A "Shell" Is Developed to Protect the Shape of Gold Nanoparticles

Gold nanoparticles, which are about one-thousandth the width of a human hair, can convert light they receive from a laser into heat. This capacity, known in medicine as photothermal therapy, is effective at destroying cancer cells without harming the surrounding healthy tissue. It's one of the techniques the scientific community is exploring in depth as an alternative chemotherapy, as it is less aggressive.

However, the very superpower they use to attack tumors - heat - is also their own kryptonite, as it ends up deforming the gold nanoparticles and, in turn, weakening their effectiveness. Specifically, these nanoparticles have a very distinct shape and outline, resembling two pyramids connected at their bases. When exposed to heat, the pyramids gradually round out and lose their shape, making it difficult for them to direct heat precisely a specific area. A laboratory experiment conducted by an international team comprised of members from the Universities of Córdoba, Strasbourg, and the Sorbonne, has identified a new formula to stabilize gold nanoparticles, which allows them to retain their shape longer, thereby prolonging their effectiveness.

The key was to target the outermost layer (or plasmon) of these nanoparticles, where the laser light is absorbed, and add a new molecule to it, like a protective shell. Among the various molecules the team used, a polymer proved to be most effective at stabilizing the nanoparticle. As UCO researcher Irene López Sicilia explains, "It's a long-chain polymer that provides excellent protection for the nanoparticle, and it positions itself on specific parts of it, offering better protection than other molecules."

The polymer has performed better than a more biocompatible molecule, like sodium citrate, which is derived from citric acid and found in lemons and oranges, for example. While this acid isn't harmful to humans, it does affect the morphology of nanoparticles. "In our study, we found that a biocompatible molecule like sodium citrate isn't the best alternative for these nanoparticles; instead, a polymer that doesn't have biological properties as good as citrate is," says López Sicilia.

They observed this by using a technique called liquid cell transmission electron microscopy, made possible through collaboration with a team in Strasbourg. This technique allows them to see in real time what is happening during irradiation and how the nanoparticle's morphology changes. The study, which stemmed from López Sicilia's predoctoral research during a mobility grant from the University of Córdoba, has been published in the journal Advanced Functional Materials. Other contributors include Valentina Girelli Consolaro, Sophie Marbach, Nancy Rahbany, Grégoire Petit, Ovidiu Ersen, Juan J. Giner Casares, and Ali Abou-Hassan. The goal is to understand how these particles work and to control their function during medical therapies that use heat, such as those being studied to treat cancer.

Read the original article on University of Córdoba.