GOLD: VERSACE TO THE LAST ATOM

The first thing a scientist must learn when working in nanotechnology is that scale isn’t neutral: materials change their properties dramatically as they shift from macroscopic to microscopic. One of the most striking illustrations of this behavior is gold.

Gold has a striking color-changing ability, a phenomenon known as surfaceplasmon resonance: the electrons on the surface of gold nano particles vibrate and absorb specific frequencies of visible light. The chameleonic beauty of gold changes with scale, revealing more unexpected facets the deeper we look.

"The color of the material changes depending on the size and shape of the constituent particles, despite the substance itself remaining the same."

Laura Tripaldi, Ph.D. Materials Science and Nanotechnology

Gold nanoparticles, in fact, are even more surprising when you observe them through a microscope. Regular microscopes use visible light and optical lenses to enlarge microscopic objects. Gold nanoparticles, however, are so small that a typical microscope is unable to resolve them. Even smaller than the wavelength of visible light, these particles can only be seen with an electron microscope: a much more advanced technology that uses an electron beam capable of revealing objects as small as atoms.

When visualized with electron microscopy, gold nanoparticles disclose another secret. Their shapes are surprisingly regular, with uniform size and perfectly geometrical appearance. They spontaneously arrange themselves in beautiful regular patterns, as if they were tiles in an ancient mosaic.

Scientists’ interest in gold nanoparticles does not stop at their aesthetic beauty. Today, gold nanoparticles play a foundational role in the most advanced biomedical technologies. You may not know that the pink lines that show up in pregnancy tests or COVID-19 self-tests are in fact the result of gold nanoparticles, whose surfaces were precisely engineered to attach to specific biochemical compounds in your own body.

In the future, gold nanoparticles may even be used to fight cancer in a treatment known as “photodynamic therapy”. When irradiated, gold nanoparticles heat up, killing the surrounding tumor cells.

The ever-evolving allure of gold unfolds beckoning us to peer deeper, and remind us that beneath the surface often lies a world of hidden beauty and profound significance.