On Earth, vertical temperature profiles can be obtained using electronic temperature sensors mounted on weather balloons. These balloons go up to different heights in the atmosphere and relay real-time measurements of the atmospheric temperatures. While these electronics are easy to obtain and replace if they are broken on Earth, in the context of planetary exploration, they are irreplaceable and unreliable because it would take years to send replacements if they break and are impossible to fix without also sending replacement parts along the mission. Thus, a biological temperature sensor was developed in order to address these concerns. This biological temperature sensor can be expressed in a small culture of E.coli and be easily replaced simply by maintaining a culture of that particular bacteria.

In order to build a biological temperature sensor, we used chromogenic proteins from the DNA2.0 paintbox and from the iGEM registry. Chromogenic proteins or chromoproteins are colored proteins that have been extracted from a variety of organisms such as the sea anemone, Actinia equine (Citation 2) or have been synthetically produced (as was the case for the chromoproteins from DNA2.0). Like all proteins, chromogenic proteins are sensitive to heat; however, their sensitivity to heat is coupled with a visible color loss or change. Our research has shown that different chromoproteins respond to different temperatures by either losing their color or changing to a different color. These differential responses to temperature allowed us to build a biological temperature sensor.

The basic structure of a chromogenic protein consists of a large beta barrel and a chromophore which is supported by the beta barrel. The chromophore interacts with light and gives the protein its distinctive color. Additionally, the shape of the beta barrel is supported by water molecules that interact with the side chains of the amino acids that the beta barrel comprises of. These water molecules are essential for the chromogenic protein to maintain its structure. In response to heat, our hypothesis is that these water molecules are released from the beta barrel, thus allowing the barrel to collapse and the chromophore to no longer be supported enough to produce color. (Citation 3) Because planetary exploration requires a sensor that can function in a variety of environments, we tested our chromogenic proteins in a sealed environment and in an open air environment. The following sections details those experiments.