Isomotive dielectrophoresis for enhanced analyses of cell subpopulations.

As the relentless dream of creating a true lab-on-a-chip device is closer to realization than ever before, which will be enabled through efficient and reliable sample characterization systems. Dielectrophoresis (DEP) is a term used to describe the motion of dielectric particles/ cells, by means of a non-uniform electric field (AC or DC). Cells of different dielectric properties (i.e., size, interior properties, and membrane properties) will act differently under the influence of dielectrophoretic force. Therefore, DEP can be used as a powerful, robust, and flexible tool for cellular manipulation, separation, characterization, and patterning. However, most recent DEP applications focus on trapping, separation, or sorting particles. The true value of DEP lies in its analytical capabilities which can be achieved by utilizing isomotive dielectrophoresis (isoDEP). In isoDEP, the gradient of the electric field-squared is constant, hence, upon the application of electric field, all particles/cells that share the same dielectric properties will feel the same constant dielectrophoretic force i.e., translate through the micro-channel at the same velocity. However, DEP is not the only acting force upon particles inside an isoDEP device, other electrokinetics, including but not limited to electrothermal hydrodynamics, might act on particles simultaneously. Within this dissertation, electrothermal-based experiments have been conducted to assess the effect of such undesired forces. Also, to maximize the relative DEP force over other forces for a given cell/particle size, design parameters such as microchannel width, height, fabrication materials, lid thickness, and applied electric field must be properly tuned. In this work, scaling law analyses were developed to derive design rules that relate those tunable parameters to achieve the desired dielectrophoretic force for cell analysis. Initial results indicated that for a particle suspended in 10 mS/m media, if the channel width and height are below 10 particle diameters, the electrothermal-driven flow is reduced by ∼ 500 times compared to the 500 µm thick conventional isoDEP device. Also, Replacing glass with silicon as the device’s base for an insulative-based isoDEP, reduces the electrothermal induced flow by ∼ 20 times. Within this dissertation, different device designs and fabrication methods were attempted in order to achieve an isoDEP platform that can characterize and differentiate between live and dead phytoplankton cells suspended in the same solution. Unfortunately, unwanted electrokinetics (predicted by the previously mentioned scaling law analysis) prevented comprehensive isoDEP analysis of phytoplankton cells. Due to isoDEP device limitations and other complications, other techniques were pursued to electrically characterize phytoplankton cells in suspension. An electrochemical-based platform utilizing impedance spectroscopy measurements was used to extract the electrical properties of phytoplankton cells in suspension. Impedance spectroscopy spectra were acquired, and the single-shell model was applied to extract the specific membrane capacitance, cytoplasm permittivity, and conductivity of assumingly spherical cells in suspension utilizing Maxwell’s mixture theory of a controlled volume fraction of cells. The impedance of suspensions of algae were measured at different frequencies ranging from 3 kHz to 10 MHz and impedance values were compared to investigate differences between two types of cells by characterizing their change in cytoplasm permittivity and membrane capacitance. Differentiation between healthy control and nitrogen-depleted cultured algae was attempted. The extracted specific membrane capacitances of Chlamydomonas and Selenastrum were 15:57 ± 3:62 and 40:64 ± 12:6 mF/m2 respectively. Successful differentiation based on the specific membrane capacitance of different algae species was achieved. However, no significant difference was noticed between nitrogen abundant and nitrogen depleted cultures. To investigate the potential of isoDEP for cell analysis, a comparison to existing dielectrophoresis-based electrokinetic techniques was encouraged, including electrorotation (ROT) microfluidic platforms. The ROT microfluidic chip was used to characterize M17, HEK293, T-lymphocytes, and Hela single cells. Through hands-on experience with ROT, the advantages and disadvantages of this approach and isoDEP are apparent. IsoDEP proves to be a good characterization tool for subpopulation cell analysis with potential higher throughput compared to ROT while maintaining simple fabrication and operation processes. To emphasize the role of dielectrophoresis in biology, further studies utilizing the 3DEP analytical system were used to determine the electrical properties of Drosophila melanogaster (Kc167) cells ectopically expressing Late embryogenesis abundant (LEA) proteins from the anhydrobiotic brine shrimp, Artemia franciscana. Dielectrophoretic-based characterization data demonstrates that single expression of two different LEA proteins, AfrLEA3m and AfrLEA6, both increase cytoplasmic conductivity of Kc167 cells to a similar extend above control values. The extracted DEP data supported previously reported data suggesting that AfrLEA3m can interact directly with membranes during water stress. This hypothesis was strengthened using scanning electron microscopy, where cells expressing AfrLEA3m were found to retain their spherical morphology during desiccation, while control cells exhibited a larger variety of shapes in the desiccated state

Configurable circuits and their impact on multi-standard RF front-end architectures

This thesis studies configurable circuits and their impact on multi-standard RF front-end architectures. In particular, low-voltage low-power linear LNA and mixer topologies suitable for implementation in multi-standard front-ends are subject of the investigation. With respect to frequency and bandwidth, multi-standard front-ends can be implemented using either tunable or wideband LNA and mixer topologies. Based on the type of the LNA and mixer(s), multi-standard receiver RF front-ends can be divided into three groups. They can be (tunable) narrow-band, wide-band or combined. The advantages and disadvantages of the different multi-standard receiver RF front-ends have been discussed in detail. The partitioning between off-chip selectivity, on-chip selectivity provided by the LNA and mixer, linearity, power consumption and occupied chip area in each multi-standard RF front-end group are thoroughly investigated. A Figure of Merit (FOM) for the multi-standard receiver RF front-end has been introduced. Based on this FOM the most suitable multi-standard RF front-end group in terms of cost-effectiveness can be selected. In order to determine which multi-standard RF front-end group is the most cost-effective for a practical application, a GSM850/E-GSM/DCS/PCS/Bluetooth/WLANa/b/g multi-standard receiver RF front-end is chosen as a demonstrator. These standards are the most frequently used standards in wireless communication, and this combination of standards allows to users almost "anytime-anywhere" voice and data transfer. In order to verify these results, three demonstrators have been defined, designed and implemented, two wideband RF front-end circuits in 90nm CMOS and 65nm CMOS, and one combined multi-standard RF front-end circuit in 65nm CMOS. The proposed multi-standard demonstrators have been compared with the state-of the art narrow-band, wide-band and combined multi-standard RF front-ends. On the proposed multi-standard RF front-ends and the state-of the art multi-standard RF front-ends the proposed FOM have been applied. The comparison shows that the combined multi-standard RF front-end group is the most cost effective multi-standard group for this application

The Epidemiology, Aetiology, and Histopathology of Developmental Enamel Defects in Human Teeth

PhDThe prevalence of developmental enamel defects in t11 permanent dentition was investigated in a sample of 2923 East London schoolchildren aged 5 to 15 years. Enamel discolourations and hypoplasias were identified using well defined criteria. Two-thirds of the children had at least one tooth with- an enamel defect. In the group of 1518 children with 24-28 erupted permanent teeth, 68 per cent had enamel defects with. a mean of 3.6 per child. The upper central Incisors and first molars had the highest prevalence of enamel defects. In these teeth., the proportion of defects decreased with.. age. The majority of defects were discolourations; 67 per cent of children..with a "complete" -permanent dentition had discolouration defects whereas only iS. per cent had enamel bypoplasia. The aetiology of defects-found in children with. two or more hypoplastic teeth was investigated in a family study. Four of the 101 index cases had amelogenesis imperfecta and 18 had chronological hypoplasia caused by systemic diseases. The defects in a further 18 subjects had a probable systemic aetiology. Bilateral hypoplasia of the lower incisors was found in 22 subjects and a multifactoria]. mode of inheritance was postulated for this condition. For one third of the index cases no cause could be found for their hypoplasia. A histological study. complemented thesurveys by describing structural characteristics of different types of enamel defects. The investigation highlighted a number of differences between enamel defects caused by systemic upsets and those caused by genetic factors. An archaelogical. study assessedthe prevalence-of enamel h-ypoplasia in a cällection of early British skulls. Thirty-seven per cent had a number of hypoplastic teeth. There were few severe cases of hypoplasia; the most common type of defect being shallow horizontal grooves. The many teeth with shallow defects suggested periodic disturbances in enamel formation between 2 and 6 years of age. This thesis has provided further information about the complex nature of enamel defects. The different aspects of enamel defects which have been investigated have contributed to a greater understanding of their prevalence, aetiology and histology

Kabul Times, May 1975

Kabul Times, May 1975 *This is a large file and may take a couple of minutes to download