By cladding a living cell with graphene quantum dots, researchers at the University of Illinois at Chicago (UIC) claim to have created a nanoscale biomicrorobot (or cytobot) that responds electrically to changes in its environment. This work promises to lay the foundations for future generations of bio-derived nanobots, biomicrorobotic-mechanisms, and micromechanical actuation for a wide range of applications.
The UIC team has dubbed its creation NERD (short for Nano-Electro-Robotic Device). The cytobot is built on a bacterial spore – more specifically, an endospore – which is essentially a dormant version of a bacterium.
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Endospores are strong, tough, and exceptionally responsive to liquid water, making them ideal candidates for micromechanical manipulation. The responsiveness to water, in particular, is an important aspect because it can be exploited in such microorganisms to achieve bio-actuated functionality.
In other words, scientists can use a range of naturally-occurring functions of these organisms as they respond to their environment to operate miniscule devices.
"This is a fascinating device," said Vikas Berry, UIC associate professor and principal investigator on the study. "Here we have a biological entity. We’ve made the sensor on the surface of these spores, with the spore a very active complement to this device. The biological complement is actually working towards responding to stimuli and providing information."
By applying graphene quantum dots (GQDs) to such a micro-organism, various quantum-mechanical effects like electron-tunneling, optical-blinking, and a range of mechanical and sensing functions may be integrated. In the UIC case, the GQDs used were configured to take advantage of the controllable trans-membrane hydraulic transport – the spore’s ability to eject water – to act, in this case, as an electro-biomechanical humidity sensor.
"We’ve taken a spore from a bacteria [sic], and put graphene quantum dots on its surface – and then attached two electrodes on either side of the spore," said Berry. "Then we change the humidity around the spore. When the humidity drops, the spore shrinks as water is pushed out. As it shrinks, the quantum dots come closer together, increasing their conductivity, as measured by the electrodes. We get a very clean response – a very sharp change the moment we change humidity."
The researchers also documented that the response was approximately 10 times faster than artificial humidity sensors currently manufactured, even with the best synthetic water-absorbing polymers known. They noted, too, that the electro-biomechanical device that the team created appeared to have improved sensitivity in exceptionally low-pressure, low-humidity environments compared to the artificial sensor.
The practical upshot of this work, according to the researchers, is that it may exploit the unique biomolecular structure of micro-organisms in a way that achieves both controlled nanoscale architecture and membrane transport for micromechanical actuation. This, then, could be applied to a wide range of fields including, cellular control, microbotics, biochemical analysis, targeted molecular or ionic detection, as well as implants for biological monitoring.
The research is published in the journal Nature Scientific Reports.