Self-luminescent horizontal air-slot microdisk resonators for biosensing applications

Abstract

The applications of photonic devices for optical biosensing have been actively studied for the past decade. Yet there remain several problems on low cost and on？site applications. One problem is that bulky and expensive apparatus such like tunable lasers and complex coupling setups for generating resonant modes are usually required for measurement. In order to address this problem, we fabricated and applied visible range self-luminescent Si-rich silicon nitride (SRN) horizontal slot disk resonators for biosensors. In 2011, the self-luminescent SRN disk resonators that whispering gallery modes (WGM) can be generated by a simple optical pumping have been developed and high Q factors about $10^4$ were demonstrated. In order to improve the SRN disk resonator into a more sensitive biosensor, we fabricated and characterized a 25nm thin slot inserted SRN disk resonator with $8 \mu m$ diameter. The Q factors and free spectral positions of WGMs of the slot disk resonator were calculated using finite difference time domain (FDTD) method, and experimentally verified by measuring micro PL spectra. The Q factors of higher than 6000 near 800nm wavelength were demonstrated. Then, the slot disk resonator was applied for biosensing. The sensitivity of 4.6 nm/nm was calculated with finite element method (FEM) and experimentally verified by using Bovine Serum Albumin (BSA). In the actual biosensing experiment of streptavidin detection, the movements of resonance peaks after dipping in streptavidin solutions were measured and a sensitivity of 4.79 nm/($\mu g/ml$) was demonstrated. Finally, a micro prism mirror and PDMS micro fluidic channel were integrated with the slot disks in order to detect the PL signals in an aqueous environment. Using the platform, the bulk sensitivity of 260 nm/RIU of the slot disk was experimentally verified with glycerol solutions.