Adsorption of organic phosphate as a means to bind biological molecules to GaAs surfaces

GaAs-based electronic devices have interesting applications in spintronics and as sensors. In the past, methods were developed to stabilize the surface of GaAs, since it is known to be highly sensitive and unstable. It turns out, however, that these particular properties can be used for controlling the electronic characteristics of the devices, by adsorbing molecules that affect the surface properties. Here, we concentrate on the adsorption of molecules that can be bound to GaAs through their phosphate group. Phosphate functional groups can be found in many biological molecules; therefore, the binding of organic phosphate to a semiconductor surface can provide the first step toward a new line of hybrid bioorganic/inorganic electronic devices. We investigated the adsorption of tridecyl phosphate (TDP) and compared its adsorption to that of dodecanoic acid (lauric acid), which contains a carboxylic binding group. The alkyl phosphate monolayer is found to bind to the GaAs surface more strongly than any other functional group known to date. In addition, we show that the adsorption of a DNA nucleotide (5'-AMP), as well as single-stranded DNA (ssDNA), on the GaAs surface occurs through the phosphate groups. Hence, DNA can be bound to these surfaces with no need for chemical modifications.