Silicon has been very good to us. It has given us Angry Birds and virtual protests we can participate in from the comfort of our home, but it may be time to enter the Age of the Biological Computer.

Writing in the journal Materials Today,researchers reveal details of logic units built using living slime molds, which might act as the building blocks for computing devices and sensors.

You're more likely to find the slime mold Physarum polycephalum living somewhere dark and damp rather than in a computer science lab. In its "plasmodium" or vegetative state, the organism spans its environment with a network of tubes that absorb nutrients. The tubes also allow the organism to respond to light and changing environmental conditions that trigger the release of reproductive spores.

But the researchers have previously found that such a tube network could absorb and transport different colored dyes. They then fed it edible nutrients - oat flakes - to attract tube growth and common salt to repel them, so that they could grow a network with a particular structure. They then demonstrated how this system could mix two dyes to make a third color as an "output".

Using the dyes with magnetic nanoparticles and tiny fluorescent beads allowed them to use the slime mold network as a biological "lab-on-a-chip" device. This represents a new way to build microfluidic devices for processing environmental or medical samples on the very small scale for testing and diagnostics, the work suggests.

The extension to a much larger network of slime mold tubes could process nanoparticles and carry out sophisticated Boolean logic operations of the kind used by computer circuitry. The team has so far demonstrated that a slime mold network can carry out XOR or NOR Boolean operations. Chaining together arrays of such logic gates might allow a slime mold computer to carry out binary operations for computation.

Andrew Adamatzky of the University of the West of England, and Theresa Schubert of Bauhaus-University Weimar have constructed logical circuits that exploit networks of interconnected slime mold tubes to process information.

"The slime mold based gates are non-electronic, simple and inexpensive, and several gates can be realized simultaneously at the sites where protoplasmic tubes merge," conclude Adamatzky and Schubert.


Silicon is not dead just yet. Stewart Bland, Editor of Materials Today, notes instead that "although more traditional electronic materials are here to stay, research such as this is helping to push and blur the boundaries of materials science, computer science and biology, and represents an exciting prospect for the future."