Surface Modification and Ordered Monolayers

According to the definition of chemical sensors (Chap. 1), they have an interface in direct contact with the sample. This interface is the preferred place where the critical interaction with the sample takes place. This interaction is connected with the fimctions of recognition (receptor function) and signal 

Films on a substrate, either thick or thin films, caimot act generally as receptor or transducer immediately. An exception to this rule exists with layers of semiconducting metal oxide films like Sn02, which can interact directly with reducing gases. It is much more common io functionalize sensor siuTaces prior to use and to use metalhc or ceramic layers as a support only for the sensitive film. Functionalizing is the role of surface modification. The latter has become a broad special field, important in particular for electrochemical sensors. 

Surface Cleaning. The first step in surface modification is generally cleaning. Prior to cleaning, every surface is dirty, i.e. at the very least it is covered by adsorptive layers. But sometimes native adsorption layers are usefiil or can fulfil a receptor function, as with the oxide film on a platinum surface. In the majority of cases, adsorbed layers must be removed to establish a definite initial state for further modification. 

Sensor surfaces can consist of most materials. Metals, oxide ceramics and carbon in its different modifications including diamond, silicates and organic 

A very elegant method of attaching functional groups is linkage to ordered layers. This is a special case of covalent attachment mentioned in the above list. 

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