Digital microfluidic liquid-liquid extraction device and method of use thereof

Abstract

Methods and devices for liquid-liquid extraction using digital microfluidic arrays are provided. A polar droplet is transported to a separation region containing a substantially non-polar solvent, where non-polar impurities may be extracted from the polar droplet while maintaining a distinct phase separation. In a preferred embodiment, biological samples containing hormones are dried on a digital microfluidic array, lysed by a lysing solvent, dried, subsequently dissolved in a polar solvent, and further purified in a separation step in which droplets are transported through a volume of non-polar solvent. The method disclosed herein provides the distinct advantage of an automated sample preparation method that is capable of extracting hormones from low sample volumes with high precision and recovery.

What is claimed is: 
     
         1 . A digital microfluidic device for the transfer of an analyte from a substantially polar droplet to a substantially non-polar liquid, said device comprising:
 a first substrate;   at least one input electrode formed on said first substrate;   a separation array in flow communication with said input electrode, said separation array comprising at least two electrodes formed on said first substrate;   at least one output electrode in flow communication with said separation array, said at least one output electrode formed on said first substrate;   a second substrate provided in a spaced relationship with said first substrate such that a gap is formed therebetween, wherein said first substrate and said second substrate enclose a volume including said input electrode, said separation array, and said output electrode, and wherein said second substrate comprises at least one electrode, such that the substantially polar droplet is transportable among said input electrode, said separation array, and said output electrode while contacting said second substrate under the application of voltages between respective electrodes of said first substrate and said second substrate; and   a retaining wall enclosing said separation array, said retaining wall having a first opening positioned between the inlet electrode and the separation array and a second opening positioned between the outlet electrode and the separation array, wherein the retaining wall is configured for retaining a substantially non-polar liquid over said separation array.   
     
     
         2 . A closed digital microfluidic device for the transfer of an analyte from a substantially polar droplet to a substantially non-polar liquid, said device comprising:
 a first substrate;   at least one input electrode formed on said first substrate;   a separation array in flow communication with said input electrode, said separation array comprising at least two electrodes formed on said first substrate;   at least one output electrode in flow communication with said separation array, said at least one output electrode formed on said first substrate;   a second substrate provided in a spaced relationship with said first substrate such that a gap is formed therebetween, wherein said first substrate and said second substrate enclose a volume including said input electrode, said separation array, and said output electrode, and wherein said second substrate comprises at least one electrode, such that the substantially polar droplet is transportable among said input electrode, said separation array, and said output electrode while contacting said second substrate under the application of voltages between respective electrodes of said first substrate and said second substrate; and   a first retaining well enclosing a first side of the separation array and a second retaining well enclosing a second side of the separation array, wherein the first retaining well and second retaining well are configured for retaining a substantially non-polar liquid over said separation array.   
     
     
         3 . A method of transferring an analyte from a substantially polar droplet to a substantially non-polar liquid, the method comprising:
 introducing a substantially polar droplet into a space between a first substrate and a second substrate of a digital microfluidic device, wherein the first substrate comprises a plurality of electrodes configured to move the droplet across the first substrate, wherein the substantially polar droplet comprises an analyte;   actuating a first subset of the plurality of electrodes to move the droplet into a substantially non-polar liquid that is retained in a separation zone defined by the first substrate, the second substrate and a retaining structure; and   actuating a second subset of the plurality of electrodes to move the droplet within the substantially non-polar liquid in the separation zone, thereby transferring the analyte from the droplet and into the substantially non-polar liquid.   
     
     
         4 . The method of  claim 3 , wherein the retaining structure is a wall. 
     
     
         5 . The method of  claim 3 , wherein the retaining structure is a well. 
     
     
         6 . The method of  claim 3 , wherein the analyte is substantially non-polar. 
     
     
         7 . The method of  claim 3 , wherein the analyte is a hormone. 
     
     
         8 . The method of  claim 7 , wherein the hormone is selected from the group consisting of lipid hormones, steroidal hormones, sterol hormones, prostaglandins, amine derived hormones, peptide and protein hormones. 
     
     
         9 . The method of  claim 7 , wherein the hormone comprises a steroid selected from the group consisting of estrogens, androgens, progestins, progestogens, glucocorticoids and mineralocorticoids. 
     
     
         10 . The method of  claim 7 , wherein the hormone comprises an estrogen selected from the group consisting of estradiol, estrone, estriol, estrogen metabolites, phytoestrogens, synthetic estrogens, equilin, equilenin, ethinyl estradiol, and bio-identical estrogens. 
     
     
         11 . The method of  claim 3 , wherein the analyte is selected from the group consisting of peptides, amino acids, DNA, RNA, metals, drugs, hormones, and proteins. 
     
     
         12 . The method of  claim 3 , further comprising analyzing the analyte that has been transferred from the droplet and into the substantially non-polar liquid. 
     
     
         13 . The method of  claim 3 , wherein the droplet is introduced from a sample contained in a sample reservoir, the sample comprising the analyte. 
     
     
         14 . The method of  claim 13 , further comprising:
 introducing a series of droplets from the sample into the space between the first substrate and the second substrate;   transporting the series of droplets into the substantially non-polar liquid retained within the separation zone; and   transferring the analyte from the series of droplets to the non-polar liquid.   
     
     
         15 . The method of  claim 14 , wherein the entire sample is introduced as a series of droplets. 
     
     
         16 . The method of  claim 14 , wherein a predetermined volume of the sample is introduced as a series of droplets. 
     
     
         17 . The method of  claim 14 , wherein a predetermined number of droplets are introduced as a series of droplets. 
     
     
         18 . The method of  claim 14 , further comprising transporting the series of droplets out of the substantially non-polar liquid retained in the separation zone.