Biological Production of Printed Circuit BoardsAbstract

The Columbia-Cooper iGEM team is working with Acidith-iobacillus ferrooxidans to create a light-controlled printed circuit board manufacturing process. This bacteria’s metab-olism relies on its ability to oxidize iron; the iron can then be used to oxidize, and in turn solubilize, copper. By genet-ically altering the bacteria, we will install a light sensitive mechanism which will enable controlled copper etching, leaving a finished circuit board. Once a blank printed cir-cuit board is placed in a thin layer of solid media, the bac-teria will be applied onto the surface of the media and light of the appropriate wavelength will be focused on it in a desired pattern. The light sensitive mechanism in A. ferro-oxidans will activate a self-destructing mechanism prevent-ing copper etching in these locations. In the end, the cir-cuit board will be "etched" by the bacteria everywhere that is not illuminated, leaving a desired pattern on the circuit board under the cells in the path of the light.

ObjectivesIn deciding on a project to work on for iGEM, Cooper Union and Columbia University students looked for some-thing that was both relevant in the modern world and envi-ronmentally friendly. It was brought to the team’s attention that current electronics manufacturing processes are harm-ful to the environment.

In particular our team focused on the manufacturing process of printed circuit boards (PCBs) which in-volves the extensive use of toxic ferric chloride for the majority of the process. In addition, this process is messy, and inconvenient to run at home, or in any small batch manufacturing run. With such problems in mind, the team began to plan a synthetic biology based approach to etch copper in order to redefine the manufacturing of printed circuit boards in a way that make the process more environmentally friend-ly by reducing the quantity of waste materials, and more accessible to those outside of large scale man-ufacturing. In pursuing for solutions to the problem, we came across Acidithiobacillus ferrooxidans, an acidophilic prokaryote that oxidizes Fe2+ to Fe3+. The oxidized iron can then oxidize the copper. When copper is ox-idized, it becomes soluble. This means that circuit boards can be printed provided the ability to exert spatial control over these chemical reactions.The following question ensued: what would provide the ability to exert spatial control over copper oxida-tion on a circuit board? Light is non-intrusive, cheap, and widely available. Furthermore, light can be ma-nipulated easily in terms of wavelength and resolu-tion. By inserting a light-activated mechanism, the bacteria could etch in the desired pattern by turning a gene on or off.What gene would allow controlled etching? If light activated a gene that induced cell death through ly-sis, the bacteria that survived would continue to etch away at the copper while the dead bacteria would stop etching. This would achieve what was desired: spatially controlled etching.

Experimental

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3. Valdes J, Pedroso I, Quatrini R, Dodson RJ, Tettelin H, Blake R 2nd, Eisen JA, Holmes DS. Acidithiobacillus ferroo-xidans metabolism: from genome sequence to industrial applications. BMC Genomics. 2008; 9: 597

4. Hocheng H., Chang J., Jadhav U. Micromachining of var-ious metals by using Acidithiobacillus ferrooxidans 13820 culture supernatant experiments. Journal of Cleaner Pro-duction. 2012;20:180-185

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6. Möglich A, Ayers RA, Moffat K. Design and signaling mechanism of light-regulated histidine kinases. J Mol Biol. 2009; 385: 1433–1444

References

While our team learned a lot over the course of iGEM 2012, we still face a number of obstacles, which we hope to over-come in the near future. Our list of future goals includes:Fusing FphA with other histidine kinase domains in order to build a precise, tightly controlled, photoreversible red light sensitive promoter systemRefining and solidifying a protocol for effective transforma-tion of A. ferrooxidansModifying pJRD215 (the plasmid which we have been using with A. ferrooxidans), and possibly constructing a viable plasmid of our own designFine tuning our etching media in order to better facilitate our overall goal of creating an easy to use, easy to access, green process for the manufacture of printed circuit boards

Future DirectionsThe following graph depicts the etching rates for copper in liquid media with and without bacteria. Results show that the bacteria do accelerate the etching rate of copper in the liquid media.

The following graph depicts the etching rates for the cop-per in solid media with and without bacteria. The results showed that the etching rate by the bacteria is equal to that of the basal etching rate of the solid media.

The graph shows our procedure of figuring out the min-imum amount of liquid media necessary so the bacteria etch at a rate faster than that of the basal rate. Plots that stay above the x axis were those that were able to successfully etch faster than the basal rate with the given volume of liq-uid in our mixed-media.

Columbia- Cooper

iGEM 2012