Nature.com has published an article about the work of Ravi Saraf, a chemist from the University of Nebraska, Lincoln and his student Vikas Berry in integrating living bacteria into an electrical circuit that is part of a humidity-detecting device. While there have been other instances of circuits built to react to microorganisms, this “cellborg,” as it has been dubbed, is the first time they have actually been built into the circuits themselves. This work has excited many biotechnologists as they see this as the first step towards developing biological computers.
A regular silicon chip with gold electrodes is coated with Bacillus cereus bacteria which forms bridges between the electrodes. The chip is soaked in a solution of peptide-covered gold particles which then stick to the bacteria. This gold layer conducts electricity through the device. As the circuit encounters increasing humidity, the bacteria swells forcing the gold particles apart causing a drop in current flow. The change in current flow per change in humidity is much greater for this device than in traditional electronic sensors. This increased sensitivity makes them ideal for environments where small humidity changes must be measured. Although the bacteria must be alive and remain undamaged during the manufacturing process, they will continue to swell and contract even after death so the devices do function much longer than the two day period that the bacteria can go without nutrients.
According to Saraf, the next step in the evolution of cyborg circuits will be a physiological interface between micororganisms and the circuit, not just a physical coupling. This would allow the electrical properties of the bacteria itself to control or even generate the current in the circuit.
The full text of the article is available here: “Cyborg cells sense humidity.”