Diamond exhibits several special properties, for example good biocompatibility and a large electrochemical potential window, that make it particularly suitable for biofunctionalization and biosensing. Here we show that proteins can be attached covalently to nanocrystalline diamond thin films. Moreover, we show that, although the biomolecules are immobilized at the surface, they are still fully functional and active. Hydrogen-terminated nanocrystalline diamond films were modified by using a photochemical process to generate a surface layer of amino groups, to which proteins were covalently attached. We used green fluorescent protein to reveal the successful coupling directly. After functionalization of nanocrystalline diamond electrodes with the enzyme catalase, a direct electron transfer between the enzyme's redox centre and the diamond electrode was detected. Moreover, the modified electrode was found to be sensitive to hydrogen peroxide. Because of its dual role as a substrate for biofunctionalization and as an electrode, nanocrystalline diamond is a very promising candidate for future biosensor applications.

We report on the operation of ungated surface conductive diamond devices in electrolytic solutions. The effect of electrolyte pH on the channel conductivity is studied in detail. It is shown that fully hydrogen terminated diamond surfaces are not pH sensitive. However, a pronounced pH sensitivity arises after a mild surface oxidation by ozone. We propose that charged ions from the electrolyte adsorbed on the oxidized surface regions induce a lateral electrostatic modulation of the conductive hole accumulation layer on the surface. In contrast, charged ions are not expected to be adsorbed on the hydrogen terminated surface, either due to the screening induced by a dense layer of strongly adsorbed counter-ions or by the absence of the proper reactive surface groups. Therefore, the modulation of the surface conductivity is generated by the oxidized regions, which are described as microscopic chemical in-plane gates. The pH sensitivity mechanism proposed here differs qualitatively from the one used to explain the behavior of conventional ion sensitive field effect transistors, resulting in a pH sensitivity higher than the Nernstian limit.

Charge build-up at the solid/aqueous interface is a ubiquitous phenomenon that determines the properties of interfacial electrical double layers. Due to its unique properties, the surface of diamond offers an attractive platform to investigate charging mechanisms in aqueous solutions. We investigate the surface charge by studying the ion sensitivity of H-terminated single crystalline diamond surface conductive layers. The effect of monovalent and divalent salts has been probed at different pH values. For a pH above 3.5, increasing the ionic strength results in a decrease of the surface conductivity, in contrast to the results obtained for pH below 3.5. Electrokinetic experiments are in good agreement with the surface conductivity measurements, showing an isoelectric point at pH 3.5 for the H-terminated diamond surface. We discuss the results in terms of the Coulombic screening by electrolyte ions of the surface potential, which is induced by a pH-dependent surface charge. The origin of this surface charge is discussed in terms of charge regulation by amphoteric hydroxyl surface groups and unsymmetrical adsorption of hydroxide and hydronium ions induced by the hydrophobic nature of the H-terminated diamond surface. This surface charge can have important consequences for processes governed by the diamond/aqueous interface, such as electron transfer to charged redox molecules, adsorption of charged molecules and proteins, and ion sensitivity.

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Background The treatment of large vessels such as leg veins is successfully performed in clinical practice using pulsed Nd:YAG lasers. However, it is still unclear how laser parameters such as wavelength, fluence and pulse duration influence vessel destruction in leg veins. Objectives To elucidate the governing parameters in selective photothermolysis of large vessels. Methods A recently developed mathematical model for photothermolysis has been adapted for the treatment of leg veins. The model was used to analyse the effectiveness of the selective photothermolysis process in laser treatment of leg veins by Nd:YAG at 1064 nm. The efficiency of laser-induced vessel heating was defined as a ratio between the absorbed and delivered energy. Results The efficiency improved with increasing vessel diameter, in agreement with clinical findings in various studies. The pulse duration made a minor contribution for laser fluences of 100-400 J cm )2 , whereas the efficiency was better for a small spot. The use of moderate fluences of 100-200 J cm )2 reduced excess dermis heating and pain. Conclusions We provide reference parameters for optimal treatment of leg veins using Nd:YAG lasers at 1064 nm. Our model predicts a maximal efficiency of a range of fluences (100-200 J cm )2 ) and pulse durations (10-100 ms).

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We have investigated the electrochemical interface between diamond electrodes and aqueous electrolytes using electrochemical techniques such as cyclic voltammetry and ac impedance spectroscopy. High-quality CVD-grown boron-doped polycrystalline diamond electrodes and IIa single crystalline natural diamond electrodes have been used in this study. In the case of hydrogen-terminated diamond electrodes, the electrochemical interface is dominated by the electrochemical double layer. Frequency-dependent impedance spectroscopy reveals a potential regime in which the contribution of ion adsorption becomes relevant. We have conducted experiments to evaluate the effect of pH and ionic strength on the double layer. Our results suggest that only ions resulting from water auto-dissociation, i.e., hydroxide and hydronium ions, are responsible for ion adsorption and, thus, able to modify the charge at the double layer. In contrast, no effect of the adsorption of several dissolved ions (such as Na+, K+, Cl-) has been observed On the basis of the electrochemical characterization of H-terminated diamond surfaces, we also discuss the phenomenon of the surface conductivity in diamond, as well as the pH sensitivity of the diamond surface. The influence of the O2/OH- and H2/H3O+ redox couples on the origin of the surface conductivity is discussed.

We investigate the origin of the surface conductivity of H-terminated diamond films immersed in aqueous electrolyte. We demonstrate that in contrast to the in air situation, charge transfer across the diamond interface does not govern the surface conductivity in aqueous electrolyte when a gate electrode controls the diamond/electrolyte interfacial potential. Instead, this almost ideally polarizable interface allows the capacitive charging of the surface. This description resolves the observed disagreement of the pH sensitivity of the diamond surface conductivity in air and in aqueous electrolyte.