Optical Sciences

Biomolecules and nanostructures

The Optical Sciences group studies the interaction of light and matter. Our current focus is on detection and sensing/imaging with an emphasis on the development of integrated photonics. We are part of Twente University's Department of Science and Technology and member of the MESA+ institute.


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

Willemsen OH, Snel MME, Kuipers L, Figdor CG, Greve J, De Grooth BG
vol 76 issue 2: p716-p724 FEB 1999

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 tow 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 I (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.
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