The necessary condition of the active sites for the NO decomposition reaction on copper ion-exchanged ZSM-5-type zeolite (CuZSM5) has been investigated by using an adsorbed species that is one of the N 2 products of the decomposition reaction of NO. Two dominant types of exchangeable sites in the CuZSM5 sample were identiÐed by means of IR spectra using CO as a probe molecule ; these sites are responsible for giving a 2159 and 2151 cm~1 band due to the chemisorbed CO species. From exploration of the decomposition reaction of NO on the samples having di †erent amounts of preadsorbed CO molecules, it was found that the NO decomposition reaction occurs only under the condition that both types of sites coexist. The quantitative relationship between the number of these sites and the ion-exchange capacity of the sample was also evaluated from the IR spectra for CO adsorption. Combination with a similar relationship between the NO decomposition activity and the copper ion-exchange capacity found in the reference convinces us that the presence of both types of sites located closely to each other is a necessary condition for the NO decomposition reaction. The structure of the copper ion in CuZSM5 under di †erent exchange levels was also studied by Cu-K-edge X-ray absorption spectroscopy, from which, evidence supporting an existence of dimer species of copper ions was obtained for samples that have excessive ion-exchanged copper ion exceeding the stoichiometric amount. In addition, the oxidationÈreduction process of copper ion species was also examined during NO adsorption and subsequent heat treatment in vacuo. It is concluded that zeolite having an appropriate Si/Al ratio, in which it is possible for the copper ion to exist as dimer species, may provide the key to the redox cycle of copper ion as well as catalysis in NO decomposition.

The circulating tumor cell test is used to evaluate the condition of breast cancer patients by counting the number of cancer cells in peripheral blood samples. Although microfluidic systems to detect or separate cells using the inertial migration effect may be applied to this test, the hydrodynamic forces acting on cancer cells in high hematocrit blood flow are incompletely understood. In the present study, we investigated the inertial migration of cancer cells in high hematocrit blood flow in microchannels. The maximum hematocrit used in this study was about 40%. By measuring the cell migration probability, we examined the effects of cell-cell interactions, cell deformability, and variations in cell size on the inertial migration of cancer cells in blood. The results clearly illustrate that cancer cells can migrate towards equilibrium positions up to a hematocrit level of 10%. We also performed simple scaling analysis to explain the differences in migration length between rigid particles and cancer cells as well as the effect of hematocrit on cancer cell migration. These results will be important for the design of microfluidic devices for separating cells from blood.

Bifurcations and confluences are very common geometries in biomedical microdevices. Blood flow at microchannel bifurcations has different characteristics from that at confluences because of the multiphase properties of blood. Using a confocal micro-PIV system, we investigated the behaviour of red blood cells (RBCs) and cancer cells in microchannels with geometrically symmetric bifurcations and confluences. The behaviour of RBCs and cancer cells was strongly asymmetric at bifurcations and confluences whilst the trajectories of tracer particles in pure water were almost symmetric. The cell-free layer disappeared on the inner wall of the bifurcation but increased in size on the inner wall of the confluence. Cancer cells frequently adhered to the inner wall of the bifurcation but rarely to other locations. Because the wall surface coating and the wall shear stress were almost symmetric for the bifurcation and the confluence, the result indicates that not only chemical mediation and wall shear stress but also microscale haemodynamics play important roles in the adhesion of cancer cells to the microchannel walls. These results provide the fundamental basis for a better understanding of blood flow and cell adhesion in biomedical microdevices.

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