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In cell culture, the pH of the culture medium is one of the most important conditions. However, the culture medium may have non-uniform pH distribution due to activities of cells and changes in the environment. Although it is possible to measure the pH distribution with an existing pH meter using distributed electrodes, the method involves direct contact with the medium and would greatly increase the risk of contamination. Here in this paper, we propose a computed tomography (CT) scan for measuring pH distribution using the color change of phenol red with a light-emitting diode (LED) light source. Using the principle of CT scan, we can measure pH distribution without contacting culture medium, and thus, decrease the risk of contamination. We have developed the device with a LED, an array of photo receivers and a rotation mechanism. The system is firstly calibrated with different shapes of wooden objects that do not pass light, we succeeded in obtaining their 3D topographies. The system was also used for measuring a culture medium with two different pH values, it was possible to obtain a pH distribution that clearly shows the boundary.

In cell culture, the pH of culture liquid is one of the most important conditions. However, culture liquid may have pH-gradient due to the activity of cells and change of the environment. In order to confirm the existence of pH-gradient, we propose a method for 3D pH measurement using the color change of phenol red. Using the principle of CT scan, we can measure pH-gradient without contacting culture liquid, and thus, decrease the possibility of contamination. In this paper, we consider the influence of light refraction by a cylindrical vessel, and show that we can measure local pH of culture liquid by light absorbance.