Silicon nitride (SiN) microdisk resonators with a 40-nm horizontal air slot and a nanocrystal Si (nc-Si) emitting top layer are investigated. The whole structure is fabricated using only a single deposition and lithography step, with the light-emitting layer self-aligned to excite the slot-mode within the air slot. The nc-si are excited via top-pumping using a UV laser diode, and the visible light emission from nc-Si is coupled into the whispering gallery mode (WGM) with the light concentrated in the air slot. The WGM resonances are observed via side-photoluminescence setup using a Si charge-coupled device. The feasibility of applying this structure as a biosensor is demonstrated, with an estimated surface sensitivity of 2.8 nm/nm.