Photo‐ and electrochemical bonding of DNA to single crystalline CVD diamond

Abstract

AbstractAlkene and nitrophenyl molecules have been covalently bonded to single crystal diamond using photochemical and electrochemical techniques. The surface density of electrochemically grafted nitrophenyl groups is about 5% of a monolayer (8 × 1013 molecules/cm2) on initially H‐terminated diamond. Covalently‐bonded nitrophenyl groups on single‐crystalline diamond are characterized to have two successive reversible one‐electron transfer reactions due to a regularly‐oriented arrangement. On oxidized surface of boron doped electrodes, a slightly (10%) smaller density is detected. Photochemical attachment of alkene molecules results also in a well arranged films as detected by angle resolved X‐ray photoelectron spectroscopy (XPS). The density of 10‐amino‐dec‐1‐ene molecules protected with trifluoroacetic acid (“TFAAD”) is calculated to be in the range 2 × 1014 molecules/cm2. The bonding mechanism of Alkene molecules to high quality hydrogen terminated single crystalline CVD diamond has been characterized using a variety of experiments which show that photo‐excited electrons of 5 eV energy trigger the photochemical attachment. The minimum time required to achieve a monolayer attachment of TFAAD molecules on (100)(2 × 1):H diamond is discussed and compared with experimental data from XPS. The benzene and alkene linker molecules are then reacted with the heterobifunctional cross linker sulphosuccinimidyl‐4‐(N‐maleimidomethyl)cyclohexane‐1‐carboxylate and finally with thiol‐modified ss‐DNA to produce a DNA‐modified diamond surface. The interaction with complementary and partially mismatched DNA is characterized by fluorescence microscopy. Microscopic properties of DNA layers on diamond have been characterized by contact‐ and oscillatory‐mode atomic force microscopy (AFM). A comparison of bonding forces, detected by contact mode AFM, reveals significant bonding strength differences. For both, electro‐ and photochemically bonded DNA, tilted molecule arrangements are detected, with angles in the range 30 ° to 46° with respect to the diamond surface. The DNA films are dense with a surface roughness of about 5 Å. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)