Thiols are organic compounds which are terminated by an -SH group. It is this terminal that favourably interacts with the electrode surface. The other terminal generally consists of a carboxyl or amine group for the immobilisation of biomolecules. The formation of a thiol-based SAM consists of a two-step process; the first step is the fast, physical adsorption of the thiol molecules onto the surface, with some of the molecules perpendicular to the surface. The second step is much slower as the physisorbed layer is converted to a chemisorbed monolayer and reordered to be parallel to the surface. Alkanethiols are the most established SAMs used for biosensors . Long alkyl chain thiols have a higher degree of order due to the attractive van der Waals forces between adjacent chains, and exhibits a tilt of ∼30° in the direction of its nearest neighbour, suggesting longer alkanethiols (≥10 alkyl carbons) would be advantageous for an electrode modification. However, long chains produce a densely packed monolayer which restricts access to the underlying electrode surface, inhibiting electrochemical processes. Whereas short chains have a large tilt angle and low coverage. For electrochemical sensing applications, mixed thiols are often employed, using a short chain thiol to disrupt the long chain SAM. Mixed monolayers also allow for large biorecognition elements to be sufficiently spaced apart, reducing steric hindrance, as well as allowing access for mediator molecules to the electrode surface.