Design and fabrication of an omnidirectional reflector as ultra-sensitive biochemical sensing platform

Fluorescence has important applications in chemical and biological sensing and analysis due to the large selection of fluorescent markers and their specificity in staining. In order to achieve high sensitivity, the strength and the collection efficiency for the fluorescence signal is a critical issue that needs to be addressed. In this paper, we study the use of one dimensional photonic band gap (1D PBG) structures to enhance the florescence excitation and collection. The 1D PBG structure is designed to create an enhanced evanescent field for the excitation wavelength at the interface of last layer of the PBG and the sample. Meanwhile, the 1D PBG also serves as an omnidirectional reflector for the florescence signal, leading to higher collection efficiency. The combination of both effects provides a significant enhancement of florescence signal. In order to verify the feasibility, GaP/SiO2 multilayer thin film stack is designed and fabricated. High quality GaP/SiO2 multilayer thin film stack is fabricated using sputtering technique. The sputtered GaP thin film is characterized using ellipsometer. GaP thin film with very high refractive index (n=3.45 at 633 nm) was obtained. The performance of the multilayer stack as omnidirectional reflector is also reported.