The primary tool that we use for our experiments is a custom-built total internal reflection microscope (TIRFM) equipped with a back-illuminated CCD camera. We also rely on microfluidic flowcells that are machined and assembled in house and we "look" at biochemical reactions that are tethered to the sample chamber surface within the flowcells. This state-of-the-art optical approach to biochemistry relies on the evanescent field that is generated beyond a reflecting surface at the interface between two transparent materials of differing refractive indexes (in this case the aqueous buffer and the fused silica slide). The evanescent field penetrates approximately 100-200 nanometers into the aqueous sample and only illuminates fluorescent molecules that reside within this very tiny volume (less than 1 trillionth of a liter!) near the sample chamber surface. This surface selective illumination is what allows the detection of single fluorescent molecules by TIRFM because it reduces the background signal by several orders of magnitude compared to conventional epi-illumination.