Fiber-Optic Surface Plasmon Resonance Sensor for Trace Cadmium-Ion Detection Based on Ag-PVA/TiO2 Sensing Membrane

A reflective fiber-optic surface plasmon resonance (RFSPR) sensor was proposed for detection of cadmium ion (Cd ²⁺ ) in water based on polyvinyl alcohol/titanium dioxide (PVA/TiO ₂ ) composite sensing film. The silver (Ag) was deposited on the side and end surfaces of plastic cladding multimode fiber (PCMF), and then uniform PVA/TiO ₂ was coated on the outside surface of Ag covered PCMF. The Ag films on the end face and the side face of the fiber are respectively playing the roles in enhancing light reflection and exciting SPR effectively. The Ag-PVA/TiO ₂ composite film is served as the sensing film of Cd ²⁺ . The results show that the sensor can detect 0- $1~\mu \text{M}$ Cd ²⁺ in aqueous solution. The maximum sensitivity of Cd ²⁺ is 315.2 nm/ $\mu $ M, and the minimum detection concentration is $0.006~\mu $ M (about 0.76 ppb), which is much less than that (3 ppb) of the international standard. This assay for Cd ²⁺ detection possesses high sensitivity, excellent selectivity and good stability. The fiber- optic method might become a potential Cd ²⁺ detection tool in aqueous solution.