Diamond for bio-sensor applications

A summary of photo- and electrochemical surface modifications applied on single-crystalline chemical vapour deposition (CVD) diamond films is given. The covalently bonded formation of amine- and phenyl-linker molecule layers is characterized using x-ray photoelectron spectroscopy, atomic force microscopy (AFM), cyclic voltammetry and field-effect transistor characterization experiments. Amine- and phenyl-layers are very different with respect to formation, growth, thickness and molecule arrangement. We detect a single-molecular layer of amine-linker molecules on diamond with a density of about 1014?cm?2 (10% of carbon bonds). Amine molecules are bonded only on initially H-terminated surface areas to carbon. In the case of electrochemical deposition of phenyl-layers, multi-layer formation is detected due to three-dimensional (3D) growths. This gives rise to the formation of typically 25?? thick layers. The electrochemical grafting of boron-doped diamond works on H-terminated and oxidized surfaces.After reacting such films with hetero-bifunctional crosslinker molecules, thiol-modified ss-DNA markers are bonded to the organic system. Application of fluorescence and AFM on hybridized DNA films shows dense arrangements with densities of up to 1013?cm?2. The DNA is tilted by an angle of about 35? with respect to the diamond surface. Shortening the bonding time of thiol-modified ss-DNA to 10?min causes a decrease of DNA density to about 1012?cm?2. Application of AFM scratching experiments shows threshold removal forces of around 75?nN for DNA bonded on phenyl-linker molecules and of about 45?nN for DNA bonded to amine-linker molecules. DNA sensor applications using Fe(CN6)3?/4? mediator redox molecules, impedance spectroscopy and DNA-field effect transistor devices performances are introduced and discussed.