On last May 1, 2017, Sarah Ben Maamar, (a post-doc in the Hartmann Lab) and Marco Alsina (Gaillard Lab) took part into the Sixth French Science Fair to introduce basics scientific concepts to young students (primary School up to middle School) from different French-American schools in the Chicago area.
The French-American Science Festival is held every year at the University of Illinois at Chicago, and organized by the Office for Science and Technology of the French Embassy in the US.
As part of this event, Sarah and Marco explained to students how bacteria can be genetically engineered to produce light or “bioluminescence” in presence of Mercury (Thomas et al., 2014, Dahl et al., 2011).
As an illustration of the bioluminescence process, Sarah and Marco demonstrated a similar concept called “fluorescence”. To that end, they used a compound commonly found in tonic water called “quinine”, which is highly soluble in water and naturally fluoresces in blue (at 500nm) when excited with high energy UV light.
Left figure: The Quinine molecule
Right figure: Excitation (by UV light) and Emission (in Blue light) spectra of Quinine
To explain the principles of bioluminescence and fluorescence to students, a little game was organized. Three similar bottles containing, each containing a transparent liquid were presented to the students. Two of these bottles contained quinine while the third one was water. One of the quinine containing bottles was slightly more concentrated than the other one. Of course, Sarah and Marco didn’t share these details with the students. Students were first asked to find which bottles contained quinine. To help them, Sarah and Marco designed a black box with a UV lamp included on the top, and in which the bottles could be inserted and observed under UV light.
Once students found the two fluorescent bottles using the black box, Sarah asked them to guess which fluorescent bottle was more concentrated in quinine based on the fluorescence intensity. Most of students could barely see a difference in fluorescence between the two bottles.
This was of course a perfect opportunity to explain to students what a UV-spectrometer does, how it can be used to visualize the spectrum emitted by a given source of light and to quantify the fluorescence intensity. Marco and Sarah designed the black box to allow the spectrophotometer captor to measure the spectrum and intensity of light emitted by each bottle when exposed to UV light. Measurements of the two fluorescent bottles spectra under UV light excitation was done in front of the students, allowing them to observe real-time spectra of the emitted blue light for each bottle.
By simple spectrum observation, students were able to notice the emitted blue light peak for each bottle, and on the basis of the peak height they were able to determine which bottle was more concentrated in quinine.
Schema of the device used for the experiment.
The main idea of this little experiment was to introduce students to the principles of bioluminescence and fluorescence, and how through bacterial activity and luminescence one can determine the presence, the bioavailability and concentration of a compound of interest within a given unknown environmental sample. The students also learned about visible and invisible spectra, wavelength and visible colors.
Photos of the event will be soon available!
References:
Thomas S.A., Tong T., Gaillard J.-F. (2014) Hg(II) bacterial biouptake: The role of anthropogenic ligands present in solution and spectroscopic evidence of ligand exchange reactions at the cell surface. Metallomics, 6, 2213-2222.
Dahl A.L., J. Sanseverino, and J.-F. Gaillard (2011) Bacterial Bioreporter Detects Mercury in the Presence of Excess EDTA. Environmental Chemistry, 58, 552-560.