Integrating voltammetry and substrate-enhanced luminescence for noninvasive glucose sensing

Abstract

This study presents a novel noninvasive and enzyme-free dual sensor based on porous silicon (PSi) for the detection of D-glucose through tear fluid analysis. The sensor incorporates NaGdF₄:20% Yb³⁺, 2% Er³⁺ nanoparticles (YbEr-NPs) immobilized on a PSi substrate functionalized with a phenylboronic ester molecule. The YbEr-NPs enable luminescence-based sensing, exploiting the sensitivity of Er³⁺ ions to the OH vibrational groups present in D-glucose. Electrodes fabricated on a PSi substrate allow for voltammetric analysis, providing a second detection method. The voltammetric sensor achieved a limit of detection (LoD) of 20 mg/dL in the range of 20–200 mg/dL, which is suitable for detecting D-glucose concentrations in the tear fluid of diabetic patients. The luminescence-based sensor, utilizing the red-to-green emission ratio of YbEr-NPs, reached a LoD of 140 mg/dL in the range of 10–70 mg/dL, covering the hyperglycemic range. The interaction between the YbEr-NPs and the PSi substrate led to the appearance of new emission bands and increased intensity, attributed to surface defects acting as an additional excitation source. The 556 nm emission band showed a strong dependence on the D-glucose concentration, improving the LoD to 110 mg/dL. This provides a novel strategy for D-glucose detection based on the effect of the molecule on the interaction between the Rare-earth-doped nanoparticles and the PSi substrate. This triple-sensing approach offers a promising solution for noninvasive glucose monitoring, enabling detection in both the hypoglycemic and hyperglycemic ranges.