Nanowire micromachine : ion tolerance enhancement and polarotactic navigation

Abstract

The micro/nanomotors (MNMs) are considered as a novel and promising tools towards many critical biomedical applications such as precision surgery and targeted drug delivery. Over the last decade, many artificial MNMs have been demonstrated which generate thrust by harnessing chemical reaction and developing an asymmetric field around itself. However, the operation in the high concentration electrolyte solution, such as biological fluid, is a significant challenge for these MNMs as the self-generated electric field quickly diminished due to the double layer collapsing by ionic screening. This challenge is well backed by the classical Helmholtz-Smoluchowski theory and seems to be insurmountable which shadowed the otherwise promising biomedical applications for the artificial MNMs. In the first part of this thesis, we report the development of a quantitative model and demonstrate that the Dukhin number plays a critical role in the ion tolerance of the electric field propelled MNMs. By significantly increasing the Dukhin number of microswimmers with polyelectrolyte coating and geometry optimization, the self-electrophoresis efficiency in high concentration phosphate buffered saline (PBS) solution is dramatically enhanced, which enables the operation of the MNMs in biocompatible solution. Given the already demonstrated versatility and programmability of MNMs, this result heralds the advent of the long-envisioned practical biomedical and environmental application of artificial nanorobots. On the other hand, for the control of MNMs, light-driven MNMs are promising candidates for long envisioned next generation robotics for targeted drug delivery, noninvasive surgery and nano-manipulation. To achieve these fantastic applications, the communication channels between the light and MNMs are essential, involving closely with the design and fabrication process of these tiny robotics. In the second part of this thesis, a polarization direction sensible microswimmer based on one-dimensional single crystal Sb2Se3 nanowire is reported to broaden the tool list for light communication. Owing to the anisotropic crystal structure, the linear polarization light shows different absorption ability along the axis direction and the perpendicular direction of Sb2Se3 nanowire, confirmed by the single nanowire core-shell Sb2Se3/ZnO photovoltaic device. The core-shell Sb2Se3/ZnO microswimmers without any catalyst exhibit coordinate migration speed with polarization direction of the incident light. In addition, the cross-assembled microswimmer is successfully navigated by the polarization direction of the incident linear polarized light, demonstrating the polarotactic migration behavior. Moreover, this work open the bridge to use anisotropic material for MNMs design and optimization.