Opto-Mechanical Coupling in Interfaces under Static and Propagative Conditions and Its Biological Implications

Abstract

Fluorescent dyes are vital for studying static and dynamic patterns and pattern formation in cell biology. Emission properties of the dyes incorporated in a biological interface are known to be sensitive to their local environment. We report that the fluorescence intensity of dye molecules embedded in lipid interfaces is indeed a thermodynamic observable of the system. Opto-mechanical coupling of lipid-dye system was measured as a function of the thermodynamic state of the interface. The corresponding state diagrams quantify the thermodynamic coupling between intensity I and lateral pressure π. We further demonstrate that the coupling is conserved upon varying the temperature T. Notably, the observed opto-mechanical coupling is not limited to equilibrium conditions, but also holds for propagating pressure pulses. The non-equilibrium data show, that fluorescence is especially sensitive to dynamic changes in state such as the LE-LC phase transition. We conclude that variations in the thermodynamic state (here π and T, in general pH, membrane potential V, etc also) of lipid membranes are capable of controlling fluorescence intensity. Therefore, interfacial thermodynamic state diagrams of I should be obtained for a proper interpretation of intensity data.

Propagation of a thermo-mechanical perturbation on a lipid membrane

“…They report a sound velocity of surface waves derived from k s and ρ A as well as the dependence of propagation of pulses with the state of the lipid monolayer. This was also studied by Shrivastava et al [40]: the fluorescence intensity of dye molecules embedded in a lipid interface is sensitive to phase transitions. The same group has recently shown two-dimensional solitary elastic pulses in an air-water interface [28].…”

Solitary shock waves and adiabatic phase transition in lipid interfaces and nerves

“…In particular we extracted the curvature ( 0 ) j of the adiabatic state diagram from solitary waves observed in lipid monolayers and tied it to the observations of excitation threshold, amplitude saturation, and stability of solitary waves (against splitting). Since this is an attempt to apply shock com pression science to soft interfaces, several questions remain open and there are predictions to be tested; For example, our approach predicts the culmination of metastable regimes into a critical point near heat block in nerves [11,45], Furthermore the saturation in amplitude, which in our case originates from crossing over the spinodal condition, should correspond to a similar phase transition in nerve pulse propagation, which remains to be confirmed [46], Another aspect arises from the fact that optomechanical coupling deserves some attention, as the calibration is done for the isothermal case [20], Obviously the interpretation of the experiments in the present work has been intentionally oversimplified, as for a more quantitative description further analysis, both theoretical and experimental, is required. Insights will arise from challenging the quasi-2D nature of the propagation, as the role of thickness of the hydration layer as well as its interaction with the bulk or other interfaces nearby needs to be investigated.…”

“…Thus they provide an excellent platform to study 2D interfacial sound waves, both experim entally and theoretically [5,6]. The optom echanical setup has been described in detail else w here [6,20]. A cantilever excites the m onolayer [containing the lipids (D PPC ), the donor (N B D -PE), and acceptor dye m olecules (Texas Red-D H PE) (100:1:1)] longitudinally w ith a piezo-controlled deflection producing 2D sound waves.…”

Nonlinear fractional waves at elastic interfaces

“…This maximal compression is in the experiments measured by the locally resolved fluorescence of pressure sensitive dyes that are incorporated into the monolayer [63], as will be further explained below. The other important observable is the wave speed, defined by…”