Manipulating the Position and Orientation of Nanoparticles using Feedback Control

To advance the development of miniaturized systems, there is a need to place nanostructured materials in very precise locations. Only then can practical applications move forward, such as bonding particles to sensors, connecting nanowires to electrical leads, fabricating waveguides, probing biological cells, building chemical sensors for sensing trace levels of toxins, or combining nanoscale building blocks to build up functioning micro- and nano- scale systems.  To address the needs of reliably completing this difficult task on a mass-producible scale, we are developing new methods to more accurately locate and then place atomic and nanoscale objects.  The goal of this project is to create high resolution, feedback control-based methods to move particles with greater precision via electrical fields, fluid dynamics, or other means.

Liquid flows formed by applying voltages to microfluidic devices can be used to move particles suspended in the liquid through the phenomenon of electro-osmotic flow.  The application of multiple voltages at strategic locations around such a device enables a particle to be steered in any arbitrary direction.  If information on the particle location obtained through video microscopy is combined with a physical model of the way the applied voltage affects the fluid flow, then a feedback control system can be created.  Such a system enables the motion of several particles to be controlled independently and simultaneously.  In this project, we are combining the microscale control expertise developed at the University of Maryland with the nanoscale precision and accurate sensing capabilities created at the CNST to enable precise control of particle motion at the nanoscale.  

A second goal of this project is to control not only the position, but also the orientation of non-spherical nanoscale objects such as nanorods.  Previous approaches for controlling the orientation of nanorods relied on the particle having specific properties, such as electric charge, dipole moment, or magnetic moment, and required the fabrication of intricate devices. The approach we are developing relies on creating the appropriate amount of shear flow, which offers significant advantages compared to techniques.  For example, our method allows for manipulation of a wider class of particles because the particle does not have to be charged, or have a dipole or magnetic moment; the particle can be controlled over hundreds of micrometers with sub-micrometer accuracy; and the device is very inexpensive and easy to make, requiring only molding a low-cost elastomer (PDMS).  Ultimately, we plan to couple our device to a robust control law as well as a robust vision algorithm so that it can be used to translate and rotate multiple, sub-micron, rigid particles of arbitrary shape to an accuracy commensurate with wide scale commercial applications.