Photonic Force Microscopy: A New Tool Providing New Methods to Study Membranes at the Molecular Level

Author :Arnd Pralle, Ernst-Ludwig Florin, Ernst H.K. Stelzer and J. K. Heinrich Hörber
Publication :Single Molecules
Volume :2
Pages :129-133
Year :2000

The PFM is a three-dimensional scanning probe microscope
based on optical tweezers. It evolved from AFM techniques
by replacing the mechanical cantilever of the AFM with
optical tweezers and the cantilever tip by a trapped bead.
Various detection systems measure the three-dimensional
position of the bead with a spatial and temporal resolution
in the nanometer and microsecond range, respectively. Due
to the small trapping force constants, thermal position
fluctuations of the probe are relatively large in comparison
to the thermal motion of an AFM cantilever. However, these
position fluctuations provide information about the local
environment and specific interactions of the probe with
molecules such as membrane proteins.
Within the few last years, the instrument turned out to
be a powerful tool to study properties of the plasma
membrane of intact cells at the nanometer scale. For
instance, the diffusion of membrane components could be
observed over minutes at high spatial and temporal
resolutions. For the first time, the diffusion coefficient
measured locally in the plasma membrane of an intact cell
agreed well with previous measurements for lipid model
membranes, thus providing new ways to characterize
membrane structures with unknown properties, such as lipid
rafts. Furthermore, the technique can be used to determine
the elasticity of the lipid bilayer and the binding properties
of membrane components to the cytoskeleton.