Microfabricated diamond waveguides, between 5 and 20 μm thick, manufactured by chemical vapor deposition of diamond, followed by standard lithographic techniques and inductively coupled plasma etching of diamond, are used as bio-chemical sensors in the mid infrared domain: 5-11 μm. Infrared light, emitted from a broadly tunable quantum cascade laser with a wavelength resolution smaller than 20 nm, is coupled through the diamond waveguides for attenuated total reflection spectroscopy. The expected advantages of these waveguides are a high sensitivity due to the high number of internal reflections along the propagation direction, a high transmittance in the mid-IR domain, the bio-compatibility of diamond and the possibility of functionalizing the surface layer. The sensor will be used for analyzing different forms of proteins such as α-synuclein which is relevant in understanding the mechanism behind Parkinson's disease. The fabrication process of the waveguide, its characteristics and several geometries are introduced. The optical setup of the biosensor is described and our first measurements on two analytes to demonstrate the principle of the sensing method will be presented. Future use of this sensor includes the functionalization of the diamond waveguide sensor surface to be able to fish out alpha-synuclein from cerebrospinal fluid.
A molecular approach to understand the photocatalytic degradation of small organic molecules adsorbed from the gas phase on anatase, rutile and doped TiO2 nanoparticles is presented. Using in situ Fourier transform infrared (FTIR) spectroscopy and mass spectrometry the rate determining steps for the photocatalytic degradation of formic acid, acetone and propane are unraveled. Key intermediates are identified and correlated to structural properties of the TiO2 nanoparticles. Specifically, stable bridging bidentate carboxylate (R-CO2) and (bi)carbonate species forms preferentially on rutile particles, and are proposed to inhibit the total photodegradation efficiency. In particular, the concentration of R-CO2 is found to decrease with increasing size of the anatase particles, and may at least partly explain why Degussa P25 is a good photocatalyst. Means to avoid R-CO2 site-blocking is discussed. Improved solar light efficiencies are difficulty to achieve in cation doped TiO2 despite higher visible light absorption and stronger adsorbate-surface interactions.
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