So far, the Harvard group has used the modular system to record electrical activity in beating heart tissues. In one experiment, says Lieber, they were able to orient the tissue over the nanowire arrays to make detailed recordings of the electrical connections between three heart cells. “The propagation speeds are not uniform and depend on the details of their connectivity,” he says. For example, the connection between two of the cells showed more electrical resistance than between others.
To understand what these detailed biophysical measurements mean in terms of health and disease, many more of them will need to be made and analyzed. But, says Yang, Lieber’s work shows that making complex, high spatial and temporal resolution measurements is feasible.
“This study extends the application of nanotechnology for cell interfacing, which is probably one of the most promising biological applications of nanowires,” adds Nicholas Kotov, a professor of chemical engineering at the University of Michigan. “Development of nanomaterials for this purpose can help a lot of people with devastating diseases related to the breakdown of signal transmission between cells.”
Lieber is now using the modular system to make recordings from neural tissue, which is more fragile, and he’s developing new ways of arranging the nanowires. One reason that these tiny wires can make such good electrical connections with cells is that a large amount of surface area comes into contact with the surrounding tissue. By making nanowire arrays with different configurations, Lieber hopes to expose even more of the wires’ surfaces for interaction with cells.
The group is also working on nanowire devices that can simultaneously record both electrical and chemical signals. Lieber’s previous work has shown that nanowire transistors decorated with binding molecules can act as extremely sensitive chemical sensors: their conductivity changes in a predictable way when they bind to a molecule of interest, such as a neurotransmitter. Simultaneously recording the effects of electrical signals, hormones, neurotransmitters, and other chemicals would give a more integrated picture of biological functions.