Controlled functionalization and multistep chemical manipulation of covalently modified Si(111) surfaces

A hydrogen-terminated Si(111) surface has been covalently modified by UV ir radiation in the presence of ethyl undecylenate leading to a Si(111)-C10H20 CO2Et surface. It is possible to carry out a diverse range of chemical mani pulations of the ester group on the surface. For example, reduction with so dium borohydride provides a surface terminated with a primary alcohol. Reac tion with an alkyl Grignard reagent gives a tertiary alcohol that can be ac ylated with acetyl chloride. Finally, hydrolysis of the ester leads to a ca rboxylic acid terminated surface that can be coupled to an amino acid using a standard solid phase amide coupling protocol. The surface density of the ester function can be controlled by dilution of the reacting ester with a long-chain alkene. This has the beneficial effects of minimizing the disrup tion of the alkyl chain packing in the monolayers and avoiding steric block ing of the ester group. It is expected that the ability to precisely contro l the average distance between large biomolecules on surfaces will impact o n future molecular electronic, sensor, and biochip technologies.