Gold Twinkling “Nanostars” and the Promise of New Imaging Modality

By using specially designed gold nanoparticles (“nanostars”) that can be spun around and made to gyrate via a magnetic field, Purdue University scientists are developing a new imaging method that can help to differentiate various tissues from each other. The gyration, which can be affected by the local environment, can already be detected on a single particle level.

The nanostars gyrate when exposed to a rotating magnetic field and can scatter light to produce a pulsating or “twinkling” effect. This twinkling allows them to stand out more clearly from noisy backgrounds like those found in biological tissue.
The gold nanostars are about 100 nanometers from tip to tip and contain an iron-oxide core that causes them to spin when exposed to a rotating magnet. The arms of the nanostar are designed to respond to a light source and reflect light to a camera when properly aligned. This gives nanostars the appearance of twinkling at rates that can be precisely controlled by the speed of the rotating magnetic field. The unique signature of the twinkling nanostars enables them to be picked out easily from a field of stationary particles, some of which can be brighter than the nanostars.
Any signal that doesn’t have the frequency corresponding to the rotating magnetic field can be suppressed in the images, eliminating background noise, Ritchie [Kenneth Ritchie, Purdue associate professor of physics] said.
“It was surprising how well this method enhanced the imaging,” he said. “It can improve the contrast of the particles to the background noise by more than 20 decibels and can clearly reveal a gyrating nanostar, where with existing direct imaging methods in many cases you wouldn’t be able to definitively find a particle.”
Gold nanostars and other gold nanoparticles have recently been examined as contrast agents for biomedical imaging because of their brightness at near-infrared wavelengths, which can penetrate through tissue better than visible light. However, giving them the ability to twinkle was key to developing a novel dynamic imaging method, Wei [Alexander Wei, a professor of chemistry] said.

Full story at Purdue: Twinkling nanostars cast new light into biomedical imaging…