Washington University in St. Louis professor Tae Seok Moon hopes to develop biological circuits made from genes and regulatory proteins. He plans to use the circuits to act as controllers inside synthetic bacteria to make fuel, remove pollutants, or eliminate cancerous cells or infectious bacteria. Moon envisions that the minuscule circuits eventually could be used to make cells that can monitor and respond to their environments. As he was developing the genetic circuits, Moon had to identify a gene whose activation could be controlled by at least two molecules. The circuit Moon developed consists of four sensors for four different molecules that feed into three two-input "AND" gates. To eliminate crosstalk, or interference, in the circuits, Moon used parts from three different strains of bacteria: Shigella flexneri, Pseudomonas aeruginosa, and Salmonella typhimurium. Moon says in the future, a synthetic bacterium with this circuit might be able to detect four different cancer indicators and release a tumor-killing factor.