Actively tunable prism-free SPR biosensor using an atomic medium for malaria stage diagnosis

Abstract

Malaria remains a critical global health challenge, where rapid and stage-specific diagnosis differentiating ring, trophozoite, and schizont forms is essential for effective treatment. Surface plasmon resonance biosensors offer a powerful label-free detection platform; however, conventional implementations rely on bulky prism couplers that limit miniaturization and point-of-care applicability. In this work, we present a purely theoretical and numerical investigation of a novel prism-free SPR biosensor for malaria stage diagnosis, integrating a five-level 87 Rb atomic medium as an actively tunable substrate. Unlike passive dielectric layers, this atomic system exploits electromagnetically induced transparency (EIT) and microwave-driven double-dark resonances to achieve active, independent control over the real and imaginary parts of its dielectric permittivity, satisfying the stringent wavevector matching condition without an external prism. The sensor architecture comprises a blood analyte layer, a protective monolayer of MoS 2 , an optimized 38 nm copper film, and the atomic medium. Our full-wave numerical simulations, conducted using the transfer matrix method (TMM) at a 633 nm wavelength, systematically evaluate sensor performance across normal blood and infected stages. Our results demonstrate that the microwave field strength serves as a critical tuning parameter. At the optimal condition, the sensor achieves a maximum sensitivity of 227.7277 degree/ Refractive Index Unit (RIU), a minimum reflectivity of 0.0015, a narrow full width at half maximum (FWHM) of 0.5263 ∘ , a figure of merit (FOM) of 432.666 RIU − 1 , and an ultra-low limit of detection (LOD) of 4.42 × 10 − 6 RIU. The resonance angle exhibits a clear, progressive shift across infection stages, with a total angular variation of approximately 3.93 ∘ between normal and schizont stages. This theoretical work establishes a new paradigm for compact, actively tunable SPR sensing, offering a promising pathway toward high-precision, stage-specific malaria diagnostics in resource-limited settings.