In this study, the potential of low-frequency AC insulator-based DEP (iDEP) was explored for the separation of polystyrene microparticles and yeast cells. An EOF gradient was generated by employing an asymmetrical, 20 Hz AC electrical signal in an iDEP device consisting of a microchannel with diamond-shaped insulating posts. Two types of samples were analyzed, the first sample contained three types of polystyrene particles with different diameters (0.5, 1.0, and 2.0 μm) and the second sample contained two types of polystyrene particles (1.0 and 2 μm) and yeast cells (6.3 μm). This particular scheme uses a tapered AC signal that allows for all particles to be trapped and concentrated at the insulating post array, as the signal becomes asymmetrical (more positive), particles are selectively released. The smallest particles in each sample were released first, since they require greater dielectrophoretic forces to remain trapped. The largest particles in each sample were released last, when the applied signal became cyclical. A dielectropherogram, which is analogous to a chromatogram, was obtained for each sample, demonstrating successful separation of the particles by showing "peaks" of the released particles. These separations were achieved at lower applied potentials than those reported in previous studies that used solely direct current electrical voltages. Additionally, mathematical modeling with COMSOL Multiphysics was carried out to estimate the magnitude of the dielectrophoretic and EOF forces acting on the particles considering the low-frequency, asymmetrical AC signal used in the experiments. The results demonstrated the potential of low-frequency AC-iDEP systems for handling and separating complex mixtures of microparticles and biological cells.

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Objective:To describe bauxite mining and alumina refining processes and to outline the relevant physical, chemical, biological, ergonomic, and psychosocial health risks.Methods:Review article.Results:The most important risks relate to noise, ergonomics, trauma, and caustic soda splashes of the skin/eyes. Other risks of note relate to fatigue, heat, and solar ultraviolet and for some operations tropical diseases, venomous/dangerous animals, and remote locations. Exposures to bauxite dust, alumina dust, and caustic mist in contemporary best-practice bauxite mining and alumina refining operations have not been demonstrated to be associated with clinically significant decrements in lung function. Exposures to bauxite dust and alumina dust at such operations are also not associated with the incidence of cancer.Conclusions:A range of occupational health risks in bauxite mining and alumina refining require the maintenance of effective control measures.

Microfluidic devices can make a significant impact in many fields where obtaining a rapid response is critical, particularly in analyses involving biological particles, from deoxyribonucleic acid (DNA) and proteins, to cells. Microfluidics has revolutionized the manner in which many different assessments/processes are carried out, since it offers attractive advantages over traditional bench-scale techniques. Some of the advantages are: small sample and reagent amounts, higher resolution and sensitivity, improved level of integration and automation, lower cost and much shorter processing times. There is a growing interest on the development of techniques that can be used in microfluidics devices. Among these, electrokinetic techniques have shown great potential due to their flexibility. Dielectrophoresis (DEP) is an electrokinetic mechanism that refers to the interaction of a dielectric particle with a spatially non-uniform electric field; this leads to particle movement due to polarization effects. DEP offers great potential since it can be carried out employing DC and AC electric fields, and neutral and charged particles can be manipulated. This work is focused on the use of insulator based dielectrophoresis (iDEP), a novel dielectrophoretic mode that employs arrays of insulating structures to generate dielectrophoretic forces. Successful micro and nanoparticles manipulation can be achieved employing iDEP, due to its unique characteristics that allow for great flexibility. In this work, microchannels containing arrays of cylindrical insulating posts were employed to concentrate, sort and separate microparticles. Mathematical modeling with COMSOL V R was performed to identify optimal device configuration. Different sets of experiments were carried out employing DC and AC potentials. The results demonstrated that effective and fast particle manipulation is possible by fine tuning dielectrophoretic force and electroosmotic flow.