Disclosed herein are methods of immobilizing a particle which comprise focusing the flow of a sample fluid containing the particle into a virtual channel which flows towards an unoccupied hydrodynamic trap in a microfluidic channel such that the particle flows into the hydrodynamic trap and becomes immobilized therein. Also disclosed are microfluidic devices which comprise at least one microchannel having at least one hydrodynamic trap, at least one focusing fluid inlet, said focusing fluid inlet is upstream of the hydrodynamic trap such that a focusing fluid introduced therein results in a virtual channel of a sample fluid when present which preferentially flows toward the hydrodynamic trap.
STATEMENT OF GOVERNMENT INTEREST
 The United States Government has rights in this invention pursuant to Contract No. DE-AC04-94AL85000 between the United States Department of Energy and Sandia Corporation, for the operation of the Sandia National Laboratories.