Hydrodynamic Trap for Single Cells and Particles

Abstract

Particle trapping and micromanipulation techniques have revolutionized biological sciences during the last two decades. Proteins, enzymes and cells have been studied extensively through manipulation methods based on optical, magnetic and electric fields. In this work, we present an alternative trapping method called the hydrodynamic trap which is based solely on hydrodynamic forces generated in a microfluidic device. The hydrodynamic trap is based on a purely extensional flow field created at the junction of two perpendicular microchannels where opposing laminar flow streams converge. The flow field in the vicinity of the microchannel junction can be described as a potential flow with a semi-stable potential well and a stagnation point. We implement an automated feedback-control mechanism to adjust the location of the stagnation point, thereby actively trapping arbitrary particles in free solution. Using the hydrodynamic trap, we successfully demonstrate trapping and manipulation of single cells and single particles with micron and sub-micron dimensions for arbitrarily long observation times. Brownian dynamics simulations show that the trap stiffness is comparable to alternative trapping techniques including magnetic traps. Overall, this new technique offers a venue for observation of biological materials without surface immobilization, eliminates potentially perturbative optical, magnetic and electric fields, and enables the ability to vary the surrounding medium conditions of the trapped object in real-time.