Current clinical methods for the separation of whole blood into blood cells and cell-free plasma are currently based on large facility equipment, such as centrifuges. The disadvantage of this process is that the patients must have assays performed at the hospital or laboratory where the separation facility is located. The present study presents a design for microfluidic chips with different microchannel structures, which utilizes backward facing step geometry and centrifugal force to extract the cell-free plasma from whole blood samples at the branch of the microchannel for further assay, avoiding the influence of blood cells. Numerical simulation was performed on a personal computer to analyze the effects of inlet velocity and the structures of the microchannel on the flow field and back-flow in the microchannel, as well as the efficiency of separation and the volumetric fraction of the flowrate of plasma extraction. The minimum radius of particles (R) that can be excluded from the side channel, and fraction of the volumetric flowrate were obtained to evaluate the efficiency of plasma extraction. Based on the numerical simulations, the design with both converging and bending channels was the best design among the four layouts proposed. In this design, the value of R could be set to less than the critical value (set as 1 mm because of the radius of platelets), and the volumetric fraction of the extraction flowrate was approximately 8.4% when Re was about 20. The preliminary experiments indicated the fluorescent particles with 2.5 mm in radius were successfully excluded from side (plasma outlet) channel of the microfluidic chip with converging a inlet channel and the bent microchannel, when the Reynolds number of the inlet flowrate equals 50.

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The detection of rare cells, such as circulating tumor cells, circulating fetal cells, and stem cells, is important for medical diagnostics and characterization. The present study develops a handheld electric module which provides stepping electric fields for dielectrophoresis (DEP) to selectively concentrate cervical carcinoma cells (HeLa) from red blood cells, making it low-cost and automated. To observe the experiments, transparent electrodes were fabricated by patterning indium-tin-oxide-coated glass. Positive dielectrophoretic cells were guided toward the center of the microchamber due to the movement of the high-electric-field region. The magnitude of the DEP force acting on HeLa cells is about seven-fold that acting on red blood cells under a given electric field distribution, making it possible to separate HeLa cells from normal blood cells. HeLa cells were successfully concentrated in 160 seconds with an applied peak-to-peak voltage of 16 V at a frequency of 1 MHz.

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A supercritical fluid extraction (SFE) method was developed in the present study as an effective sample pretreatment technique of petroleum distillates from fire debris. Three petroleum distillates were used as target analytes, including 95 unleaded gasoline, kerosene, and premium diesel. An orthogonal array (L16) experimental design was adopted to separately evaluate primary SFE experimental factors. The SFE efficiencies of petroleum distillates at various extraction conditions were examined and the optimized SFE conditions were identified. Experimental results demonstrated that the optimized SFE method not only provided an effective extraction method for the spiked sample, but also successfully recovered residues of petroleum distillates from fire debris.