Counterflow dielectrophoresis for trypanosome enrichment and detection in blood

Human African trypanosomiasis or sleeping sickness is a deadly disease endemic in sub-Saharan Africa, caused by single-celled protozoan parasites. Although it has been targeted for elimination by 2020, this will only be realized if diagnosis can be improved to enable identification and treatment of afflicted patients. Existing techniques of detection are restricted by their limited field-applicability, sensitivity and capacity for automation. Microfluidic-based technologies offer the potential for highly sensitive automated devices that could achieve detection at the lowest levels of parasitemia and consequently help in the elimination programme. In this work we implement an electrokinetic technique for the separation of trypanosomes from both mouse and human blood. This technique utilises differences in polarisability between the blood cells and trypanosomes to achieve separation through opposed bi-directional movement (cell counterflow). We combine this enrichment technique with an automated image analysis detection algorithm, negating the need for a human operator

Shear Strength of Copper Joints Prepared by Low Temperature Sintering of Silver Nanoparticles

In this work, mechanical properties of Cu-to-Cu joint samples prepared by low temperature sintering of Ag nanoparticle paste have been investigated. The silver nanopaste was prepared by a controlled thermal decomposition of an organometallic precursor. The as-synthesized Ag particles were spherical, with an average diameter of 8.5 nm. The Cu-to-Cu joint samples were made by placing a small amount of Ag nanopaste between two polished Cu plates and sintering at 150C, 200C, 220C and 350C in air. A normal load was applied to aid sintering. Mechanical properties were measured by imposing a uniform stress across the sample bond area and measuring the corresponding strain. The application of external load was found to have a positive effect on the material’s mechanical properties. Furthermore, interestingly high values of shear strength were observed.Byly zkoumány mechanické vlastnosti Cu-to-Cu spojů připravených nízkoteplotní sintrací pasty Ag nanočástic. Ag nanopasta byla připravena řízeným tepelným rozkladem organokovových prekurzorů. Syntetizované Ag NPs byly kulovité, o středním průměru 8,5 nm. Cu-to-Cu spoje byly vyrobeny umístěním malého množství Ag nanopasty mezi dvě leštěné Cu desky a sintrováním při 150C, 200C, 220C and 350C na vzduchu. Zatížení bylo použito na k podpoře sintrace. Mechanické vlastnosti byly měřeny stanovením napětí lomu a deformace. Bylo zjištěno, že aplikace vnějšího zatížení má pozitivní vliv na mechanické vlastnosti spoje

Electrically addressable vesicles: Tools for dielectrophoresis metrology

Dielectrophoresis (DEP) has emerged as an important tool for the manipulation of bioparticles ranging from the submicron to the tens of microns in size. Here we show the use of phospholipid vesicle electroformation techniques to develop a new class of test particles with specifically engineered electrical propserties to enable identifiable dielectrophoretic responses in microfabricated systems. These electrically addressable vesicles (EAVs) enable the creation of electrically distinct populations of test particles for DEP. EAVs offer control of both their inner aqueous core and outer membrane properties; by encapsulating solutions of different electrolyte strength inside the vesicle and by incorporating functionalized phospholipids containing poly(ethylene glycol) (PEG) brushes attached to their hydrophilic headgroup in the vesicle membrane, we demonstrate control of the vesicles’ electrical polarizabilities. This combined with the ability to encode information about the properties of the vesicle in its fluorescence signature forms the first steps toward the development of EAV populations as metrology tools for any DEP-based microsystem.National Institutes of Health (U.S.) (Grant RR199652)National Institutes of Health (U.S.) (Grant EB005753)Merck/CSBi (Fellowship)Solomon Buchsbaum AT&T Research Fun

Label-free cell separation and sorting in microfluidic systems

Cell separation and sorting are essential steps in cell biology research and in many diagnostic and therapeutic methods. Recently, there has been interest in methods which avoid the use of biochemical labels; numerous intrinsic biomarkers have been explored to identify cells including size, electrical polarizability, and hydrodynamic properties. This review highlights microfluidic techniques used for label-free discrimination and fractionation of cell populations. Microfluidic systems have been adopted to precisely handle single cells and interface with other tools for biochemical analysis. We analyzed many of these techniques, detailing their mode of separation, while concentrating on recent developments and evaluating their prospects for application. Furthermore, this was done from a perspective where inertial effects are considered important and general performance metrics were proposed which would ease comparison of reported technologies. Lastly, we assess the current state of these technologies and suggest directions which may make them more accessible

Separation of polystyrene microbeads using dielectrophoretic/gravitational field-flow-fractionation.

The characterization of a dielectrophoretic/gravitational field-flow-fractionation (DEP/G-FFF) system using model polystyrene (PS) microbeads is presented. Separations of PS beads of different surface functionalization (COOH and none) and different sizes (6, 10, and 15 microm in diameter) are demonstrated. To investigate the factors influencing separation performance, particle elution times were determined as a function of particle suspension conductivity, fluid flow rate, and applied field frequency and voltage. Experimental data were analyzed using a previously reported theoretical model and good agreement between theory and experiment was found. It was shown that separation of PS beads was based on the differences in their effective dielectric properties. Particles possessing different dielectric properties were positioned at different heights in a fluid-flow profile in a thin chamber by the balance of DEP and gravitational forces, transported at different velocities under the influence of the fluid flow, and thereby separated. To explore hydrodynamic (HD) lift effects, velocities of PS beads were determined as a function of fluid flow rate in the separation chamber when no DEP field was applied. In this case, particle equilibrium height positions were governed solely by the balance of HD lift and gravitational forces. It was concluded that under the experimental conditions reported here, the DEP force was the dominant factor in controlling particle equilibrium height and that HD lift force played little role in DEP/G-FFF operation. Finally, the influence of various experimental parameters on separation performance was discussed for the optimization of DEP/G-FFF

Circulating serum CK level vs. muscle impairment for in situ monitoring burden of disease in Mdx-mice

BACKGROUND: Duchenne muscular dystrophy (DMD) consists of a lack in the expression of the subsarcolemmal protein dystrophin causing progressive muscle dysfunction. Among the widely applied animal models in DMD research is the C57BL/1010ScSn-Dmdmdx mouse, commonly referred to as the "mdx mouse". The potential benefit of novel interventions in this model is often assessed by variables such as functional improvement, histological changes, and creatine kinase (CK) serum levels as an indicator for the extent of in situ muscle damage. OBJECTIVE: Our objective was to determine to what extent the serum CK-level serves a surrogate for muscle dysfunction. METHODS: In this trial mdx mice were subjected to a four-limb wire-hanging test (WHT) to assess the physical performance as a reference for muscle function. AsCKis a component of the muscle fiber cytosol, its serum activity is supposed to positively correlate with progressing muscle damage. Hence serum CK levels were measured to detect the degree of muscle impairment. The functional tests and the serum CK levels were analyzed for their specific correlation. RESULTS: Although physical performance decreased during the course of the experiment, latency to fall times in the WHT did not correlate with the CK level in mdx mice. CONCLUSION: Our data suggests that the serum CK activity might be a critical parameter to monitor the progression of muscle impairment in mdx mice. Further this study emphasizes the complexity of the DMD phenotype in the mdx mouse, and the care with which isolated parameters in this model should be interpreted