We developed a plasmonic refractive index (RI) with ametal-dielectric-metal (MDM) structure that utilizes two Persian Orsi windows-like separated cavities with a high figure of merit (FoM) and ultrasensitivity. The simulated and optimized Ag-air-Ag MDM sensor for surface plasmon resonance (SPR) offers high RI sensitivity (SRI) and the ability to detect blood plasma concentration (BPC). The results verified that structural parameters have an effect on SRI, full width at half maximum (FWHM),FoM, sensitivity of blood plasma (Sp) for right and left peaks, whose values are 1 345.45 nm?RIU?1, 32 nm, 42.04 RIU?1, 0.26 and 0.19 nm?L?g-1, respectively. The proposed design opens a new horizon in sensor devel- opment.