On-chip Monitoring of pH Change in Agar-gels during Fungi Growth by Integrating Impedance and Colorimetric Principles

In this work, we present a miniaturized sensor for detecting pH changes in agar-gel culture medium during fungal growth. For the first time an integrated approach of impedance and colorimetric principles for real-time monitoring of pH changes (7.6 to 2.0) in agar-gels on-chip is demonstrated. The designed sensor comprises a 7 mm diameter chamber with pre-loaded agar-gel medium which promotes the growth of the fungi. Detection of pH change in the medium is carried out by measuring changes in the impedance of the culture medium with integrated electrodes. As a second measurement principle, a pH indicator dye is added to the agar-gel which changes the color of the gel with respect to the pH change. The colorimetric principle serves as a reference measurement that indicates a pH change after which further pH shifts can be determined using impedance measurement.