Direct Force Measurements between Sub-Micron Rod-Shaped Colloids by AFM

Titelangaben

Sittl, Sebastian ; Das, Mohan ; Helfricht, Nicolas ; Petekidis, George ; Papastavrou, Georg:
Direct Force Measurements between Sub-Micron Rod-Shaped Colloids by AFM.
In: Colloids and Surfaces A: Physicochemical and Engineering Aspects. Bd. 697 (2024) . - 134319.
ISSN 0927-7757
DOI: https://doi.org/10.1016/j.colsurfa.2024.134319

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Abstract

The colloidal probe (CP) technique is an essential tool for quantitative direct force measurements by atomic force microscopy (AFM). By attaching a colloidal particle to the free end of an AFM-cantilever, not only a defined interaction geometry can be accomplished, but also a nearly arbitrary surface chemistry becomes possible. Commonly, the CP-technique is utilized for spherical particles in the sphere/sphere or sphere/plane interaction geometry. Here, the CP-technique has been extended to rod-shaped colloids with diameters well below one micrometer, thus preparing ‘rod probes’ based on a procedure similar to that known from DNA combing, allowing for a controlled alignment between these rods and the rod probe. In combination with AFM-imaging by the rod on the probe, sufficiently orthogonally aligned pairs of rods can be identified, and direct force measurements in the crossed-cylinder geometry, similar to the surface force apparatus (SFA), can be accomplished. A proof-of-concept of direct force measurements between silica rods with diameters of 270 ± 50 nm has been presented. The acquired interaction force profiles have been quantitatively evaluated within the framework of the full solutions of the Poisson-Boltzmann equation, including charge regulation.