Temperature‐Controlled High‐Speed AFM: Real‐Time Observation of Ripple Phase Transitions

Abstract

With nanometer lateral and Angstrom vertical resolution, atomic force microscopy (AFM) has contributed unique data improving the understanding of lipid bilayers. Lipid bilayers are found in several different temperature-dependent states, termed phases; the main phases are solid and fluid phases. The transition temperature between solid and fluid phases is lipid composition specific. Under certain conditions some lipid bilayers adopt a so-called ripple phase, a structure where solid and fluid phase domains alternate with constant periodicity. Because of its narrow regime of existence and heterogeneity ripple phase and its transition dynamics remain poorly understood. Here, a temperature control device to high-speed atomic force microscopy (HS-AFM) to observe dynamics of phase transition from ripple phase to fluid phase reversibly in real time is developed and integrated. Based on HS-AFM imaging, the phase transition processes from ripple phase to fluid phase and from ripple phase to metastable ripple phase to fluid phase could be reversibly, phenomenologically, and quantitatively studied. The results here show phase transition hysteresis in fast cooling and heating processes, while both melting and condensation occur at 24.15 °C in quasi-steady state situation. A second metastable ripple phase with larger periodicity is formed at the ripple phase to fluid phase transition when the buffer contains Ca . The presented temperature-controlled HS-AFM is a new unique experimental system to observe dynamics of temperature-sensitive processes at the nanoscopic level.

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

“…It allows for obtaining relevant information about the structural and physical changes of the membrane occurring during the phospholipid phase transitions [9,53,66,67]. Recently, insights on the dynamics of the DMPC (1,2-dimyristoyl- sn -glycero-3-phosphocholine, 14:0 PC; T m = 24 °C) transition from ripple phase to fluid phase reversibly in real time by HS-AFM have also been reported [68]. A second type of ripple phase with larger periodicity has been identified when heating DMPC SLBs from the ripple phase to the fluid phase.…”

Biological physics by high-speed atomic force microscopy

“…HS-AFM coupled to a temperature-controlled system reported directly ripple to fluid phase transitions (reversibly) in real time and at high resolution [59]. When the fluid bilayer was cooling down, ripples appeared as concentric rings progressing from the edge region of the lipid patch towards the centre upon cooling.…”

Recent development of high‐speed atomic force microscopy in molecular biology

“…Under certain conditions, certain lipid bilayer structures employ a so-called ripple phase, a structure in which the solid phase and the liquid phase alternate at a constant period. Takahashi et al [45] developed a temperature control device for HS-AFM that is capable of observing the reversible phase transition of the ripple phase to the liquid phase in real time. The experiment results demonstrate that the phase transition hysteresis is obvious during the fast cooling and rapid heating process, while in the quasi-steady state, both melting and condensation occur at 24.15°C.…”