ZIF-8/β-cyclodextrin composite-based plasmonic sensor for selective detection of copper ions in water

The selective detection of different metal-ion pollutants is of great significance for assessing water quality and investigating pollution sources. To address this issue, a composite suspension of zeolitic imidazolate framework-8 and β-cyclodextrin (ZIF-8@β-CD) and functionalized a prism-based surface plasmon resonance (SPR) sensor with the suspension via drop casting has been prepared for the selective detection of Cu²⁺ in water. The interaction between ZIF-8 and Cu²⁺ is mainly related to ion exchange and coordination interaction, while the hydroxyl group on the surface of cavity-structured β-CD confers excellent selective binding ability with Cu²⁺. Based on these combined effects, the maximum resonance wavelength shift of the ZIF-8@β-CD-functionalized SPR sensor was 23.03 nm within a Cu²⁺ concentration range of 0-320 µM, while that was merely 5.12 nm for the sensor modified with ZIF-8 alone. Additionally, the introduction of β-CD produces a synergistic effect with ZIF-8, significantly enhancing the sensor's selective capture capacity for Cu²⁺ relative to the tested interfering metal ions, including Cd²⁺, Zn²⁺, Cr³⁺, Fe³⁺, Co²⁺, Mn²⁺, Ca²⁺, and Mg²⁺. Consequently, the resonance wavelength shift showed a good linear relationship with Cu²⁺ concentration over the range 0-80 µM, yielding a sensitivity of 0.2 nm/µM and a LOD of 4.35 µM. This study presents a novel, straightforward strategy for functionalizing SPR sensor interfaces to enable high-performance, selective detection of Cu²⁺, with significant value for aquatic ecosystem monitoring and freshwater resource safety.