Multilayer Ag-Au Surface Plasmon Resonance Biosensor for Enhanced Refractive Index Sensitivity in the Biological Range

Vibhor Kumar Bhardwaj (Login required)
Teerthanker Mahaveer University, Moradabad, Uttar Pradesh, India

Alka Verma
Teerthanker Mahaveer University, Moradabad, Uttar Pradesh, India




DOI: 10.18287/JBPE26.12.010301

Abstract

Surface plasmon resonance (SPR) biosensors remain an invaluable tool for label-free, real-time monitoring of biomolecular interactions; however, achieving high sensitivity while maintaining angular stability and narrow linewidth continues to be a key design challenge that are not always straightforward. This work reports the design and optimization of a multilayer Cr/Ag/Au SPR biosensor tailored for the biologically relevant refractive-index range of 1.33−1.40, although slight deviations was observed in some simulations. Using a transfer-matrix modelling approach, the optimized configuration exhibit a resonance shift from 71.84° to 85.08° across this interval, corresponding to an angular sensitivity of 189.14 °/RIU, but a few outlier points did not fit perfectly. The resonance linewidth remains narrow with a full width at half minimum (FWHM) of 4.0°, yielding a figure of merit of 47.3 RIU⁻1, though some values fluctuates mildly under different grid resolutions. With an angular resolution of 0.01°, the theoretical limit of detection (LOD) is estimated to be 5.29×10⁻5 RIU, indicating excellent capability for detecting minute refractive-index variations even if noise sometimes slightly increases. Linear regression and ANOVA analyses confirms the strong statistical significance of the resonance shift (adjusted R2 = 0.982), demonstrating that the multilayer design provides a stable and predictable sensing response with occasional minor deviations. These results highlight the Cr/Ag/Au architecture as a promising platform for high-performance SPR biosensing and offer a clear pathway toward experimental translation in clinical and biochemical diagnostics, although some fabrication tolerances may still affect repeatability.

Keywords

Surface plasmon resonance; biosensors; Ag-Au multilayer; transfer-matrix method; biomedical diagnostics

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