Around the size of a human egg cell, these robots consist of tiny electronic circuits made of 2D materials, piggybacking on minuscule particles called colloids.
Colloids, which insoluble particles or molecules anywhere from a billionth to a millionth of a metre across, are so small they can stay suspended indefinitely in a liquid or even in air, the researchers explain. By coupling these tiny objects to complex circuitry, the MIT team hope to lay the groundwork for devices that could be dispersed to carry out diagnostic journeys through anything from the human digestive system, to oil and gas pipelines.
The robots are self-powered, with a simple photodiode providing the trickle of electricity that the tiny robots’ circuits require to power their computation and memory circuits.
The belief is that these devices could be inserted into one end of the pipeline, carried along with the flow, and then removed at the other end, providing a record of the conditions they encountered along the way, including the presence of contaminants that could indicate the location of problem areas. The initial proof-of-concept devices didn’t have a timing circuit that would indicate the location of particular data readings, but the researchers say adding this capability is part of ongoing work.
Similarly, the researchers believe such particles could be used for diagnostic purposes in the body, for example to pass through the digestive tract searching for signs of inflammation or other disease indicators.
Conventional microchips 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. With this in mind, the researchers used 2D electronic materials, including graphene and transition-metal dichalcogenides, to attach to the colloid surfaces. The team found these remained operational even after being launched into air or water, and such thin-film electronics require only tiny amounts of energy.
Substrates are needed to carry the electronics, because the tiny materials are too fragile to hold together and function, the researchers explain. “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,” explains Professor Michael Strano of MIT.
The 2D materials are strong and robust enough to maintain their functionality even on unconventional substrates such as the colloids, the researchers add.
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.
