Use of liquid junction potentials for electrophoresis without applied voltage in a microfluidic channel

Abstract

This invention provides methods for using liquid junction potentials to control the transport of charged particles in fluid streams that are in laminar flow within microfluidic channels. Applications of the methods of this invention include sample preconditioning (removal of interfering substances), electrophoretic separation (fractionation) of charged particles, enhanced or delayed mixing of charged particles across a fluid interface relative to diffusion only, focusing charged particles in a fluid stream in one or two dimensions, and concentration of charged reactants at a fluid interface.

1 . A microfluidic device comprising: 
 a microfluidic channel containing:    a) at least a first and a second fluid stream in parallel laminar flow in said microfluidic channel to form at least one fluid interface;    b) charged particles contained in at least one of said fluid streams;    c) ions contained in at least one of said fluid streams of a charge, concentration, mobility and/or charge magnitude selected to control movement of said charged particles with respect to said interface.    
     
     
         2 . The microfluidic decice of  claim 1  wherein said interface is non-linear.  
     
     
         3 . A method for determining the concentration of charged particles in a first fluid in laminar flow with a second fluid in a microchannel by a method based on correlating the rate of diffusion of said charged particles across an interface between said first and second fluids with the concentration of said charged particles, the method comprising determining the concentration of charged particles in said fluid by: 
 a) measuring the rate of diffusion of said charged particles across said interface or the position of said particles with respect to said interface to obtain a first diffusion value;    b) determining the presence of an electric potential across said interface;    c) calculating the effect of said electric potential on said rate of diffusion to obtain a correction value;    d) adjusting said first diffusion value by said correction value to obtain a second diffusion value;    e) correlating said second diffusion value with the concentration of said charged particles.