Aggregation and settling in aqueous polydisperse alumina nanoparticle suspensions

Nanoparticle suspensions (also called nanofluids) are often polydisperse and tend to settle with time. Settling kinetics in these systems are known to be complex and hence challenging to understand. In this work, polydisperse spherical alumina (Al2O3) nanoparticles in the size range of ~10-100nm were dispersed in water and examined for aggregation and settling behaviour near its isoelectric point (IEP). A series of settling experiments were conducted and the results were analysed by photography and by Small Angle X-ray Scattering (SAXS). The settling curve obtained from standard bed height measurement experiments indicated two different types of behaviour, both of which were also seen in the SAXS data. But the SAXS data were remarkably able to pick out the rapid settling regime as a result of the high temporal resolution (10s) used. By monitoring the SAXS intensity, it was further possible to record the particle aggregation process for the first time. Optical microscopy images were produced on drying and dried droplets extracted from the suspension at various times. Dried deposits showed the rapid decrease in the number of very large particles with time which qualitatively validates the SAXS prediction, and therefore its suitability as a tool to study unstable polydisperse colloids. Keywords: Nanoparticles, nanofluids, polydisperse, aggregation, settling, alumina, microscopy, SAX

Long-term Effect of Convulsive Behavior on the Density of Adenosine A1 and A2A Receptors in the Rat Cerebral Cortex

Purpose: Adenosine is a neuromodulator that has been proposed to act as an anticonvulsant mainly via inhibitory A1 receptors, but recent data show that genetic deletion of facilitatory A2A receptors might also attenuate convulsions. Since both A1 and A2A receptors are prone to down- and upregulation in different stressful situations, we investigated if convulsive behavior leads to a long-term change in A1 and A2A receptor density in the rat cerebral cortex. Methods: Stage 4-5 convulsions (Racine's scale) were induced in adult Wistar rats either through amygdala stimulation (kindling) or by intraperitoneal injection of kainate (10 mg/ml). Rats were killed after 4 weeks to evaluate adenosine A1 and A2A receptor density in the cerebral cortex using both Western blot and membrane binding assays. Results: The binding density of the A1 antagonist, 3H-DPCPX, decreased by 40. ± 4.4% and by 20.7 ± 0.5% after kindling or kainate injection. Likewise, A1 receptor immunoreactivity in cortical membranes from kindled or kainate-injected rats decreased by 19.1 ± 3.3% and 12.7 ± 5.7%, respectively. In contrast, the binding density of the A2A receptor antagonist 3H-SCH 58261 increased by 293 ± 34% and by 159 ± 32% in cortical membranes from kindled or kainate-injected rats, and A2A receptor immunoreactivity also increased by 151 ± 12% and 79.6 ± 7.0%. Conclusions: This indicates that after convulsive behavior there is a long-term decrease of A1 receptors accompanied by an increased density of A2A receptors, suggesting that A2A antagonists rather than A1 agonists may be more promising anticonvulsive drugs