HERmark uses two monoclonal antibodies specific for unique epitopes on the HER2 receptor. This results in both antibodies binding to the same HER2 receptor in close proximity1 The fluorescent VeraTag (V) reporter is conjugated to a monoclonal antibody (Ab1) specific for HER2. A second HER2-specific monoclonal antibody (Ab2) is conjugated to biotin, which is then linked to a photosensitizer molecule (PM)1 Photoactivation of the sample at a specific wavelength activates the PM, generating free radical oxygen. The free radical oxygen can cleave the VeraTag reporter in close proximity. The released VeraTag reporter is collected and subsequently quantified using standard capillary electrophoresis1 The amount of cleaved VeraTag reporter is proportional to the concentration of HER2 in the sample1

1. Shi, Y., Huang, W., Tan, Y. et. al. A Novel Proximity Assay for the Dectection of Proteins and Protein Complexes: Quantitation of HER1 and HER2 Total Protein Expression and Homodimerization in Formalin-fixed, Paraffin-Embedded Cell Lines and Breast Cancer Tissue. Diagn Mol Pathol. 2009,18:11-21.