For a growing number of scientists and engineers, salmon is much more than dinner: it's the natural biological source of genomic DNA that lays the foundation for their research. The use of DNA derived from salmon waste products in photonic and electronic device applications has been growing in scope for the past decade.
The field has developed so extensively, in fact, that recently a new term has been coined to describe it: biotronics. Biotronics is a newly emerging research area that uses biologically based materials for photonics and electronics applications. Currently, DNA and silk are the most prevalent of these materials.1
The applications for the DNA-based biopolymer range from the commercial (telecom2) to the whimsical (cigarette filters3) to the practical (efficient LEDs4). Many applications, however, are focused on security and defense. This is due, in large part, to the role of the U.S. Air Force Research Laboratory (AFRL) in promoting this material for optical and electronic device applications.
Several of the DNA-based applications for security and defense have been developed in the past few years. These include electro-optic (EO) modulators, bio-field-effect transistors (BioFETs), electrochromics, energy storage, and electromagnetic interference (EMI) shielding. The research teams in this field are both national and international and hail from academia, government, and the commercial sector.
Salmon waste is used in photonic and electronic device applications because it is so plentiful in Japan, inexpensive and is almost 90% pure DNA.
Salvaging salmon waste
The DNA biopolymer most frequently integrated into photonic and electronic devices was developed in collaboration with researchers in Hokkaido, Japan, and the AFRL.
Shown below, the DNA is derived from salmon milt and roe sacs, waste products of the Japanese fishing industry.5The DNA in this form, however, is water soluble, which is incompatible with electronic and optical device fabrication. It is then precipitated with a surfactant complex, hexadecyltrimethylammonium chloride (CTMA), to make a water-insoluble biopolymer.6
The new DNA biopolymer, commonly referred to as DNA-CTMA, is now water insoluble, is soluble in chloroform and many of the alcohols and is resistant to other common polymer solvents such as cyclopentanone and dibromomethane. The DNA-CTMA forms either a white powder or crystalline-like solid depending on the processing.
Purified DNA processed from salmon waste products.
For device fabrication, the DNA-CTMA is typically dissolved in butanol, then spin-coated to a 1-4 micron thick film, depending on the desired application. It can also be drop-cast to form thicker films. Usually these films are a few microns thick and have a surface area of a few inches square, again, depending on the desired application. They are almost always on a substrate such as glass or silicon because free standing films usually are of poor optical quality and would not be used in an optical application.
The unique properties of this low-cost material make it well suited for many photonics applications. It is easily fabricated into a spin-coated thin film and thermally stable. It has low optical loss, low microwave-insertion loss, and has tunable properties such as refractive index, dielectric constant, electric permittivity, and electrical resistivity.
Salmon DNA is used in this area of biotronics research simply because it is so prevalent. Naoya Ogata, the Hokkaido scientist who first began purifying the salmon DNA, found that Japanese fishers were throwing away 15 to 20 tons of salmon waste each year, and that almost 90% of it was pure DNA. He turned a waste product into a valuable material for photonics applications.
AFRL researchers have found that integrating DNA as the cladding layer in electro-optic waveguide modulators can increase the poling efficiency while maintaining low optical loss.7 This will potentially allow for low-power EO technology alternatives for applications such as telecom, beam steering, and optical sensing. DNA is also being investigated for use as the active and passive layers in organic FETs. AFRL researchers were able to demonstrate a field-effect current amplification by doping the DNA to increase its conductivity.8
Additional DNA research being conducted at the AFRL focuses on the design and fabrication of flexible sensor systems. DNA or RNA oligomer sequences (also known as aptamers) can be specifically selected to bind a target. These targets can range from small molecules to proteins to bacteria, or to other DNA sequences. These aptamers can then be integrated into a number of photonic or electrical systems to transduce the target-binding event into a detectable signal.
Some of the DNA- and RNA-aptamer-based systems currently being investigated are nanoparticles-based colorimetric sensors,9 fluorescent reporting riboswitches,10 and aptamer-integrated field-effect transistors (AptaFET).11
Several other research teams from academia and the commercial sector are collaborating with the AFRL to develop DNA-based devices with security and defense applications. At the University of Arizona, researchers have been looking at DNA/sol-gel blends to improve the performance in capacitor applications in energy storage.12 They found that a 5% DNA /sol-gel blend gave an energy-storage capacity about 50 times larger than that of commercial polypropylene capacitors.
This technology is expected to impact an array of avionics needs ranging from providing energy storage for solid-state elements to providing materials with exceptional dielectric properties that can be used for a variety of specialized applications.
AFM topography image of printed DNA biopolymer nanostructures. Color intensity scale indicates height of pillars.
Also at the University of Arizona, researchers have developed a variant of the nanoimprint lithography (NIL) technique with which nano- and microstructures and devices can be printed in a DNA biopolymer without the need for high temperature and pressure.
The attractive advantage of this approach is that it is possible to incorporate any optically active organic component into this biopolymer, and optical/photonic devices can be faithfully replicated with high fidelity and ease. The figure above shows an AFM topography image of the pillar structures of about 380nm diameter.
Researchers at the Universidade de São Paulo in Brazil have been investigating DNA-based, ion-conducting membranes for electrochromic device applications.13 They found that electrochromic devices made with DNA-based membranes exhibited inserted/extracted charge densities suitable to make them promising materials to be used as solid electrolytes in electrochromic devices.
Electrochromic devices such as these have potential widespread use in security as well as commercial applications. Smart windows can regulate the solar gains of buildings, for instance, and other electrochromic devices can attenuate the glare in windows and mirrors.
Finally, work is being done by researchers at U.S.-based Ipitek on DNA-based composite materials consisting of the DNA biopolymer and metal particles for EMI shielding applications. The materials exhibit excellent EMI shielding effectiveness over a wide RF spectrum ranging from DC to tens of GHz while being non-conductive. The unique properties of these materials (non-conductive, light-weight, easy, and inexpensive to process) could have a significant impact for anti-Electro-Magnetic Pulse (EMP) military defense applications as well as for commercial applications such as EMI-suppression in broadband and high-speed electronics.
These applications are only a small sampling of the many possibilities in this emerging research field. As the properties of these biopolymer materials continue to be explored and understood, the applications are sure to expand in scope.
For now, the field of biotronics remains a small but growing community that views their research with delicious potential.
1. Amsden, J.J., et al. "Rapid nanoimprinting of silk fibroin films for biophotonic applications," Advanced Materials 22, 1746-1749 (2010).
2. Grote, J. G., et al. "DNA- new class of polymer," Proceedings of SPIE 6117, 61170J-1 (2006).
3. Matsunaga, Masaji. "Eyeing overseas advancements with a salmon milt DNA filter"
4. Hagen, J.A., et al. "Enhanced emission efficiency in organic light-emitting diodes using deoxyribonucleic acid complex as an electron blocking layer," Applied Physics Letters 88, 171109 (2006).
5. Wang, L., et al. "Self-assembled supramolecular films derived from marine deoxyribonucleic acid (DNA)-cationic surfactant complexes: large-scale preparation and optical and thermal properties," Chemistry of Materials 13, 1273-1281 (2001).
6. Heckman, E., et al. "Processing techniques for DNA: a new biopolymer for photonics applications," Applied Physics Letters 87, 211115 (2005).
7. Heckman, E., et al. "Poling and characterization studies in electro-optical polymers with DNA cladding layers," Proceedings of SPIE 7765, 776505 (2010).
8. Ouchen, F., et al. "DNA thin films as semiconductors for BioFET," Proceedings of SPIE 7403, 74030F (2009).
9. Chavez, J., et al. "Theophylline detection using an aptamer and DNA-gold nanoparticle conjugates," Biosensors and Bioelectronics 26, 23-28 (2010).
10. Harbaugh, S., et al. "FRET-Based optical assay for monitoring riboswitch activation," Biomacromolecules 10, 1055-1060 (2009).
11. Hagen, J., et al. "DNA aptamer functionalized zinc oxide field effect transistors for liquid state selective sensing of small molecules," Proceedings of SPIE 7759, 775912 (2010).
12. Norwood, R.A., et al. "Hybrid DNA materials for energy storage," Proceedings of SPIE 7765, 77650H-1 (2010).
13. Pawlicka, A., et al. "Gelatin- and DNA-based ionic conducting membranes for electrochromic devices," Proceedings of SPIE 7487, 74870J (2009).
SPIE member Emily Heckman, who has a PhD in electro-optics from the University of Dayton, is an electronics research engineer with the Sensors Directorate at the U.S. Air Force Research Laboratory. She is currently the Sensors Directorate representative of the AFRL Biotronics Strategic Technology Thrust (STT) research program.
Heckman has served as co-chair of the Nanobiosystems conference at SPIE Optics and Photonics and is co-chair for the Optical Materials in Defence Systems Technology conference at SPIE Security and Defence.
More on security and defense
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Biotronics engineering is interdisciplinary
The area known as biotronics or bioelectronics is an interdisciplinary research field that includes elements from biology, chemistry, engineering, and the physical sciences. It can be broadened further to include nanotechnology and nanoscience.
Biotronics engineering technology has the potential to revolutionize the next-generation of polymers and organic-based photonics devices.
In a 2008 article in the SPIE Newsroom, SPIE Fellow James Grote discusses how the field of nano/biotronics has opened up a whole new field for bioengineering, with applications in genomic sequencing, clinical diagnosis and treatment, materials research, and more.
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