Long-Range Electrostatic Trapping of Single-Protein Molecules at a Liquid-Solid Interface
Xiao-Hong Nancy Xu,
*
Edward S. Yeung
The motion of single, dye-labeled protein molecules was monitored
at various pH and ionic strengths within the 180-nanometer-thick evanescent-field layer at a fused-silica surface. Below the isoelectric point, molecules partitioning into the excitation region increased in
number but maintained a random spatial distribution, implying that
surface charge can influence the charged protein at distances beyond
that of the electrical double-layer thickness. The residence times of
the molecules in the interfacial layer also increased below the
isoelectric point. However, immobilization on the solid surface for
extended periods was not observed. Histograms of residence times
exhibit nearly identical asymmetry as the corresponding elution peaks
in capillary electrophoresis. These results are a direct verification
of the statistical theory of chromatography at the single-molecule
level, with the caveat that long-range trapping rather than adsorption
is the dominant mechanism.
Ames Laboratory-U.S. Department of Energy and Department of
Chemistry, Iowa State University, Ames, IA 50011, USA.
*
Present address: Department of Chemistry and Biochemistry, Old
Dominion University, Norfolk, VA 23529, USA.
To whom correspondence should be addressed. E-mail:
yeung{at}ameslab.gov
