Localized Chemical Microgradients

Abstract

A device for creating microgradients in solution is disclosed. The device contains a microfluidic channel with openings at each end and two or more small apertures to a bath. Electrodes are placed in the openings at either end of the channel and an electrical power supply is connected to the electrodes. Several distinct current paths exist from one end of the channel to the other. For example current may flow from one electrode, through a portion of the channel, through an aperture into the bath, back through another aperture into the channel, and along another portion of the channel to the other electrode. Current flows along all possible connected paths when an electric field is applied along the channel and induces fluid flow into and out of the apertures in the channel. Fluid flow through the apertures results in the formation of microgradients in solution near the microfluidic channel device.

What is claimed is: 
     
         1 . A method of creating microgradients in solution comprising:
 providing a microchannel having two or more apertures;   filling the microchannel with a solution;   providing a bath in contact with the apertures of the microchannel; and,   applying an electric field along the microchannel.   
     
     
         2 . A method for positioning or sorting cells comprising:
 providing a microchannel having two or more apertures to a bath;   applying an electric field along the microchannel;   introducing cells in solution into the microchannel; and,   moving the solution and the cells by electroosmotic flow until electric current flow along the channel drops essentially to zero.   
     
     
         3 . A method of delivering reagents to cells comprising:
 providing a microchannel having two or more apertures to a bath;   applying an electric field along the microchannel;   introducing reagents into the microchannel; and,   positioning cells in the bath near the apertures.