Quantification of Molecule-Defect Site Binding Force Via Single‑Molecule Adhesion

The binding strength between reactant molecules and active sites fundamentally governs reaction selectivity and efficiency, as it determines adsorption energy and activation barriers at the molecular level. However, direct quantification of such molecule-site binding forces remains challenging, since conventional spectroscopic and microscopic techniques only provide ensemble-averaged information. Here, we leverage a single-molecule force imaging strategy that enables quantitative mapping of local binding forces with high spatial resolution under realistic liquid conditions. By covalently tethering functional molecules such as dopamine onto an atomic force microscopy tip, we directly measure site-specific interaction forces, revealing markedly stronger adhesion at defective sites on MoS₂ with 218 pN compared to non-defective regions with 120 pN. Correlating these force signatures with catalytic performance allows quantitative linking of local binding strength to reactivity, yielding reactivity maps at the nanometer scale. This approach extends to other catalysts, including TiO₂, providing a broadly applicable route to visualize structure-reactivity relationships at the single-molecule level.