Single molecules as sensors for local molecular adhesion studies

Area of Science:

• Surface Science
• Physical Chemistry
• Materials Science

Background:

• Understanding macromolecule interactions at interfaces is crucial for various applications.
• Characterizing binding forces at the molecular level provides fundamental insights into surface chemistry.

Purpose of the Study:

• To develop and apply an experimental method for measuring single macromolecule interactions at electrolyte/single-crystal interfaces.
• To investigate the desorption forces of poly(acrylic acid) on ZnO surfaces across a range of pH conditions.

Main Methods:

• Single-molecule desorption spectroscopy was employed.
• Experiments were conducted on atomically defined single-crystal ZnO(0001)-Zn surfaces.
• Aqueous electrolytes with varying pH and constant ionic strength were used.

Main Results:

• Poly(acrylic acid) showed weak adsorption (60-80 pN) on terraces and strong binding (up to 700 pN) at step edges, likely via coordinative bonds.
• Distinct force-distance profiles allowed identification of individual binding sites.
• Maximum desorption force was observed at pH 7 due to electrostatic and charge interactions.

Conclusions:

• Single-molecule desorption spectroscopy effectively identifies individual binding sites on surfaces.
• The study elucidates the interplay of electrostatic, van der Waals, and coordinative forces in macromolecule-surface interactions.
• Results provide a detailed understanding of poly(acrylic acid) adsorption behavior on ZnO surfaces.