Soumita Chakraborty, Rajib Chakraborty
Early detection of cancer requires highly sensitive, label-free biosensing platforms capable of resolving extremely small refractive-index variations in biological media. In this paper, we have proposed a novel, to our knowledge, graphene-coated rib–ridge photonic crystal Bragg cavity waveguide (PCW) for early-stage cancer detection. This particular PCW structure is monomaterial-based, and as such, thermal stress generation due to deposition of multi-layers of dissimilar materials as well as the number of lithographic steps can be reduced. Graphene has been chosen and employed as the plasmonic sensing layer owing to its superior infrared plasmonic response and tunable quantum conductivity, and its performance is comparatively evaluated against conventional gold and silver coatings. The sensor operates in the near-infrared to mid-infrared spectral range (60–300 THz), which is optimal for biological sensing. For the actual sensing case, normal blood ( n =1.376) and cancerous blood ( n =1.390) are introduced into the defect region. The stopband-edge spectral marker shows a wavelength shift of 3.5 nm and a sensitivity of 250 nm/RIU. In addition, graphene-thickness optimization shows that sensitivity can exceed 600 nm/RIU in the monolayer graphene regime, where strong surface interaction is achieved with minimal optical-field screening. Three-dimensional finite-difference time-domain (FDTD) method is used for the simulations to get accurate and more realistic results. In order to improve diagnostic reliability and lower false-positive responses, multiple optical parameters are methodically examined to guarantee reliable, noise-resilient detection of subtle refractive-index changes linked to malignant cells. Furthermore, a quantum-enhanced interrogation framework has been introduced, where squeezed optical states are employed to suppress measurement noise below the standard quantum limit, thereby improving the limit of detection without altering the physical sensor architecture. The proposed graphene-assisted Bragg cavity PCW, combined with quantum-enhanced readout, offers a highly sensitive and clinically viable platform for early cancer biosensing.