Engineering Seminar Series 22_2010: Small Stuffs Move In Big Steps - The Transport Behaviors of Tini-Tiny Particles

Dr. JitKang Lim, senior lecturer, School of Chemical Engineering, Universiti Sains Malaysia (USM)

Date: 2010-11-04
Time: 11:00 to 12:00
Venue: 9-5-04


To investigate within living cells, it is desirable to use a movable magnetic probe that approaches the size of the molecules of interest, normally, within the range of few to tens of nanometers. However, micromanipulation of magnetic nanoparticles is extremely challenging, due to random Brownian motion and viscous drag forces, in addition to the desired magnetophoresis. All three of these types of motion have difference size dependency.

In this talk I’ll discuss the combined influences of Brownian, viscous and magnetic effects on the magnetophoretic motion of individual magnetic nanoparticles. To track their positions as a function of time, the iron oxide cores are coated with gold nanoparticles so that they can be imaged by their plasmonic response using darkfield optical microscopy. To generate a large and controllable magnetic field gradient, a thin tip of mu-metal, a soft magnetic material, was attached to the core of a solenoid. When current was passed through the solenoid coil, the tip became magnetically saturated, and rapid magnetic collection of nearby particles was achieved in a few seconds. However strong Brownian displacement was still observed, even with a magnetic field gradient as high as 3000 T/m. More deterministic magnetophoresis was seen as the particles got closer to the magnetic field source. The trajectories of the particles were analyzed to distinguish the contributions of Brownian, viscous drag, and magnetic forces.

Peclet number analysis is also performed to probe the convective motion of nanospheres and nanorods under the influence of magnetophoresis and diffusion. Under most circumstances, magnetophoretic behaviour dominates diffusion for nanorods, as the magnetic field lines tend to align the magnetic moment along the rod axis. This technique could be an important new tool for detecting binding events and local viscosity variations within cells.

About the Speaker

Dr. JitKang Lim is currently a senior lecturer in School of Chemical Engineering, Universiti Sains Malaysia (USM). In addition, since Oct., 2009, he also holds a courtesy appointment as Visiting Research Professor in School of Physics, Carnegie Mellon University (CMU) in United States. He obtained his Ph.D. degree from Dept. of Chem. Eng (CMU) in 2009, working with Prof. Robert D. Tilton and Prof. Sara A. Majetich on the design and synthesis of magnetic, plasmonic nanoparticles. He was previously a Dowd Fellow (2006) of Institute for Complex Engineered Systems and also the recipient of Mark Dennis Karl Outstanding Graduate Teaching Award (2007) by Carnegie Mellon University. His work on design and synthesis of iron oxide-core, gold-shell nanoparticles has earned him a Travel Grant Award by The International Center for Material Research of University California at Santa Barbara (UCSB) which fully sponsored his visit to Jawaharlal Nehru Center for Advanced Scientific Research, India. He is also the Most Popular Lecturer of School of Chemical Engineering (2009), USM. JitKang research interest centered on the understanding of the interactions between the nano-objects based upon the existing framework of colloid science. Besides, he is also keen to study the magnetophoretic and electrohydrodynamic transport behaviors of colloidal particles. His most recent research efforts are on the integration and assembly of magnetic colloid into three dimensional polymeric networks and the usages of aforementioned structure for water treatment.