Recent studies show that inter-particle interaction can affect particle trajectories and particle deposition causing fouling in the microfilters used for metal working fluids (MWFs). Inter-particle interaction depends on various factors: particle geometry and surface properties, membrane pore geometry and surface properties, MWF’s properties and system operating conditions, etc. A mathematical model with a Langevin equation for particle trajectory and a hard sphere model for particle deposition has been used to study the effect of particle’s size, particle’s surface zeta potential, inter-particle distance, and shape of membrane pore wall surface on particle trajectory and its deposition on membrane pore wall. The study reveals that bigger particles have a lesser tendency to be deposited on membrane pore walls than smaller particles. The shape of the membrane pore wall surface can also affect the particle deposition behavior.

Concentration of bio-molecules prior to detection is very critical in the development of an integrated, multifunctional lab-on-a chip device for detection of ultra trace molecules from complex biological fluids such as serum, urine, or saliva. In this work, the preconcentration of a clinically relevant biomarker, cardiac troponin I (cTnI), is demonstrated in a cascade microfluidic channel using cationic isotachophoresis (ITP). The cascade chip is formed on PMMA (poly methyl methacrylate) with gradual changes in size both in width and depth direction to achieve a 100× reduction in overall cross sectional area between inlet (anode) and outlet (cathode) sections. The ITP experiments were conducted with two fluorescent proteins, FITC (Fluorescein isothiocyanate-conjugated) albumin and cTnI labeled with Pacific Blue. Potassium ions were used as the leader and hydronium ions were used as the terminator for these cationic ITP experiments. The microchip ITP demonstrates that it is possible to increase the concentration of cTnI by 10,000 folds using a potential drop of 400 V across a 3.5 cm long microchannel. The reduction in cross sectional area facilitates additional concentration gain, as the proteins migrate through cascade microchannel under discontinuous electric field and stacked into nearly pure zones.