The accuracy of these measurement methods is much higher than that of the previously mentioned bulk fluid measurement www.selleckchem.com/products/epz-5676.html methods. However, as the number of cells that are available for measurement is quite small, these methods are not suitable for clinical diagnoses.Microchannels and microsensors have recently come to be considered as powerful tools in clinical diagnoses. The use of microsensors offers not only the advantages mentioned earlier, but also an effective solution to problems encountered in the measurement of RBC deformability with a high accuracy. Tracey et al. [16] fabricated a microchip with several embedded microchannels having a width of 4 ��m and visually measured the deformation rate of cells that passed through the microchannels. Korin et al.
[17] proposed an interesting method to visualize the behavior of RBCs in a microchannel; the cell deformation is measured by analyzing their images as they are stretched by high shear flows. However, this method requires high-resolution image-recording equipment that is bulky and expensive.The microsensor proposed in this study measures the electric resistance of RBCs as they pass between its electrodes. Figure 1 shows a schematic of the basic elements of the proposed sensor. As shown in Figure 1(a), micro-membrane-type electrodes are attached to the bottom wall of the microchannel. An RBC is suspended in the flow and is controlled such that it passes between the electrodes. An equivalent circuit that represents the electric characteristics of the region between the electrodes is shown in Figure 1(b).
The circuit consists of the cell, a solution, and an electric double layer formed on the surface of the electrodes. The cell is composed of the cytoplasm and cytomembrane. The resistance of the cytomembrane is much larger than that of the solution and is less than 1 �� 10�C6 S/m. This value is less than that of the cytoplasm and normal saline solution; thus, the cytomembrane acts as an insulating material. In this case, Drug_discovery the resistance obtained from the impedance measured by the electrodes will be influenced mainly by two factors: that are, the resistance of the membrane www.selleckchem.com/products/Tubacin.html and how the current flux in the electric field is interruption by the cell. This means that the measured resistance will reflect the size, height position, and shape of the cell. In addition to this, when the RBC passes the electrodes, the resistance will increase as it approaches the center of the electrodes and then decreases as it moves away; namely, the resistance will show a time-series distribution similar to the one shown by the graph in Figure 1(a). The previously mentioned parameters are considered to not only influence the resistance itself but also this time-series distribution of the resistance.Figure 1.