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<h5>  Fabrication of Semiconducting Biofilms for Solar Cell Application </h5>
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<p>Since common energy resources such as oil and gas become rare and rare, the importance of renewable and sustainable energy resources rises continuously. Considering sustainability, nature provides a vast field for future power supply reaching from wind and water to solar energy. Further the production of biomass and the formation of biogas (methane) by bacteria should also be considered. The iGEM Team of the University Erlangen-Nuremberg aims to integrate current research in the preparation of conducting and semiconducting biofilms [1] to fabricate a series of novel highly absorbing layers in a bottom-up approach from the initial salts. We focus on the control of electron transport through the biofilms as it is crucial for optimization of the system. The result of our research can pave the way to a novel class of solar cells mainly fabricated by living cells. 
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In a first set of experiments, we will combine chemically and biologically synthesized zinc oxide (ZnO) as a wide band gap semiconductor with organic dye molecules and fluorescing proteins to inspect the charge transfer through a biofilm matrix. The emphasis lies on the layer thickness and the morphology of the biofilm, as well as the size of the ZnO colloids, which will affect the electron transport. 
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In the second part, we will address the integration of chemically synthesized, strongly absorbing nanoscale semiconductors into biofilms to analyze the film morphology and the affinity of the different types of nanoparticles to the biofilms.  
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In the third stage we plan to replace the chemical route by biological fabrication of the nanoparticles. Both biofilms (ZnO/Absorber) will be deposited on a substrate, yielding the basic structure of a solar cell, which can be expanded to a complete device using physical or chemical deposition techniques. This primary device will be characterized regarding its photoinduced electron transfer and efficiency. </p>
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<p><i>State of the Art </i></p>
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<p>The rising field of nanoparticular systems is attributed to their unique properties in terms of reactivity and spectroscopic behavior.[2, 3] Thus, biologic routes towards different types of nanoparticles are of current interest, as their “biosynthesis” avoids toxic stabilizing ligands and solvents, which is a crucial aspect of sustainable synthesis.[4] The formation of metal clusters exploits the natural defense mechanism of microorganisms against high metal concentrations.[5] With this strategy, a broad variety of colloids have already been realized, from metallic [6] to semiconducting nanoparticles, also called quantum dots.[4] In the field of semiconducting nanoparticles, metal sulfides are promising absorber materials, being easy to fabricate using bacteria and achieving good yields and morphology.[7] Additionally, Zinc oxide, which can serve as transparent top layer for solar cells, can also be fabricated by bacteria that can tolerate high amounts of zinc in solution.[8] </p>
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<p>Biofilms are aggregates of microorganisms frequently embedded within an extracellular matrix promoting adherence of cells to each other and to surfaces.[9] Biofilms are dynamic structures, selforganizing and highly adaptive to their environment. As materials, biofilms and similar multicellular consortia such as bone or shells have various characteristics that are of interest for technological applications.[10]
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Recently, semiconducting nanoparticles such as CdTe, CdS and ZnS have been successfully integrated into biofilms.[1] This was accomplished by conjugating the nanoparticles with antibodies or appropriate peptide tags, which in turn were linked to amyloid fibrils (curli) produced by E. coli cells. This attempt was further expanded by integrating gold nanoparticles into the film to address electric conductivity in biofilms. A direct preparation of silver nanoparticles within the biofilm matrix has also been shown to facilitate conductivity.[11]
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We intend to pick up this approach to program bacteria to build a scaffold for a solar cell, utilizing the unique ability of living materials to self-organize into nanoscale structures. </p>
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<a href="#">Team FAU Erlangen- Nuremberg: Coli- voltaic</a>
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<p>Nanoscale semiconductors provide a powerful platform for the development of numerous classes of solution-processed optoelectronic devices such as photovoltaic cells, photodetectors and lightemission devices. In addition to enabling solution processing, a key advantage of quantum dots is the size confinement effect: optical and electrical properties can be adjusted by varying the size and shape of the nanoparticles. In photovoltaic devices, quantum dot films are combined with a metal (Schottky junction cells) or with another semiconductor (TiO2/ZnO) to form a functional device.[12, 13]
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Against the background of nanoparticle solar cells, thin film solar cells provide a powerful tool to reduce the amount of material required for fabrication of solar cells. Different highly absorbing metal sulfide and metal selenide materials present the opportunity to reduce the layer thickness of the absorption layer to less than 5 µm. [14] A crucial limitation in the field of thin film solar cells is the Shockley-Queisser limit [15], describing the compromise between charge separation and absorption quality of the film; charge separation accelerates with decreasing layer thickness, while light absorption rises with increasing layer thickness. </p>  
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<p><i>References </i></p>
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<h1 id="">Inspiration</h1>
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<p>1 Lu T. et al. Nat. Mater. 2014, 13 (5), 515-523. </p>
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<p>2 Carey G.; Abdelhady L.; Ning Z.; Thon S.; Bakr O.; Sargent E. Chem. Rev. 2015, 115 (23), 1273212763. </p>
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The limitation of fossil fuels such as oil, coal and gas intensities the need to find different „materials“ to gain energy for a constantly rising population in the world. The energy can be provided by nature using wind, water, plants and the sun. Solar energy conversion can be a crucial factor as sun is present every day in almost every region in the world. Thereby an efficient conversion of solar energy is as important as the expenses for the solar cells. To reduce the price less expensive materials as well as the costs for production can be considered.
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<p>3 Yang Y.; Wu H.; Williams K.; Cao Y. Angew. Chem. 2005, 117 (41), 6870-6873.  </p>
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Commercially available silicon solar cells provide a good solar energy conversion rate in combination with moderate costs. To reduce the costs for the raw materials an inspiration from photosynthesis can be drawn. Here a chlorophyll molecule is excited to inject its electron into a redox cascade. The same principle can be chosen for solar cells applying dyes which can transfer electrons to a transparent semiconductor. These semiconductors can be either ZnO and TiO2, which are produced in a large scale for the application in e.g. tooth paste or sun screen.<br/> <br/>  
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<p>4 Hosseini M.; Sarvi M. Mater. Sci. Semicond. Process. 2015, 40, 293-301. </p>
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To reduce the production costs a large part can be covered by living cells, which work autonomous. In particular biofilms can be used since they provide the possibility to integrate metals inside its texture and can be mineralized. Hence the transparent semiconductor can be deposited by adding the initial salts to the bacteria solution. The process of mineralization can be done either during the growth of the biofilm or after the growth. The dyes for the solar cells can also be provided by E.Coli, which was demonstrated by the iGEM of Darmstadt in 2014 (link von deren homepage). The only technical process is the deposition of electrolyte and the sealing of the whole cell, which prevents this type of solar cell from drying out.
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<p>5 Ikuma K.; Decho A.; Lau B. Front. Microbiol. 2015, 6, 591.  </p>
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<p>6 Thakkar K.; Mhatre S.; Parikh R. Biol. Med. 2010, 6 (2), 257-262.  </p>
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<p class="cb" id="Biofilm"></p>
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<p>7 Jacob J.; Lens P.; Balakrishnan R. Microb. Biotechnol. 2016, 9 (1), 11-21. </p>
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<p>8 Jayaseelan C.; Rahuman A.; Kirthi A.; Marimuthu S.; Santhoshkumar T.; Bagavan A.; Rao K. Spectrochim. Acta, Part A 2012, 90, 78-84. </p>
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<h1 id="">Biofilm</h1>
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<p>9 http://pac.iupac.org/publications/pac/pdf/2012/pdf/8402x0377.pdf (state: 03/27/2016) </p>
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<p>
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<p>10 Rezwan K.; Chen Q.; Blaker J.; Boccachini A. Biomaterials 2006, 27 (18), 3413-3431. </p>
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A biofilm is a system that can be adapted internally to environmental conditions by its inhabitants. Note 2: The self-produced matrix of extracellular polymeric substance, which is also referred to as slime, is a polymeric conglomeration generally composed of extracellular biopolymers in various structural forms.  
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<p>11 Kalathil S.; Lee J.; Cho M. Green Chem. 2011, 13 (6), 1482-1485. </p>
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<p>12 Gur I.; Fromer N.; Geier M.; Alivisatos A. Science 2005, 310 (5747), 462-465. </p>
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<p>13 Carey G.; Abdelhady A.; Ning Z.; Thon S.; Bakr O.; Sargent E. Chem. Rev. 2015, 115 (23), 1273212763. </p>
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<img src="Biofilm/bio1.png" width="60%" height="auto" alt=""/>
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<p>14 Aberle A. Thin Solid Films 2009, 517 (17), 4706-4710. </p>
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<p>15 Shockley W.; Queisser H. J. Appl. Phys. 1961, 32 (3), 510-519. </p>
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Bacteria form these described aggregates in three-dimensional structures, to survive in the face of environmental stresses. To build these aggregates, the bacteria have to specialize themselves to attach to the surface and to communicate with other microorganisms: They will lose their flagella and will produce proteins for quorum sensing and induce expression of extracellular polymeric substances often called slime. <br/><br/>
 +
Enteric bacteria such as Escherichia coli and Salmonella spp. express proteinaceous extracellular fibers called curli that are involved in surface and cell-cell contacts that promote community behavior and host colonization. Between the basal biofilm and the outer biofilm there are pores, canals and corridors to transport a lot of substances like nanoparticles through the “slime”.  
 +
</p>
  
 +
<h2>Curli and the importance for our project</h2>
 +
<p>
 +
Enteric bacteria such as Escherichia coli and Salmonella spp. express proteinaceous extracellular fibers called curli that are involved in surface and cell-cell contacts that promote community behavior and host colonization. (paper auf studon)
 +
CsgA monomers are the major part of the Curli fibers and are secreted in the extracellular environment by E.coli W3110 itself. Being extracellular it has the opportunity to interact with various substances in a biofilm. Some bacterial strains are producing an extracellular matrix called biofilm, which is protecting them from environmental impacts. This matrix is composed of proteins, polysaccharides, lipids and nucleic acids. One of the main structural components in Escherichia coli biofilms are curli fibers, with a diameter of 4-7 nanometer that can made up to 10-40% of the whole biofilm.(Nguyen et.al) These fibers are amyloid structures, which are anchored on the bacterial cell surface and are assembled of 13 kDa CsgA proteins. For the production of these fibers the curli-system consists of two operons, containing seven genes: csgBAC and csgDEFG. The self-assembly and nucleation of CsgA on the cell surface is mediated by CsgB. CsgC/G are responsible for the secretion and CsgE/F for producing of CsgA. CsgD is the transcriptional regulator of this system. The following figure shows the Curli-producing process.
 +
For our project it was important, that the curli fibers are promoting the growth of biofilms and to interact with special nanoparticles.
 +
</p>
 +
<p align="center">
 +
<img src="Biofilm/bio2.png" width="30%" height="auto" alt=""/>
 +
</p>
 +
<p>
 +
After investigating old iGEM Team projects and other articles, we decided to ask our friends from the iGEM Team Marburg 2015 if they can send us their biobrick plasmid pPickUp (BBa_K1650047) and their E.coli strain W3110. pPickUp has the advantage having a SpyTag, which has strong similarities to some ZnO-Nanoparticle binding proteins which are already published.
 +
If the SpyTag can interact with our nanoparticles we do neither need an extra tag, which are already published nor an adaptor protein with interacts with the scaffold protein CsgA and the nanoparticles – killing two birds with one stone
 +
</p>
 +
<p class="cb" id="BioSolar"></p>
 +
<br/>
 +
<h1 id="">Biofilm Solarcell</h1>
  
 +
<p>
 +
Inhalt Biosolar
 +
</p>
 +
<p class="cb" id="GCell"></p>
 +
<br/>
 +
<h1>Grätzel Cell</h1>
 +
<h2>Setup of a Dye Sensitized Solar Cell (DSSC)</h2>
 +
<p>
 +
A dye sensitized solar cell does not require expensive material or complex working conditions. It can be basically built of tooth paste or sun screen in combination with a dye obtained from fruits or tea. The starting material is a glass slide which is coated with a transparent conducting material. The commonly used coating materials are Indium Tin Oxide (ITO) or Fluorine doped Tin Oxide (FTO). On the conducting slide the transparent semiconductors ZnO or TiO2 can be deposited, which serve as electron transporting layer. This layer can be soaked with the dye. Functional groups of the dye molecules direct and anchor them on the surface of the semiconductor. On this layer an electrolyte containing Iodine and Iodide providing the electrons to flow in the cell. The cell is completed with another glass slide coated with conducting traditional materials such as graphite or platinum.
 +
</p>
 +
<h2>Mechanism of a DSSC</h2>
 +
<p>
 +
Starting with the irradiation of the complete cell the electrons in the organic dye is excited to a higher level, which is called LUMO (lowest unoccupied molecular orbital). If the LUMO level is energetically high enough the electron can be transferred to the conduction band of the transparent semiconductor. The semiconductor, commonly made of ZnO or TiO2, can then induce the electron to the electrode. The missing electron of the dye can be restored by the electrolyte and the electrolyte can reobtain its electron from the cathode. There the cycle closes and a current is flowing continuously during light irradiation.
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Revision as of 15:50, 14 October 2016

<!doctype html> Unbenanntes Dokument


Inspiration

The limitation of fossil fuels such as oil, coal and gas intensities the need to find different „materials“ to gain energy for a constantly rising population in the world. The energy can be provided by nature using wind, water, plants and the sun. Solar energy conversion can be a crucial factor as sun is present every day in almost every region in the world. Thereby an efficient conversion of solar energy is as important as the expenses for the solar cells. To reduce the price less expensive materials as well as the costs for production can be considered. Commercially available silicon solar cells provide a good solar energy conversion rate in combination with moderate costs. To reduce the costs for the raw materials an inspiration from photosynthesis can be drawn. Here a chlorophyll molecule is excited to inject its electron into a redox cascade. The same principle can be chosen for solar cells applying dyes which can transfer electrons to a transparent semiconductor. These semiconductors can be either ZnO and TiO2, which are produced in a large scale for the application in e.g. tooth paste or sun screen.

To reduce the production costs a large part can be covered by living cells, which work autonomous. In particular biofilms can be used since they provide the possibility to integrate metals inside its texture and can be mineralized. Hence the transparent semiconductor can be deposited by adding the initial salts to the bacteria solution. The process of mineralization can be done either during the growth of the biofilm or after the growth. The dyes for the solar cells can also be provided by E.Coli, which was demonstrated by the iGEM of Darmstadt in 2014 (link von deren homepage). The only technical process is the deposition of electrolyte and the sealing of the whole cell, which prevents this type of solar cell from drying out.


Biofilm

A biofilm is a system that can be adapted internally to environmental conditions by its inhabitants. Note 2: The self-produced matrix of extracellular polymeric substance, which is also referred to as slime, is a polymeric conglomeration generally composed of extracellular biopolymers in various structural forms.

Bacteria form these described aggregates in three-dimensional structures, to survive in the face of environmental stresses. To build these aggregates, the bacteria have to specialize themselves to attach to the surface and to communicate with other microorganisms: They will lose their flagella and will produce proteins for quorum sensing and induce expression of extracellular polymeric substances often called slime.

Enteric bacteria such as Escherichia coli and Salmonella spp. express proteinaceous extracellular fibers called curli that are involved in surface and cell-cell contacts that promote community behavior and host colonization. Between the basal biofilm and the outer biofilm there are pores, canals and corridors to transport a lot of substances like nanoparticles through the “slime”.

Curli and the importance for our project

Enteric bacteria such as Escherichia coli and Salmonella spp. express proteinaceous extracellular fibers called curli that are involved in surface and cell-cell contacts that promote community behavior and host colonization. (paper auf studon) CsgA monomers are the major part of the Curli fibers and are secreted in the extracellular environment by E.coli W3110 itself. Being extracellular it has the opportunity to interact with various substances in a biofilm. Some bacterial strains are producing an extracellular matrix called biofilm, which is protecting them from environmental impacts. This matrix is composed of proteins, polysaccharides, lipids and nucleic acids. One of the main structural components in Escherichia coli biofilms are curli fibers, with a diameter of 4-7 nanometer that can made up to 10-40% of the whole biofilm.(Nguyen et.al) These fibers are amyloid structures, which are anchored on the bacterial cell surface and are assembled of 13 kDa CsgA proteins. For the production of these fibers the curli-system consists of two operons, containing seven genes: csgBAC and csgDEFG. The self-assembly and nucleation of CsgA on the cell surface is mediated by CsgB. CsgC/G are responsible for the secretion and CsgE/F for producing of CsgA. CsgD is the transcriptional regulator of this system. The following figure shows the Curli-producing process. For our project it was important, that the curli fibers are promoting the growth of biofilms and to interact with special nanoparticles.

After investigating old iGEM Team projects and other articles, we decided to ask our friends from the iGEM Team Marburg 2015 if they can send us their biobrick plasmid pPickUp (BBa_K1650047) and their E.coli strain W3110. pPickUp has the advantage having a SpyTag, which has strong similarities to some ZnO-Nanoparticle binding proteins which are already published. If the SpyTag can interact with our nanoparticles we do neither need an extra tag, which are already published nor an adaptor protein with interacts with the scaffold protein CsgA and the nanoparticles – killing two birds with one stone


Biofilm Solarcell

Inhalt Biosolar


Grätzel Cell

Setup of a Dye Sensitized Solar Cell (DSSC)

A dye sensitized solar cell does not require expensive material or complex working conditions. It can be basically built of tooth paste or sun screen in combination with a dye obtained from fruits or tea. The starting material is a glass slide which is coated with a transparent conducting material. The commonly used coating materials are Indium Tin Oxide (ITO) or Fluorine doped Tin Oxide (FTO). On the conducting slide the transparent semiconductors ZnO or TiO2 can be deposited, which serve as electron transporting layer. This layer can be soaked with the dye. Functional groups of the dye molecules direct and anchor them on the surface of the semiconductor. On this layer an electrolyte containing Iodine and Iodide providing the electrons to flow in the cell. The cell is completed with another glass slide coated with conducting traditional materials such as graphite or platinum.

Mechanism of a DSSC

Starting with the irradiation of the complete cell the electrons in the organic dye is excited to a higher level, which is called LUMO (lowest unoccupied molecular orbital). If the LUMO level is energetically high enough the electron can be transferred to the conduction band of the transparent semiconductor. The semiconductor, commonly made of ZnO or TiO2, can then induce the electron to the electrode. The missing electron of the dye can be restored by the electrolyte and the electrolyte can reobtain its electron from the cathode. There the cycle closes and a current is flowing continuously during light irradiation.