A double-core photonic crystal fiber (PCF) based refractive index sensor is introduced to detect six different cancer-affected cells. A comparatively large air hole is considered in the middle of the fiber to be injected with fluids of normal and cancer-affected cells. Transmission length, the diameter of the air hole filling with samples, and the diameter of two other important air holes are studied in this work to attain a more appropriate performance of the presented sensor. The performance of the suggested sensor is studied by analyzing the variations in the transmission spectrum because of changes in the normal and affected cell refractive indices. The results display that the proposed sensor attains spectral sensitivities of 10,000 nm/RIU, 11,250 nm/RIU, 10,714.28 nm/RIU, 12,857.14 nm/RIU, 11,428.57 nm/RIU, and 12,500 nm/RIU corresponding to Basal cell cancer, cervical cancer HeLa cells, Jurkat cancer cell, PC12 cancer cell, MDA-MB-231 breast cancer cell, and MCF-7 breast cancer cell, respectively. Also, resolution as an important parameter in sensors evaluation is studied and the obtained results are 1×10-5\documentclass[12pt]{minimal}
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\begin{document}$$8\times {10}^{-6}$$\end{document} for the above-mentioned cells, respectively. Moreover, the maximum FOM value achieved for the reported biosensor is 22.03 1/RIU for the Basal cell. The proposed refractive index sensor can be implemented to detect different cancer cells because of its high sensitivity and simple design.