Making nanoelectronics last longer for medical devices and ‘cyborgs’

March 3, 2014

Silicon nanowires. Top: uncoated; bottom, coated with aluminum oxide. (Credit: Wei Zhou et al./Nano Letters)

Harvard scientist Charles Lieber and colleagues have developed a coating that makes nanoelectronics much more stable in conditions mimicking those in the human body.

The advance could aid in the development of very small implanted medical devices for monitoring health and disease, and could speed up the debut of cyborgs who are part human, the researchers say.

Nanoelectronics devices with nanowire components are much smaller than most implanted medical devices used today, and have unique abilities to probe and interface with living cells. Laboratory versions made of silicon nanowires can detect disease biomarkers and even single virus cells, or record heart cells as they beat.

However, nanoelectronics devices have one obstacle to their practical, long-term use: they typically fall apart within weeks or days when implanted.

The researchers found that coating with a metal oxide shell allowed nanowire devices to last for several months. This was in conditions that mimicked the temperature and composition of the inside of the human body. In preliminary studies, one shell material, hafnium oxide-aluminum oxide nanolaminated shells, appeared to extend the lifespan of nanoelectronics to more than a year.

The authors acknowledge funding from the National Institutes of Health Director’s Pioneer Award and the National Security Science and Engineering Faculty Fellowship.

Abstract of Nano Letters paper

Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease.