Abstract
Phase transitions in purple membrane have been a topic of debate for the past two decades. In
this work we present studies of a reversible transition of purple membrane in the 50–60 ◦C
range in zeptoliter volumes under different heating regimes (global heating and local heating).
The temperature of the reversible phase transition is 52 ± 5 ◦C for both local and global heating,
supporting the hypothesis that this transition is mainly due to a structural rearrangement of bR
molecules and trimers. To achieve high resolution measurements of temperature-dependent
phase transitions, a new scanning probe microscopy-based method was developed. We believe
that our new technique can be extended to other biological systems and can contribute to the
understanding of inhomogeneous phase transitions in complex systems.
