Capacitance Detection in a Droplet Actuator

A method of identifying a bead type in a droplet, the method comprising:

• (a) providing on an electrode on a droplet actuator a droplet comprising a bead of a specific unknown type and having a unique capacitance;
• (b) determining capacitance at the electrode;
• (c) comparing capacitance at the electrode to expected capacitance in the presence one or more bead types;
• and
• (d) identifying the bead type.

A droplet actuator for manipulating a fluid using an electrical field, comprising:

• (a) an actuator electrode configured to communicate the electrical field to the fluid;
• (b) a reference electrode in communication with the actuator electrode and in selective communication with at least one of a ground node, a high voltage node and a high impedance node having an intermediate potential;
• (c) a capacitance detection circuit in communication with the reference electrode and configured to detect a capacitance of the fluid;
• and
• (d) a processor in communication with the capacitor detection circuit and configured to determine a position of the fluid based on the detected capacitance of the fluid.

A capacitance detection circuit for detecting a capacitance of fluid present in a droplet actuator, comprising:

• (a) an amplifier in communication with an electrode of the droplet actuator;
• (b) an analog-to-digital converter in communication with the amplifier and a processor configured to determine a position of the fluid based on the detected capacitance of the fluid;
• and
• (c) a protection circuit configured to regulate a voltage entering the capacitance detection circuit to minimize damage caused by a high voltage condition.

A method of transporting a droplet on a droplet operations surface of a droplet actuator, wherein:

• (a) the droplet actuator comprises:
• (i) a first electrode;
• (ii) a second electrode adjacent to the first electrode;
• and
• (iii) a third electrode adjacent to the second electrode;
• and
• (b) the method comprises:
• (i) monitoring impedance at the first electrode, the second electrode and/or the third electrode during a droplet operation comprising activating the second electrode to transport a droplet from the first electrode to the second electrode;
• and
• (ii) sequentially or simultaneously activating the third electrode and deactivating the second electrode when at least one of the following conditions is satisfied:
• (1) impedance at the first electrode indicates that the droplet is sufficiently on the second electrode to result in transport of the droplet from the second electrode to the third electrode upon activation of the third electrode and deactivation of the second electrode;
• (2) impedance at the second electrode indicates that the droplet is sufficiently on the second electrode to result in transport of the droplet from the second electrode to the third electrode upon activation of the third electrode and deactivation of the second electrode;
• and
• (3) impedance at the third electrode indicates that the droplet is sufficiently on the second electrode to result in transport of the droplet from the second electrode to the third electrode upon activation of the third electrode and deactivation of the second electrode.