Multiband Terahertz Spiral Metasurface for Detection of Malaria with Enhanced Sensitivity

We present the design and numerical analysis of a multiband metasurface based on a left-hand Archimedean spiral etched out of gold for malaria detection in the terahertz (THz) range. The sensor exhibits three absorption peaks, with the highest absorption efficiency of 99.98 % observed at 5.69 THz, where the highest quality factor of 100.2 is also achieved. The metasurface achieves three resonances within the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1-10 \text{THz}$</tex> range, enabling precise detection of refractive index changes in red blood cells (RBCs) during malaria progression. A peak sensitivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$632 \text{GHz} / \text{RIU}$</tex> was observed for malaria-infected samples, underscoring the sensor's high performance. The spiral design enhances sensitivity and quality factor, distinguishing healthy RBCs from those infected at different malaria stages. By leveraging the unique electromagnetic properties of the Archimedean spiral, the metasurface exhibits strong field localization, facilitating high-accuracy detection of subtle refractive index shifts as the malaria parasite advances from the trophozoite to schizont phase. The proposed approach demonstrates multiband operation, high sensitivity, and compatibility with THz frequencies, known for their safety in biological sensing. This work highlights the potential of compact, on-chip THz biosensors for rapid, non-invasive malaria screening, offering a valuable tool for early detection and monitoring in malaria-endemic regions.