Apparatus and method for performing microfluidic manipulations for chemical analysis

Abstract

A microchip apparatus and method provide fluidic manipulations for a variety of applications, including sample injection for microchip liquid chromatography. The microchip fabricated using standard photolithographic procedures chemical wet etching, with the substrate and cover plate joined using direct bonding. Capillary electrophoresis is performed in channels formed in the substrate. Injections are made by electro-osmotically pumping sample through the injection channel that crosses the separation channel, followed by a switching of the potentials to force a plug into the separation channel.

What is claimed is:  
     
         1 . A method of injecting a sample into a channel within a microchip, the microchip comprising an interconnecting channel structure and a cover enclosing the interconnecting channel structure, the method comprising: 
 a. providing an interconnecting channel structure comprising an injection channel extending between a first reservoir and a second reservoir, a separation channel extending between a third reservoir and a fourth reservoir, wherein the injection and separation channels are in fluid communication with each other at an intersection, wherein the first reservoir is supplied with a fluid, and wherein the fluid comprises at least two analytes, each analyte having a respective electrophoretic mobility;    b. applying a first set of potentials to at least the first and second reservoirs, the first set of potentials being effective to transport the fluid from the first reservoir through the injection channel toward the intersection, wherein the first set of potentials is applied for a long enough time so that the analyte with the lowest electrophoretic mobility passes through the intersection, whereby a representative sample of the fluid is contained within the intersection; and    c. applying a second set of potentials to at least the third and fourth reservoirs, the second set of potentials being effective to transport the representative sample of fluid contained within the intersection into the separation channel.    
     
     
         2 . The method of  claim 1 , wherein the step of applying a first set of potentials comprises applying potentials to the first and second reservoirs, and either the third or fourth reservoir.  
     
     
         3 . The method of  claim 1 , wherein the step of applying a second set of potentials comprises applying potentials to the first and second reservoirs, and either the third or fourth reservoir.  
     
     
         4 . The method of  claim 1 , wherein the step of applying a first set of potentials comprises applying potentials to the first, second, third, and fourth reservoirs.  
     
     
         5 . The method of  claim 4 , wherein at least one of the potentials applied to the four reservoirs is ground potential.  
     
     
         6 . The method of  claim 4 , wherein the step of applying a first set of potentials further comprises transporting the fluid through the intersection in a pinched mode.  
     
     
         7 . The method of  claim 1 , wherein the step of applying a second set of potentials comprises applying potentials to the first, second, third, and fourth reservoirs.  
     
     
         8 . The method of  claim 6 , wherein at least one of the potentials applied to the four reservoirs is ground potential.  
     
     
         9 . The method of  claim 1 , wherein the separation channel is used to perform a capillary electrophoresis process.  
     
     
         10 . The method of  claim 1 , wherein the separation channel is used to carry out a liquid chromatography process.  
     
     
         11 . The method of  claim 1 , wherein the separation channel is used to carry out a flow injection analysis.  
     
     
         12 . The method of  claim 1 , wherein the interconnecting channel structure is disposed on a glass substrate.  
     
     
         13 . The method of  claim 1 , wherein the interconnecting channel structure is enclosed by a glass cover plate.  
     
     
         14 . The method of  claim 1 , wherein the intersection comprises a cross intersection.  
     
     
         15 . The method of  claim 1 , wherein the fluid comprising at least two analytes is an amino acid solution, wherein at least one of the at least two analytes is an amino acid.  
     
     
         16 . The method of  claim 1 , wherein at least one of the two analytes is a nucleic acid.  
     
     
         17 . The method of  claim 16 , wherein all of the analytes are nucleic acids.  
     
     
         18 . A method of injecting a sample into a channel within a microchip, the microchip comprising an interconnecting channel structure and a cover enclosing the interconnecting channel structure, the method comprising: 
 a. providing an interconnecting channel structure comprising an injection channel extending between a first reservoir and a second reservoir, a separation channel extending between a third reservoir and a fourth reservoir, wherein the injection and separation channels are in fluid communication with each other at an intersection, wherein the first reservoir is supplied with a fluid, and wherein the fluid comprises at least two analytes, each analyte having a respective electrophoretic mobility;    b. applying a first set of potentials to the first, second, third, and fourth reservoirs, the first set of potentials being effective to transport the fluid from the first reservoir through the injection channel toward the intersection and to transport the fluid through the intersection in a pinched mode, wherein the first set of potentials is applied for a long enough time so that the analyte with the lowest electrophoretic mobility passes through the intersection, whereby a representative sample of the fluid is contained within the intersection;    c. applying a second set of potentials to the first, second, third, and fourth reservoirs, the second set of potentials being effective to transport the representative sample of fluid contained within the intersection into the separation channel; and to transport the portion of the fluid in the injection channel not contained in the intersection away from the intersection.    
     
     
         19 . The method of  claim 18 , wherein at least one of the first set of potentials applied to the four reservoirs is ground potential.  
     
     
         20 . The method of  claim 18 , wherein at least one of the second set of potentials applied to the four reservoirs is ground potential.  
     
     
         21 . The method of  claim 18 , wherein the separation channel is used to perform a capillary electrophoresis process.  
     
     
         22 . The method of  claim 18 , wherein the separation channel is used to perform a liquid chromatography process.  
     
     
         23 . The method of  claim 18 , wherein the separation channel is used to perform a flow injection analysis.  
     
     
         24 . The method of  claim 18 , wherein the interconnecting channel structure is disposed on a glass substrate.  
     
     
         25 . The method of  claim 18 , wherein the interconnecting channel structure is enclosed by a glass cover plate.  
     
     
         26 . The method of  claim 18 , wherein the intersection comprises a cross intersection.  
     
     
         27 . The method of  claim 18 , wherein the fluid comprising at least two analytes is an amino acid solution wherein at least one of the at least two analytes is an amino acid.  
     
     
         28 . The method of  claim 18 , wherein at least one of the two analytes is a nucleic acid.  
     
     
         29 . The method of  claim 29 , wherein all of the analytes are nucleic acids.  
     
     
         30 . A method of injecting a fluid-borne analyte into a channel within a microchip, the fluid-borne analyte comprising at least two components having different electrophoretic mobilities and the microchip comprising an interconnecting channel structure and a cover enclosing the interconnecting channel structure, the interconnecting channel structure defining at least one cross injection intersection, the method comprising flowing the fluid-borne analyte from a reservoir into the intersection until a representative sample is contained within the injection intersection, and moving the representative sample into the channel which is fluidly coupled to the injection intersection.