Representative force-indentation curves from AFM and sketches of the tip geometry.

<p>(A) The dotted and solid lines represent distinct traces of the approach of the AFM tip, as measured from samples with different physical properties. Initially, the AFM tip was located at the designed position over the sample. As the AFM tip start to approach the sample, there was no interaction force (<i>Part I</i>). After the AFM tip contacted with the sample at the contact point (shown by black arrow), further indentation generates the indentation depth. Constant force generates a greater indentation depth on the softer cell (<i>Part III</i>) than on the stiffer cell (<i>Part II</i>). (B) Tips with three different geometries were used in this study.