Abstract
A transmission fiber-optic surface plasmon resonance (SPR) sensor based on three-core optical fiber (TCF) coated with mercaptoundecanoic acid (MUA)/ nonionic polyacrylamide (NPAM)/zinc oxide (ZnO) composite film for the detection of chromium ions (Cr3+) in water was proposed and fabricated. Multi-mode fiber (MMF) was spliced with both ends of TCF to form the MMF1-TCF-MMF2 sensing structure. The silver (Ag) film was deposited on the surface of TCF cladding, and then a uniform MUA/NPAM/ZnO composite film was coated on the outer surface of the Ag film to adsorb Cr3+, resulting in the wavelength shift of the SPR resonance peak. After adsorption of Cr3+, the refractive index of the sensing film changed and the resonance wavelength shifted about 62 nm. The detection limit of the sensor is about 0.029 μΜ (1.5 ppb), and the minimum detection concentration of Cr3+ is about 0.2 µM (10 ppb), which is far lower than that of the World Health Organization standard (50 ppb). The sensor shows excellent selectivity, high sensitivity and good stability for the trace Cr3+, and has potential application for monitoring Cr3+ in water.
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