Until now, synthetic biological systems have focused exclusively on either analog or digital computation. Researchers at MIT have devised a technique for creating cellular gene circuits capable of complex computation.

Analog computation, also called continuous computation, is the type of processing happening as the human eye adjusts to changing light conditions. Digital computation involves binary decision making, on or off processes.

The new synthetic cellular circuitry designed by MIT scientists performs like a comparator, receiving analog input signals and converting them into digital output signals.

In this instance, the circuitry is designed to gauge the level of a chemical -- a potential signature of disease -- and should the level reach a threshold, the circuitry releases a dose of the relevant drug.

"Digital is basically a way of computing in which you get intelligence out of very simple parts, because each part only does a very simple thing, but when you put them all together you get something that is very smart," lead researcher Timothy Lu, an associate professor of biological engineering and head of the Synthetic Biology Group at MIT's Research Laboratory of Electronics, said in a news release.

"But that requires you to be able to put many of these parts together, and the challenge in biology, at least currently, is that you can't assemble billions of transistors like you can on a piece of silicon," Lu added.

The gene circuit features a threshold module capable of analog computation -- sensing the level of a specific chemical. The module is linked to a recombinase gene, which can turn a specific DNA segment on or off by inverting it. The gene segment can be designed to control a specific gene expression, thus, enabling a digital out -- in this case, the release of a drug.

"So this is how we take an analogue input, such as a concentration of a chemical, and convert it into a 0 or 1 signal," Lu explained. "And once that is done, and you have a piece of DNA that can be flipped upside down, then you can put together any of those pieces of DNA to perform digital computing."

Lu and his research partner, former microbiology PhD student Jacob Rubens, designed a circuit that linked both a lower and upper analog threshold to digital outputs. The circuit was capable of measuring glucose and releasing a different drug if levels got too high or too low.

The new research was published in the journal Nature Communications.