Liquid Control

After attaching a tip, your robot is ready to aspirate, dispense, and perform other liquid handling tasks. The API includes methods that help you perform these actions and the following sections show how to use them. The examples used here assume that you’ve loaded the pipettes and labware from the basic protocol template.

Aspirate

To draw liquid up into a pipette tip, call the InstrumentContext.aspirate() method. Using this method, you can specify the aspiration volume in µL, the well location, and pipette flow rate. Other parameters let you position the pipette within a well. For example, this snippet tells the robot to aspirate 200 µL from well location A1.

pipette.pick_up_tip()
pipette.aspirate(200, plate["A1"])

If the pipette doesn’t move, you can specify an additional aspiration action without including a location. To demonstrate, this code snippet pauses the protocol, automatically resumes it, and aspirates a second time from plate["A1"]).

pipette.pick_up_tip()
pipette.aspirate(200, plate["A1"])
protocol.delay(seconds=5) # pause for 5 seconds
pipette.aspirate(100)     # aspirate 100 µL at current position

Now our pipette holds 300 µL.

Aspirate by Well or Location

The aspirate() method includes a location parameter that accepts either a Well or a Location.

If you specify a well, like plate["A1"], the pipette will aspirate from a default position 1 mm above the bottom center of that well. To change the default clearance, first set the aspirate attribute of well_bottom_clearance:

pipette.pick_up_tip
pipette.well_bottom_clearance.aspirate = 2  # tip is 2 mm above well bottom
pipette.aspirate(200, plate["A1"])

You can also aspirate from a location along the center vertical axis within a well using the Well.top() and Well.bottom() methods. These methods move the pipette to a specified distance relative to the top or bottom center of a well:

pipette.pick_up_tip()
depth = plate["A1"].bottom(z=2) # tip is 2 mm above well bottom
pipette.aspirate(200, depth)

See also:

  • Default Positions for information about controlling pipette height for a particular pipette.

  • Position Relative to Labware for information about controlling pipette height from within a well.

  • Move To for information about moving a pipette to any reachable deck location.

Aspiration Flow Rates

Flex and OT-2 pipettes aspirate at default flow rates measured in µL/s. Specifying the rate parameter multiplies the flow rate by that value. As a best practice, don’t set the flow rate higher than 3x the default. For example, this code causes the pipette to aspirate at twice its normal rate:

pipette.aspirate(200, plate["A1"], rate=2.0)

New in version 2.0.

Dispense

To dispense liquid from a pipette tip, call the InstrumentContext.dispense() method. Using this method, you can specify the dispense volume in µL, the well location, and pipette flow rate. Other parameters let you position the pipette within a well. For example, this snippet tells the robot to dispense 200 µL into well location B1.

pipette.dispense(200, plate["B1"])

If the pipette doesn’t move, you can specify an additional dispense action without including a location. To demonstrate, this code snippet pauses the protocol, automatically resumes it, and dispense a second time from location B1.

pipette.dispense(100, plate["B1"])
protocol.delay(seconds=5) # pause for 5 seconds
pipette.dispense(100)     # dispense 100 µL at current position

Dispense by Well or Location

The dispense() method includes a location parameter that accepts either a Well or a Location.

If you specify a well, like plate["B1"], the pipette will dispense from a default position 1 mm above the bottom center of that well. To change the default clearance, you would call well_bottom_clearance:

pipette.well_bottom_clearance.dispense=2 # tip is 2 mm above well bottom
pipette.dispense(200, plate["B1"])

You can also dispense from a location along the center vertical axis within a well using the Well.top() and Well.bottom() methods. These methods move the pipette to a specified distance relative to the top or bottom center of a well:

depth = plate["B1"].bottom(z=2) # tip is 2 mm above well bottom
pipette.dispense(200, depth)

See also:

  • Default Positions for information about controlling pipette height for a particular pipette.

  • Position Relative to Labware for formation about controlling pipette height from within a well.

  • Move To for information about moving a pipette to any reachable deck location.

Dispense Flow Rates

Flex and OT-2 pipettes dispense at default flow rates measured in µL/s. Adding a number to the rate parameter multiplies the flow rate by that value. As a best practice, don’t set the flow rate higher than 3x the default. For example, this code causes the pipette to dispense at twice its normal rate:

pipette.dispense(200, plate["B1"], rate=2.0)

New in version 2.0.

Push Out After Dispense

The optional push_out parameter of dispense() helps ensure all liquid leaves the tip. Use push_out for applications that require moving the pipette plunger lower than the default, without performing a full blow out.

For example, this dispense action moves the plunger the equivalent of an additional 5 µL beyond where it would stop if push_out was set to zero or omitted:

pipette.pick_up_tip()
pipette.aspirate(100, plate["A1"])
pipette.dispense(100, plate["B1"], push_out=5)
pipette.drop_tip()

New in version 2.15.

Note

In version 7.0.2 and earlier of the robot software, you could accomplish a similar result by dispensing a volume greater than what was aspirated into the pipette. In version 7.1.0 and later, the API will return an error. Calculate the difference between the two amounts and use that as the value of push_out.

Blow Out

To blow an extra amount of air through the pipette’s tip, call the InstrumentContext.blow_out() method. You can use a specific well in a well plate or reservoir as the blowout location. If no location is specified, the pipette will blowout from its current well position:

pipette.blow_out()

You can also specify a particular well as the blowout location:

pipette.blow_out(plate["B1"])

Many protocols use a trash container for blowing out the pipette. You can specify the pipette’s current trash container as the blowout location by using the InstrumentContext.trash_container property:

pipette.blow_out(pipette.trash_container)

New in version 2.0.

Changed in version 2.16: Added support for TrashBin and WasteChute locations.

Touch Tip

The InstrumentContext.touch_tip() method moves the pipette so the tip touches each wall of a well. A touch tip procedure helps knock off any droplets that might cling to the pipette’s tip. This method includes optional arguments that allow you to control where the tip will touch the inner walls of a well and the touch speed. Calling touch_tip() without arguments causes the pipette to touch the well walls from its current location:

pipette.touch_tip()

Touch Location

These optional location arguments give you control over where the tip will touch the side of a well.

This example demonstrates touching the tip in a specific well:

pipette.touch_tip(plate["B1"])

This example uses an offset to set the touch tip location 2mm below the top of the current well:

pipette.touch_tip(v_offset=-2)

This example moves the pipette 75% of well’s total radius and 2 mm below the top of well:

pipette.touch_tip(plate["B1"],
                  radius=0.75,
                  v_offset=-2)

The touch_tip feature allows the pipette to touch the edges of a well gently instead of crashing into them. It includes the radius argument. When radius=1 the robot moves the centerline of the pipette’s plunger axis to the edge of a well. This means a pipette tip may sometimes touch the well wall too early, causing it to bend inwards. A smaller radius helps avoid premature wall collisions and a lower speed produces gentler motion. Different liquid droplets behave differently, so test out these parameters in a single well before performing a full protocol run.

Warning

Do not set the radius value greater than 1.0. When radius is > 1.0, the robot will forcibly move the pipette tip across a well wall or edge. This type of aggressive movement can damage the pipette tip and the pipette.

Touch Speed

Touch speed controls how fast the pipette moves in mm/s during a touch tip step. The default movement speed is 60 mm/s, the minimum is 1 mm/s, and the maximum is 80 mm/s. Calling touch_tip without any arguments moves a tip at the default speed in the current well:

pipette.touch_tip()

This example specifies a well location and sets the speed to 20 mm/s:

pipette.touch_tip(plate["B1"], speed=20)

This example uses the current well and sets the speed to 80 mm/s:

pipette.touch_tip(speed=80)

New in version 2.0.

Changed in version 2.4: Lowered minimum speed to 1 mm/s.

Mix

The mix() method aspirates and dispenses repeatedly in a single location. It’s designed to mix the contents of a well together using a single command rather than using multiple aspirate() and dispense() calls. This method includes arguments that let you specify the number of times to mix, the volume (in µL) of liquid, and the well that contains the liquid you want to mix.

This example draws 100 µL from the current well and mixes it three times:

pipette.mix(repetitions=3, volume=100)

This example draws 100 µL from well B1 and mixes it three times:

pipette.mix(3, 100, plate["B1"])

This example draws an amount equal to the pipette’s maximum rated volume and mixes it three times:

pipette.mix(repetitions=3)

Note

In API versions 2.2 and earlier, during a mix, the pipette moves up and out of the target well. In API versions 2.3 and later, the pipette does not move while mixing.

New in version 2.0.

Air Gap

The InstrumentContext.air_gap() method tells the pipette to draw in air before or after a liquid. Creating an air gap helps keep liquids from seeping out of a pipette after drawing it from a well. This method includes arguments that give you control over the amount of air to aspirate and the pipette’s height (in mm) above the well. By default, the pipette moves 5 mm above a well before aspirating air. Calling air_gap() with no arguments uses the entire remaining volume in the pipette.

This example aspirates 200 µL of air 5 mm above the current well:

pipette.air_gap(volume=200)

This example aspirates 200 µL of air 20 mm above the the current well:

pipette.air_gap(volume=200, height=20)

This example aspirates enough air to fill the remaining volume in a pipette:

pipette.air_gap()

New in version 2.0.