U-shaped Fiber Based-Long Range Surface Plasmon Resonance Sensor for Sensitive Hg2+ Detection

An U-shaped fiber long range surface plasmon resonance (LRSPR) sensor is proposed to detect trace Hg²⁺ in water system. The U-shaped fiber is bend and coated with 100 nm MgF₂ and 50 nm Au film, the U-shaped fiber LRSPR senor could combine the advantage of high sensitivity and low full width of half maximum (FWHM) by the optimization of the fiber bending radius (BR) and MgF₂ thickness. With the functionalization of single-stranded DNA (ssDNA) on the Au layer by covalent bond, the Hg²⁺ could be selectively detected by the thymine (T) base pairs, which would form stable T-Hg-T structure by the folding of ssDNA and cause the change in surface refractive index (RI). The detection range of Hg²⁺ is 50 nM-5 mM, and the limit of detection (LOD) reaches at 60 nM. The selectivity and stability are proved to be good and the recovery from the spiked tap water is also tested. The good performance and wide range of the proposed sensor indicates high potential for future Hg²⁺ sensor development and multiple using scenarios.