Optical Sensor System to Monitor the pH of Circulating Media on Biomimetic Microsystems

The pH is a physiological parameter of great importance in biomedical research. For example, during cell growth process, pH is usually lowered due to the acidic metabolites released by the cells. This decrease on the pH value can affect biological processes and, consequently, affect the accuracy of the research. To monitor the pH changes along cell engineering experiments, it is, usually, used the cell culture media along with a colorimetric pH indicator. However, this does not give a clear quantitative pH value, it outputs only an indication of pH ranges. To overcome this limitation, especially for biomimetic microsystems, where homeostasis has to be secured for long periods of time, an optical sensor that quantifies the pH values, through optical transmittance reading, was developed with features that allows integration. It was successful integrated in a microfluidic device comprising a pH-detecting microchamber of only <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1\ mm\ x\ 1\ mm$</tex> (depth x width), showing the potentiality of this sensing technology to be integrated with a broad bioplatforms used for biomedical research. Overall, the integrated beam-splitter setup allowed to obtain a sensor with a 2 mm optical path, in a 1 mm microchamber, outputting a 8.5%/pH sensitivity.