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Tipless probes calibration

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BenSD posted on Wed, Oct 10 2012 10:44 AM

Hello,

 

I would like to determin the overall elasticity of single cell using tipless cantilever (without attaching the cell to the cantilever). Is it possible to calibrate a tipless cantilever especially the deflexion sensitivity? Does anyone already tried that? Any advice?

Thank you,

Benoit.

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Top 10 Contributor
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Suggested by Joop de Vries

Sure, this is possible. The only real issue is that the high adhesion between a tipless cantilever and a clean, hard surface can make it difficult to measure a good force curve for deflection sensitivity calibration.

I addressed this issue in air for some work I published several years back (B. Ohler, Rev. Sci. Instrum. 78, 063701, 2007). I used the TGT1 calibration sample from NT-MDT. The sample is just a grid of closely spaced sharp points. It reduces the adhesion by limiting the contact area.

If you calibrate in liquid, you might find that the adhesion is manageable on a normal, clean glass substrate (not a substrate with cells on it). I don't think I've ever tried that with a tipless cantilever.

-Ben

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as a complement to Ben's answer, it depends a little bit on the AFM you have. On a Dimension with ~6 um z-range it is difficult to do it on a clean surface, on the Catalyst with a z-range of ~25 um this is not a problem any more. 

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BenSD replied on Thu, Oct 11 2012 11:29 AM

OK thank you, I will give it a try!

Benoit.

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A method we have used involves mounting a cantilever/chip with the tip facing upwards. You can then bring the tipless cantilever into feedback with the upturned tip and do your sensitivity measurements. You need to choose the bottom tip so that its cantilever has a spring constant much greater than the tipless cantilever spring constant, say 100 times greater. That essentially makes it rigid and all the deflection will be in the tipless lever. Tapping mode in air probes from most companies will do the job (k>50 N/m) but some companies sell cantilevers with k >= 200 N/m. You can also reverse AFM image the end of the tipless lever to ensure you are pressing very close to the end of the tipless cantilever. If your tipless lever is too stiff compared to the bottom cantilever then error can creep in. Hope this helps.

 

Chris G.   

 

 

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