Miniaturized fluorescence detection system to remove background noise of the incident light using micro mirror and lens

This paper reports a study on the miniaturized fluorescence detection system using reflecting mirror. It is integrated on a microfluidic chip to remove the signal offset and background noise of the incident beam. Previous approaches were integrated optical fiber, inclined incident beam, and split beams by a stop on microlens. However, they have problems of difficult assembly or loss of intensity at center. Therefore, we tried another optical configuration using microlens and mirror, which are patterned on the bottom and top surface of glass microfluidic chip, respectively. The exciting light is focused by the microlens on the bottom mirror and it is reflected out through the incident aperture. Microfluidic chip with microlens and mirror was microfabricated and fluorescence of the microchannel was measured with various size of mirror. The fluorescence signal on photomultiplier tube showed enhanced properties showing smaller offset and less background noise than that of microfluidic chip without micromirror. Theoretical model of intensity propagation of exciting beam and intensity of signal to background ratio was also analyzed to predict the improvement with low lens fluorescence and channel refraction.