Al 2 O 3 Microresonator Based Passive and Active Biosensors

Al 2 O 3 microresonators were realized for sensing applications of both passive and active devices. Passive microring resonators exhibited quality factors up to 3.2×10 5 in air. A bulk refractive index sensitivity of ~100 nm/RIU was demonstrated together with a limit of detection of ~10 −6 RIU. Functionalizing their surface allowed for the label-free detection of the biomarker rhS100A4 from urine with a limit of detection of 3 nM. Furthermore, single-mode Al 2 O 3 :Yb 3+ microdisk lasers were realized that could operate in an aqueous environment. Upon varying the bulk refractive index their lasing wavelength could be tuned with a sensitivity of ~20 nm/RIU and a LOD of ~3×10 −6 RIU.