Enhanced scattering induced fluorescence through gold nanoarrays and zinc oxide thin films

This work presents an optical analysis of zinc oxide (ZnO) thin-films employed as a sensitivity enhancer inside photonic biosensing devices. An array of gold nanocylinders is placed onto a SU-8 polymer waveguide, on a BK7 glass substrate. The system is immersed in water and is used to exploit scattering-induced fluorescence to find microcontaminants in aqueous solutions. The assessment was carried out with a 450 nm light excitation because of its compatibility with a wide range of fluorophores. ZnO thin films were implemented as buffer layers at various thicknesses. Results show how the waveguide-array coupling efficiency and the light scattering out of the array plane is greatly improved by implementing ZnO buffer layers: up to 4.2 fold enhancement is achieved when the ZnO film thickness is equal to 225 nm.In addition, a far-field analysis shows how the ZnO presence doesn't affect the collimation and the diffraction angle of the projected beam, suggesting its implementation also for light-routing applications. Such results serve as promising support for the use of ZnO thin films as buffer layers in the field of high-performance scattering-induced fluorescence for health, food, environment monitoring and telecommunication devices.