Nanoparticle positioning and sensing
The ability to manipulate and control nanoscopic particles to nanometer precision is one of the central challenges of nanoscience. Conventional methods based on optical traps or tweezers tend to fail at the nanoscale because gradient forces are proportional to particle volume. New methods are needed to manipulate nanoscopic particles that do not rely on gradient forces. One promising method is based on electroosmotic flow control (EOFC), where nanoparticles are manipulated by moving their surrounding fluid. These techniques are limited by the ability to track their position, which can be much more accurate than gradient forces for nanoscopic paryticle. The particles are manipulated in a microfluidic device, as illustrated below. Applied voltages on the four reservoirs actuate flow to manipulate the particle. By combining this technique with novel fluid engineering, we can deterministically position pre-selected nonaparticles to nanometer precision and immobilize them via UV irradiation.
Using this novel flow control method we have demonstrated the ability to position single quantum dots to 45 nm accuracy. The video below shows our ability to accurately manipulate a single QD in a well defined trajectory that spells out "QD":
Using more complex fluid chemistries, we can push QDs to the surface of the device so that the can locally interact with pre-patterned or functionalized surface structures. By incorporating cross-linking polymers, we can also immobilize the QDs using UV illumination when locally solidifies the liquid. Below is a movie where we construct a 3x3 array of QDs using positioning combined with UV illumination.
Chad Ropp, Zachary Cummins, Roland Probst, Sijia Qin, John Fourkas, Benjamin Shapiro, and Edo Waks, "Positioning and Immobilization of Pre-Selected Quantum Dots on a Two Dimensional Surface with Nanometer Precision", Nano Lett. 10, 4673-4679 (2010)
Chad Ropp, Roland Probst, Zachary Cummins, Rakesh Kumar, Andrew Berglund, Srinivasa Raghavan, Edo Waks, and Benjamin Shapiro, "Manipulating quantum dots to nanometer precision by control of flow", Nano Lett. 10, 2525-2530 (2010)