Visualization of Ion|Surface Binding and In Situ Evaluation of Surface Interaction Free Energies via Competitive Adsorption Isotherms

Abstract

Function and properties at biologic as well as technological interfaces are controlled by a complex and concerted competition of specific and unspecific binding with ions and water in the electrolyte. It is not possible to date to directly estimate by experiment the interfacial binding energies of involved species in a consistent approach, thus limiting our understanding of how interactions in complex (physiologic) media are moderated. Here, we employ a model system utilizing polymers with end grafted amines interacting with a negatively charged mica surface. We measure interaction forces as a function of the molecule density and ion concentration in NaCl solutions. The measured adhesion decreases by about 90%, from 0.01 to 1 M electrolyte concentration. We further demonstrate by molecular resolution imaging how ions increasingly populate the binding surface at elevated concentrations, and are effectively competing with the functional group for a binding site. We demonstrate that a competing Langmuir isotherm model can describe this concentration-dependent competition. Further, based on this model we can quantitatively estimate ion binding energies, as well as binding energy relationships at a complex solid|liquid interface. Our approach enables the extraction of thermodynamic interaction energies and kinetic parameters of ionic species during monolayer level interactions at a solid|liquid interface, which to-date is impossible with other techniques.

Visual Detection of Stem-Loop Primer Amplification (SPA) Products without Denaturation Using Peroxidase-like DNA Machines (PxDM)

“…The main drawback of isothermal amplification, and especially LAMP and SPA, is their susceptibility to false positive signals. The existing technologies such as turbidity [30] or ion detection [31] cannot visualize non-specific dsDNA amplicons, while the hybridization probes prevent miscomprehension positive results.…”

Resolving the intrinsic short-range ordering of K+ ions on cleaved muscovite mica

“…Yet, the intrinsic K + distribution at the surface -unaffected by the interaction with the environment -is unknown due to the absence of UHV direct imaging. AFM images of the mica surface have been obtained in air or solution 15,[24][25][26][29][30][31][32][33][34] , showing the cation hydration structures in these environments. However, these arrangements do not necessarily correspond to the intrinsic ones.…”