Theory and demonstration of fluorescence-based refractometric sensing in glass micro-capillaries with a silicon nanocrystal-embedded film

We demonstrate fluorescence-based refractometric sensing using whispering gallery modes in glass micro-capillaries with a quantum-dot film. A theoretical analysis of the device is also presented. The device exploits a solution-based method to coat the interior channel of a glass capillary with a high-quality film consisting of fluorescent silicon nanocrystals. This film supports the whispering gallery modes that propagate largely within the nanocrystal film. The inner tail of the mode samples the capillary channel; this forms the basis for a refractometric sensing method for fluids pumped through the channel. A refractometric sensitivity of 9.8 nm/RIU was observed in this structure, offering a new, fluorescence-based alternative to liquid core ring resonator structures.