A novel lossy mode resonance (LMR) based sensor modified with TiO2/PSSAu-nanoparticles (Au-NPs) bilayers is proposed for refractive index (RI) sensing. Three significant parameters of Au-NPs, including the shape, the interval between each other and the distance from the surface of LMR, are optimized using finite element method. Meanwhile, the resonance spectra of sensors with different amounts of bilayers are recorded and discussed. And then the sensitivity is studied and compared. Results indicate that Au-NPs significantly enhance the electric field strength (EFS) around sensors. In order to maximize EFS, the shape of Au-NPs is set as pyramid, the interval between each other is set as 0.1 degrees and the distance from the surface of LMR is set as 5 nm. Meanwhile, as the number of bilayers increase, the valley in resonance spectra becomes more obvious. Because of the modification of bilayers, the sensitivity of the sensor we proposed reaches 6,405 nm/RIU when surrounding RI is from 1.3667 to 1.4140, which is 1.4 times higher than that of the sensor which only modified with TiO2/PSS.
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