Microfluidic device for analyzing gene expression

Abstract

A microfluidic device is disclosed which comprises:(i) at least one reaction unit having a test chamber connected to at least one microchannel, wherein a surface of at least a portion of said reaction unit is attached to an isolated nucleic acid; and(ii) a flow-through channel having at least one inlet port and at least one outlet port, said flow-through channel and said microchannel being of dimensions to allow reactant diffusion to and from said reaction unit, wherein the diffusion time of said reactant along the microchannel is shorter than the flow time along the microchannel.

What is claimed is: 
     
         1 . A method of expressing a polypeptide comprising:
 (a) obtaining a microfluidic device which comprises:   (i) at least one reaction unit comprising a test chamber and a microchannel, said test chamber connected to said microchannel, wherein a surface of at least a portion of said test chamber of said reaction unit is attached to a nucleic acid having a sequence which encodes a promoter operatively linked to a sequence encoding a polypeptide; and   (ii) a flow-through channel having at least one inlet port and at least one outlet port, said flow-through channel being connected to said test chamber via said microchannel of said reaction unit, said microchannel being of dimensions to allow reactant diffusion to and from said reaction unit, wherein the diffusion time of said reactant along the microchannel is shorter than the flow time along the microchannel; and   (b) contacting the nucleic acid of the microfluidic device with a composition which comprises enzymes for performing expression of the polypeptide from said nucleic acid, under conditions that allow expression of the polypeptide, thereby expressing the polypeptide.   
     
     
         2 . The method of  claim 1 , wherein said composition comprises a cell extract. 
     
     
         3 . The method of  claim 2 , wherein said cell extract is devoid of nucleic acids. 
     
     
         4 . The method of  claim 1 , wherein the protein forms a gradient in the reaction unit. 
     
     
         5 . The method of  claim 1 , wherein the expressing is effected for at least 6 hours. 
     
     
         6 . The method of  claim 1 , wherein said polypeptide is a detectable polypeptide. 
     
     
         7 . The method of  claim 1 , wherein said promoter is a tissue-specific promoter. 
     
     
         8 . The method of  claim 1 , wherein said polypeptide is a transcription factor. 
     
     
         9 . The method of  claim 1 , wherein the hydrodynamic resistance of the microchannel is at least 10 5  times greater than that of the flow-channel, wherein the hydrodynamic resistance (R) is calculated according to the formula 
       
         
           
             
               R 
               = 
               
                 
                   1 
                   5 
                 
                 ⁢ 
                 
                   
                     L 
                     · 
                     η 
                   
                   
                     
                       h 
                       3 
                     
                     ⁢ 
                     
                       W 
                       ⁡ 
                       ( 
                       
                         1 
                         - 
                         
                           192 
                           ⁢ 
                           
                             h 
                             
                               
                                 π 
                                 5 
                               
                               ⁢ 
                               W 
                             
                           
                           ⁢ 
                           
                             tanh 
                             ⁡ 
                             ( 
                             
                               
                                 π 
                                 ⁢ 
                                 W 
                               
                               
                                 2 
                                 ⁢ 
                                 h 
                               
                             
                             ) 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
           
         
       
       for a channel with length L, height h, width W and with a fluid with viscosity η. 
     
     
         10 . The method of  claim 1 , wherein said test chamber is 10-200 microns in diameter. 
     
     
         11 . The method of  claim 1 , wherein said nucleic acid is attached to said surface via a reactive group. 
     
     
         12 . The method of  claim 11 , wherein said reactive group is photoreactivatable. 
     
     
         13 . The method of  claim 1 , wherein said microfluidic device comprises at least two of the at least one reaction units. 
     
     
         14 . The method of  claim 13 , wherein the length of the microchannel of the first reaction unit is identical to the length of the microchannel of the second reaction unit. 
     
     
         15 . The method of  claim 13 , wherein the length of the microchannel of the first reaction unit is non-identical to the length of the microchannel of the second reaction unit. 
     
     
         16 . The method of  claim 1 , wherein said at least one reaction unit has two test chambers connected to said microchannel and, optionally, wherein a sequence of the nucleic acid in the first of the two test chambers is different than a sequence of the nucleic acid in the second of the two test chambers.