It is significant for people with diabetes to know their body’s real-time glucose level, which can guide the diagnosis and treatment. Therefore, it is necessary to research continuous glucose monitoring (CGM) as it gives us real-time information about our health condition and its dynamic changes. Here, we report a novel hydrogel optical fiber fluorescence sensor segmentally functionalized with fluorescein derivative and CdTe QDs/3-APBA, which can continuously monitor pH and glucose simultaneously. In the glucose detection section, the complexation of PBA and glucose will expand the local hydrogel and decrease the fluorescence of the quantum dots. The fluorescence can be transmitted to the detector by the hydrogel optical fiber in real time. As the complexation reaction and the swelling–deswelling of the hydrogel are all reversible, the dynamic change of glucose concentration can be monitored. For pH detection, the fluorescein attached to another segment of the hydrogel exhibits different protolytic forms when pH changes and the fluorescence changes correspondingly. The significance of pH detection is compensation for pH errors in glucose detection because the reaction between PBA and glucose is sensitive to pH. The emission peaks of the two detection units are 517 nm and 594 nm, respectively, so there is no signal interference between them. The sensor can continuously monitor glucose in 0–20 mM and pH in 5.4–7.8. The advantages of this sensor are multi-parameter simultaneous detection, transmission-detection integration, real-time dynamic detection, and good biocompatibility.

Photonic crystal fibers (PCFs) with various micro to nano-scale features are of intensive interest for fiber sensing. Flexible fiber structures enable the selective control of fiber properties, such as transmission modes, dispersion tailoring, trigger of multiple nonlinear effects, and so on. In this paper, three pieces of few-mode PCFs (FM-PCFs) are designed and fabricated. Guided modes in each fiber are theoretically analyzed and experimentally observed through careful excitation. Later one of the PCFs (PCF1) is used as a fiber interferometer, based on the analyses of intermodal couplings/interferences of all PCFs. The intermodal interferences between linearly polarized (LP) core modes LP01/LP11 of PCF1 are experimentally investigated, using selective mode excitation technique. The fringe contrast and intensity of the interferences can be precisely manipulated by varying the relative energies of the LP01 and LP11 modes, as the basis for the intermodal interferometer. Different from most previous studies, the interferences are mainly limited to the two core modes, which intrinsically reduces the cross-influence from temperature variations, when this fiber is used for strain sensing. Experimentally, a strain sensor using this FM-PCF based Mach-Zehnder (MZ) interferometer, is demonstrated with a restrained temperature response. This work provides significant guidance for the construction of FM-PCF based fiber sensors with simple fabrication procedure and precisely controlled interference, and most critically, with reduced cross-sensitivity between temperature and strain.

A ratiometric fluorescence probe based on the conjugation of peroxyfluor-NHS (PF) and carbon dots (CDs) was designed for selective and rapid detection of glucose. When glucose was catalytically oxidized by glucose oxidase (GOx), the product H₂O₂ would react with colorless and non-fluorescent peroxyfluor moiety to give the colored and fluorescent fluorescein moiety which would absorb the energy of CDs emission at 450 nm due to the Förster Resonance Energy Transfer (FRET) and generate a new emission peak at 517 nm. The reaction between PF and H₂O₂ was slow with a rate constant of about 2.7 × 10⁻⁴ s⁻¹ under pseudo-first-order conditions (1 uM PF, 1 mM H₂O₂), which was unconducive to rapid detection. Given this, a short time detection method was proposed by studying the kinetics of the reaction between PF and H₂O₂. In this method, the detection time was fixed at three minutes. The linear detection of glucose could be well realized even if the reaction was partially done. As glucose concentration increased from 0.05 mM to 5 mM, the fluorescence intensity ratio (I₅₁₇/I₄₅₀) after 3 minutes’ reaction of CDs-PF and glucose oxidation products changed linearly from 0.269 to 1.127 with the limit of detection (LOD) of 17.19 μM. In addition, the applicability of the probe in blood glucose detection was verified.