Helical Carbon Nanowires for Magnetic-Field-Controlled Swimming

Given the low cost of batch fabrication of micro/nanorobots controlled by a magnetic field, we propose herein micro/nanorobots fabricated from helical carbon nanowires. We solve the critical problems of dispersion, cutting, and screening of the appropriate length of helical carbon nanowires and fabricate helical carbon nanowire robots (HCNRs) from 2 to 8 μm in length. We investigate the magnetic-field-controlled motion of HCNRs less than 8 μm long immersed in a low-Reynolds-number liquid. The results confirm that HCNRs have two modes of motion: translating in rotational mode and rolling. HCNRs can capture and transport small particles, which constitutes a new method to transport nanoparticles by using helical micro/nanorobots. The results show that the translational speed of HCNRs depends on the rotating-magnetic-field frequency and strength and, in particular, on the length of the helical nanowires, with the highest speed reaching 40 μm/s (13.1 body lengths per second). The configuration for maximum translational speed is a 3.05-μm-long HCNR in a 40 G magnetic field at a frequency of 60 Hz. These results demonstrate that HCNRs have good mobility and can be accurately manipulated in a microchannel chip.