Building on previous work in optofluidics using polymer waveguides, engineers from Cornell University (Ithaca, NY) have devised a comprehensive model for particle-trapping stability analysis of dielectric particles in an evanescent field of low-index and high-index solid-core waveguide structures integrated with microfluidics (see www.laserfocusworld.com/articles/314424Their approach, which is outlined in detail in Nanotechnology 19, 045704 (January 2008), could have important implications for the design of lab-on-a-chip devices.
Models for predicting propulsive velocities and trapping forces within a static fluidic environment are not new. However, developing a practical optofluidic transport system requires understanding the conditions that bring a particle to a waveguide trap and remain stably trapped within the evanescent field. David Erickson and colleagues in Cornell’s School of Chemical and Biomolecular Engineering and Sibley School of Mechanical and Aerospace Engineering used three-dimensional finite-element-based simulations to determine the electromagnetic and hydrodynamic field variables for two different waveguide systems: silicon (1550 nm) and polymer (1064 nm). A trapping stability number was obtained by comparing the work required to remove a particle from the waveguide with available random thermal energy. These forces were then correlated to controllable experimental parameters such as particle size, fluid velocity, and channel height and a series of trapping stability diagrams was produced, detailing the conditions under which optofluidic transport is possible. Contact David Erickson at [email protected].