Lipid Bilayer Phase Transformations Detected Using Microcantilevers

We report the use of microcantilevers to measure the phase transition temperature (T(m)) of supported lipid bilayers or lipid monolayers. During the solid-liquid phase transition, a supported lipid bilayer or monolayer undergoes a conformational change in which the lipid acyl chains transition from an ordered state to a disordered state. This process is accompanied by a free energy change, which is coupled to changes in the surface stress in the underlying solid support layer. These surface stress changes can be readily detected using microcantilevers. The surface stress of the solid-like phase of 1-myristoyl-2-palmitoyl-sn-glycero-3-phosphocholine (MPPC) decreases linearly as the temperature increases and abruptly jumps at the main phase transition temperature. This phase transition temperature corresponds well with that found for free membranes. For an MPPC monolayer, this phase transition temperature is shifted, indicating that the existence of the solid support affects the monolayer structure. The addition of cholesterol into the bilayer decreases the phase transition temperature by ~0.38 °C per mol % of cholesterol. Differences in MPPC stability when it is either a bilayer or a monolayer can be detected through these sensitive surface stress measurements.