Do people use multichannel pippette as a single channel by using only the outer channel?

Opentrons
1

I was listening to this opentrons webinar: https://www.youtube.com/watch?v=IgrYYL1I-X0
and the author claimed that he uses the outer channel of an 8-channel pipette for concentration normalisation (while 7 other channels simply dont pick up a tip). I wanted to ask if this a well-known trick in the community. If so is there even a point in buying an 8 channel. And finally has this been formalised in the opentrons API somehow?

2

Yes this is definitely a well known trick, I even have used an 8 channel to just pick up 2, 3, or 4 tips as well. It all depends on your requirements. The trick isnā€™t formalized in the API though. Opentrons does have a help article on it here however

As for your question, I assume you meant

ā€œis there even a point in buying a single channel p300ā€.

Well, yes there is. For one if you try this trick and try to pipette a 24 wellplate in slot 1, youā€™ll have a bad time because the multichannel will be out of bounds, and that error doesnā€™t always show up in simulation, but when you run it (as youā€™re likely picking up tips with channel A). Granted I find a lot less usage out of p300 singles rather than p1000s or p20s, so Iā€™d say the p300 single is the least useful of the bunch (in my experience).

2 Likes
3

Im following the help article you attached and getting this error:

AttributeError [line 33]: ā€˜NoneTypeā€™ object has no attribute ā€˜update_config_itemā€™

Iā€™m confused ā€“ hereā€™s the line thatā€™s causing the error, which Iā€™m lifting pretty much straight from the example:

protocol._hw_manager.hardware._attached_instruments[types.Mount.RIGHT].update_config_item('pick_up_current', pick_up_current)

Any idea what could be the issue here?

1 Like
4

This part of our API is being updated, and the hardware manager used in this code has changed. I can make it a point to try to update this article, but if this method is mission-critical for you, you might want to consider downgrading.

5

OK, understood. Any advice on which version to downgrade to?

6

6.3.1 should be the software version that works with that sample protocol. Instructions for downgrade.

7

You may find this function works, which is one we use

def pick_up_1_tip(self, pip, tiprack):
# using multi-pipette as single:
# initialize starting tiprack setup, for reference later when you try returning tips
starting_setup = self.update_tip_tracker(tiprack)

    pip_channel = "A"

    if tiprack.load_name != "opentrons_96_tiprack_300ul":
        self.logger.add_warning(
            "user",
            "othelp.pick_up_1_tip() ERROR >> This only work with opentrons_96_tiprack_300ul. Your tiprack is {}".format(
                tiprack.load_name
            ),
        )

    next_tip = tiprack.next_tip()
    next_tip_name = next_tip.well_name
    next_tip_letter = next_tip_name[0]
    # print(next_tip_name)
    skipped = []
    tip_selected = False

    # confirm dictionary per row letter
    confirm_dict = {
        "A": {
            "B": False,
            "C": False,
            "D": False,
            "E": False,
            "F": False,
            "G": False,
            "H": False,
        },
        "B": {
            "C": False,
            "D": False,
            "E": False,
            "F": False,
            "G": False,
            "H": False,
        },
        "C": {"D": False, "E": False, "F": False, "G": False, "H": False},
        "D": {"E": False, "F": False, "G": False, "H": False},
        "E": {"F": False, "G": False, "H": False},
        "F": {"G": False, "H": False},
        "G": {"H": False},
        "H": {},
    }

    while tip_selected is False:  # skips anything not in accepted tip list
        # print("checking tip {}".format(next_tip_name))
        column_number = next_tip_name[1:]
        tips_to_confirm = confirm_dict[next_tip_letter]  # check against confirmation list (from above)

        checklist = {}
        for c_tip in tips_to_confirm.keys():
            checklist[c_tip] = tiprack.well(c_tip + column_number).has_tip
        # print(checklist)

        # if tip setup matches tips to confirm, take next_tip
        if checklist == tips_to_confirm:
            tip_selected = True
        else:
            skipped.append(next_tip_name)
            tiprack.use_tips(next_tip)
            next_tip = tiprack.next_tip()
            # print(next_tip)

            next_tip_name = next_tip.well_name
            next_tip_letter = next_tip_name[0]

    

    pip.pick_up_tip(tiprack.well(next_tip_name))


    # return tips that were not actually picked up
    column_number = next_tip_name[1:]

    for name in skipped:
        if starting_setup[name] is True:  # only return if it wasnt there at the start of this function
            tiprack.return_tips(tiprack.well(name))

Itā€™s a bit different from the help article so you may get around the version error youā€™re encountering

8

As far as I can tell this doesnā€™t adjust the pick up current? Which I think works OK for the p300 but not for the p20. Thatā€™s the bit that isnā€™t working in the example code.

Thank you!

9

Oh sorry, I havenā€™t used it for a p20, my bad. I mustā€™ve missed that in your post.

Have you considered just hardcoding the movements? Telling the pipette to move to a specific spot with specific force? Bit of a pain but sometimes you gotta do what you gotta do. You can change the pipetteā€™s movement speed by:

pip.default_speed = 50

and change it back to default by calling

pip.default_speed = None