This paper is intended to demonstrate the effect of the high refractive index of an intermediary zinc oxide (ZnO) layer to improving the full width at half maximum (FWHM) of the surface plasmon resonance (SPR) reflectance curve. This case is an asymmetric dielectric structure (ADS) of low-loss surface plasmon resonance (LLSPR). The ADS-LLSPR chip is particularly interesting for two surface plasmons (SPs) mode of external and internal on a gold (Au) interface. These SPs have different energy fields, which enables separation of the surface and bulk refractive index changes. We optimize ZnO and Au thin films thicknesses through analytical comparisons with conventional SPR structures. Upon exposure to ethanol, the ADS-LLSPR chip showed a 2-times decrease in the FWHM and a 4.5-times larger shift in intensity interrogation. The ADS-LLSPR chip exhibits a widely linearity range, high accuracy and high sensitivity. This characteristic of the ADS-LLSPR chip is the basis for early diagnosis crucial in DNA-based viruses.
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