Holophrase

In many biological experiments, it is important to monitor and adjust the pH level of a solution, since the level of acidity of a given
solution determines or carries information on the process at play. The most used pH sensors are pH paper strips and conductivity
probes, which give a simple readout that depends on the acidity of a solution. These methods are very cheap and do not need
additional instrumentation, but they are not integrated and require large volumes of the solution. In microfluidics, the most common
approach monitors the change in absorption of a dye added to the cell culture medium complicating the experimental requirements
and protocols. Many other integrated solutions exist but often they come with their own caveats and limitations. Here we propose to
develop a flexible solution for the real time, label free, quantitative optical imaging readout of the pH level of a liquid solution. Our
approach brings together the ease of access, simplicity, and cost of bulkier solutions, with the accuracy and level of integration of the
most sophisticated sensors. Our device creates a holographic image that changes in real time with the pH of the solution, without
requiring the introduction of absorbing dyes or costly and complicated sensing circuitry and cumbersome calibration steps.