On measuring the acoustic state changes in lipid membranes using fluorescent probes

TL;DR

This study investigates how ultrasound influences lipid membrane properties by measuring solvation shell fluctuations with a fluorescent probe, revealing potential mechanisms for acoustic modulation of membrane functions.

Contribution

It introduces a fluorescence-based method to monitor real-time membrane state changes under acoustic impulses, linking mechanical effects to biological membrane dynamics.

Findings

Acoustic impulses induce measurable changes in membrane solvation shell fluctuations.

Membrane state changes correlate with sound wave compression and rarefaction.

Results suggest ultrasound can modulate membrane protein and channel activity.

Abstract

Ultrasound is increasingly being used to modulate the properties of biological membranes for applications in drug delivery and neuromodulation. While various studies have investigated the mechanical aspect of the interaction such as acoustic absorption and membrane deformation, it is not clear how these effects transduce into biological functions, for example, changes in the permeability or the enzymatic activity of the membrane. A critical aspect of the activity of an enzyme is the thermal fluctuations of its solvation or hydration shell. Thermal fluctuations are also known to be directly related to membrane permeability. Here solvation shell changes of lipid membranes subject to an acoustic impulse were investigated using a fluorescence probe, Laurdan. Laurdan was embedded in multi-lamellar lipid vesicles in water, which were exposed to broadband pressure impulses of the order of 1MPa peak amplitude and 10{\mu}s pulse duration. An instrument was developed to monitor changes in the emission spectrum of the dye at two wavelengths with sub-microsecond temporal resolution. The experiments show that changes in the emission spectrum, and hence the fluctuations of the solvation shell, are related to the changes in the thermodynamic state of the membrane and correlated with the compression and rarefaction of the incident sound wave. The results suggest that acoustic fields affect the state of a lipid membrane and therefore can potentially modulate the kinetics of channels and proteins embedded in the membrane.