Sirius red is an acidic hydrophilic staining that colors collagen fibers in red. The technic is based on the tight-binding of the stain sulfonic acid groups with the basic groups of collagen fibers:
– Collagen I fibers are very abundant in the body
– Collagen III fibers are constitutive of reticular fibers
When binding to collagen fibers, Sirius red molecules increase their bi-refringence. In polarized light, the thickest collagen fibers appear yellow/orange while the finest (including reticular fibers) are green. Moreover, the picric acid (a hydrophobic anionic stain) facilitates the staining by coloring in yellow.
Sirius red is the most used staining in research or routine diagnostic to evaluate the tissue destructuring levels. Typically, it allows to observe fibrosis levels in a lot of cases of inflammation induced by cancer, vascular or metabolic pathologies.
Sirius red staining may be applied on all types of organs or tissues, particularly hearth, kidney, liver and lung sections.