Nicole M.K. Blackman

Research

Chemotaxis of Non-Biological Nanorods

Chemotaxis involves the directed movement of organisms toward or away from a particular attractant or toxin. This phenomenon has been widely observed in many bacteria, but has not been shown to occur in non-biological systems. Chemotaxis of non-biological particles, in which chemical energy is converted to mechanical energy, will be of great importance for future nanotechnological applications.  As in nature, our method uses catalysis to covert chemical energy to work.

It has previously been shown that small colloidal rods (2 micrometers long, 0.2 micrometer diameter cylinders) made of half gold and half platinum become motile in the presence of aqueous hydrogen peroxide (H₂O₂). This powered motion is due to an electrokinetic mechanism, and the energy is obtained from the catalytic decomposition of H₂O₂ to O₂ occurring at the platinum end of the rods. We show that in the presence of a gradient of H₂O₂, the platinum-gold rods chemotactically move toward a higher concentration of H₂O₂. Such a directed movement of a non-biological object is a significant step towards providing motions for non-biological, colloidal-sized devices.

 

 

Charge Non-Uniformity on Colloidal Particles

Colloidal particles commonly serve as building blocks for more complex materials and devices. These range from traditional materials like paints, coatings and ceramics, to circuits, sensors and colloidal crystals. Manufacturers of these materials and devices have two major challenges that arise when processing colloidal suspensions: (1) promoting accurate particle self-assembly and (2) controlling the aggregation of particles. These challenges are of great importance when it comes to maintaining the stability of the suspensions. Currently, methods used to stabilize colloidal suspensions include the utilization of electrostatic and electrosteric forces. Electrostatic forces alone however, do not provide enough dispersion for most applications.

My research currently focuses on measuring the charge nonuniformity of colloidal particles. The existence of charge nonuniformity has been hypothesized as the reason for the inability of electrostatics to keep particles dispersed. Traditionally, colloidal particles have been thought to be uniformly charged. However, in the past 15 years, researchers have determined that particles are often non-uniformly charged and in a random manner that affects the stability of the particles. Research has also shown that a uniformly charged particle is much more stable than a non-uniformly charged particle.

The technique of rotational electrophoresis has been used to successfully measure charge nonuniformity. Rotational electrophoresis involves measuring the angular velocity of several particles and interpreting the results using electrokinetic theory. This process is based on the fact that a uniformly charged particle will not rotate when an electric field is applied but a nonuniformly charged particle will.

 

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