Diabetes treatment requires reliable blood glucose monitoring to allow for appropriate adjustments and interventions. The conventional finger-prick test is associated with significant discomfort and poor compliance, highlighting the critical need for non-invasive, user-friendly solutions. This study proposes and validates an open-source, multi-wavelength spectroscopy system that combines visible (660 nm) and near-infrared (940 nm) wavelengths through six distinct transmission and reflection strategies. The system was validated through a rigorous three-phase process. Phase I established a preliminary regression model against a commercial meter using 500 controlled samples ( \(R^2\) up to 0.8832). Phase II expanded this validation in 96 healthy volunteers, confirming high clinical acceptability (over 95% in Zone A, Clarke Error Grid) and a mean absolute error of 8.438 mg/dL relative to the commercial device. Critically, Phase III performed a definitive clinical validation, comparing our system and the commercial meter against the venous plasma glucose (VPG) gold standard. This analysis definitively established the clinical failure of all reflection-based strategies (resulting in Zone D errors), while confirming 100% clinical safety (Zones A/B) for all transmission modes. Notably, our multi-wavelength transmission (MT) strategy achieved 100% Zone A accuracy and demonstrated superior analytical precision (tighter ISO 15197:2015 compliance) than the ISO-compliant commercial benchmark when both were compared to the VPG. This work validates a transparent, open-source platform as a clinically reliable and accurate non-invasive alternative for intermittent glucose monitoring.
