Wednesday, August 22, 2012

Robot Updates

As part of ongoing attempts to get the system to work to our liking we run into two problem.

First, many of the steps in our yeast growth protocols use individual pipetting actions for each well. For this reason we have an arm with individual pipettes. Initially we configured the arm with four fixed tips and four disposable pipettes. The fixed tips are easier to use and do not consume plasticware. On the other hand to get perfect sterility we need to use plastic tips.

So far we learned that the fixed tips (with a wash between uses) is sufficiently clean for our purposes. And so we use these a lot. The problem is that the time it takes to "process" a plate (e.g., remove individually tailored amounts per well for growth dependent dilutions) was too long. The main time consuming steps is the tip washing. 

After consultation with Neotec people, we decided to switch two of the disposable pipette heads with fixed tips. This will give us more tips and thus less washes (as the washes are done in parallel and take the same amount of time for 4 or for 6 tips).

Six fixed tips in action
The second problem is much more serious - the robotic manipulation arm kept getting out of alignment. This lead to serious of failure in our longer experiments. The blame fell onto the plate shaker, which we use a lot in our protocol. The design of the shaker has to allow a robotic arm to place/remove a plate, but at the same time hold the plate firmly during the shaking. The solution in the shaker we had was a spring that held the plate in place. Every time the arm came down to the shaker it would press on a lever and release the plate from the spring. Apparently these repeated presses moved the arm out of place (not by much but sufficiently to cause problems)

The solution was to replace the shaker head to one with a different locking mechanism based on a higher stand that kept the plate sitting down. This required adaptation of a solution Tecan built for arms that hold the plate from above (and not from the side like ours).

New shaker head
So far it seems that the system is indeed more stable. It worked for two days without issues and we are counting.


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