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 (μ-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 μm 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 μ-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 μ-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.