitivity. Three results have been obtained from this random structure. The first result is that increasing the air filling fraction does not necessarily reduce the confinement losses. The second result is that the wavelength sensitivity has a slight dependence on the location of the central holes (up to 20%). The third result, by changing the location of the central holes, the fiber may lose its sensing properties. The central air holes have been changed from two to four and have been randomly positioned. The highest amplitude sensitivity of 5160 (RIU^− 1) and the highest wavelength sensitivity of 7000 (nm/RIU) have been established for the sensor in the refractive index of 1.4 and in the fiber with three central holes.</p>