I am trying to image fixed cells in liquids with a Veeco Dimension V AFM in tapping mode. Only with a few exceptions it is rather difficult for me to obtain useful images. The first problem is the handling of the V-shaped cantilevers and the re-adjustment of the laser after moving into the liquid, though I think that's a matter of experience?!
The bigger problem is to adjust the imaging forces for image acquisition. In most of the cases the cantilever runs into the cell, when approaching the surface and I am not sure how to solve this issue.
So my question is, what is the best way to adjust imaging forces before and while measuring the fixed cells? I am thankful for any advice!
Nils,
I'm not sure that this may help but want to share my experience with you. We experienced similar problems wen imaging fixed cells with NSOM (Nanonics) in a tapping mode. We were advised to try several things like using more flatter cells and different fixing solvent. Not much of results still. However, changing a spring constant of a probe as far as I remember made a difference. Note, that we used S-shape cantilever probes based on optical fibers. Good luck to you!
Cheers,
Serge
Hi Nils,
I think what Serge said, that selecting cantilever of suitable spring constant could be helpful. In case of your sample may be you can use probes of smaller spring constant. For selecting minimum forces for imaging If you first increase the set-point parameter to a certain value that the tip is retracted and then slowly decrease set-point again until your tip starts to (sense) the surface again. At this point forces between tip and sample are minimum. From here on-wards you can increase Drive amplitude and change feedback gains values to get better results.
Ishtiaq
Hi you two, thanks a lot for your response! I am using cantilevers with a spring constant of 0.06N/m, I think that should be fine?! I will definitely try to adjust the setpoint and drive amplitude, hope that works. However, before the actual cantilever-engage I cannot adjust thesetpoint, because it is automatically tuned by the device while engaging the surface. Or is there a way to set it fixed before?
Nils,
Try to talk to the manufacturer about ways of adjusting the setpoint. They fixed it for a reason, no doubts about it but you may want to have more flexibility in the control software. Nanonics reps did give us a few useful tips and helped troubleshooting the system. I hope you can get the same type of service from Veeco.
Hi Nils,
First of all you need to readjust the laser after moving into liquid, that is purely experience. After that, you need to find the right resonance frequency. This sounds easy but mostly this is the problem! There might be several peaks due to fluid cell vibrations, the problem was described as "forest of peaks":
http://www.physics.uoguelph.ca/psi/papers/AFM/Schaffer_JApplPhys96.pdf
You could try to use the thermal tune after moving into liquid, it can help you to find the true resonance. As for the beginning, try a high drive amplitude and low setpoint (it will probably damage your cells). Once you have a feeling for stable imaging parameters, try to lower the drive amplitude, increase the setpoint and increase the gains to get the lowest possible interaction force.
Your spring constant is fine! If possible, think about another Imaging mode. Peak force tapping is much easier to handle than standard tapping.
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