Figure 4

Refractive index sensitivity measurement of gold thin film with many gold cylindrical bumps of an approximate height of 180 nm. (a) The resonance peak wavelength with saline water of different concentration (pure water, 1%, 5%, 10%, 15%, 20%, 25%) and the refractive index is 1.3333, 1.3348, 1.3419, 1.3508, 1.3597, 1.3687, 1.3776 respectively. For each concentration of saline water, 10 gathered data is averaged to get the final resonance peak wavelength of the corresponding saline concentration. The inset depicts the transmission spectrum of deionized water and 25% saline water. The peak wavelength around 600 nm is blue-shifted with increased refractive index from deionized water to 25% saline water. (b) The refractive index sensitivity fitting line of periodic nano-hole array perforated gold film using saline water, and the refractive index sensitivity is −71.15 nm/RIU with R-square = 0.98. Error bars represent the residual error, which is the difference between measured value and fitted value with the confidence coefficient of 0.95.