Difference between revisions of "Team:CHINA CD UESTC/Modeling"

Biological fuel cell (BFC) is a device with the use of enzymes or microorganisms as catalysts. According to the types of catalysts, it can be divided into microbial fuel cells（MFC）and enzymatic biofuel cell (EBFC). Our project is focused on improving the catalytic efficiency of laccase in biofuel cell. Laccase, which produced by advanced plants, fungi, and some bacterial strains, is a multicopper oxidoreductase and oxidizes phenolic compounds while reducing oxygen to water directly without requiring H₂O₂ or any other co-factors for its catalysis ^[1] . In addition to be applied in the biological fuel cells, it also has various applications containing pulp and paper industry, environmental applications, food industry, and biosensors.

One criteria of evaluating a microbial fuel cell is potential. We use the laccase as a bio-cathode to achieve electron transfer function from pole to oxygen.

According to E. Laviron's article ^[2] , we can use the Laviron formula to estimate the cathodic peak potential:

If we want to do some analysis, hypothesis condition is necessary from existing literatures.

From the formula (1), we can judge that the electron transfer coefficient determines the potential size. In order to study the relationship between them, we use MATLAB for the operation. The results are as follows:

Figure 1. With the increase of electron transfer coefficient, cathodic peak potential is also increasing rapidly. But the value of α is form 0.3 to 0.7 in general.

We want to improve the catalytic efficiency of laccase to make biological fuel cells more efficient. So we guess that enrichment of laccase in the electrode can improve the efficiency of electron transfer.The following figure 2 shows our conjecture:

Figure 2. We predict the enrichment of laccase will improve the efficiency of the BFC.

The Michaelis–Menten curve describes the relationship between an enzyme (at constant concentration) and the concentration of enzyme’s substrate.

Figure 3. We predict the enrichment of laccase will improve the efficiency of the BFC.

Form figure 1, we learn about the electron transfer coefficient determines the potential. So what determines the electron transfer coefficient? We think enzyme quantity per unit area and the distance between enzymes and electrodes are the main influence factors. So we establish the formula:

In order to verify whether our formula is correct. We need some ideal assumptions to meet calculation conditions.

We calculate the equation (3), and simulate the results with MATLAB. The electron transfer coefficient variation tendency are as follows:

Figure 4. The electron transfer coefficient variation tendency relates with enzyme quantity per unit area and the distance between enzymes and electrodes. Our model result is consistent with the experimental conclusions[3].

There are many methods to fix laccase on the electrode. However, we came up with a novel idea utilizing biology magnetotaxis. Magnetotactic bacterium(MTB) is a special microbe in nature which can be attracted by magnet . Magnetosome, covered by membrane with some Fe3O4s nanocrystals, which is the reason why MTB has the ability to be attracted. We design a expression system for E.coli expressing Magnetosomes. And then we link laccase to Magnetosomes by the method of structuring fusion protein with MamW. The ultimate goal is showing in the figure 5:

Figure 5. Fixing laccase on the electrode with Magnetosome. It has the advantage of simple operation , environmental protection, as well as good biocompatibility.

According to previous experiments and papers, we verifiy our model by their experiment data. For exampe, Maryam Nazari et al ^[3] assembled a MFC with laccase. Detected voltage was 256mV, and when =0.75, the result our model predicted was 0.238mV. In the error range, our model is correct!