In any step involving a pipette you can tell the robot when it should get a new tip. Not every choice is available all the time- they are limited by what type of Transfer you are building.
Here are all the possible options:
- Before every aspirate- The robot will get a new tip after every dispense so each aspirate is done with a fresh tip. This is the most sterile choice.
- Once at the start of step- The robot will get a new tip at the start of the step and then keep the same tip for the rest of the step.
- Per source well- The robot will get a new tip every time it is about to aspirate from a new source well. This prevents cross contamination between source wells.
- Per destination well- The robot will get a new tip every time it is about to dispense into a new destination well. This prevents cross contamination between destination wells.
- Never- Use the same tip your pipette was using for the last step. You cannot use this option if it is the first step. That's because your pipette has no tip on it yet to use.
A combination of your step type, volume, and change tip setting determines what path choices are available. Read more here.