Blow out on STAR backend

General
1

Trying to use the blow out backend argument for dispense because there is still a small drop of liquid on the end of the tips after the dispense.

await lh.dispense(dpw["A2:H2"], vols=[7.5]*8, blow_out=[True]*8)

It looks like it registers the argument but nothing happens on the robot. Does anyone use blow_out or any combination of blow out, blow_out_volume, jet, etc on STAR?

2

confusingly, blow_out needs to be set to True AND you need to specify blow_out_air_volume (I should rename to `blow_out_air_volumes plural because it’s a list :thinking: )

blow_out is the dispense mode on the STAR, and blow_out_air_volume is an lh-parameter (meaning it’s shared across robots)

3

Ah got it. What are the limitations for each tip/does it track the air as part of the volume? Like if I aspirate 50uL with 1mL tips, can I blow out 20uL or will that not work because it exceeds the max tip volume?

4

it uses the same plunger and tip of course, so you’re constrained by that. For transport air volume, there’s a limit of 50uL, but for blowout air there’s no such limit.

not sure if i follow the example, 50uL + 20uL < 1mL?

5

Sorry, meant 50uL tips, not 1mL tips, but I get the picture there.

I tried again with blow_out_air_volume and it still didn’t do anything different. Is there an additional command to check to see if it’s actually doing the blow out?

6

Have you added the desired blowout air volume also to the aspirate command preceding your dispense command?

1 Like
7

Ah no - so it needs blow_out_air_volume and blow_out for both aspirate and dispense?

8

As far as I understand it, yes. The reasoning I’ve pieced together (behind STAR firmware, not PLR, so it would be good to test and maybe get a Hamiltonian to check correctness):

Any air displacement technology-based pipette moves a plunger inside it to create suction/negative pressure for aspiration.
Hamilton STAR channels fall in this category.

When you give an aspirate or dispense command a volume parameter it moves the plunger by that volume up or down, respectively.
I.e. you are not stating in the command how much liquid you intend to aspirate or dispense. (To convert plunger movement volume to liquid volume you’d need to give the command a “LiquidClass”, i.e. a bag of parameters + a volume correction factor).

But, if you haven’t told the channel how much air you want to have above your liquid inside the tip (i.e. how much the plunger should have moved up just before aspirate), then it has no air volume to blowout during dispense.

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9

I’m hoping to find some time in the next couple of months to generate an animation that visually explains the internal workings of air displacement pipettes in general (similar in style to the Plate definition video) because I haven’t actually seen any explainer videos on this even though it’s the foundation of accurate liquid transfers across different liquid handlers :slight_smile:

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10

Update for this thread. I am not 100% sure which thing worked but this is what I ended up doing:

await lh.aspirate(vols=vols... blow_out_air_volume=[10]*len(vols), blow_out=[True]*len(vols))
await lh.dispense(vols=vols,...  blow_out_air_volume=[10]*len(vols), blow_out=[True]*len(vols), empty=[True]*len(vols), jet=[True]*len(vols))

I used both jet and empty from the STAR backend, along with blow_out_air_volume and blow_out parameters. This worked well for me to do a tip emptying transfer for any tip size (tested with 50uL, 300uL, and 1mL tips) of volumes >= 5uL.

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11

sharing updates for posterity is based, thank you mister harley