While digital circuits classify all values as zeros and ones, analog circuits can handle a continuous range of inputs, allowing for other values. The analog circuits harness the cell's natural biochemical functions, sensing the input of various molecules, such as glucose.
Most synthetic biologists up to now have pursued digital circuits. But digital circuits also require many more parts, which can drain the energy of the cell hosting them, according to Rahul Sarpeshkar and Timothy Lu, the two senior authors on the paper, describing the circuits in the May 15 online edition of Nature.
“You could do a lot of upfront sensing with the analog circuits ... and have that output go into a [digital] circuit that makes a decision -- is this true or not?” says Lu.
The researchers are now trying to create analog circuits in larger nonbacterial cells, including mammalian cells. They are also working on expanding the library of genetic parts that can be incorporated into the circuits.
Sarpeshkar believes the new approach of what he terms “analog synthetic biology” will create a new set of fundamental and applied circuits that can improve the fine control of gene expression, molecular sensing and computation.