Fluorescence enhancement via single-core liquid waveguides in microfluidic channels

A single-core liquid waveguide is reported to be used in the fluorescence enhancement. The liquid waveguide consists of the high refractive index liquid core and the low refractive index sheath liquid. The diameter of the liquid core can be tuned by sheath flow, and the liquid waveguide can work in different status of the refractive index profiles by the diffusion of the high refractive index solution. Because of the total internal reflection on the liquid interface and the focusing by the gradient refractive indices, the intensity of the fluorescent light collected inside the liquid core is increased. The fluorescence enhancement by the liquid waveguide is characterized by measuring the intensities from the top and the end of the liquid waveguide by the spectrometer. The result shows that the fluorescence enhancement is successfully achieved in the liquid waveguide by controlling the refractive index profiles of the liquids.