Electrokinetic tweezing: three-dimensional manipulation of microparticles by real-time imaging and flow control

Electrokinetic tweezing in three dimensions is achieved for the first time using a multi-layer microfluidic device, a model-based control algorithm, and a 3D imaging algorithm connected in a feedback loop. Here we demonstrate steering of microparticles along 3D trajectories and trapping in all three dimensions with accuracy as good as 1 μm.

Fabrication of nanoassemblies using flow control

Synthetic nanostructures, such as nanoparticles and nanowires, can serve as modular building blocks for integrated nanoscale systems. We demonstrate a microfluidic approach for positioning, orienting, and assembling such nanostructures into nanoassemblies. We use flow control combined with a cross-linking photoresist to position and immobilize nanostructures in desired positions and orientations. Immobilized nanostructures can serve as pivots, barriers, and guides for precise placement of subsequent nanostructures.

Planar Steering of a Single Ferrofluid Drop by Optimal Minimum Power Dynamic Feedback Control of Four Electromagnets at a Distance

Any single permanent or electro magnet will always attract a magnetic fluid. For this reason it is difficult to precisely position and manipulate ferrofluid at a distance from magnets. We develop and experimentally demonstrate optimal (minimum electrical power) 2-dimensional manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets. The control algorithm we have developed takes into account, and is explicitly designed for, the nonlinear (fast decay in space, quadratic in magnet strength) nature of how the magnets actuate the ferrofluid, and it also corrects for electro-magnet charging time delays. With this control, we show that dynamic actuation of electro-magnets held outside a domain can be used to position a droplet of ferrofluid to any desired location and steer it along any desired path within that domain - an example of precision control of a ferrofluid by magnets acting at a distance.

Positioning and immobilization of individual quantum dots with nanoscale precision

We demonstrate a technique for the precise immobilization of nanoscale objects at accurate positions on two-dimensional surfaces. We have developed a water-based photoresist that causes nanostructures such as colloidal quantum dots to segregate to a thin layer at surfaces. By combining this material with electroosmotic feedback control, we demonstrate the ability to position selected, individual quantum dots at specific locations and to immobilize them with 130 nm precision via localized UV exposure.

Manipulating quantum dots to nanometer precision by control of flow

We present a method for manipulating preselected quantum dots (QDs) with nanometer precision by flow control. The accuracy of this approach scales more favorably with particle size than optical trapping, enabling more precise positioning of nanoscopic particles. We demonstrate the ability to position a single QD in a 100 microm working region to 45 nm accuracy for holding times exceeding one hour and the ability to take active quantum measurements on the dynamically manipulated QD.