Can someone suggest a suitable AFM probe and their spring constant range for soft hydrogels ? I would like to have force vs indentation depth (displacement) curves for my samples.
You can start by trying a ScanAsyst-Air (Bruker) or equivalent. It has a nominal spring constant of 0.4 N/m and provides a good lateral resolution if you need it. It's a standard tip used for nanomechanics in soft polymers, elastomers and even biological applications.
Another option is th qp-CONT (0.1N/m) or qp-SCONT (0.01N/m). With the qp-SCONT we stably worked with force triggers at 200pN and measure elasticities below 1kPa. Nice thing about the probes is that the elasticity deviates less than 10% of the nominal value: The value by the manufacturer might even more accurate than that of a calibration. If you don't need lateral resolution, but better modelling, they are also available with colloidal tips.
Thank you so much Patrick Frederix. I am also trying to convert the force curves to stress-strain curves. I am unable to catch up with the physical parameters involved in converting the force curve.