Accurate and accessible glucose detection is essential for clinical diagnostics, point-of-care testing, food safety, and biosensing applications. In this study, we present a simple, scalable, and dual-mode glucose sensor that integrates commercial potassium permanganate (KMnO) with glucose oxidase to enable sensitive and selective detection in the clinically critical range of 1-5 mM. Leveraging the strong oxidative power and distinct optical characteristics of KMnO, the sensor operates via both absorbance measurement at 400 nm and visual colorimetric analysis, displaying a clear color change from purple to pink and yellow upon reaction with glucose. The system achieves a low detection limit of 0.63 mM and demonstrates high specificity, effectively minimizing interference from substances such as maltose, sucrose, galactose, citric acid, thiourea, and uric acid. Recovery rates ranging from 84.8% to 104.8% in glucose-spiked solutions and up to 99.6% in artificial saliva validate its reliability and practical applicability. By combining colorimetric simplicity with quantitative absorbance measurements, this platform provides an efficient, eco-friendly, and cost-effective solution for glucose monitoring with strong potential for integration into disposable test strips, portable devices, and wearable biosensors for real-time health tracking.