Holophrase

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In many biological experiments, it is important to monitor and adjust the pH level of a solution, since the level of acidity of a givensolution determines or carries information on the process at play. The most used pH sensors are pH paper strips and conductivityprobes, which give a simple readout that depends on the acidity of a solution. These methods are very cheap and do not needadditional instrumentation, but they are not integrated and require large volumes of the solution. In microfluidics, the most commonapproach monitors the change in absorption of a dye added to the cell culture medium complicating the experimental requirementsand protocols. Many other integrated solutions exist but often they come with their own caveats and limitations. Here we propose todevelop a flexible solution for the real time, label free, quantitative optical imaging readout of the pH level of a liquid solution. Ourapproach brings together the ease of access, simplicity, and cost of bulkier solutions, with the accuracy and level of integration of themost sophisticated sensors. Our device creates a holographic image that changes in real time with the pH of the solution, withoutrequiring the introduction of absorbing dyes or costly and complicated sensing circuitry and cumbersome calibration steps.