Similarly, Briand et al. compared the immobilisation of rabbit IgG using a pure mercaptoundecanoic acid (MUA); a mixed SAM of MUA and MCH; and a SAM of cystamine. The most homogenous layer was observed for the pure MUA SAM and cystamine appeared the least homogenous. Crosslinking protocols (Section 5.1) enabled Protein A to be immobilised to the surface, which formed a homogenous layer on the pure MUA, and the cystamine SAMs, while the mixed SAM showed aggregations of Protein A. Once the capture molecule IgG was bound to the Protein A, it was found the steric hindrance caused by the closely packed cystamine layer, caused this to have the lowest antigen binding of the three SAMs. Despite these drawbacks, cystamine has successfully been utilised in biosensors as the short carbon chain molecule in a mixed SAM and in conjunction with nanoparticles. ProLinker™ B is a calixarene derived, cup-shaped molecule, with two -SH groups, permitting thiol chemisorption. The biorecognition element can be immobilised directly on to the ProLinker™ B layer, with favourable orientation of the antigenic binding sites. With the thiol groups interacting with the substrate surface, the ether's oxygens form the upper rim of the cup, the crown ring, locking it into a cone conformer. Due to the direction of the ProLinker™ B dipole and the antibody dipole, the lowest energy and therefore most favourable orientation is an end-on interaction with the ProLinker™ B. The ionised amino group from a protein has a guest-host interaction with the crown ring, with hydrophobic interactions between methoxy group of the linker and hydrophobic residues of the protein as seen in Figure .