Characterizing Probe Tips for Nanomechanical Mapping

Before a relocation system with a built-in characterizer could be prepared, the potential characterizers had to be characterized themselves. A detailed description is given in ESI (SI-1, step 1).† Briefly, a sharp nitride lever tip (k = 0.12 N m⁻¹, SNL-10, Bruker, USA) was characterized by scanning a titanium roughness sample (RS-12M, Bruker, USA, ESI-Fig. 1a†) in Peak Force Quantitative Nanomechanical Mapping (PFQNM) mode in air with an atomic force microscope (AFM, Dimension Icon, Bruker Corporation, USA) and further used as built-in characterizer for the kaolinite modified probe. The titanium roughness sample allows the characterization of the very end of the AFM tip^{25 (link)} which was needed to precisely define the dilation length of the ∼40 nm thick kaolinite sheets. As a characterizer for the bacterial modified tipless probe, the more elongated Tap150A probe (k = 5 N m⁻¹, Bruker, USA) was characterized by tapping mode using a test grating TGT1 (NT-MDT Spectrum Instruments, USA). The TGT1 characterizes the overall tip shape at a sub-micron scale, which was essential for the morphology imaging of the bacteria in μm scale. We always used the frame down command, i.e., a horizontal fast scan direction. The resultant images were flattened by first order and subjected to blind tip reconstruction analysis using NanoScope Analysis software (version 8.15, Bruker).