Prototype v2.1 – First Tests

We have begun testing our prototype, as said in this article!

Cream :

This test was done to see how the scattering and excitation LED’s are sensed when measuring with different concentration of scattering medium.

The plotting of the fluorescence vs the scattering measurements shows that the two values are consistent for different dilutions of cream. Each point corresponds to an average of 3 measurements of the same dilutions, the point with higher values corresponding to less diluted solutions.

We can assume that the tweaking of the power of the LEDs was correct, and that in these conditions the scattering is the same.

Dextran :

The same experiment was then conducted on different dilutions of dextran, that were adjusted to match the fluorescence that would be obtained when the biosensor would be in contact of arsenic. For now such dilutions where not made, and measurements were done with dilutions that would be 5 to 10 fold greater than the fluorescence of the biosensor.

We can conclude that as expected, Dextran does not cause scattering. But we can also see that we sense the same quantity of light from scattering and excitation for the lowest concentration of dextran, we have three explanations for that :

• The dextran solutions were old, the dextran was less fluorescent than in the previous experiments (not likely as the vials were tested in the laboratory fluorimeter and were fluorescent, but less than 2 weeks ago).
• The light we use for the excitation is much less powerful than the one we used before, perhaps it is not powerful enough.
• The sensor is not sensible enough for very dilute solution of a fluorescent molecule.

These hypothesises will be tested and the tests will be done again to be sure that the results are consistent.

E. Coli :

The same rounds of tests were done with sample containing only E.Coli bacteria, to evaluate the effect of scattering in a biological medium.

We can see that scattering is the same as in the cream sample. These tests tell us that now, if we were to detect fluorescence in a bioreporter sample, we would need to subtract the scattering to the fluorescence value, to find the effective fluorescence intensity.

eGFP

Now that we know how our system behaves with E.Coli, we can try with eGFP producing bacteria to test if can detect fluorescence.

The results are the same as in the experiment with only E.Coli, we have not yet solved our problem, we cannot detect this level of fluorescence yet.

• The power of the LED is not adapted to the situation
• The sensor is not sensitive enough
• The emitted light is lost in the sample, the shape of the vial is not adapted

We will do these test again and more precisely to be able to confirm these results. More details will follow!