The FocalCheck Thin-Ring Fluorescent Microspheres Kit is specifically designed to help researchers examine the alignment, sensitivity and stability of confocal laser scanning microscopes. We have treated the microspheres in this kit with dyes to stain the surface of each bead, resulting in a well-defined dye layer that creates a ring in optical sections. These microspheres produce a striking visual representation of instrument misalignment or other optical aberrations, making them ideal tools for optimizing the performance of confocal microscopes. Each suspension in the kit contains beads with a different color configuration. One suspension contains beads with two ring stains (green and red). The second suspension contains beads that have a green ring stain and a dark red stain throughout. The beads in the third suspension have a red ring stain and are stained blue throughout.