Early and precise detection of cancer biomarkers is essential for improving treatment outcomes and survival rates. In this work, we propose a highly sensitive surface plasmon resonance (SPR) biosensor that incorporates a mirror-symmetric sandwich structure using Ti₃C₂Tₓ MXene layers. The biosensor architecture is based on a Kretschmann configuration, comprising a BK7 prism, a dual-metallic Cu/Ni film, and two symmetrically placed MXene nanosheets that encapsulate the analyte region. This mirrored sandwich design enhances the electromagnetic field-analyte interaction, thereby significantly boosting sensing performance. The optical response of the structure was modeled using the transfer matrix method (TMM), accounting for multi-layer interference and complex refractive indices. Performance was evaluated by detecting two breast cancer cell lines—MCF-7 and MDA-MB-231—based on their refractive index signatures. The proposed biosensor achieved a sensitivity of 315.9°/RIU for MCF-7 cells and 302.8°/RIU for MDA-MB-231 cells, with corresponding figures of merit (FOM) of 48.7 RIU⁻1 and 47.99 RIU⁻1, respectively. These results represent a significant improvement over existing SPR biosensors. Analyses of power loss revealed that a single MXene layer configuration facilitates maximal energy transfer between incident light and surface plasmons, contributing to the observed sensitivity enhancements. This study underscores the potential of MXene-based mirror-symmetric sandwich architectures for next-generation, label-free cancer diagnostics, combining high sensitivity, structural simplicity, and scalability for practical biomedical applications.
