Enzyme-linked immunosorbent assay (ELISA) has been widely used in medical diagnostics, environmental analyses, and biochemical studies. To reduce assay time and lower consumption of reagents in cytokine ELISA analysis, a polymeric microfluidic biochip has been designed and fabricated via several new techniques: Polyaniline-based surface modification for superhydrophobic capillary valving and oxygen plasma-poly(ethyleneimine)-tyrosinase-protein A modification for high sensitivity protein detection. The proper flow sequencing was achieved using the superhydrophobic capillary valves. The burst frequency of each valve was experimentally determined and compared with two capillary force equations and the fluent finite element simulation. This fully automated microfluidic biochip with an analyzer is able to provide high fluorescence signal of ELISA with a wider linear detection range and a much shorter assay time than 96-well microtiter plates. It is applicable to a variety of nonclinic research and clinically relevant disease conditions. The modification technologies in this study can be implemented in other lab-on-a-chip systems, druggene delivery carriers, and other immunoassay biosensor applications.
We have recently developed a semi-continuous flow electroporation (SFE) device for in vitro DNA delivery. Cells mixed with plasmid DNA continuously flowed through a serpentine channel, the side walls of which also serving as electrodes. Using pWizGFP plasmid and K562 cells as a model system, SFE showed better transgene expression (10~15%) compared to a commercial electroporation system. Quantitative results via MTS assay also revealed a 50% or higher cell viability. Similar observations were also found with pWizGFP transfection to mouse embryonic stem cells. Such improvements were attributed to less gas formation and joule heating in SFE.
Fluid shear stress has been implicated as a regulator of sprouting angiogenesis. However, whether endothelial cells within capillary sprouts in vivo experience physiologically relevant shear stresses remains unclear. The objective of our study is to estimate the shear stress distribution along the length of a capillary sprout through computational modeling of blood flow in a blind-ended channel branching off a host vessel. In this model, we use sprout geometries typical for the rat mesenteric microvasculature and consider three types of boundary conditions: (1) a non-permeable vessel wall, (2) a uniformly permeable vessel wall, and (3) a non-permeable vessel wall with open slots (representative of endothelial clefts). Our numerical simulation predicts that for each boundary condition a local maximum shear stress (13.9, 8.9, and 13.3 dyne cm À2 , respectively) occurs at the entrance of a 50 lm long, 6 lm diameter sprout branching at 90°off of a 11 lm diameter host vessel. The shear stress dropped below 0.2 dyne cm À2 , a threshold for endothelial cell activation, within 4.1 lm of the entrance for the non-permeable wall case and 4.2 lm for the uniformly permeable wall case. Shear stress magnitudes within the sprout were above 0.2 dyne cm À2 for longer sprout scenarios and peaked at 5.9 dyne cm À2 at endothelial cell clefts. These results provide a first estimate of relative fluid shear stress magnitudes along a capillary sprout and highlight the importance of investigating endothelial cell responses to flow conditions during angiogenesis in tumors and other altered microenvironments.
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