Numerical Analysis of WS2/Si3N4 for Improved SPR-Based HIV DNA Detection

Talia Tene^1*Yesenia Cevallos²Jessica Alexandra Marcatoma Tixi³Natalia Alexandra Pérez Londo³Lala Gahramanli⁴Cristian Vacacela Gomez^5*

• ¹Universidad Técnica Particular de Loja, Loja, Loja, Ecuador
• ²National University of Chimborazo, Riobamba, Chimborazo, Ecuador
• ³Escuela Superior Politécnica del Chimborazo, Riobamba, Chimborazo, Ecuador
• ⁴Baku State University, Baku, Azerbaijan
• ⁵National Laboratory of Frascati (INFN), Frascati, Italy

Surface-plasmon-resonance (SPR) sensors provide label-free nucleic-acid diagnostics, yet they must detect the sub-nanometre refractive-index changes generated by short HIV-DNA hybridisation. Using a transfer-matrix framework, we design a multilayer architecture that couples a 50 nm silver mirror to the analyte through a 7 nm (10 nm) silicon-nitride spacer capped with a monolayer of WS₂. This impedance-matched stack (Sys₃) concentrates the evanescent field at the recognition surface while chemically passivating the metal. Numerical screening calibrated with published optical constants predicts an angular sensitivity of 167 ° RIU⁻¹, a limit of detection of 2.99 × 10⁻⁵ RIU and a quality factor of 56.9 RIU⁻¹, outperforming gold-based benchmarks and approaching values reported for more reactive ZnSe buffers. Reversing the dielectric sequence (Sys₄) increases sensitivity to 201 ° RIU⁻¹ but lowers fabrication yield and storage stability, establishing Sys₃ as the most scalable option.Proof-of-concept measurements demonstrate sub-picomolar quantification of HIV DNA in phosphatebuffered saline without enzymatic amplification. The materials palette is compatible with complementary-metal-oxide-semiconductor processes, enabling streamlined integration of highresolution SPR sensing into point-of-care viral-load platforms for resource-limited settings.