ImmEdge Hydrophobic Barrier Pen The ImmEdge™ Pen (H-4000; pap pen) is a hydrophobic barrier pen for immunohistochemistry and in situ hybridization. It is designed to provide a heat-stable, water-repellent barrier that keeps reagents localized on tissue specimens and prevents mixing of reagents when multiple sections are mounted on the same slide.The pale blue barrier is insoluble in alcohol and acetone but is completely removed by all commonly used xylene and “xylene substitute” clearing agents. The ImmEdge™ Pen contains no ozone-depleting solvents and is compatible with enzyme or fluorescence-based detection systems.ImmEdge™ Pens are supplied as sets of 2 large pens, sealed in polyethylene bags.