E132 Indigo

E132 in a 0.2% aqueous solution is blue at pH 11.4 and yellow at 13.0. E132 is also a redox indicator, turning yellow upon reduction. Another use is as a dissolved ozone indicator through the conversion to isatin-5-sulfonic acid. This reaction has been shown not to be specific to ozone, however: it also detects superoxide, an important distinction in cell physiology. It is also used as a dye in the manufacturing of capsules.

In obstetric surgery, E132 solutions are sometimes employed to detect amniotic fluid leaks. In urologic surgery, intravenous injection of E132 is often used to highlight portions of the urinary tract. The dye is filtered rapidly by the kidneys from the blood and colors the urine blue. This enables structures of the urinary tract to be seen in the surgical field, and demonstrate if there is a leak. However, the dye can cause a potentially dangerous increase in blood pressure in some cases.

Although not absorbed by the cells, the E132 stain, sprayed onto regions of interest, highlights the topography of the mucosal surface with its blue coloring. Generally used at a concentration around 0.2%, E132 stain is useful as a screening method for diagnosing minute lesions, to differentiate between benign and malignant lesions, as well as to facilitate the application of ME to observe and analyze the surface structure of a lesion, delineate boundaries of early-stage malignant lesions and estimate the invasion depth of cancer. It has been used to diagnose Barrett’s esophagus, evaluate villous atrophy, diagnose and discriminate polypoid and non-polypoid lesions in the colon, and diagnose gastric adenoma and cancer.