Specific interactions between biotin and avidin studied by atomic force microscopy using the Poisson statistical analysis method

The interactions between biotin and avidin or streptavidin, a prototypical example of a specific biological ligand-receptor system, were studied by at omic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ti me-of-flight secondary ion mass spectrometry (TOF-SIMS). Although this and other ligand-receptor systems have been studied by several techniques, incl uding AFM, in this paper, a statistical analysis method which makes use of the properties of the Poisson distribution was applied, and the rupture str ength of an individual interaction was obtained from the total adhesion for ces measured by the AFM. Tip- and surface-modification chemistries were inv estigated by XPS and TOF-SIMS. The magnitudes of the interactions between b iotin-avidin and biotin-streptavidin pairs, as determined by the Poisson me thod, were found to be 173 +/- 19 and 326 +/- 33 pN, respectively, for load ing rates between 2 x 10(5) and 8 x 10(5) pN s(-1). These values are compar able to the values reported by other groups for the same systems. The stati stical method used in this work has several advantages. It requires no assu mptions about the surface energies or contact area between the AFM tip and the substrate, it is not limited by the force resolution of the instrument, and the number of measurements required to extract the individual unbindin g force is significantly lower than that required by other methods.