Upconversion nanoparticle-based optical glucose sensing using phosphoresce lifetime spectroscopy excited with 980 nm laser sources

Upconversion nanoparticles (UCNPs) hold strong promise for the development of durable, contactless, and implantable photonic sensors owing to the deep tissue penetration of their near-infrared (NIR) excitation source and minimal photodamage by NIR light. Here, we report a Ba 2 ErF 7 @Ba 2 La 4 F 7 @Ba 2 Yb 0.98 F 7 Tm 0.02 @Ba 2 La 4 F 7 UCNP-based glucose sensor that functions under 980 nm NIR laser excitation. The sensor is comprised of two layers, including an oxygen-sensitive bottom layer of PtTFPP-UCNPs doped in a xerogel film, and a top layer of glucose oxidase (GOx) immobilized within a hydrogel matrix. Excitation of oxygen-sensitive platinum (II) tetrakis(pentafluorophenyl)porphyrin (PtTFPP) complex is mediated by luminescence resonance energy transfer (LRET) from UCNPs. Glucose detection is based on oxygen consumption during the GOx-glucose reaction, which modulates the phosphorescence lifetime of PtTFPP. The glucose level is obtained from the slope of the time-dependent phosphorescence lifetime response instead of conventional end-point phosphorescence lifetime measurements, providing faster glucose quantification. The slope varies linearly with glucose concenrtation, which covers the physiologically relevant levels for detecting abnormalities in diabetic patients. Optical characterization of the sensors revealed a sensitivity of 13.4E-12 µs·dL·mg⁻¹ ·min⁻¹ , a limit of detection (LOD) of 11 ± 1.45 mg/dL, short-term and long-term instabilities of 0.25 ± 0.02 % and 1.6 ± 0.9 %, respectively, and a reproducibility of 1.4 %. An in vitro cytotoxicity assay using human dermal fibroblasts (HDFs) demonstrated 94 ± 7 % cell viability after 24 h incubation, confirming excellent biocompatibility of the sensor.