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I have a question about PF-QNM for measuring modulus in cells and tissues. I am noticing that the data obtained in the DMTModulus channel is either very noisy/streaky or is completely flat at exactly 1/2 the value of the set DMT Modulus Limit. I usually lower this limit to about 20MPa (usually the software sets its between 400-500MPa), because I'm looking at very soft biological samples that should have moduli in the <100 kPa range. I also get some percentage of negative modulus values in these scans.
I've noticed my best modulus results with somewhat softer tips (k between 0.06 and 0.12N/m) and lower peak force setpoints (<1nN).
Any recommendations on how to improve the quality of data?
I think you get negative values either because the deflection sensitivity is not correct (too high, like more than 50 nm/V) or because the elasticity and deformation are not properly calibrated. For super soft samples (<500 kPa), we don't yet offer a standard calibration sample. Personally when I work on cells, I calibrate the probe on gelatin or agarose samples. We are currently working on an application note on that specific topic. It should be released middle of this year. For more details, you can contact me directly:
alexandre.berquand@bruker-nano.com
Alex.
I have further comments on this:
I found the for most of eukaryotic cells, the commercial gelatin (~100 kPa) can be a good calibration sample. If your cells are really soft (<10 kPa) I found 2 papers describing how to prepare gelatin- or agarose-based calibration sample allowing you to calibrate down to 1 kPa. If you are interested, please give me your email address and I will forward you those papers.