Marangoni stress-driven droplet manipulation on smart polymers for ultra-low voltage digital microfluidics

Abstract

An ultra-low voltage microfluidic device for manipulating droplets of liquid by inducing Marangoni stress therein includes a plurality of smart-polymer electrodes having films of smart polymer exposed at their surfaces. The surface of the smart polymer becomes hydrophobic or hydrophilic in response to different electromagnetic potentials. The smart polymer is reversibly oxidized by applying an electrical potential such that the smart polymer acquires a positive electrical charge. The oxidized smart polymer is reduced by applying an electrical potential such that it loses its positive electrical charge. The smart polymer is doped with a chemical compound having a negatively-charged end and a long-chain hydrophobic tail. The smart polymer is a polypyrrole and the dopant is a dodecylbenzene sulfonate. The microfluidic device includes a plurality of individually-addressable control electrodes, each of which is electrically-connected with smart-polymer electrodes. Droplets are transported, cut, or mixed by selectively applying electrical potential to individual electrodes.

1 . An ultra-low voltage microfluidic device, comprising:
 a patterned substrate including a plurality of smart-polymer electrodes, each of said plurality of smart-polymer electrodes having a smart polymer film exposed at a surface thereof, said smart polymer being reversibly oxidized by a first electromagnetic potential so as to acquire a positive electrical charge, said oxidized smart polymer being reversibly reduced by a second electromagnetic potential such that said oxidized smart polymer loses its positive electrical charge, said smart-polymer film including a dopant having an negatively-charged end and a long-chain hydrophobic tail, each of said plurality of smart-polymer electrodes being proximate another of said plurality of smart-polymer electrodes and separated from said another of said plurality of smart-polymer electrodes by an electrical insulator;   a plurality of addressable electrically-conductive control electrodes, each of said control electrodes being in electrical communication with at least one of said plurality of smart-polymer electrodes such that when said first electrical potential and/or second electrical potential is applied to said each of said plurality of smart-polymer electrodes, said electrical potential is communicated to said at least one of said plurality of said smart-polymer films;   a means for selectively and individually applying said first and second electrical potentials to said each of said plurality of control electrodes such that a droplet of liquid is manipulated across at least some of said smart-polymer films by inducing a Marangoni stress on said droplet by means of selectively and individually oxidizing and/or reducing at least some of said smart polymer films, thereby altering the orientation of said dopant within said smart-polymer films.   
     
     
         2 . The microfluidic device of  claim 1 , wherein said smart polymer is a polypyrrole and said dopant is a dodecylbenzene sulfonate,