Michael Daenen

Structural and optical properties of DNA layers covalently attached to diamond surfaces

Label-free detection of DNA molecules on chemically vapor-deposited diamond surfaces is achieved with spectroscopic ellipsometry in the infrared and vacuum ultraviolet range. This nondestructive method has the potential to yield information on the average orientation of single as well as double-stranded DNA molecules, without restricting the strand length to the persistence length. The orientational analysis based on electronic excitations in combination with information from layer thicknesses provides a deeper understanding of biological layers on diamond. The pi-pi* transition dipole moments, corresponding to a transition at 4.74 eV, originate from the individual bases. They are in a plane perpendicular to the DNA backbone with an associated n-pi* transition at 4.47 eV. For 8-36 bases of single- and double-stranded DNA covalently attached to ultra-nanocrystalline diamond, the ratio between in- and out-of-plane components in the best fit simulations to the ellipsometric spectra yields an average tilt angle of the DNA backbone with respect to the surface plane ranging from 45 degrees to 52 degrees . We comment on the physical meaning of the calculated tilt angles. Additional information is gathered from atomic force microscopy, fluorescence imaging, and wetting experiments. The results reported here are of value in understanding and optimizing the performance of the electronic readout of a diamond-based label-free DNA hybridization sensor.

Diamond-Based Molecular Platform for Photoelectrochemistry

Boron doped diamond (BDD) thin film was found to exhibit higher photocurrent conversion efficiencies and photostability compared to commonly used transparent conducting oxides (ITO and FTO) owing to the matching energy levels and strong C-C bonding at the organic/diamond interface.

Topographical and Functional Characterization of the ssDNA Probe Layer Generated Through EDC-Mediated Covalent Attachment to Nanocrystalline Diamond Using Fluorescence Microscopy

The covalent attachment method for DNA on nanocrystalline diamond (NCD), involving the introduction of COOH functionalities on the surface by photoattachment of 10-undecenoic acid (10-UDA), followed by the 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)-mediated coupling to NH 2-labeled ssDNA, is evaluated in terms of stability, density, and functionality of the resulting biological interface. This is of crucial importance in DNA biosensor development. The covalent nature of DNA attachment will infer the necessary stability and favorable orientation to the ssDNA probe molecules. Using confocal fluorescence microscopy, the influence of buffer type for the removal of excess 10-UDA and ssDNA, the probe ssDNA length, the probe ssDNA concentration, and the presence of the COOH-linker on the density and functionality of the ssDNA probe layer were investigated. It was determined that the most homogeneously dense and functional DNA layer was obtained when 300 pmol of short ssDNA was applied to COOH-modified NCD samples, while H-terminated NCD was resistant for DNA attachment. Exploiting this surface functionality dependence of the DNA attachment efficiency, a shadow mask was applied during the photochemical introduction of the COOH-functionalities, leaving certain regions on the NCD H-terminated. The subsequent DNA attachment resulted in a fluorescence pattern corresponding to the negative of the shadow mask. Finally, NCD surfaces covered with mixtures of the 10-UDA linker molecule and a similar molecule lacking the COOH functionality, functioning as a lateral spacer, were examined for their suitability in preventing nonspecific adsorption to the surface and in decreasing steric hindrance. However, purely COOH-modified NCD samples, patterned with H-terminated regions and treated with a controlled amount of probe DNA, proved the most efficient in fulfilling these tasks.

Nanocrystalline diamond enhanced thickness shear mode resonator

A nanocrystalline diamond coated thickness shear mode resonator has been fabricated as an alternative to the quartz crystal microbalance. Due to the low temperature phase transition of quartz, the piezoelectric material was replaced with langasite, a piezoelectric with no phase transition up to its melting point. The resulting device shows clear resonant behavior and oscillates in both air and in liquid. The diamond coating shows clear faceting by scanning electron microscopy and sp3 bonding by Raman spectroscopy.

Head-On Immobilization of DNA Fragments on CVD-Diamond Layers

Synthetic diamond is regarded as a promising material for biosensors: it forms a stable platform for genetic assays and its biocompatibility opens the possibility for in vivo sensing. In this study the use of a thymidine linker for covalent DNA attachment was evaluated. Contact angle measurements provided a qualitative test of the initially oxidized surface. X-ray photoemission spectroscopy was used for further analysis of the oxides and for monitoring the effect of subsequent chemical treatments. The presence of FITC-labelled DNA was confirmed by confocal fluorescence microscopy. Enzyme linked immunosorbent assays indicated that this DNA was merely adsorbed on the diamond surface instead of covalently bound.

Irreversible damage at high levels of potential-induced degradation on photovoltaic modules: A test campaign

Potential-induced degradation (PID) of photovoltaic (PV) modules gets a lot of attention since 2010 when Solon published their findings about a degradation mechanism in their PV modules caused by high potential differences between the solar cell and the grounded frame [1]. Module level efficiency drops of 30% and more caused by PID have been reported [2], [3]. A stress test for PID according to IEC 62804 and a recovery test in the same conditions were conducted on a set of 49 commercially available PV modules. In this paper we report the irreversibility of highly affected (i.e. over 85% PID) PV modules. From this point of view, it is important to detect and recover PID before the point of no return. Furthermore, the impact of PID on the different parameters of a PV module and their relevance in order to detect PID in the field are reported.

Interlaboratory comparison of photovoltaic performance measurements using CIGS solar cells

An interlaboratory test involving four PV laboratories was carried out to compare performance measurements using nonencapsulated CIGS solar cells. 15 samples were sorted according to their electrical parameters measured in the first lab and distributed to the three remaining ones, where the cells were remeasured. The comparison of the cells performance showed significant differences between the tested institutions, with variances in Voc, Jsc and FF. The method for contacting the cells, as well as the hardware and software used, were identified as the probable causes for the differences, suggesting that improvements in methodology and equipment, as well as constant monitoring, are necessary to assure the reliability of the measurements.

Nanocrystalline Diamond-Based Field-Effect Capacitive pH Sensor

The pH-sensitive properties of field-effect capacitive electrolyte-diamond-insulator- semiconductor (EDIS) sensors with undoped nanocrystalline diamond (NCD) thin films (100-500 nm) having hydrogen (H)- and oxygen (O)-terminated surfaces have been investigated. The NCD films were grown on p-Si-SiO2 substrates by a microwave plasma-enhanced chemical vapour deposition from a mixture of methane and hydrogen. The EDIS sensors have been characterised by means of capacitance- voltage spectroscopy, constant-capacitance and impedance-spectroscopy method. The developed EDIS sensors with O-terminated and H-terminated NCD surfaces show an average pH sensitivity of 38 mV/pH and 34-36 mV/pH, respectively. A possible mechanism of the pH sensitivity is discussed.

Biological applications of nanocrystalline diamond

Nanocrystalline diamond films have generated substantial interest in recent years due to their low cost, extreme properties and wide application arena. Diamond is chemically inert, has a wide electrochemical window and is stable in numerous harsh environments. Nanocrystalline diamond has the advantage of being readily grown on a variety of substrates at very low thickness, resulting in smooth conformal coatings with high transparency. These films can be doped from highly insulating to metallically conductive and at very high concentrations become superconducting.