 The sample is then deposited onto the sample window where it is pulled through the test and control regions by a paper wick via passive diffusion.The RSID unit is impregnated with fluid-specific antibodies conjugated to colored complexes that will re-dissolve and diffuse at this time.If the fluid in question is present in the questioned sample, antibodies at the test line will react to the colored antibody complexes and form a colored line.