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| − | <h3 class="wow fadeInDown">Understanding an MFC</h3> | + | <h3 class="wow fadeInDown">The power of the sun</h3> |
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| − | <p>A microbial fuel cell exploits the electrons produced by the bacteria metabolism placed in the anodic chamber to make energy. When building a MFC several parameters ust be taken into consideration:</p> | + | <p>We observed that bacteria engineered with proteorhodopsin produced more ATP when exposed to light, due to the activation of the proton pump (more info on the proteorhodopsin section). We wanted to see if this makes bacteria more MFC friendly (i.e. live happily in the anode chamber) and if that would produce more electricity.</p> |
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| − | <ul class="customlist arrowed">
| + | <p>Cells transformed with BBa_K1604010 (araC-pBAD + proteorhodopsin) and BBa_K731201 (negative control) were grown in M9 media and induced with arabinose (5 mM) and all-trans retinal (10 μM) for 4 hours in darkness. Preliminary tests showed that the optimal medium to be used was M9 medium supplemented with glucose, which gave a more stable signal (data not shown). </p> |
| − | <li>The anodic chamber must be under anerobic conditions to favor the transfer of
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| − | electrons to the electrode.</li>
| + | <p>The bacterial cultures were split and then placed in the anodic chamber of a small Microbial Fuel Cell borrowed from one of our instructor Martin Hanczyc. |
| − | <li>The two chambers need to be separated by a proton exchange membrane
| + | In total we had 4 MFCs, one for each construct in the dark and one exposed to the light of a blue LED. The experiment was repeated for 3 days, keeping the same experimental conditions. </p> |
| − | (Nafion) for the equilibration of the total charges.</li>
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| − | <li>The material of the electrodes needs to be highly conductive (carbon cloths
| + | <p>In the presence of a blue-light LED, the proteorhodopsin expressing strain showed in all three cases a better electrochemical response than the negative control (i.e. PR expressing strain shows higher polarization and power curves), with a higher voltage and maximum power (<i>Pmax</i>). In a biological scale this means that there is an increased transfer of electrons from the culture media to the electrode, and this is directly related to bacteria’s increased viability. </p> |
| − | connected with a tinned copper wire).</li>
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| − | <li>In the cathode it needs to be placed an acceptor with a high redox potential
| + | <p>When exposed to light BBa_K160410 showed a remarkable response to the external load applied, as shown by the higher values of voltage and current in the light. However, it has to be pointed out that this behavior was not always consistent and a few times we also observed the reverse effect (more electricity in the dark). This data are in agreement with the functional characterization, in which it was shown that a few times there was a basal activation of the proton pump also in the dark.</p> |
| − | (i.e. Ferricyanide, air cathode).</li>
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| − | <li>In the anode it is important to place an electroactive bacteria (i.e.
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| − | <i>Schewanella oneidensis</i>) or supplement the media with chemical mediators (i.e.
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| − | methylene blue, neutral red) that can cross the bacterial membrane to steal the
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| − | electrons and bring them outside.</li>
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| − | <li>Additionally, our Solar pMFC needs to be built with a material that allows the
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| − | light to go through.</li>
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| − | </ul>
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| − | <p>Our goal was to build a functional prototype to:</p>
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| − | <ul class="customlist arrowed">
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| − | <li><strong>Enhance current production</strong>. This was achieved by connecting <span class="i_enph">6 small MFCs in parallel</span>.</li>
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| − | <li>Avoid dispersion of energy due to the different potential of the units MFC
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| − | connected in parallel. This is possible if the potential values of the single units are
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| − | identical, which is difficult when working with bacteria. To overcome this problem in our
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| − | design, the 6 cathode chambers are individually <span class="i_enph">connected with the same anode</span>, so that
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| − | they share the same homogenous bacterial culture.</li>
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| − | <li><strong>Maximize the surface of contact</strong> between the bacteria and the anode, and
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| − | simultaneously increase light exposure of the bacteria.
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| − | Exploit the redox potential of oxygen with a cathode partially in contact with
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| − | air (i.e. the cathodic chambers are open to the air, although filled with
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| − | water).</li>
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| − | <li>Have a sealed anodic chamber to maintain anaerobic conditions.</li>
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| − | </ul>
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| | </div> | | </div> |
| | </section> | | </section> |