ETH 2006 Half adder


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Half-adder or Full-adder

An implementation of a half-adder or full-adder: 1-bit adder with carry

Idea: Pattern recognition

→ Illustration of the concepts:

Main Goal:

  1. Write something with a chemical on a petri plate (like ETH for example)
  2. Let Bacteria grow uniformly on the plate
  3. Expose the plate to a picture (black and white) of the same pattern
  4. Result:
    • Bacteria gets green when pattern on the plate and picture match (light and chemical)
    • Bacteria does not express fluorescent protein when pattern on the plate and picture match (no light and no chemical)
    • Bacteria gets red when pattern on the plate and picture do not match

Implementation from the ingenieur point of view

  • Half Adder
  • = opportunity to build an AND and an XOR Gate

Implementation from the biologist point of view

  • AND Gate: presence of chemical induces the production of an inactive protein, which is activated by a second protein (produced when light is present): the first protein is then activating GFP production
  • XOR Gate: I think Marko had a good idea about that (I didn't really got it)
  • a light sensible promoter (there are some, see here)
  • a chemical sensible promoter (chemical to be defined)
  • we would need to give a kind of first signal to the system (to don't have light reactions before a certain moment, otherwise we have to work in a dark room...), an activation signal after the bacterias have grown on the plate

Pro's & Con's


  • meaningful from engineering point
  • valuable parts for synthetic biology
  • stepwise proceeding applicable (→ intermediate and partial results!)
  • experiments visually attractive
  • probably simple enough


  • cheap copy of “bio-film” project (iGEM 2004)
  • sensational experiments, have little in common with half adder
  • maybe that a big vision is lacking
  • general/practical benefit? (counter-argument: is this required?)
  • too simple?
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