While the transition from optical fiber to planar waveguide substrates in LMR-based sensors has allowed for the development of more robust, cost-effective, and easily manufactured platforms, it has also presented challenges in optimizing critical sensor parameters such as resolution and sensitivity in biosensing. In this work, we introduce the application of gold nanoparticles (AuNPs) to enhance the sensitivity of a Lossy Mode Resonance (LMR)-based biosensor for the detection of vascular endothelial growth factor (VEGF) protein. The sensor was developed by depositing a nanometric TiO2 film on a planar waveguide, and its performance was assessed using three detection approaches: label-free, sandwich assay, and AuNP-labeled sandwich assay. The integration of AuNPs significantly improved sensitivity, enabling detection at concentrations as low as 0.1 ng/mL, surpassing the sensitivity of traditional label-free LMR-based sensors. These results demonstrate the potential of AuNP-enhanced LMR sensors for detecting low concentrations of biomarkers with high specificity and sensitivity, positioning them as promising tools for biosensing applications.