Event Information
Solid Surface Modification for Force Spectroscopy Measurements of Interactions at Single-Molecule Level
- Abstract:
Applying force spectroscopy in chemistry research requires modification to the technique. This dissertation work considers and implements changes to force spectroscopy methodology, improving its ability to characterize interactions between individual molecules in aqueous solution.
For measurements of intermolecular interactions by force spectroscopy, molecules and their counterparts have to be immobilized at the end of AFM tips and on the surface of opposing substrates. Chemical grafting is selected as the immobilization strategy. To facilitate the detection and analysis of target rupture events, double tether approach is adopted in our force spectroscopy studies. Detailed protocols employed in our measurements are provided. By these protocols, several interactions have been successfully characterized, including catechol–catechol mediated by Fe(III), C60 fullerene–C60 fullerene, and hexadecane–hexadecane in aqueous solution.
Common force spectroscopy data analysis uses simplified model of the potential of mean force to extract kinetic parameters pertinent to interaction energy landscape. However, the data analysis introduced in this work does not make typical simplifying assumptions. The results show that the standard data analysis may lead to significant systematic errors in estimating kinetic parameters. Also, force spectroscopy measurements of samples with various surface grafting densities indicate that multiple bond ruptures may occur during one rupture event and thus interfere with the detection of single-molecule interactions. An analytical model for the probability density of simultaneous rupture of two bonds in force spectroscopy experiments is proposed and applied in the data analysis. It is suggested that the observed effects of multiple bonds rupture may be a common feature of force spectroscopy experiments and therefore should be considered to reduce the systematic errors in extracted kinetic parameters.
The work presented here establishes an experimental approach to determine kinetic parameters of non-covalent bonds in aqueous solution and provides molecular level insights into hydrophobic interactions.
Ph.D. Defense Examination Seminar
Student Exams Seminar