Waveguide-assisted plasmonic nanoparticle sensor using light scattering-based optical interrogation

Biosensing platforms based on localised surface plasmon resonance (LSPR) have become prominent due to their capability for label-free and real-time detection of biomolecular interactions. This paper proposes a slab waveguide-enhanced scattering-based nanoplasmonic sensing approach that utilizes the strong light-matter interaction of gold nanoparticles (AuNPs) to achieve refractive index (RI) sensing and biomolecule detection. Unlike conventional transmission or spectral-shift-based methods, the proposed system relies on monitoring variations in the scattered light intensity, providing a high-contrast and simplified detection mechanism. The sensing principle is governed by plasmonic scattering, where the intensity of scattered light increases with the surrounding RI owing to enhanced local electromagnetic field confinement. Experimental results demonstrate a clear and linear response of the normalized scattered intensity to RI variations, confirming a reliable sensing performance. A waveguide-integrated AuNP plasmonic sensor based on light scattering detection is demonstrated for RI sensing. The platform achieves high sensitivity (1.60 RIU^-1) and resolution (6.21 × 10^-5RIU), outperforming absorption-based detection. Enhanced evanescent coupling and LSPR significantly improve the signal response, enabling accurate, reliable, and high-resolution optical sensing in compact configurations. Furthermore, biosensing experiments using immunoglobulin G reveal a concentration-dependent signal with a limit of detection of 3.26 ng ml^-1(21.7 pM) and excellent linearity (R²= 0.99), enabling accurate quantitative detection. The obtained results underscore the suitability of slab waveguide-enhanced scattering-based nanoplasmonic sensing platforms for enabling compact, cost-efficient, and high-performance solutions across biomedical diagnostics, environmental analysis, and point-of-care testing.