"Silanes" refer to a group of compounds with four substituents on a silicon atom, customarily in the form of RSiX 3 . Though these are often described in regards to a silicon surface, they have been successfully bound to several electrode surfaces in construction of electrochemical biosensors. The three most commonly used silanes for SAM formation are 3-aminopropyltrimethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPMS) and 3-glycidoxypropyldimethylethoxysilane (GPMES), all which contain methoxy groups to facilitate binding to the surface. Alkyltrichlorosilanes will also be discussed which have the general formula RSiCl 3 . The growth of a silane SAMs includes an irreversible covalent cross-linking step. The silicon forms bonds with the hydroxyl groups on the hydrolysed surface. The remaining Si-X bonds are hydrolysed resulting in the Si-O-Si linkage between adjacent silanes and the formation of silanols (SiOH), stabilising the layer. Water is necessary for this cross-linking step, without it the silicon will form three bonds (or however many X groups it has) to the hydroxyl groups at the surface. The most commonly used solvents are hexadecane, Isopar™ G and bicyclohexyl; sometimes with the inclusion of small volumes of either chloroform or carbontetrachloride to the solution to control agglomeration caused by the predominance of the cross-linking. 63 For alkyltrichlorosilanes, such as octadecyltrichlorosilane (OTS), there is a threshold temperature, below which an ordered monolayer will form and this threshold temperature is affected by the chain length. This is due to the competition between the reaction of the hydrolysed trichlorosilyl groups for the formation of a polymer or to react with the surface for the formation of a SAM. The surface reaction becomes more favourable as the temperature decreases. Biernbaum et al. compared SAMs formed from OTS and octadecyltrimethoxysilane (OTMS) and observed a difference in the tilt of the alkyl chain to the substrate surface. OTS' carbon chain was practically perpendicular to the surface (0 ± 5°), whereas, OTMS has a higher tilt angle of 20 ± 5°. It was proposed this was due to the different adsorption mechanisms since chlorine atoms are more reactive than methoxy groups and thus more likely to form oligomers in solution.