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After having spent two weeks learning the basics of DIY Arduino and reading a lot of background material on the project I have come up with the first part of the project. We will begin by building the prototype anew, v1.0 whilst paying attention to all of the parts that could need improvements so that we can create a prototype v1.1 afterwards. There are a number of points that can be improved in the current prototype, regarding the containment of the sample, the light detection and the Arsenic calibration.

Sample :

  • The transport and containment of the genetically modified bacteria in the field. We could use a vial already used by the ARSOLux sensor that was approved by the german authorities.
  • Attention has to be paid to the water sampling, that means the behavior of the sample between its collection and the measurement. One detail is the interaction of the arsenic with the vial, as the ARSOLux vial works for their sensor we can also consider using it.
  • Water filtering : Maybe it would be intersting to filter water so that there are less molecules that disrupt our measurements.
  • We don’t want the sample to be exposed to sunlight, the vials could be surrouned by tin foil or stored in a dark container.

Prototype :

  • The transmission of the GFP emitted light, without interference with other metabolites present in the filter. We have to concentrate it on the light sensor and pay attention that it is not modified by other sources of light (the blue LED for example). Instead of the lenses we could investigate the use of a flashlight parabola that easily focuses the rays of light, and the material is cheaper than the lenses. But we have to pay attention to the angle of incidence of the rays on the detector when we use a parabola.
  • The inside of the prototype has to be pitch black so that most of the rogue rays are absorbed and do not interfere with our measurements,
  • We could imagine using tin foil to direct the light rays, as it reflects 98% of the light.
  • Special attention has to be given to the position of the sample that has to remain the same during in field measurements so that the prototype produces reproducible results.
  • The design of the prototype has to be sturdy enough to be brought in the field without breaking to pieces.
  • Make it field compatible by adding a battery, and therefore a voltage regulator to ensure that the same current passes through the lens during the whole battery life.

Calibration :

  • Test with known concentrations of Arsenic will have to be done so that we can precisely correlate the light intensity with the Arsenic concentration in all types of water.
  • Evaluate the effect of real-world water on the measurements.

There are many improvements to be made, therefore the prototype improvements will be made after having built the prototype. Our priority now is to see if the calibration can be made with the actual prototype. We will also make sure that the new design is already sturdy enough for a field outing.

When the prototype will be built four sets of tests will be done with it. Firstly we will try it in the laboratory with a fluorescent molecule such as dextran. Then We will try it with bacteria expressing GFP. The next step will be to test the prototype with our Arsenic biosensor in a sample containing Arsenic to evaluate the results. The final test phase will be to go in the field with our prototype and test it with water in Switzerland that are known to contain Arsenic. It could also maybe interesting to develop a DIY filter to process field water before putting it in our prototype, that would perhaps produce better results of Arsenic detection.

In parallel we will investigate the feasibility of reproducing a microchip that was developed as a collaboration between the laboratories of professors Van der Meer and Renaud and that has excellent Arsenic detection properties. To achieve this Thomas will visit Gaudilabs in Luzern to go and lear how to do DIY microfluidics.

Reference : “Compact portable biosensor for arsenic detection in aqueous samples with Escherichia coli bioreporter cells” Buffi, N. & al.

One thought on “Future needs for Arsenic prototype

  1. Pingback: Fluorometer v1.0 | biodesign for the real world

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