Experimental confirmation of strong fluorescence enhancement using one-dimensional GaP/SiO_2 photonic band gap structure

In this paper we report the experimental confirmation of the fluorescence enhancement effect using a one-dimensional photonic band gap (1D PBG) structure. This 1D PBG structure consists of periodic multilayer thin films with gallium phosphide (GaP) and silicon dioxide (SiO2) as the alternating high and low index materials. Strong evanescent field enhancement can be generated at the last interface due to the combination of total internal reflection and photonic crystal resonance for the excitation wavelength. In addition, the 1D PBG structure is designed as an omnidirectional reflector for the red-shifted fluorescent signal emitted from the surface bounded molecules. This omnidirectional reflection function helps to improve the collection efficiency of the objective lens and further increase the detected fluorescent signal. Compared with the commonly used bare glass substrate, an average enhancement factor of 69 times has been experimentally verified with quantum dots as the fluorescent markers. This fluorescence enhancer may find broad applications in single molecular optical sensing and imaging.