This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.106.093328v1 92/6/1966    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Yang, Y. Articles by Hafner, J. H. Search for Related Content PubMed PubMed Citation Articles by Yang, Y. Articles by Hafner, J. H.

Quantitative Membrane Electrostatics with the Atomic Force Microscope

Yi Yang ^*, Kathryn M. Mayer ^* and Jason H. Hafner ^* 

^* Department of Physics & Astronomy, and Department of Chemistry, Rice University, Houston, Texas

Correspondence: Address reprint requests to J. Hafner, Tel.: 713-348-3205; E-mail: hafner{at}rice.edu.

The atomic force microscope (AFM) is sensitive to electric double layer interactions in electrolyte solutions, but provides only a qualitative view of interfacial electrostatics. We have fully characterized silicon nitride probe tips and other experimental parameters to allow a quantitative electrostatic analysis by AFM, and we have tested the validity of a simple analytical force expression through numerical simulations. As a test sample, we have measured the effective surface charge density of supported zwitterionic dioleoylphosphatidylcholine membranes with a variable fraction of anionic dioleoylphosphatidylserine. The resulting surface charge density and surface potential values are in quantitative agreement with those predicted by the Gouy-Chapman-Stern model of membrane charge regulation, but only when the numerical analysis is employed. In addition, we demonstrate that the AFM can detect double layer forces at a separation of several screening lengths, and that the probe only perturbs the membrane surface potential by <2%. Finally, we demonstrate 50-nm resolution electrostatic mapping on heterogeneous model membranes with the AFM. This novel combination of capabilities demonstrates that the AFM is a unique and powerful probe of membrane electrostatics.