Bead manipulation techniques

Abstract

The invention provides a method of redistributing magnetically responsive beads in a droplet. The method may include providing a droplet including magnetically responsive beads. The droplet may be provided within a region of a magnetic field having sufficient strength to attract the magnetically responsive beads to an edge of the droplet or towards an edge of the droplet, or otherwise regionalize or aggregate beads within the droplet. The method may also include conducting on a droplet operations surface one or more droplet operations using the droplet without removing the magnetically responsive beads from the region of the magnetic field. The droplet operations may in some cases be electrode-mediated. The droplet operations may redistribute and/or circulate the magnetically responsive beads within the droplet. In some cases, the droplet may include a sample droplet may include a target analyte. The redistributing of the magnetically responsive beads may cause target analyte to bind to the magnetically responsive beads. In some cases, the droplet may include unbound substances in a wash buffer. The redistributing of the magnetically responsive beads causes unbound substances to be freed from interstices of an aggregated set or subset of the magnetically responsive beads.

1 . A method of redistributing magnetically responsive beads in a droplet, the method comprising:
 (a) providing a droplet comprising magnetically responsive beads within a region of a magnetic field having sufficient strength to attract the magnetically responsive beads to an edge of the droplet; and   (b) using electrodes to conduct on a droplet operations surface a droplet operation using the droplet without removing the magnetically responsive beads from the region of the magnetic field, thereby redistributing the magnetically responsive beads within the droplet.   
     
     
         2 . The method of  claim 1  wherein the droplet comprises a sample droplet comprising a target analyte. 
     
     
         3 . The method of  claim 1  wherein the redistributing of the magnetically responsive beads causes target analyte to bind to the magnetically responsive beads. 
     
     
         4 . The method of  claim 1  wherein the droplet comprises unbound substances in a wash buffer. 
     
     
         5 . The method of  claim 4  wherein the redistributing of the magnetically responsive beads causes unbound substances to be freed from interstices of an aggregated set or subset of the magnetically responsive beads. 
     
     
         6 . The method of  claim 1  wherein the droplet operation is selected to agitate contents of the droplet. 
     
     
         7 . The method of  claim 1  wherein the droplet operation comprises transporting the droplet. 
     
     
         8 . The method of  claim 1  wherein the droplet operation comprises elongating the droplet. 
     
     
         9 . The method of  claim 8  wherein elongating the droplet comprises flowing the droplet onto a region of the droplet operations surface atop two or more activated droplet electrodes causing the droplet to take on an elongated configuration. 
     
     
         10 . The method of  claim 1  wherein the droplet operation comprises merging the droplet with another droplet. 
     
     
         11 . The method of  claim 1  wherein the droplet operation comprises splitting the droplet to yield two or more daughter droplets. 
     
     
         12 . The method of  claim 11  wherein two or more of the daughter droplets each comprise a substantial subset of the magnetically responsive beads. 
     
     
         13 . The method of  claim 11  wherein the droplet operation comprises merging two or more of the daughter droplets. 
     
     
         14 . The method of  claim 1  further comprising removing the droplet or a sub-droplet thereof including at least a subset of the magnetically responsive beads from the magnetic field. 
     
     
         15 . The method of  claim 1  wherein one or more droplet operations is repeated in a series of two or more incubation cycles. 
     
     
         16 . The method of  claim 1  wherein the droplet operations surface is in a droplet operations gap of a droplet actuator. 
     
     
         17 . The method of  claim 1  wherein the droplet operations surface is coated by a liquid filler fluid. 
     
     
         18 . The method of  claim 1  wherein the droplet is surrounded by a liquid filler fluid. 
     
     
         19 . The method of  claim 1  wherein the droplet operation is electrode-mediated. 
     
     
         20 . The method of  claim 1  wherein the droplet operation is electrowetting-mediated. 
     
     
         21 . The method of  claim 1  wherein the droplet operation is dielectrophoresis-mediated. 
     
     
         22 . A method of redistributing magnetically responsive beads in a droplet, the method comprising:
 (a) providing a droplet comprising magnetically responsive beads within a region of a magnetic field having sufficient strength to attract the magnetically responsive beads to an edge of the droplet; and   (b) using electrodes to conduct on a droplet operations surface a droplet operation using the droplet without removing the magnetically responsive beads from the magnetic field, thereby redistributing the magnetically responsive beads within the droplet.