In this research article, we introduce a novel oxidation-resistant approach in a Metal–Insulator–Metal (MIM) plasmonic biosensor, specifically designed for the detection and diagnosis of diabetes and kidney disease severity using urea and glucose biomarkers in urine. The proposed biosensor features a four-hand-shaped fan resonator with integrated nanodots and stubs within its waveguide. We optimized its performance through Finite Element Method (FEM) simulations, achieving a maximum sensitivity of 2470.48 nm/RIU and a Figure of Merit (FOM) of 50.15. To ensure chemical stability, we utilized an oxidation-resistant plasmonic material (Au) in our sensor, a critical factor for reliable biosensing applications. Additionally, we focus on Diabetic Kidney Disease (DKD), a significant global health challenge, emphasizing the need for early detection and point-of-care treatment. By exploiting minute changes in resonant wavelength resulting from light–matter interactions through the properties of Surface Plasmon Polaritons (SPPs) and MIM structures, our biosensor demonstrates promising capabilities for real-time and quantitative analysis of biomarkers critical for monitoring the stages of DKD.