Find Your Control: A Technical Note

Feel the love…

At Solus, we love our DS2 robots. We think they are a fantastic everyday ‘workhorse’ that makes testing hundreds of samples daily so much easier. Along with our Solus Salmonella ELISA™ and Solus Listeria ELISA™ kits and protocols, the Solus Pathogen Testing system can be a blessing for busy food testing laboratories. However, occasionally a human eye needs to investigate the little hiccups that can occur, such as when the DS2 loses control. More precisely, the positive control.

Visualise the problem…

Following reports that assays were failing due to a low positive control value, we started investigating the possible causes of this problem. We also put some procedures into place to try to help in the meantime.

Firstly, a black dye introduced into our positive control bottles now makes it is easy to tell which is the positive and which is the negative control.

We also introduced a step into our protocol on the DS2 to “look” for the positive control in the allotted well at the beginning of the run before pipetting out the samples. With this check in place, an alarm sounds if the robot fails to detect the positive control in the well. If the alarm sounds, then the technician can inspect the plate and manually add positive control before continuing the run.

Find your control…

But there was still the question; why was DS2 failing to pipette the positive control? After all, the other reagents and samples were being pipetted correctly, why did this one keep failing?

It took a little bit of investigating but we eventually realised it was a bubble issue. Not bubbles on the surface of the liquid. No, this problem is caused by a “film” forming across the rim of the tube as the lid is removed. It’s not always easy to spot this as, with a casual glance, the tube looks normal and ready for use.

Reveal the answer’s…

We’ve written up a technical note about this issue so if you have been experiencing occasional positive control pipetting failures you can see what the issue is and how you can deal with it.

If you have any further questions on this or any other issue then please contact us and we’ll do our best to help.


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