A physical approach to reduce nonspecific adhesion in molecular recognition atomic force microscopy

Biophys J. 1999 Feb;76(2):716-24. doi: 10.1016/S0006-3495(99)77238-3.

Abstract

Atomic force microscopy is one of the few techniques that allow analysis of biological recognition processes at the single-molecule level. A major limitation of this approach is the nonspecific interaction between the force sensor and substrate. We have modeled the nonspecific interaction by looking at the interaction potential between a conical Si3N4 tip with a spherical end face and a mica surface in solution, using DLVO (Derjaguin, Landau, Verwey, Overbeek) theory and numerical calculations. Insertion of the tip-sample potential in a simulation of an approach-retract cycle of the cantilever gives the well-known force-distance curve. Simulating a force-distance curve at low salt concentration predicts a discrete hopping of the tip, caused by thermal fluctuations. This hopping behavior was observed experimentally and gave rise to a novel approach to making measurements in adhesion mode that essentially works in the repulsive regime. The distance between tip and sample will still be small enough to allow spacer-involved specific interactions, and the percentage of nonspecific interactions of the bare tip with the mica is minimized. We have validated this physical model by imaging intercellular adhesion molecule 1 (ICAM-1) antigen with a tip functionalized with anti-ICAM-1 antibody. The measurement demonstrated that a significant decrease in the number of nonspecific interactions was realized, and the topographical image quality and the specific bonding capability of the tip were not affected.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Aluminum Silicates / metabolism
  • Antibodies / immunology
  • Antibodies / metabolism
  • Computers
  • Intercellular Adhesion Molecule-1 / chemistry*
  • Microscopy, Atomic Force / instrumentation
  • Microscopy, Atomic Force / methods*
  • Protein Binding
  • Static Electricity

Substances

  • Aluminum Silicates
  • Antibodies
  • Intercellular Adhesion Molecule-1
  • mica