Application of Fuzzy Logic Algorithm to Single-Molecule Force Spectroscopy of the Streptavidin-Biotin System

The rupture force of the streptavidin-biotin complex was investigated using atomic force microscopy (AFM). The most frequently observed rupture force (MFOF), which is essential for the evaluation of the potential landscape, was evaluated by processing 22,500 force curves using two methods. One method is a conventional method, which is usually built in commercial AFM systems, i.e., difference between the baseline value and the minimum force value in the force curve. The other is a detection of rupture events based on a fuzzy logic algorithm to detect the rupture event from analyzing the shape of the force curves. Our statistical analysis revealed that the conventional method exhibited a significant artifact, which is the increase in the population of small forces comparable to thermal noise of cantilevers, resulting in a smaller MFOF. Based on this finding, we discuss the choice of a method and its effecton the illustrated potential landscapes of ligand-receptor complexes.