Sensitive monitoring of refractive index by surface plasmon resonance (SPR) with a gold α-iron (III) oxide thin film

In order to solve the problem that the optical fiber surface plasmon resonance (SPR) sensor is insufficiently sensitive for biomolecule detection, a novel sensing probe was proposed and designed, where the semiconductor material α-Fe2O3 was introduced for the first time. The α-Fe2O3 with high refractive index enhances the electric field and evanescent field depth at the interface between the α-Fe2O3 film and the ambient medium, resulting a sensitive performance. The characteristics of the sensors with gold film and α-Fe2O3 film at different thicknesses were analyzed and compared by finite element method. The thicker the α-Fe2O3 film, the higher the sensitivity. When the thickness of gold nanofilm is 50 nm and the thickness of α-Fe2O3 nanofilm is 20 nm, the highest figure of merit (FOM) is 50.98 RIU−1, corresponding to a sensitivity of 4800 nm/RIU, which is 2.16 times more sensitive than the traditional SPR sensor. In addition, three α-Fe2O3 film thickness-assisted SPR sensors were successfully prepared with the highest sensitivity of 4173.1 nm/RIU, which is nearly two times higher than without the α-Fe2O3 film. The enhancement after introducing α-Fe2O3 nanofilms and its promising application in the field of biosensing were confirmed through experiments and simulations.