Fiber-Optic Surface Plasmon Resonance Sensor for Trace Cadmium-Ion Detection Based on Ag-PVA/TiO<sub>2</sub> Sensing Membrane
Ting Li, Wenlin Feng
Abstract
A reflective fiber-optic surface plasmon resonance (RFSPR) sensor was proposed for detection of cadmium ion (Cd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) in water based on polyvinyl alcohol/titanium dioxide (PVA/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> composite film is served as the sensing film of Cd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> . The results show that the sensor can detect 0- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{M}$ </tex-math></inline-formula> Cd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> in aqueous solution. The maximum sensitivity of Cd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> is 315.2 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> M, and the minimum detection concentration is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.006~\mu $ </tex-math></inline-formula> M (about 0.76 ppb), which is much less than that (3 ppb) of the international standard. This assay for Cd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> detection possesses high sensitivity, excellent selectivity and good stability. The fiber- optic method might become a potential Cd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> detection tool in aqueous solution.