Local Enhancement of lipid membrane permeability induced by irradiated gold nanoparticles

TL;DR

This study uses molecular dynamics simulations to analyze how gold nanoparticles, when irradiated, locally increase membrane permeability by creating temperature gradients that induce transient structural changes.

Contribution

It provides a quantitative prediction of temperature gradients and membrane permeability changes at the nanoscale during photothermal nanoparticle irradiation.

Findings

Water permeability increases locally around nanoparticles.

Temperature inhomogeneities cause free volume pockets in membranes.

Permeability enhancement is confined to a few nanometers from the nanoparticle.

Abstract

Photothermal therapies are based on the optical excitation of plasmonic nanoparticles in the biological environment. The effects of the irradiation on the biological medium depend critically on the heat transfer process at the nanoparticle interface, on the temperature reached by the tissues as well as on the spatial extent of temperature gradients. Unfortunately, both the temperature and its biological effects are difficult to be probed experimentally at the molecular scale. Here, we approach this problem using nonequilibrium molecular dynamics simulations. We focus on photoporation, a photothermal application based on the irradiation of gold nanoparticles by single, short-duration laser pulses. The nanoparticles, stably bound to cell membranes, convert the radiation into heat, inducing transient changes of membrane permeability. We make a quantitative prediction of the temperature gradient around the nanoparticle upon irradiation by typical experimental laser fluences. Water permeability is locally enhanced around the NP, in an annular region that extends only a few nm far from the nanoparticle interface. We correlate the local enhancement of permeability at the NP-lipid interface to the temperature inhomogeneities of the membrane and to the consequent availability of free volume pockets within the membrane core.