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Evaluation and diagnosis of blood alterations is a common request for clinical laboratories, requiring a complex technological approach and dedication of health resources. In this paper, we present a microfluidic device that owing to a novel combination of hydrodynamic and dielectrophoretic techniques can separate plasma from fresh blood in a microfluidic channel and for the first time allows optical real-time monitoring of the components of plasma without pre- or post-processing. The microchannel is based on a set of dead-end branches at each side and is initially filled using capillary forces with a 2-μL droplet of fresh blood. During this process, stagnation zones are generated at the dead-end branches and some red blood cells (RBCs) are trapped there. An electric field is then applied and dielectrophoretic trapping of RBCs is used to prevent more RBCs entering into the channel, which works like a sieve. Besides, an electroosmotic flow is generated to sweep the rest of the RBCs from the central part of the channel. Consequently, an RBC-free zone of plasma is formed in the middle of the channel, allowing real-time monitoring of the platelet behavior. To study the generation of stagnation zones and to ensure RBC trapping in the initial constrictions, two numerical models were solved. The proposed experimental design separates up to 0.1 μL blood plasma from a 2-μL fresh human blood droplet. In this study, a plasma purity of 99 % was achieved after 7 min, according to the measurements taken by image analysis. Graphical Abstract Schematics of a real-time plasma monitoring system based on a Hydrodynamic and direct-current insulator-based dielectrophoresis microfluidic channel.

With thermally stimulated depolarization currents, we researched the relaxations of crosslinked polyethylene as it is used in medium-voltage cable insulation. Through conventional polarization two heteropolar peaks stand up in the spectra, at 80 and 105°C. As the sample is annealed, a homopolar peak is developed at about 99°C. With window polarization, our results indicated that the 80°C peak is a structured peak related to polar crosslinking subproducts and impurities. The 105 and 99°C peaks are fitted to the general kinetic-order model because the 105°C peak is related to free-charge detrapping at the crystalline phase, in the bulk and maybe at the amorphous-crystal interphases, and the peak that is observed at 99°C is due to injected charge. Annealing at high temperatures promotes the creation of traps in the material. Charge trapping at T Ͻ 70°C seems to be related to the increased insulator resistivity with annealing time.

Dynamic electrical analysis shows that at high temperatures (above the glass transition temperature), the electrical properties of polyetherimide are strongly influenced by space charge. In this article we have studied the relaxation of space charge in two commercial varieties of polyetherimide: Ultem 1000 and Ultem 5000. Their conductive properties were determined by dynamic electrical analysis, using the electric modulus formalism. The complex part of the electric modulus was fitted to Coelho’s model which considers ohmic conductivity and diffusion as the prevailing charge transport mechanisms. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with space charge. A good agreement between experimental and calculated data is observed after the fitting process to Coelho’s model. Differences in the electrode behavior were required: blocking electrode conditions in the case of Ultem 5000 and partially blocking electrode for Ultem 1000. In both cases the conductivity determined is thermally activated and it increases with the temperature due to an increasing mobility, as their carrier densities do not vary significantly in the temperature range studied.