Near-infrared quantum dot-doped hydrogel fiber for ratio-metric fluorescence sensing of Cu²⁺ ions

Copper ions (Cu²⁺) play critical roles in biological systems but induce toxicity at elevated concentrations. This study, to our knowledge, reports a novel ratio-metric fluorescence sensor based on near-infrared (NIR)-emissive PbS quantum dot (QD)-doped hydrogel fiber sensor for real-time, selective detection of Cu²⁺. The sensor employs a biocompatible and mechanically flexible HF with a core-cladding structure to confine light within the core for efficient transmission. Densely silica-coated PbS QDs (Si-QDs, emission at 1000 nm) serve as a stable reference signal, while copolymer-functionalized PbS QDs (P-QDs, emission at 1300 nm) exhibit Cu²⁺-specific fluorescence quenching via photoinduced electron transfer. By ratiometrically monitoring the dual emission intensities (F = I₁₃₀₀/I₁₀₀₀), the sensor achieves quantitative Cu²⁺ detection with a linear range of 0−100 µM and a limit of detection of 1.57 µM, effectively mitigating environmental interference. This work synergistically integrates the biocompatibility of hydrogels with the deep tissue penetration advantages of the NIR window. It has been preliminarily tested in laboratory environments, establishing a foundational platform for future-deep tissue implantable sensors.