Research from a team of Indian scientists suggests that, thanks to graphene, we may be one step closer to creating micron-scale motors that can be navigated through our bloodstream.

No, this is not the opening line for a new ‘grey goo’ inspired sci-fi movie! This work, from a team at the Indian Institute of Technology Guwahati reports on the synthesis and development of microbots enhanced with graphene and nanoparticles that move in response to an array of stimuli.

These coated microparticles are the latest in a long line of small-scale, biocompatible devices that show huge potential for use in biomedical applications. Over the last decade, there has been a gradual move away from the whole-body approach and toward a more focused treatment of certain medical conditions. Targeted delivery of nanomedicines and high-precision sensors based on nanoparticles are already in early clinical trials, with many more at the pre-trial stage.

This latest effort reported in Carbon [doi: 10.1016/j.carbon.2015.03.012], and led by Dipankar Bandyopadhyay, looked at producing a versatile motor that could be accurately controlled in order to carry out a range of tasks, both in-vivo and ex-vivo. By coating an 80 µm glass bead with reduced graphene oxide and ferromagnetic iron nanoparticles, they produced a ‘microbot’ that displayed directed movement under an applied electric field, a chemical potential gradient and an external magnetic field.

When placed in a bath of hydrogen peroxide (H2O2), to which small volumes of (alkaline) sodium hydroxide (NaOH) were gradually added, the motor moved toward the region of higher pH. Following this, the motor was placed in NaOH and an electric field (0.4 – 0.7 kVm-1) applied. It was found to migrate toward the positively-charged anode, at the rate of ~0.3 body lengths per second.

But Bandyopadhyay and his team found that it was possible to control the velocity of the microbot’s motion and its trajectory by applying a magnetic field. By applying 103 mT, the motor’s velocity was increased to almost 10-3 ms-1 (or 13 times its body length). The motor could also trace ‘figure of eight’ paths under the coupled influence of a pH gradient and magnetic field. In addition, the team demonstrated that their motor could attach itself to a non-magnetic polymer bead, and then drag the huge particle (almost 1000 times heavier than the motor) through water.

These results suggest that micromotors could eventually find use as bio-carriers, or even as futuristic cleansing agents cleaning blockages in blood vessels.

Carbon 89 (2015) 31–40, “Graphene based multifunctional superbots” DOI: 10.1016/j.carbon.2015.03.012