Surface Chemistry for Stable and Smart Molecular and Biomolecular Interfaces via Photochemical Grafting of Alkenes

Abstract

Many emerging fields such as biotechnology and renewable energy require functionalized surfaces that are "smart" and highly stable. Surface modification schemes developed previously have often been limited to simple molecules or have been based on weakly bound layers that have limited stability. In this Account, we report on recent developments enabling the preparation of molecular and biomolecular interfaces that exhibit high selectivity and unprecedented stability on a range of covalent materials including diamond, vertically aligned carbon nanofibers, silicon, and metal oxides. One particularly successful pathway to ultrastable interfaces involves the photochemical grafting of organic alkenes to the surfaces. Bifunctional alkenes with a suitable functional group at the distal end can directly impart functionality and can serve as attachment points for linking complex structures such as DNA and proteins. The successful application of photochemical grafting to a surprisingly wide range of materials has motivated researchers to better understand the underlying photochemical reaction mechanisms. The resulting studies using experimental and computational methods have provided fundamental insights into the electronic structure of the molecules and the surface control photochemical reactivity. Such investigations have revealed the important role of a previously unrecognized process, photoelectron emission, in initiating photochemical grafting of alkenes to surfaces. Molecular and biomolecular interfaces formed on diamond and other covalent materials are leading to novel types of molecular electronic interfaces. For example, electrical, optical, or electromechanical structures that convert biological information directly into analytical signals allow for direct label-free detection of DNA and proteins. Because of the preferential adherence of molecules to graphitic edge-plane sites, the grafting of redox-active species to vertically aligned carbon nanofibers leads to good electrochemical activity. Therefore researchers could graft electrocatalytic materials to carbon nanofibers to develop new types of selective electrocatalytic interfaces. Extending this chemistry to include metal oxides such as TiO(2) may lead to highly specific and efficient chemical reactions and new materials with useful applications in photovoltaic and photocatalytic energy conversion.

Methods of surface chemical patterning

“…В этом случае для взаимодействия с поверхностью молекуле-пре-курсору требуется УФ-активация, поэтому при-менение шаблонов позволяет создать моно-слой из органических молекул исключительно в местах облучения [2]. В дальнейшем получен-ный органический слой может быть использован для построения более сложных функциональных поверхностей [3,4].…”

“…In this case a precursor molecule demands UV activation for interaction with the surface, thus, the use of masks permits to create a monolayer of organic molecules exactly in the points of UV exposure [2]. Subsequently this monolayer can be used as a base for construction of more complex functional surfaces [3,4].…”

Carbon Substrates: A Stable Foundation for Biomolecular Arrays

“…We focus here on hydrogen plasma treatment. Exposing the carbon surfaces to an inductively coupled hydrogen plasma ( a ) results in a substrate in which carbon dangling bonds at the surface are bonded to hydrogen atoms (61, 62) and ( b ) ensures substrates prepared at different times have a uniform composition because oxygen species on the surface are removed or reduced (59); this uniformity is important when performing mechanistic studies or comparing different surfaces chemistries. Finally, it ( c ) changes the electronic properties of the material (e.g., its work function or electron affinity) and determines its chemical reactivity (61–63).…”

“…Several chemistries have been developed to modify the surface of hydrogen-terminated carbon substrates (62, 64–66). We highlight here three chemistries that result in the formation of a carbon-carbon bond between the surface and ( a ) an alkyl magnesium halide (67), ( b ) an aryldiazonium salt(68), or ( c ) an alkene-containing molecule (62).…”

“…We highlight here three chemistries that result in the formation of a carbon-carbon bond between the surface and ( a ) an alkyl magnesium halide (67), ( b ) an aryldiazonium salt(68), or ( c ) an alkene-containing molecule (62). …”