Human plasma protein adsorption on carbon-based materials.

In this study the initial reactions of different carbon-based materials with human blood were investigated by short-time exposure to platelet poor plasma (PPP). Extent of protein adsorption and conformational changes of proteins adsorbed on material surfaces are known to be keys factors affecting further biological reactions. Plasma protein adsorption on multi-walled carbon nanotubes (MWCNTs), highly oriented pyrolytic graphite (HOPG) and nanocrystalline graphite (NG) were investigated and the results obtained on these materials were compared with those obtained studying pyrolytic carbon (PyC), a material showing good anti-trombogenic properties. The quantification of adsorbed plasma proteins on sample surfaces was obtained by Micro BCA Protein Assay, while immunofluorescence analysis was employed to monitor the surface density and distribution of two selected proteins, namely fibrinogen (Fg) and Hageman factor (FXII), proteins playing a leading role in mediating platelet adhesion. The dependence of the biological response on the surface chemical and morphological properties were also investigated and data obtained using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) are presented. After PPP incubation PyC is characterized by the presence of low level of whole proteins and FXII adsorption, in contrast to a high adhesion of Fg. Compared to PyC the analysis of the other carbon-based materials result in a higher whole protein adsorption with an increasing trend moving from MWCNTs, NG and HOPG respectively. The Fg surface density on PyC, NG and MWCNTs is about four times higher than on HOPG while only HOPG show a detectable fluorescent signal of FXII. If AFM data indicate that surface morphology does not play a crucial role in protein adhesion, XPS analysis show chemical differences that can be correlated with this biological response.

Whispering-gallery modes and light emission from a Si-nanocrystal-based single microdisk resonator.

We report on visible light emission from Si-nanocrystal based optically active microdisk resonators. The room temperature photoluminescence (PL) from single microdisks shows the characteristic modal structure of whispering-gallery modes. The emission is both TE and TM-polarized in 300 nm thick microdisks, while thinner ones (135 nm) support only TE-like modes. Thinner disks have the advantage to filter out higher order radial mode families, allowing for measuring only the most intense first order modal structure. We reveal subnanometer linewidths and corresponding quality factors as high as 2800, limited by the spectral resolution of the experimental setup. Moreover, we observe a modification of mode linewidth by a factor 13 as a function of pump power. The origin of this effect is attributed to an excited carrier absorption loss mechanism.