(411c) Hydrodynamic Trap for Single Cells and Micro- and Nanoparticles

Over the past twenty-five years, a diverse set of methods based on optical, electrokinetic, magnetic, acoustic, and hydrodynamic forces has been developed to confine and manipulate particles through control of particle position and velocity. In this work, we present a novel flow-based confinement method called the hydrodynamic trap which enables free-solution trapping, manipulation, stretching and sorting of objects ranging from single molecules to individual cells [1]. The hydrodynamic trap is an automated, non-contact and high resolution confinement technique based on a stagnation point flow generated in a microfluidic device. Using this method, we demonstrate trapping of single micro- and nanoscale particles (100 nm-15 μm fluorescent and non-fluorescent polystyrene beads), single DNA molecules, single cells (bacterial and mammalian) and confinement of micron-sized particles with high resolution (within 1 μm) for extended time scales (minutes to hours).

The hydrodynamic trap consists of a hybrid PDMS/glass microfluidic device with a cross-slot channel geometry. Two laminar inlet streams converge at the microchannel junction from opposing directions and exit the junction through the perpendicular channels in opposite directions, thereby generating a planar extensional flow. We implement an automated feedback-control mechanism to adjust the location of the stagnation point using an integrated on-chip metering valve, thereby manipulating and confining single particles at the microchannel junction. To characterize trap stiffness, we measured the power spectral density (PSD) of position fluctuations for a trapped particle. The PSD is well-described by a Lorentzian, yielding a trap stiffness κ = 1.99 × 10^-4 pN/nm, which compares favorably to optical, magnetic and electrophoretic traps.

The hydrodynamic trap presents several advantages as a micromanipulation tool. Hydrodynamic trapping is feasible for any particle with no specific requirements on the material composition or the chemical/physical nature (optical, magnetic, surface charge) of the trapped object. The hydrodynamic trap inherently enables confinement of a single target object in dilute or concentrated particle or cell suspensions, due to the semi-stable nature of trapping potential. The ability to trap a single particle in a ?crowded? solution represents a key advantage for a trapping method. In addition, the hydrodynamic trapping force scales linearly with particle radius, therefore, this technique is expected to enable straightforward confinement and manipulation of small nanoparticles (<100 nm) in solution, which is difficult if not impossible using alternative trapping methods. In summary, the hydrodynamic trap offers a new platform for observation of cells and particles without surface immobilization, eliminates potentially perturbative optical, magnetic and electric fields, and provides the ability to change the surrounding medium of a trapped cell in real time. This technique will enable new scientific exploration in the fields of molecular biophysics, systems biology, enzymology, cellular mechanics, and fluid dynamics. [1] M. Tanyeri, E. M. Johnson-Chavarria and C. M. Schroeder, Applied Physics Letters, in press (2010).