A Highly Selective Fiber-Optic Surface Plasmon Resonance Sensor Based on an alkaline MXene/Layered Double Hydroxide Hybrid for Trace-Level Detection of Ni(II).

A highly selective fiber-optic surface plasmon resonance (SPR) sensor was developed for trace detection of Ni2+. A gold nanolayer was deposited onto a single-mode optical fiber, yielding a refractive index sensitivity of 1925.9 nm/RIU. An alkaline MXene/layered double hydroxide (alk-MXene/LDH) hybrid structure was subsequently fabricated via mechanical self-assembly using a two-dimensional Ti3C2 MXene substrate and immobilized on the SPR sensing interface for selective Ni2+ detection. Benefiting from the layered structure of LDH and the abundant oxygen-containing functional groups on MXene, the composite effectively adsorbs and enriches Ni2+, thereby enhancing the sensing response. The sensor exhibits a sensitivity of 4.7 nm/(μg·mL-1) over a concentration range of 0-4 μg/mL with a limit of detection of 5.6 × 10-2 μg/mL. These results demonstrate its applicability for trace heavy metal ion detection in environmental and industrial water systems and provide a strategy for the development of high-performance, cost-effective sensing platforms.