Improved glucose detection limit based on phosphorescence from protected metalloporphyrin triplet state

Non-invasive indirect blood glucose monitoring can be realized by detecting low concentrations of glucose (0.05-5 mM) in tears, but sensitive optical indicators are required. The intensity of the phosphorescence of a candidate optical indicator, palladium hematoporphyrin monomethyl ether (Pd-HMME), is increased by oxygen consumption under sealed conditions in the presence of glucose and glucose oxidase. However, the glucose detection limit based on this mechanism is high (800 μM) because the phosphorescence is completely quenched under ambient oxygen conditions and hence a large amount of glucose is required to reduce the oxygen levels such that the phosphorescence signal is detectable.

To improve the glucose detection limit of Pd-HMME phosphorescence-based methods, the triplet protector imidazole was introduced, and strong phosphorescence was observed under ambient oxygen conditions. Detectable phosphorescence enhancement occurred at low glucose concentrations (<200 μM). Linear correlation between the phosphorescence intensity and glucose concentration was observed in the range of 30-727 μM (R² = 99.9 %), and the detection limit was ∼10 μM. The glucose sensor has a fast response time (∼90 s) and excellent selectivity for glucose.

These results indicate the potential of the developed optical indicator for fast, selective, and reliable low-concentration glucose sensing.