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Hi all,
I would be interested in any tips and tricks to get PeakForce Tapping working with OBL cantilevers in fluid (buffered saline). Best would be the softer OBL B, but OBL A would also maybe work (my samples are flat super-soft polymers, so no issue with cantilever touching surface).
I was not able to engange with the OBL so far... are there recommended settings that I should use for engange? I'm using Bioscope Catalyst with Nanoscope 8.15
The engange stops immediately again after pressing the engage button. I tried increasing the engange setpoint in "Engage settings" dialogue, but even the max value did not help. I tried different gain and engange gain settings with no success.
Thanks a lot in advance for any help!
Janne
Hi Jane,
Modify the engage setpoint was a good idea. You can also try to increase the engage gain. If this is not enough, you can go into the Microscope---Engage Settings and decrease the SPM engage step (which is 15 um by default).
Also (I guess you already know that) make sure you wait at least 30 min before engaging. OBL probes are among the softest existing ones so you need a lot of time to equilibrate the laser.
If you manage to engage, the levers might be trapped by the viscous drag, since they are really soft. Then you have to play with the PF amplitude to optimize the force curves.
I must say I hardly got good results on live cells using OBLs. I got much better results with MLCTs (newly released ones).
Good luck!
Alex.
Thanks Alex.
Yes I am doing the long equilibration already
I will try to decrease the SPM engage step, that was one parameter that I haven't changed yet.
Do you have any recommended settings for the engage gain? I have only values from experience for contact mode, I have to set them extremely low (0.05 or 0.1), otherwise the cantilever immediately starts to oscillate.
Also why can't you set engage setpoint (in volts) higher than a certain value? That value looks rather arbitrary to me and with the super soft OBL I could go to much higher setpoint without fear of damaging the tip or sample
I am using the OBL not to image cells but soft polymeric films, and in my experience other cantilevers are just too stiff. Although the MLCT could indeed work, I will have to try once I get any.
Janne,
with respect to the engage gain, usually 0.3 (up to 0.4) should be enough. But that's usually for levers of 0.1 N/m (or higher). For very soft levers like OBLs, I would say 0.2.
Regarding your 2nd question, what I would try is:
1) Engage in contact mode or force volume mode.
2) Go to Ramp and update the deflection sensitivity.
3) Withdraw and go to Thermal Tune. Calculate the spring constant.
4) Note the values for defl. sens. and k; and go to the PFT/PFQNM workspace.
5) Enter the values.
Now you should be able to enter a setpoint in pN instead of V (not in the Microscope - Engage setting menu), but at least in the RealTime pannel.
And maybe try the MLCTs too ;-)...
Good luck,