We studied the migration of nonmagnetic, submicrometer polystyrene beads submerged in a magnetic fluid in the presence of nonuniform magnetic fields as a potential method for size-based separation of submicrometer, nonmagnetic species. Since the polystyrene beads are much larger than the magnetic fluid nanoparticles, the magnetic fluid was treated as a one-component continuum with respect to the beads. We found that the polystyrene beads will migrate in the direction of decreasing magnetic fields and will focus over a region where the magnetic field or its gradient vanishes, as predicted by our model. The concentration profiles predicted by our model, which has no adjustable or fitted parameters, agree reasonably well with the experimental data both qualitatively and quantitatively. / Singapore-MIT Alliance (SMA)

Microfluidics promises to re-shape the current health-care system by transferring diagnostic tools from central laboratories to close vicinity of the patient (point-of-care). One of the most important operational steps in any diagnostic platform is sample preparation, which is the main subject in this thesis. The goal of sample preparation is to isolate targets of interest from their surroundings. The work in this thesis is based on three ways to isolate bacteria:  immune-based isolation, selective cell lysis, size-based separation. The first sample-preparation approach uses antibodies against lipopolysaccharides (LPS), which are surface molecules found on all gram-negative bacteria. There are two characteristics that make this surface molecule interesting. First, it is highly abundant: one bacterium has approximately a million LPS molecules on its cell-wall. Second, the molecule has a conserved region within all gram-negative bacteria, so using one affinity molecule to isolate disease-causing gram-negative bacteria is an attractive option, particularly from the point of view of sample preparation. The main challenge, however, is antigen accessibility. To address this, we have developed a treatment protocol that improves the capturing efficiency. The strategy behind selective cell lysis takes advantage of the differences between the blood-cell membrane and the bacterial cell-wall. These fundamental differences make it possible to lyse (destroy) blood-cells selectively while keeping the target of interest, here the bacteria, intact and, what is more important alive. Viability plays an important role in determining antibiotic susceptibility. Difference in size is another well-used characteristic for sample- separation. Inertial microfluidics can focus size-dependent particle at high flow-rates. Thus, particles of 10 µm diameter were positioned in precise streamlines within a curved channel.  The focused particles can then be collected at defined outlets.  This approach was then used to isolate white blood cells, which account for approximately 1% of the whole blood.  In such a device particles of 2µm diameter (size of bacteria) would not be focused and thereby present at every outlet. To separate bacteria from blood elasto-inertial microfluidics was used. Here, e blood components are diverted to center of the channels while smaller bacteria remain in the side streams and can subsequently be separated. / <p>QC 20141212</p>

Doctor of Philosophy / Department of Grain Science and Industry / R. P. Kingsly Ambrose / Praveen V. Vadlani / Wheat flour processing involves gradual size reduction and size-based fractionation of milled components. The size-based separation efficiency of wheat flour particles, with minimum bran contamination, is an important flour mill operational parameter. The flour particles often behave as imperfect solids with discontinuous flow and agglomerates during the separation process due to their differences in physical and chemical characteristics. Noticeable loss in throughput has been observed during sieving of soft wheat flour compared to that of hard wheat flour due to differences in inter-particle cohesion. However, there is limited understanding on the factors that influence the inter-particulate forces. Direct and indirect methods were applied to investigate the effects of moisture content, particle size, sifter load, and chemical composition on the cohesion behavior of flours from different wheat classes. Image analysis approach was used to quantify the particle characteristics such as surface lipid content, roughness, and morphology with respect to particle size to better understand the differences between hard and soft wheat flours. Surface lipid content and roughness values showed that the soft wheat flours are more cohesive than hard wheat flours. The morphology values revealed the irregularity in flour particles, irrespective of wheat class and particle size, due to nonuniform fragmentation of endosperm particles. The chemical composition significantly contributes to the differences in cohesion and flowability of wheat flours. Based on the particle parameters, a granular bond number (GBN) model was developed to predict the dynamic flow of wheat flour. In order to further understand the wheat flour flow behavior during size-based separation, a correlation was developed using the discrete element method (DEM). The error of predictions demonstrated that this correlation can be used to estimate the sieving performance and sieve blinding phenomenon of wheat flour. The experimental results from this dissertation work and the numerical model could eventually be instrumental to improve the efficiency of size-based separation of flour from various wheat classes. In addition, the models developed in this study will contribute significantly to understand the inter-particle cohesion as influenced by chemical composition.