Apparatus and method for performing microfluidic manipulations for chemical analysis and synthesis

Abstract

A microchip laboratory system and method provide fluid manipulations for a variety of applications, including sample injection for microchip chemical separations. The microchip is fabricated using standard photolithographic procedures and chemical wet etching, with the substrate and cover plate joined using direct bonding. Capillary electrophoresis and electrochromatography are performed in channels formed in the substrate. Analytes are loaded into a four-way intersection of channels by electrokinetically pumping the analyte through the intersection, followed by switching of the potentials to force an analyte plug into the separation channel.

What is claimed is:  
     
         1 . A method for separating component species in a sample, comprising: 
 a. providing a microfluidic device that includes a body having at least first, second, third and fourth channels disposed therein, the body comprising a cover plate covering the first, second, third and fourth channels, wherein the first, second, third and fourth channels communicate at a first intersection, the first channel connecting at least a first sample source to the first intersection;    b. transporting a sample material from the first sample source, through the first intersection and into the second channel by applying a first voltage difference between the first sample material source and the second channel to move sample material from the first channel, through the intersection and into the second channel, and simultaneously applying a second voltage differences between the third channel and the first intersection and a third voltage difference between the fourth channel and the first intersection, to direct movement of the sample material through the intersection into the second channel; and    c. injecting an amount of sample material in the first intersection into the third channel by applying a fourth voltage difference between the first intersection and the third channel, the component species of the sample material separating as the sample material is transported through the third channel.    
     
     
         2 . The method of  claim 1 , wherein the first channel communicates with the first intersection between the third and fourth channels, and the third channel communicates with the first intersection between the first and second channels, and wherein in the transporting step, the second and third voltage differences move a material from the third and fourth channels, respectively, into the second channel, pinching the sample material in the intersection.  
     
     
         3 . The method of  claim 2 , wherein the injecting step further comprises removing the second and third voltage differences concurrently with the step of applying the fourth voltage difference between the third and fourth channels through the first intersection, to move material in the intersection, into the third channel.  
     
     
         4 . The method of  claim 3 , wherein the injecting step further comprises applying a fifth voltage difference between the first channel and the first intersection, and a sixth voltage difference between the second channel, and the first intersection to move the sample material in the first and second channels away from the intersection.  
     
     
         5 . The method of  claim 1 , wherein the first channel communicates with the first intersection between the fourth channel and the second channel and the second channel communicates with the first intersection between the first channel and the third channel, and wherein in the transporting step, the second and third voltage differences applied in the transporting step move a material from the fourth channel into the third channel to gate movement of the sample material into the second channel.  
     
     
         6 . The method of  claim 5 , wherein the injecting step further comprises removing the third voltage difference concurrently with the step of applying the fourth voltage difference between the first and third channels through the first intersection, to move material in the first channel into the third channel.  
     
     
         7 . The method of  claim 1  further comprising the step of introducing a sieving medium into at least the third channel prior to the injecting step.  
     
     
         8 . The method of  claim 7 , wherein the sieving medium is introduced into the first, second, third and fourth channels.  
     
     
         9 . The method of  claim 7 , wherein the sieving medium is selected from cellulose and acrylamide polymers.  
     
     
         10 . The method of  claim 9 , wherein the sieving medium is selected from hydroxyethylcellulose and polyacrylamide.  
     
     
         11 . The method of  claim 1 , wherein the component species of the sample material comprise nucleic acids.  
     
     
         12 . The method of  claim 11 , wherein the nucleic acids comprise DNA.  
     
     
         13 . The method of  claim 12 , wherein the DNA comprises restriction enzyme fragments of DNA.  
     
     
         14 . The method of  claim 11 , wherein the nucleic acids comprise different size nucleic acids.  
     
     
         15 . The method of  claim 14 , wherein the different size nucleic acids are prepared in a sequencing reaction.  
     
     
         16 . The method of  claim 1 , wherein the component species of the sample material comprise proteins.  
     
     
         17 . The method of  claim 16 , wherein the sample material further comprises a micellar material.  
     
     
         18 . The method of  claim 17 , wherein the miscellar material is sodium dodecyl sulfate.  
     
     
         19 . The method of  claim 1  further comprising the step of detecting the separated component species.  
     
     
         20 . The method of  claim 19 , wherein the third channel includes a detection zone, and the detecting step comprises detecting the separated component species in the third channel as the separated species are transported past the detection zone.  
     
     
         21 . The method of  claim 19 , wherein at least a portion of the component species comprise a fluorescent label, and the detecting step comprises detecting fluorescence in the third channel.  
     
     
         22 . The method of  claim 21 , wherein the fluorescent label is a fluorescein dye.  
     
     
         23 . The method of  claim 21 , wherein the label is a rhodamine dye.  
     
     
         24 . The method of  claim 21 , wherein the component species comprise nucleic acids and the fluorescent label is an intercalating dye.  
     
     
         25 . The method of  claim 1 , wherein the sample material comprises ionic species which are transported by electrophoresis.  
     
     
         26 . The method of  claim 1 , wherein the sample material is transported through the first, second, third and fourth channels by electroosmosis.  
     
     
         27 . The method of  claim 1 , wherein the sample material is transported by a combination of electroosmosis and electrophoresis.  
     
     
         28 . The method of  claim 1 , wherein the first channel communicates with the intersection between the third and fourth channels, and the third channel communicates with the intersection between the first and second channels, and wherein the transporting step comprises simultaneously electrokinetically moving a material from the third and fourth channels, respectively, into the second channel, pinching the sample material in the intersection.  
     
     
         29 . The method of  claim 28 , wherein the step of electrokinetically injecting a quantity of the sample material from the intersection into the third channel comprises concurrently electrokinetically moving the sample material in the first and second channels away from the intersection.  
     
     
         30 . The method of  claim 28  further comprising the step of detecting the separated component species in the third channel.  
     
     
         31 . The method of  claim 28 , wherein the third channel includes a detection zone, and the detecting step comprises detecting the separated component species in the third channel as the separated species are transported past the detection zone.  
     
     
         32 . The method of  claim 28 , wherein at least a portion of the component species comprise a fluorescent label, and the detecting step comprises detecting fluorescence in the third channel.  
     
     
         33 . The method of  claim 32 , wherein the fluorescent label is a fluorescein dye.  
     
     
         34 . The method of  claim 32 , wherein the label is a rhodamine dye.  
     
     
         35 . The method of  claim 32 , wherein the component species comprise nucleic acids and the fluorescent label is an intercalating dye.  
     
     
         36 . A method for separating component species in a sample, comprising: 
 a. electrokinetically moving a sample material from a first covered microfluidic channel through an intersection of the first channel with second, third and fourth covered microfluidic channels, and into the second channel, while simultaneously electrokinetically moving material into the intersection from at least one of the third and fourth channels to control movement of the sample material through the intersection;    b. electrokinetically injecting a quantity of the sample material from the intersection into the third channel; and    c. electrokinetically separating the sample material into component species in the third channel.    
     
     
         37 . The method of  claim 36 , wherein the sample material comprises ionic species which are transported by electrophoresis.  
     
     
         38 . The method of  claim 36 , wherein the sample material is transported through the first, second, third and fourth channels by electroosmosis.  
     
     
         39 . The method of  claim 36 , wherein the sample material is transported by a combination of electroosmosis and electrophoresis.