One of the common approaches to achieve a well-oriented immobilisation of antibodies is the use of Protein G or A which are bacterial proteins from Streptococci and Staphylococcus aureus, respectively. They can be immobilised onto the modified electrode surface using cross-linking protocols discussed in Section 5.1. These proteins selectively bind to the Fc region of antibodies controlling the orientation of the bioreceptor and leaving the Fab paratope containing regions free and accessible to the antigens. Once the antibody is bound to either Protein A or Protein G it can be further stabilised by cross-linking the antibody to the Protein A/Protein G support .