Chem321:Bacteriophage Solar Energy
Bacteriophage Solar Energy
Anthropogenic climate change is an unfortunate and undeniable reality that has a plethora of far-reaching and adverse consequences that not only impact Homo sapiens, but the entirety of our planet (Heede, 2013). This dilemma has the potential to impair human health, cripple economies, and destabilize communities, as well as causing immense and potentially irreparable harm to ecosystems (Heede, 2013). This bleak scenario can largely be attributed to our dependence on fossil fuels, which have various negative attributes, such as producing greenhouse gases as a result of their combustion (e.g. carbon dioxide and methane) and carbonic acid (from carbon dioxide, leading to ocean acidification) (Heede, 2013). Thus, it is undoubtedly necessary that we must wean ourselves off our fossil fuel dependence and replace our primary means of energy production with other sources that are environmentally benign and sustainable. One such source is solar energy, which has the highest theoretical potential of the earth’s renewable energy sources, as one and a half hours of solar radiation on the earth’s surface is the equivalent of an entire year of global energy (in 2001) (Tsao et al., 2006). Although solar energy has tremendous potential, the high costs and low efficiencies of solar (photovoltaic) cells have been hindrances in the progress of this incredibly beneficial technology (Choubey et al., 2012). However, there are various advances that are helping to negate these hindrances, such as the utilization of bacteriophages, which will be the focus of this paper.
To begin, it is necessary to develop a satisfactory understanding of solar (photovoltaic) cells and how they function. Solar cells in the most basic sense convert solar radiation to electrical energy (Choubey et al., 2012). This direct conversion from solar radiation into electricity occurs at the atomic level, and can be attributed to the photoelectric effect (NASA, 2002). The photoelectric effect is the basis for solar cell functionality and entails the absorption of incoming photons (from solar radiation) by photoelectric materials (contained in solar cells), thereby releasing electrons (NASA, 2002). Semiconductors (e.g. thin silicon wafer semiconductors) function to capture freed electrons, which produce an electric current that can be harnessed as electricity (an electric circuit must exist within solar panels for this to be attainable) (NASA, 2002). Most traditional solar cells only contain a single junction (limited band gap), meaning that they are limited to absorbing only a portion of the electromagnetic spectrum (i.e. photons that have an equal or greater amount of energy than the band gap are absorbed, whilst lower energy photons are not) (NASA, 2002). Thus, a major goal in the solar industry has been the improvement of solar cell photon conversion efficiencies (PCEs), which is the ability to convert more of the electromagnetic spectrum to electrical energy (NASA, 2002).
Secondly, it is also necessary to develop a sufficient understanding of bacteriophages and their morphologies, which is integral to their application in solar energy. Bacteriophages (phages) are viruses that have an affinity for the realm of bacteria, and they are the most abundant entities in the world (Haq et al., 2012). Phages have an incredibly diverse range in their morphologies; however, there are fundamental physiological similarities within this incredibly diverse group (Haq et al., 2012). For example, phages can contain either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), which is contained (encapsidated) in phage capsids (Haq et al., 2012). Capsids can be considered the protective protein coats that ensure the safety of the nucleic acid whilst also creating a boundary, thereby separating the intracellular and extracellular components (Haq et al., 2012). Shortly after the discovery of phages (in the early 20th century) researchers realized that phages could be used as potential therapeutic agents against bacteria, which is now a feasible alternative to antibiotics (and a solution to multiple drug-resistant bacteria) (Haq et al., 2012). However, there are a plethora of laudable applications that have been developed, such as improved vaccine delivery methods, targeted gene delivery techniques, and in the production and storage of energy (Haq et al., 2012).
M13 is a filamentous bacteriophage that is being successfully harnessed in improving the efficiency of solar cells, as well as reducing the amount of materials that are required for their production (Chen et al., 2013). In regards to solar cell efficiencies, researchers have been attempting to incorporate single-walled carbon nanotubes (SWNTs) to increase their PCEs, although, the initial attempts prior to employing phages were largely unsuccessful (Dang et al., 2011). SWNTs are incredibly advantageous components in solar cell production, which can be attributed to their 1-dimensional conformations and exceptional electron mobility (Dang et al., 2011). However, the initial SWNTs that were incorporated into solar cells were ineffective for a number of reasons. Firstly, the traditional SWNTs manufacturing process produced a hodgepodge of both metallic and semiconducting SWNTs (Dang et al., 2011). The semiconducting SWNTs were highly efficient in facilitating the diffusion of electrons, whereas the metallic SWNTs became problematic (Dang et al., 2011). The metallic SWNTs have the unfortunate tendency of forming short-circuits; thereby negative any improvements therein (Dang et al., 2011). Secondly, SWNTs have the dogged tendency to form aggregates (bundles) that put the metallic and semiconducting SWNTs in contact with one another, which further reduces the efficiency of the system (Dang et al., 2011). There have been attempts that utilized chemical modifications to the SWNTs in order to eliminate the bundling issue, however, these modifications inadvertently caused the degradation of their electronic properties (i.e. a considerable loss in functionality) (Dang et al., 2011). Thus, these initial problems were largely pertaining to the incorporation of SWNTs into solar cells, which was successfully eliminated through the implementation of M13 bacteriophages (Dang et al., 2011).
Researchers were able to circumvent the issue of incorporating (as well as the aforementioned accompanying issues) the SWNTs through the genetic engineering of M13 phages (Dang et al., 2011). This has been approached with a variety of different methods; however, the core principle is to genetically modify the M13 phage capsid (Chen et al., 2013). For example, Chen et al. have modified the M13 capsid to contain gold nanoparticles (AuNPs), thereby producing an affinity for inorganic materials (Chen et al., 2013). This affinity was then exploited, and the modified M13 phages were employed to construct three-dimensional scaffolds that managed to improve both light harvesting and electron collection in dye-sensitized solar cells (DSSCs) (Chen et al., 2013). Dang et al. produced M13 phages that contained nanocrystals in their capsids, which allowed the SWNTs to bind to the phages (Dang et al., 2011). These phage/SWNTs were then dispersed throughout the dye-sensitized solar cell and effectively incorporated, thereby successfully improving the PCE (Dang et al., 2011).
The phage/SWNT complexes are specifically incorporated into the solar cell photoanodes, which is attained by exploiting the chemical properties of both the phages and SWNTs (Dang et al., 2011). For example, both the phages and SWNTs are negatively charged, thus they are effectively incorporated into the photoanodes by manipulating the pH (i.e. a pH-dependent control mechanism, which promotes their binding to the photoanodes) (Dang et al., 2011). This approach allowed Dang et al. to significantly boost the photon conversion efficiency of DSSCs from 8.3% to 10.6%, which is remarkably a 27.7% increase in efficiency with the phage SWNTs integration technique (Dang et al., 2011). Furthermore, Dang et al. attained improved efficiency by integrating only 0.1 percent SWNTs by mass (relative to the mass of the solar cell), which is an incredible feat (Dang et al., 2011). Thus, bacteriophages are clearly quite useful and efficacious in improving the photon conversion efficiencies of solar cells, however, they simultaneously reduce the amount of material required in the production of photovoltaic devices (Dang et al., 2011).
Reducing the required materials for producing solar cells (and subsequently the waste upon disposal) is a pertinent goal, as there are various hazardous chemicals within solar cells (Brouwer et al., 2011). Solar cells are indeed environmentally benign and favorable vis-à-vis exploiting fossil fuels; however, there are a number of hidden emissions and pollutants that cradle-to-grave analyses have indicated are problematic and environmentally harmful (Brouwer et al., 2011). For example, this can be divided into three problem areas: the amount of materials used in production, the transportation of solar cells, and their disposal (Brouwer et al., 2011). The transportation of solar cells is more so a widespread issue of excessive greenhouse gas emissions due to the vehicles required in the transportation of goods across long distances (e.g. cargo ships, freight trains, jumbo jets, etc.) (Klein, 2011). Naomi Klein’s remedy for this scenario is certainly applicable to solar cells, and would significantly reduce emissions generated through transportation (Klein, 2011). The other two issues have much more severe consequences, due to the hazardous materials that are included in solar cells (Brouwer et al., 2011). For example, solar cells contain lead (which is highly toxic), cadmium (a potent carcinogen, which can result in lung cancer due to inhalation), and various rare metals (e.g. gallium, indium, etc.) (Brouwer et al., 2011). The disposal of cadmium and lead in landfills poses the risk of leaching into the soil, which could eventually contaminate drinking water (amongst other adverse consequences) (Brouwer et al., 2011). Improperly disposing of the rare metals is also problematic, as this could lead to their permanent depletion (and a hodgepodge of ensuing disastrous consequences) (Brouwer et al., 2011). Thus, these issues can be addressed certainly at the source (reducing the quantity of materials in production), and at the end of the product’s life through the proper reuse and recycling of the various components (Brouwer et al., 2011). The M13 phage dye-sensitized solar cell produced by Chen et al. eliminated the need for 63.5% of the photoactive materials that would normally have been used in the production of the non-phage solar cell, thereby reducing the environmental impact at both the production and disposal phases (Chen et al., 2013).
In all, solar energy clearly has tremendous potential and the capacity to revolutionize our means of energy production, whilst simultaneously reducing our immense impact on the health of the environment. Although there are certainly numerous issues that must continue to strive to mitigate and eventually eliminate, such as the somewhat low efficiencies of the current solar cells, the exorbitant costs (and the consequential inaccessibility for most), the huge and varied material requirements for their production, and the inevitable disposal of the solar cells. However, the implementation of bacteriophages (specifically M13) in solar cell production has laudably contributed to the mitigation of these issues, as these phage solar cells have indeed increased photon conversion efficiencies, reduced the quantity of photoactive materials required in solar cell production, and reduced the overall environmental impact when considering a cradle-to-grave life cycle analysis. These factors have the potential to create less expensive solar panels, which will make the acquisition of solar panels more feasible. Thus, the future of solar energy does indeed seem quite bright, and hopefully it will be consistent with the Citibank predictions. For example, Citibank predicted that by 2020 solar energy will be successfully competing with fossil fuels, which will be occurring in the absence of subsidies (Register, 2014). In conclusion, there are numerous methods being applied to improve solar cells, of which the M13 bacteriophage technique has proven to be an effective endeavor that has both increased solar cell efficiencies whilst reducing their overall environmental impact.
References:
1) Brouwer et al. (2011). METHODS AND CONCERNS FOR DISPOSAL OF PHOTOVOLTAIC SOLAR PANELS. 1-64. Retrieved from http://generalengineering.sjsu.edu/docs/pdf/mse_prj_rpts/fall2011/METHODS AND CONCERNS FOR DISPOSAL OF PHOTOVOLTAICS.pdf
2) Chen et al. (2013). A Versatile Three-Dimensional Virus-Based Template for Dye- Sensitized Solar Cells with Improved Electron Transport and Light Harvesting. 6563-6574. doi:doi:10.1021/nn4014164.
3) Choubey et al. (2012). A review: Solar cell current scenario and future trends. Recent Research in Science and Technology, 4(8), 99-101. Retrieved from recent-science.com/index.php/rrst/article/download/14896/7598
4) Dang et al. (2011). Virus-templated self-assembled single-walled carbon nanotubes for highly efficient electron collection in photovoltaic devices. Nature Nanotechnology, 377-384.
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6) Haq et al. (2012). Bacteriophages and their implications on future biotechnology: A review. Virology Journal, 9, 1-8. Retrieved from http://www.virologyj.com/content/pdf/1743-422X-9-9.pdf
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8) NASA. (2002). How Do Photovoltaics Work? NASA Science NEws. Retrieved from http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/
9) Register, C. (2014). Solar Continues Trumping Fossil Fuel Pricing, With More Innovations To Come. Retrieved from http://www.forbes.com/sites/chipregister1/2014/09/11/solar-continues-trumping-fossil-fuel-pricing-with-more-innovations-to-come/
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