Diamond is a very attractive material to realize radiation detectors due to its exceptional properties (thermal, mechanical, optical, electronic, etc). But, the detector performances are highly dependent on the film quality. In this work, two chemical vapour deposition (CVD) diamond films, differing in film quality, obtained by a hot-filament CVD technique were used to fabricate radiation detectors. The measurements of photocurrents and pulse height distributions (PHDs) of the two detectors were carried out using 5.9 keV x-rays from a 55Fe source. For the detector with a better film quality, the electrical contact is fine Ohmic for bias voltages up to 150 V, and a dark current of 23.3 nA and the photocurrent of 16.8 nA are obtained at an electrical field of 50 kV cm−1. The peak of the PHD is well separated from the noise, indicating a high counting efficiency and a high signal-to-noise ratio. After several minutes' stabilization, the time-dependent photocurrent reveals that the photocurrent increases and then levels off due to the polarization effect.
Anti-double-stranded DNA (dsDNA) IgG causes renal damage in patients with lupus nephritis by cross-reacting with multiple autoantigens, including alpha-actinin-4, in mesangial cells (MCs). However, how the cross-reactions play a role in mesangial phenotypic abnormalities is not well understood. Here, we investigated the effects of the fragment antigen-binding (Fab) of anti-dsDNA IgG3 on the biochemical properties of alpha-actinin-4. Experiments revealed that anti-dsDNA Fab specifically binds to alpha-actinin-4, but not G-actin. The binding by anti-dsDNA Fab sequentially increases the positive charge of alpha-actinin-4 and inhibits the affinity of alpha-actinin-4 to calcium ions. By the low shear viscosity and a co-sedimentation assay, we found that the alpha-actinin-4-induced F-actin gelation improves when anti-dsDNA Fab is added. However, the Fab control has no such effect on F-actin gelation. Furthermore, the in vitro cultured MCs exhibit higher F-actin expression and transforming growth factor-β1 synthesis after the incubation with anti-dsDNA Fab. Therefore, our results indicated that anti-dsDNA Fab may enhance F-actin formation by the proprietary modification of alpha-actinin-4, which could partially explain the myofibroblast-like phenotype of MCs in anti-dsDNA-positive lupus nephritis.
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