The paper ticket you see pictured above is actually a little biology machine. It’s a gene circuit stored on a slip of paper. To turn the gene circuit on, you simply wet the paper with a dropper and all of its microscopic components will come to life. Depending on what circuit scientists freeze-dry onto the paper, these slips could be used to detect disease-causing microbes or medically important molecules, such as glucose. They could even produce molecules scientists want.
As a demonstration, the development team made two types of sensors on paper tickets. One sensor had circles that changed colors when they were wetted with a solution that contained antibiotic-resistant bacteria. The other had circles that changed into one of two colors when it was wetted with samples of the Sudan versus the Zaire strains of Ebola virus. The sensors still aren’t able to detect low amounts of bacteria and viruses, so they won’t be used to detect outbreaks anytime soon. But their makers are hoping they’re a first step toward cheap, easy-to-use field sensors. The paper slips might also show up sooner in labs, for other scientists looking to perform quick experiments, and for scenarios in which the stakes aren’t life-or-death.
A gene circuit works a bit like an electronic one, only all its components are biological. Gene circuits include dozens of genes, plus the proteins needed to read those genes. Together, the genes and proteins perform a task. There are natural gene circuits, such as the genes and proteins that work together to perform photosynthesis in plants. On these paper tickets, however, scientists are able to design any circuits they like, not just naturally-occurring ones. They might mix together genes from different species, for example, to get the paper to react how they want. The team that developed the paper slips, including biologists and engineers from Boston and Chevy Chase, Maryland, came up with a circuit that triggers color changes after detecting specific genetic material—such as genes from certain bacteria, or those Ebola viruses.
The tickets’ makers freeze-dry their circuit components onto the paper slips, which users can store for up to a year at room temperature. They published an article describing their work yesterday in the journal Cell.