For the purposes of this project it was necessary to select a method in which our system could inform the user of a positive test result; a reporter system. Many choices were considered to be our reporter systems. We decided upon an enzyme/catalyst reporter as we believed that using a reporter such as green fluorescent protein (GFP) simply would not provide a strong enough of a signal for a portable device. GFP would only provide a constant signal that would not increase in intensity over time. The fluorescent output of GFP would also require the device to have the ability to excite the protein with the appropriate wavelength of light. This would add to both the complexity and cost of the device.

With this knowledge in mind we knew an enzyme with a colour output would be more suitable and easier to understand out in the field. Many common enzymes were analyzed for this purpose. One example is horseradish peroxidase. This enzyme has high enzymatic activity and is commonly used in many biological applications. One problem with its use however is that it cannot be effectively produced within E. coli. There are other common enzymes that do not have this issue such as alkaline phosphatase. These enzymes however are often multimeric which presents an issue with our in vitro strip system. If the enzymes are not able to assemble correctly with the rest of our proteins the device will be ineffective. Based on this knowledge we decided to move forward with two potential reporter systems; the ampicillin resistance enzyme beta-lactamase and chemically modifying ferritin to become a strong catalyst. Click the links below to learn more about these two systems: