Spectrometric analysis using liquid metal mirrors in a microfluidic device

Abstract

This paper presents a new absorbance measurement device using multiple internal reflections and a new novel spectrometer for both of them using fluidic mirrors filled with liquid metal. Liquid metal mirrors reflect and gather light from LED with high reflectivity and small sample volume. Optical path length has been extended with various incident angles of 20$\deg$, 30$\deg$, 40$\deg$ and 50$\deg$. We demonstrated the enhancements of the sensitivity and limit of detection (LOD) compared to the air mirrors and linear channel. As incident angle lowers, optical path length extension becomes more effective without trade-offs of sensitivity and LOD. This device with incident angle of 50$\deg$ has a 84 nM of LOD and 3.62 x $10^{-4}$ of sensitivity for absorbance measurement of fluorecein diluted in deionized water. The spectrometer is suitable for direct spectral analysis in the sample channel plane using fluidic slit and mirror filled with liquid metal. Solutions of phenol red and trypan blue which are used widely for biomolecular detection are measured for spectrometric analysis. This platform can be simply adapted to the applications using the fiber optics integration. The measurements of phenol red and trypan blue result 212 nM, 154 nM of LOD and 1.09 x $10^{-3}$, 8.10 x $10^{-4}$ of sensitivity respectively.