Most conventional microchips, such as silicon-based or CMOS, have a flat, rigid substrate and would not perform properly when attached to colloids that can experience complex mechanical stresses while travelling through the environment. In addition, all such chips are “very energy-thirsty,” Strano says. That’s why MIT postdoc Volodymyr Koman, the paper’s lead author, decided to try out two-dimensional electronic materials, including graphene and transition-metal dichalcogenides, which he found could be attached to colloid surfaces, remaining operational even after after being launched into air or water. And such thin-film electronics require only tiny amounts of energy. “They can be powered by nanowatts with subvolt voltages,” Koman says.
Why not just use the 2-D electronics alone? Without some substrate to carry them, these tiny materials are too fragile to hold together and function. “They can’t exist without a substrate,” Strano says. “We need to graft them to the particles to give them mechanical rigidity and to make them large enough to get entrained in the flow.”
But the 2-D materials “are strong enough, robust enough to maintain their functionality even on unconventional substrates” such as the colloids, Koman says.
The nanodevices they produced with this method are autonomous particles that contain electronics for power generation, computation, logic, and memory storage. They are powered by light and contain tiny retroreflectors that allow them to be easily located after their travels. They can then be interrogated through probes to deliver their data. In ongoing work, the team hopes to add communications capabilities to allow the particles to deliver their data without the need for physical contact.