Magnetic manipulation of colloids at the micro and nanoscale

Derek Stieler Halverson

doi:10.17918/etd-2923

Manipulation and assembly of colloidal sub-micron and nanometer sized particles is important in many applications ranging from drug delivery and separation of biologically different species of micro-organisms and molecules to fabrication of meta-material micro- and nanostructures consisting of regular arrays of particles. Most of the methods that have been proposed are based on short-range interactions including chemical affinity and surface forces. Such forces are difficult and, most often, impossible to manipulate using externally tunable apparatus. Electric fields have been employed to create longer range forces. However, electric fields often affect biological molecules and can be substantially screened in ionic solutions. Magnetic field manipulation is a relatively unexplored method of manipulation of colloidal particles. Some work has been performed in the recent decade to develop methods of manipulation and assembly of non-magnetic colloidal particles near surfaces. However, the developed methods have been limited mainly to particles greater than 1 micrometer in diameter which experience relatively small Brownian motion. The question can arises: To what extent similar methods are applicable to manipulation of much smaller particles and molecules? Can Brownian motion be helpful for some applications? Another important question is: Can non-magnetic colloidal objects be manipulated away from surfaces?These are the main questions addressed in this work. The main contribution of this thesis is the development of a series of magnetic manipulation methods by which non-magnetic colloidal sub-micron particles and molecules can be manipulated near surfaces and in the bulk of a fluid suspension. One specific important contribution of this thesis is demonstration of magnetic trapping and transport of non-magnetic sub-micron particles and molecules near surfaces patterned with ferromagnetic material. This work is the first to demonstrate that biological molecules can be attached to designated areas on a substrate using magnetic trapping, for example. Development of a method for magnetic fractionation of non-magnetic colloids by size in bulk fluid suspension is also an important specific contribution of this thesis. Such fractionation dramatically improves on the speed of previously proposed depletion fractionation technique. Each specific method mentioned above will be described in separate chapters of this thesis.

Magnetic manipulation of colloids at the micro and nanoscale

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Magnetic manipulation of colloids at the micro and nanoscale

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