Design Criteria

Having chosen to focus on Arsenic detection, the design criteria are more precise. We also try to not forget E.Coli detection which is linked to Coliform bacteria proportion. We want to create a device to detect Arsenic presence in water but that could also be adapted to E.Coli detection by means of some minor changes. We decide that our device has to present these criteria:

General:

• Portability: We want to have a kit that we can take in the field to do measurements. In the end, the idea is that we can measure easily in the field instead of bringing the field in the lab. The portability will allow the users to take the device and travel with it to the place where the water is. The portability forces us to think not only to the size but to all the components we use, the energy sources they need, and their ability to be manipulated in the field.
• Low-cost: The kit must be affordable for non-occidentalized countries, and also by thoses who care about water quality but are not employed by a big lab. This means either choosing low-cost components or using things that most people already have and use daily.
• Replicability: We have to documentate well enough the prototype building for other people to be able to build it by themselves. The next team will also have to prepare a calibration protocol that is replicable.

Fluorescence kit: We decided to use a bacteria expressing green fluorescent protein when put in presence of Arsenic as a sensor. It implies to find a way to measure the fluorescence and relate it to a quantity of Arsenic. Furthermore, E.Coli can also be detected by fluorescence (but with other wavelenght than GFP). To design a kit measuring fluorescence we need:

• Light-source: Both E.Coli and GFP need to be excited by a specific wavelenght to fluoresce. We have to find the right light-source as well as respect the general design criteria.
• Filter: In order to excitate the sample at a certain wavelenght but collect only the wavelenght emitted by the fluorescing sample, we need an optic filter that will cut the non-wanted wavelenght. The nearer the wavelenght for excitation and emission are one from another, the more difficult it is to find a good filter... and it is even more difficult to find a cheap one!
• Sample-holder: The sample with the collected water and the bacterias has to respect some conditions. It must be transparent to have a possible excitation and a measurable emission. It must act as a confinment for the GMO bacterias acting in the sample. It has to allow oxygen presence for bacteria growth and be made of a material that will not react with Arsenic. It also has to allow the measurement to be done in the right direction (where the GFP emits fluorescence).
• Receptor: The most challenging part is to find a receptor that will transform the fluorescence quantity into a countable data we can relate to the Arsenic presence. This receptor must be sensitive to the emitted wavelenght and the order of magnitude with which it is emitted.
• Data analysis: We need to provide a way to analyze the data the receptor provides. It means both an instrument to quantify Fluorescence presence  and the necessary calibrations to relate it to real Arsenic presence.