Team:TU Delft/Demonstrate
Demonstration a functional proof of concept
Testing our biological microlenses on solar panels
Overview
Abstract
Due to global warming and to prevent shortage of currently used fossil fuels, a variety of measures needs to be taken. The potential of solar energy is seemingly limitless, so this seems to be a good alternative for fossil fuels. The efficiency of solar panels is nowadays still too low to make them profitable. Using microlens arrays (MLAs) appeared to significantly increase its efficiencies, however these are expensive to produce and not environmentally friendly.
Here we have used our biologically produced microlenses to test if these could also improve the efficiency of solar panels and therefore create an alternative for chemically produced MLAs. After testing them, using a solar simulator and well characterized solar panels, results showed that the efficiency was increased.
Introduction
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. These include 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).
stukje over hoe die MLAs de zonnecellen kunnen improven , zie proof of concept in businessplan.
stukje over dat huidige MLAs duur zijn en slecht voor het milieu.
Alternatief: biologische microlenzen.
Voordelen van biolenzen ten opzichte van chemically produced : kleiner, biologisch produced, less expensive.
Realization of the biological microlenses
Preparation of biolenses
To produce a biolens, E. coli was covered in a layer of polysilicate. This will give the cell optical properties and act as a lens by focusing light. As E. coli cells are not intrinsically able to cover themselves in polysilicate. However, upon transformation of the silicatein-α gene, originating from sponges, it is possible to coat the bacterium in a layer of polysilicate (Müller et al., 2008; Müller et al., 2003). Therefore, we are transforming E. coli with silicatein-α. We test the use of two different silicateins, one originating from the marine sponge Suberites domuncula (Müller, 2011) and one originating from the marine sponge Tethya aurantia (Cha et al., 1999). We express the enzyme in three different ways. First of all, we expressed the gene from S. domuncula (Part K1890000) and see if the enzyme is transported outside the cell as described by Müller et al, 2008. Furthermore, we express a fusion of silicatein from T. aurantia to the trans-membrane protein OmpA (outer membrane protein A) from E. coli to anchor the silicatein to the membrane (Part K1890002) (Curnow, Kisailus, & Morse, 2006; Francisco et al. 1992), which might make coating the cell specifically in polysilicate more efficient. We also express a fusion of silicatein from S. domuncula to the transmembrane Ice Nucleation Protein (INP) from Pseudomonas syringae (Part K1890001), a popular protein for membrane fusions (Kim & Yoo, 1998). Using these different approaches we expect to coat the cell in polysilicate, an overview is shown in figure 1. This glass coating around the cell will be the basis of our biolens .
-----------------------------------------------------------------------------------------------------
Improving the way we capture light
The ultimate goal of our research was to be able to capture light more light in a new way. We used synthetic biology to produce biological microlenses. Once these microlenses are placed in a 2D-matrix, which we call a microlens array, we can use them for applications where capturing light is important. Capturing light is vital in many applications, including microscopy, photography, or solar cells.
Although the focus of our project is mainly improving microscopy, we also saw a new and exciting opportunity to also improve solar cells with our biological microlenses. 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 (Crabtree, 2006). 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. It is already proven that the use of a microlens array as an encapsulation layer for the solar panels results in 20% to 50% increase of the efficiency (Jutteau, Paire, Proise, Lombez, & Guillemoles, 2015; Nam, Kim, Lee, Yang, & Lee, 2013). However, the production of these microlens arrays is both expensive and environmentally unfriendly. Therefore, this technology is not used yet in day-to-day life.
Production of biological microlenses
In our project, we believe to have found a solution for the costly and environmentally unfriendly microlens arrays. The goal of our project was to produce biological microlenses to improve microscopy, but these can also be used for more efficient solar panels. In our study we have successfully produced biological microlenses by expression of the silicatein gene in Escherichia coli. Silicatein is a protein that is able to concert the molecule monosilicate to polysilicate, a kind of biological glass. By fusion of the silicatein protein to the membrane protein OmpA we were able to express the enzyme of the membrane and therefore coat the cells in a layer of polysilicate. Once the cells are coated in this layer of glass, they are able to function as microlenses.
Also, we have demonstrated that we are able to produce spherical microlenses of only 1 µm in diameter. This is revolutionary, since typical microlenses are usually in the 10-100 µm range, since current techniques cannot produce smaller lenses (Krupenkin, Yang, & Mach, 2003).
Testing our cells under real-world conditions
The improvement of solar panels using microlens arrays have already been proven (Jutteau, Paire, Proise, Lombez, & Guillemoles, 2015). Our models have shown that our microlenses have a defined focal point at around 1 µm of the lens, so the lenses are suitable for focusing light on a surface, such as a solar cell. Unfortunately, we are not yet able to produce a well-defined microlens array as we have seen in literature, since we were not able to position the cells in a 2D array. Therefore, we cannot yet give a definitive conclusion on whether our cells can improve solar cells. However, there were other real-world conditions that we could test already.
The main difference between the structure of our microlenses and conventional microlenses is that our biological microlenses contain a core of live bacteria. This has two consequences for our project. First of all, we couldn’t take our bacteria out of the lab to put them on solar cells due to the antibiotic resistance our cells carry. In order to solve this problem, we developed two different protocols to sterilize the cells without harming the shape of the lens. One method was based on autoclaving and the other on UV-sterilization. The protocol based on UV-sterilization has shown to be successful: we have successfully sterilized our cells without harming the integrity of the lens.
The second challenge we face was that the core of bacteria in our lens, either dead or alive, could mean our cells had different optical properties compared to conventional microlenses. The best way to test this was to test our cells under real-world conditions, by applying the cells onto an actual solar cell and testing them on 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. Our results show 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.
Outlook
The most important follow-up experiment would be to construct an actual microlens array with our microlenses. Now our microlenses were positioned randomly on the solar cells. This way, the light is not focused as efficiently as in a microlens array, so we expect to see increases in solar cells once we have a well-structured microlens array. Furthermore, there is still a variation in the sizes and shapes of our microlenses, even though we are already able to control the cell shape. An interesting future study would be sorting the cells in size using FACS, so we can produce a homogeneous layer of microlenses.
References
- Berezin, M. Y., & Achilefu, S. (2010). Fluorescence lifetime measurements and biological imaging. Chemical reviews, 110(5), 2641-2684.
- Einstein, A. (1917). Zur quantentheorie der strahlung. Physikalische Zeitschrift, 18.
- Gather, Malte C., and Seok Hyun Yun. "Single-cell biological lasers." Nature Photonics 5.7 (2011): 406-410.
- Jonáš, Alexandr, et al. "In vitro and in vivo biolasing of fluorescent proteins suspended in liquid microdroplet cavities." Lab on a Chip 14.16 (2014): 3093-3100.
- Shaner, N. C., Patterson, G. H., & Davidson, M. W. (2007). Advances in fluorescent protein technology. Journal of cell science, 120(24), 4247-4260.
- Svelto, Orazio. Principles of lasers. Ed. David C. Hanna. London, New York, Rheine: Heyden, 1976.
