To add a small stone to this objective, we decided to contribute
the "good custody" of antibiotics with the creation of a new
diagnostics device (DIANE) to detect pathogens in blood with
selectivity, rapidity and sensitivity. To achieve this ambitious
goal, we had to develop in parallel: the aptamers against
members of a WHO list of pathogens, the carbon nanotube-based
electrodes for their detection, the millifluidic
analysis system which serves respectively to introduce and
remove sample into and from the detection cavity of the device,
the context dependant usage scenario, the electronic system
which displays the results and address ethical and regulatory
issues that may arise from the use of DIANE.
To develop a device as sensitive as possible we decided to design
its core around an aptamer-based carbon nanotube electrode.
Indeed, this kind of electrode is extremely responsive as it can
react to as little as 1 bacterium per 5 ml of solution. First, we
needed to find a selective set of aptamers for two of the
pathogens we decided to work on: Staphylococcus aureus and
Enterococcus faecium. These aptamer sets were identified by the
whole-cell SELEX approach (wiki1 link). Afterwards aptamers were
attached to carbon nanotube electrodes chemically (wiki2 link).
Thanks to their 3D structure, the aptamers can recognize
selectively bacterial membrane proteins (surface or trans) or
other molecules (lipopolysaccharides). When the aptamer, linked on
the carbon nanotube electrode, binds to another molecule on the
surface of the cell, the aptamer undergoes conformational changes.
This alteration in geometry leads to a change in electrostatic
interactions (charge attraction/repulsion) with ions, which in
turn induces a potential difference along the electrode. It is
this potential difference that we want to measure.
