Droplet Actuators that Include Molecular Barrier Coatings

Abstract

Droplet actuators that include molecular barrier coatings are provided. The molecular barrier coating may be provided atop the conductive layer of the top substrate, atop the droplet operations electrodes of the bottom substrate, or both. Where the conductive layer of the top substrate and/or the droplet operations electrodes of the bottom substrate are formed of an electrically conductive organic polymer, such as poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), the molecular barrier coating helps to immobilize the contents of the PEDOT:PSS layer. Further, the molecular barrier coating reduces, preferably entirely eliminates, moisture from seeping into the electrically conducting organic polymer. Methods of conducting droplet operations using the disclosed droplet actuators are also provided.

We claim: 
     
         1 . A droplet actuator comprising:
 a bottom substrate comprising droplet operations electrodes;   (b) a top substrate separated from the bottom substrate to form a gap, the top substrate comprising a conductive layer; and   (c) a molecular barrier layer atop the conductive layer of the top substrate, and/or a molecular barrier layer atop the droplet operations electrodes of the bottom substrate.   
     
     
         2 . The droplet actuator of  claim 1 , further comprising a hydrophobic layer atop the molecular barrier layer. 
     
     
         3 . The droplet actuator of  claim 1 , wherein the conductive layer of the top substrate and/or the droplet operations electrodes of the bottom substrate are formed of an electrically conductive organic polymer. 
     
     
         4 . The droplet actuator of  claim 3 , wherein the electrically conductive organic polymer is poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). 
     
     
         5 . The droplet actuator of  claim 4 , wherein the molecular barrier layer immobilizes the contents of the conductive layer of the top substrate and/or the contents of the droplet operations electrodes of the bottom substrate. 
     
     
         6 . The droplet actuator of  claim 1 , wherein the thickness of the molecular barrier layer is from about 1 nm to about 100 μm. 
     
     
         7 . The droplet actuator of  claim 1 , wherein the molecular barrier layer is a molecular barrier coating. 
     
     
         8 . The droplet actuator of  claim 7 , wherein the molecular barrier coating comprises a stretchable gel or a hard coating. 
     
     
         9 . The droplet actuator of  claim 8 , wherein the stretchable gel is selected from the group consisting of silicones, hydrogels, and polyethylene glycol derivatives. 
     
     
         10 . The droplet actuator of  claim 8 , wherein the hard coating is a ceramic selected from the group consisting of silicon oxides, silicon nitrides, barium-strontium titanate, bismuth-zinc niobiate, and tantalum oxides. 
     
     
         11 . The droplet actuator of  claim 4 , wherein the molecular barrier layer is a moisture barrier. 
     
     
         12 . The droplet actuator of  claim 4 , wherein the molecular barrier layer is a sieve that allows water to pass through the molecular barrier layer while larger molecules are blocked from passing through the molecular barrier layer. 
     
     
         13 . The droplet actuator of  claim 1 , wherein the molecular barrier layer atop the conductive layer of the top substrate is excluded when the conductive layer of the top substrate is formed of an electrically conductive material that is less affected by moisture. 
     
     
         14 . The droplet actuator of  claim 13 , wherein the conductive layer of the top substrate is formed of indium tin oxide. 
     
     
         15 . The droplet actuator of  claim 1 , wherein the molecular barrier layer atop the droplet operations electrodes of the bottom substrate is excluded when the droplet operations electrodes of the bottom substrate are formed of an electrically conductive material that is less affected by moisture. 
     
     
         16 . The droplet actuator of  claim 15 , wherein the droplet operations electrodes of the bottom substrate are formed of copper, aluminum, gold, or silver. 
     
     
         17 . The droplet actuator of  claim 1 , wherein the droplet operations electrodes are on the side of bottom substrate that is facing droplet operations gap. 
     
     
         18 . The droplet actuator of  claim 1 , wherein the conductive layer of the top substrate comprises a ground or reference electrode with respect to droplet operations electrodes of the bottom substrate. 
     
     
         19 . A method of performing droplet operations on one or more droplets in a droplet actuator, comprising:
 (a) providing the droplet actuator of  claim 11 ;   (b) filling the droplet operations gap the of droplet actuator with a filler fluid;   (c) transporting the one or more droplets in the droplet operations gap via droplet operations along the droplet operations electrodes and through the filler fluid;   wherein the one or more droplets are aqueous or are emulsions that include aqueous components and the molecular barrier layer is a moisture barrier to water passing from the droplet operations gap to the droplet operations electrodes of the bottom substrate and/or to the conductive layer of the top substrate.   
     
     
         20 . A method of performing droplet operations on one or more droplets in a droplet actuator, comprising:
 (a) providing the droplet actuator of  claim 12 ;   (b) filling the droplet operations gap the of droplet actuator with a filler fluid;   (c) transporting the one or more droplets in the droplet operations gap via droplet operations along the droplet operations electrodes and through the filler fluid;   wherein high-temperature electrowetting-on-dielectric (EWOD) methods are performed on the one or more droplets, and wherein only water expelled from the PEDOT:PSS may pass through the molecular barrier layer while larger molecules that may negatively affect the performance of the high-temperature EWOD methods are blocked from passing through the molecular hastier layer.   
     
     
         21 . The method of  claim 20 , wherein the high-temperature EWOD methods comprise thermocycling in a polymerase chain reaction (PCR).