A specific fluorescent dye for ex situ staining of vital islets of Langerhans: neutral red.

We present a new technique for specific ex situ fluorescent staining of islets of Langerhans with neutral red. Depending on the concentration of neutral red (1 microgram/ml), this technique allows the differentiation between exocrine and endocrine pancreatic tissue, according to differences in fluorescence intensity. Pancreatic islets can be stained not only in situ, but in particular ex situ after pancreas digestion. Since intravital staining of the pancreas in situ with neutral red is not applicable in human transplantation, the staining procedure ex situ may be a useful tool for islet purification by particle sorting, using a fluorescent-light-activated system; thus, a sufficient mass of purified islets for free transplantation may be isolated.