Team:TU Delft/Design

iGEM TU Delft

Best applied design

Applying our Biolenses

Improving the way we capture light

The capturing of light is vital in many applications, including microscopy, photography, or solar cells. Especially in development of solar cells, there is a lot of research done how to improve these systems. Since fossil fuels are running out and global warming is becoming a bigger issue, ‘green’ forms of energy are becoming more and more popular. Most people agree that to curb global warming and to prevent shortage, a variety of measures needs to be taken. Probably the best response to the growing energy problem is to switch to renewable energy sources. Renewable energy is collected from resources which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat. Since in less than an hour, the theoretical potential of the sun represents more energy striking the earth’s surface than worldwide energy consumption in one year, this is considered to be the most promising renewable energy source (Crabtree, 2006). Solar panels would therefore be a perfect solution to solve the energy problem. However, the efficiency of solar panels is still very low nowadays and has to be increased to make them profitable. One promising finding is the use of microlens arrays (MLAs). It is already proven that the use of a MLA as an encapsulation layer for the solar panels results in 20% to 50% increase of the efficiency (Jutteau et al., 2015; Nam et al., 2013). However, the production of these MLAs is still relatively expensive and especially very environmental unfriendly. The production uses caustic chemicals, high temperatures and low pressure (Nam et al., 2013). Therefore, economically it is not favorable to use MLAs at this moment and perhaps even more important for us, it absolutely does not fit the idea about environmentally friendly solar panels. After all, the production is very environmentally unfriendly.

Microlens array
Figure 1: An example of a solar cell covered by microlenses.

Escherichia coli Biolenses: a green alternative to improve solar cells

We believe to have found a solution for this problem. In our project, we are producing biological microlenses. By transforming E. coli with a gene encoding the enzyme silicatein, we are able to cover the cell in a layer of biological glass, transforming the cell into a microlens. We have successfully proven that we are able to produce these microlenses. We produce these microlenses at mild physiological conditions without using any harmful chemicals. This enables us to produce microlens arrays that are environmentally friendly. By adding a layer of our biological microlenses on the surface of a solar cell, we can have the same effect as using a conventional microlens array but with a much smaller environmental footprint. Furthermore, we have shown that by also genetically modifying the bacteria with the gene BolA we are able to produce spherical microlenses that are 10-100x smaller than conventional microlenses. Current techniques are not sufficient enough to produce microlenses of this size at large scale (Krupenkinet al., 2003). Therefore, our microlenses are not only greener, but also solve production limitations encountered in the conventional microlens industry.

Microlenses
Figure 2: SEM images of (A) regular E. coli and (B) our spherical microlenses.

Since there is a core of bacteria in our lens, either dead or alive, it could mean our cells had different optical properties compared to conventional microlenses. We have tested these cells in professional in real-world conditions, by applying the cells onto an actual solar cell and testing them using a solar simulator. A solar simulator is a light source that reproduces the light emitted by the sun. First of all, we measured the absorption of our cells. Because our lenses contain cells on the inside, they could absorb the light instead of focus it. We tested this feature with spectroscopy.

Here we have found that our cells did not absorb significantly more light than the glass layer that is usually applied on solar cells. Furthermore, testing our cells on solar cells under the solar simulator showed no detrimental effects of our cells on the efficiency of solar cells. Therefore, we can conclude that our cells do not have a negative impact on the solar cells, which is a promising outlook for our biological microlens arrays. More information can be found on the demonstrate page.

The safety of our Biolenses

Since our biological lenses are produced under mild physiological conditions, the production process is already much greener compared to conventional microlenses. However, the production of the lenses is ot the only factor to take into account when evaluating the environmental impact of our product. We are bringing our product out of the lab, in the outside world, so the direct impact on the environment and the disposal of the product are also issues. Our product consists of a live bacterium with a glass shell around its membrane. Several safety issues have to be taken into account when bringing a GMO in the environment. The specific design of our microorganism is not associated with any significant risks, see our risk assessment, so it could be possible to get a license to use the organism on solar panels. However, we have made use of antibiotic resistance to transform the cells. This could be transferred to other bacteria by horizontal gene transfer, resulting in new antibiotic resistant strains. This could impose a serious health risk for the population. Therefore, we have researched ways to sterilize the biolenses, without disturbing the optical properties of the lenses. We have developed a method of UV-sterilization to kill the cells inside the lens, without disturbing the lens itself. This makes the application of our cells into the outside world very safe.

Other applications of our Biolenses

There is also research done into the use of micro lenses to produce lightweight cameras that can be used in, for example, smartphones. For smartphones it is important that the cameras are both lightweight and have a high resolution. Microlenses could be used to create both lightweight and high resolution cameras. Another possibility to use microlenses is when you want to focus multiple focal planes at the same time. This means that you can focus upon different points that are not at the same height (z-direction). Regular cameras or microscopes can currently only focus upon one height at the same time.

For the last two options, it is important that the microlenses have always exactly the same properties. This means that they always should have the same size and the same optical properties. We have already solved this problem by using the BolA gene, making the shape of the cells spherical and more homogeneous. A FACS scanner could probably be used to do detect the cells with certain properties. However, more research is required to make this possible. For the applications were the goal is purely to capture more light, it is not necessarily a requirement that every microlens has the exact same properties. The biologically produced microlenses can easily be implemented in these kind of applications.

Microlens array
Figure 3: An example of a Lytro camera, a camera that uses an array of microlenses to generate multiple images.

References

  1. Crabtree, J. T. N. L. G. (2006). Solar FAQs Retrieved from http://www.sandia.gov/~jytsao/Solar%20FAQs.pdf
  2. Jutteau, S., Paire, M., Proise, F., Lombez, L., & Guillemoles, J. F. (2015, 14-19 June 2015). Micro solar concentrators: Design and fabrication for microcells arrays. Paper presented at the Photovoltaic Specialist Conference (PVSC), 2015 IEEE 42nd.
  3. Krupenkin, T., Yang, S., & Mach, P. (2003). Tunable liquid microlens. Applied Physics Letters, 82(3), 316-318.
  4. Nam, M., Kim, K., Lee, J., Yang, S. S., & Lee, K.-K. (2013). Solar cell packaged by a microlens array and its long-term optical efficiency enhancement. Paper presented at the Proc. of SPIE Vol.
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