Ultraviolet Absorbance Spectroscopy in a 3-Dimensional Microfluidic Chip

Abstract

The strength of absorbance by a compound is linearly dependent on the path length of the detection cell. Because of this, performing high sensitivity absorbance measurements on samples in microfluidic chips, where channel depths are roughly 10–50 µM, is extremely challenging. There have been several attempts to overcome this inherent difficulty, including 1) coupling optical fibers into the chip and directing light along a section of the channel [1], and 2) creating a multi-reflection cell [2]. We have taken another approach, which is to construct a chip containing a three-dimensional fluid path. In our chips, the section of the fluid path running perpendicular to the plane of the chip forms a detection cell with a path length equal to 720 µm, allowing for highly sensitive absorbance measurements.