Highly Sensitive TIT4T Fiber-Based WaveFlex Biosensors Functionalized With MXene-QDs for Xanthine Detection

In this study, we present an optical fiber biosensor (i.e., a WaveFlex biosensor) developed for the precise quantification of xanthine, a crucial metabolite presents in the human body, and certain food items. Elevated xanthine levels are often indicative of various health conditions, making accurate concentration detection essential for disease diagnosis, assessing physiological states, and pre-emptively evaluating food quality. Our WaveFlex biosensor is fabricated using a single-mode fiber with a unique taper-in-taper with four tapered (TIT4T) fiber structure, achieved through a series of meticulous tapering processes. After nanoparticle coating and enzyme functionalization, this fiber-based biosensor becomes adept at detecting xanthine concentrations. The tapered structure facilitates the interaction of the optical field transmitted through the fiber with the external environment. The presence of immobilized gold nanoparticles (AuNPs) and MXene quantum dots (MXene-QDs) on the fiber's surface collectively triggers localized surface plasmon resonance (LSPR) phenomena, enhancing detection sensitivity. By functionalizing the optical fiber with the xanthine oxidase (XO) enzyme, we enable highly specific xanthine detection. Our sensor demonstrates impressive capabilities, with a sensitivity of 1.93 nm/mM, a wide linear detection range spanning from 0 to $800\,\,\mu \text{M}$ , and a low limit of detection at $146.11\,\,\mu \text{M}$ . Furthermore, we conducted rigorous tests to assess the sensor's reusability, stability, pH test, and reproducibility, further highlighting its exceptional performance.