Single-molecule adsorption at nanometer indentations

The temporal behavior of bursts from single molecules reveals whether adsorbates are diffusing at chemical interfaces or are specifically adsorbed. The chemical interface of water/C-18-monolayer on silica is studied. Burst data for single molecules of DiI show that regions of the surface having more nanoindentations are associated with a greater number of specific adsorption events. Lysozyme is shown to adsorb irreversibly, and an oligonucelotide (24-mer) is shown to adsorb reversibly but more strongly than DiI to nanoindentations at this interface. For each adsorbate, the specific adsorption at the nanoindentations is attributed to hydrogen bonding to exposed silanols.