Stephanie D Lauback

DNA nanotechnology has enabled complex nanodevices, but the ability to directly manipulate systems with fast response times remains a key challenge. Current methods of actuation are relatively slow and only direct devices into one or two target configurations. Here we report an approach to control DNA origami assemblies via externally applied magnetic fields using a low-cost platform that enables actuation into many distinct configurations with sub-second response times. The nanodevices in these assemblies are manipulated via mechanically stiff micron-scale lever arms, which rigidly couple movement of a micron size magnetic bead to reconfiguration of the nanodevice while also enabling direct visualization of the conformation. We demonstrate control of three assemblies-a rod, rotor, and hinge-at frequencies up to several Hz and the ability to actuate into many conformations. This level of spatiotemporal control over DNA devices can serve as a foundation for real-time manipulation of molecular and atomic systems.

Central to the advancement of many biomedical and nanotechnology capabilities is the capacity to precisely control the motion of micro and nanostructures. These applications range from single molecule experiments to cell isolation and separation, to drug delivery and nanomachine manipulation. This dissertation focuses on actuation of biological micro- and nano-entities through the use of weak external magnetic fields, superparamagnetic beads, and ferromagnetic thin films. The magnetic platform presents an excellent method for actuation of biological systems due to its ability to directly control the motion of an array of micro and nanostructures in real-time with calibrated picoNewton forces. The energy landscape of two ferromagnetic thin film patterns (disks and zigzag wires) is experimentally explored and compared to corresponding theoretical models to quantify the applied forces and trajectories of superparamagnetic beads due to the magnetic traps. A magnetic method to directly actuate DNA nanomachines in real-time with nanometer resolution and sub-second response times using micromagnetic control was implemented through the use of stiff DNA micro-levers which bridged the large length scale mismatch between the micro-actuator and the nanomachine. Compared to current alternative methods which are limited in the actuation speeds and the number of reconfiguration states of DNA constructs, this magnetic approach enables fast actuation ( ̃milliseconds) and reconfigurable conformations achieved through a continuous range of finely tuned steps. The system was initially tested through actuation of the stiff arm tethered to the surface, and two prototype DNA nanomachines (rotor and hinge) were successfully actuated using the stiff mechanical lever. These results open new possibilities in the development of functional robotic systems at the molecular scale. In exploiting the use of DNA stiff levers, a new technique was also developed to investigate the emergence of the magnetization of individual superparamagnetic beads as a function of the applied field. Last, since proteins are frequently used for surface adhesion in assembling biomedical devices, preliminary tests were implemented to dynamically pattern proteins on a substrate using transformed E. coli that are magnetically labeled.

Technologies that control matter at the nano- and micro-scale are crucial to realizing engineered systems that can assemble, transport, and manipulate materials at submicron length scales. Two principles: (1) the domain wall structure of patterned magnetic structures and (2) the superparamagnetic properties of nanoparticles, have been previously used to remotely manipulate and transport magnetic entities to specific sites on a platform. In this paper, changes to the energy landscape during transport as well as the local energy profile of individual stationary traps, both of which are central to the functionality of the platform, are evaluated using directed forces and stochastic (Brownian) trajectories of trap-confined microparticles. Hybrid magnetic-fluorescent micelle nanoconstructs, which are compatible with physiological conditions and safeguard functionality of biomaterials, are shown to be viable markers to label and manipulate individual cells across the platform.

We report on the various phases formed by sulfur adsorbed on Au(111), at less than 1 monolayer (ML) coverage, as monitored by low-energy electron diffraction (LEED). The phases transform from one to another via coexistence regions. The observation of ordered phases was matched to the coverage information obtained from Auger measurements, using as a calibration point the S coverage of 0.28 ML, corresponding to the sharpest (5 × 5) LEED pattern observed. The influence of emitting filaments (the Auger beam, ion gauge, or LEED electron beam) upon the adsorption itself is discussed. LEED structural investigations were performed on two particular S–Au phases. The analysis of the Au(1 × 1)–S structure provided the values for the first four gold interlayer spacings, showing a 1% expansion of the top layer, interpreted as a remnant of the expansion of the Au(111)–(22 × √3) reconstructed phase. The analysis of the Au(5 × 5)–7S phase confirmed the fcc adsorption site of the S atoms reported previously, and resulted in an average S–Au distance of 1.57 ± 0.10 Å, and an S–Au bond length of 2.29 ± 0.07 Å.