Direct measurements of particle-surface interactions in aqueous solutions with total internal reflection microscopy

Non-covalent intermolecular forces, such as van der Waals, electrostatic, steric, and hydrophobic interactions, have played essential roles in determining the association, aggregation, adhesion and sedimentation processes of colloidal particles, surfactant micelles, and macromolecules, in solutions and biological systems. These interaction forces, however, are normally weak (<pN) and are challenging and difficult to be directly measured by common force techniques. In this feature article, we discuss recent advances in the development of the non-intrusive optical technique of Total Internal Reflection Microscopy (TIRM) for studying the interactions between a single colloidal particle and a flat surface. We begin with a brief overview of quantitative measurements of particle-surface interactions in aqueous solutions, and then show recent developments associated with TIRM for measuring kT-scale interactions between a single particle and surface in the presence of polymer chains, micelles, and colloidal particles with different softness based on our recent work. We also highlight how TIRM can be used to measure particle-surface interactions after the particle and the flat surface are physically adsorbed or grafted with polyelectrolytes, as well as to investigate the non-specific and specific interactions between proteins and protein-carbohydrate in biological systems. Lastly, we conclude with some perspectives on future research efforts in this field.