Micromachined Multigroove Silicon ATR FT-IR Internal Reflection Elements for Chemical Imaging of Microfluidic Devices

The performance of low-cost, microgroove silicon (Si)-based internal reflection elements (mu-groove IREs) for infrared chemical imaging of microfluidic devices is described. A custom-designed, horizontal microscope coupled with an imaging focal plane array area detector is described. After characterizing the inherent distortions of the microscope under wide field illumination, a checkerboard pattern lithographically printed on the principal reflection surface was imaged to determine the spatial resolution of the experimental setup which was approximately 14 mu m per pixel. The image contains different regions of varying quality. Geometric ray tracing indicates that the different components in the image are caused by multiple beam paths through the mu-groove IRE. Regions of high image quality can be selected to cover a field of view with lateral dimensions of several hundred micrometers. Proof of concept chemical imaging with mu-groove IREs is demonstrated through the successful mapping of isotope exchange between two co-laminar flows of water and heavy water in a single microfluidic channel. A prospective on how imaging quality with near diffraction limited spatial resolution could be achieved is also provided.