Excitation coupling of Au/ZnO band-gap energy for enhancing the performance of surface plasmon resonance biosensor

This paper reports a novel design of a surface plasmon resonance (SPR) device that can be developed into a high-performance biosensor. The design utilizes wurtzite crystal structure semiconductor (zinc oxide, ZnO) layers to enhance the SPR signal quality and to improve the full width at half maximum (FWHM) of the SPR reflectivity curve. There exists a new mechanism when the excitation in the plasmon energy is in resonance with the ZnO band-gap (BG) energy transfer process. The excitation energy between Au and ZnO causes an interactive, coupled phenomenon with the ZnO BG (λ_BG = 360-430 nm, 3.1-3.4 eV) when it matches the ZnO-Au interface surface plasmon (400 nm). We have optimized the design of the ZnO and Au thin films thicknesses through analytical comparisons with conventional SPR structures. Upon exposure to ethanol, the ZnO-Au device showed a 2-times decrease in the FWHM and a 4.5-times larger shift in intensity interrogation. The ZnO-Au device exhibits a wider linearity range and very higher sensitivity. This characteristic of the ZnO-Au device is the basis for realizing accurate and specific biomolecular detection.