Employing radioactivation to track gold nanoparticles in vivo

Gold nanoparticles (AuNPs) are a highly promising tool for cancer treatment, due to their tendency to cluster in tumor cells and their ability to transport several kinds of chemotherapy drugs. However, their inert nature makes visualizing these nanoparticles in vivo challenging because they cannot show up using traditional imaging techniques.

Koshikawa et al. demonstrated a technique to visualize AuNPs in vivo using radioactivation. Their method allows the precise imaging of AuNPs for several days after injection, offering insights into the movement and distribution of nanoparticles within tumors.

To create the activated nanoparticles, the authors irradiated AuNPs with neutrons to create the radioisotope ¹⁹⁸Au. When injected into a subject, the ¹⁹⁸AuNPs could be detected with a wide-band X-ray and gamma ray imager.

“We considered that direct imaging of AuNPs requires altering them to something visible from outside the body without changing their chemical properties,” said author Nanase Koshikawa. “This led to the idea of generating a radioisotope that can be visualized by using their X-rays and gamma rays with high sensitivity but that retains the same chemical properties as the original stable isotope.”

In tests, the team injected these modified nanoparticles into tumor-bearing mice. The AuNPs remained detectable for at least four days after injection, thanks to the particle’s long half-life.

This method could provide researchers with a better understanding of how AuNPs interact with tumors and the bodies of cancer patients.

“Medical application of AuNPs has been actively researched recently, and visualizing in vivo distribution of AuNPs is crucial for many studies,” said Koshikawa. “We believe activation imaging has the potential to advance AuNP-based drug delivery and contribute to more effective cancer treatments in the future.”

Source: “Activation imaging of gold nanoparticles for versatile drug visualization: an in vivo demonstration,” by N. Koshikawa, Y. Kikuchi, K. Tanaka, K. Tokoi, A. Mitsukai, H. Aoto, Y. Kadonaga, A. Toyoshima, H. Kato, K. Ooe, K. Takamiya, and J. Kataoka, Applied Physics Letters (2025). The article can be accessed at https://doi.org/10.1063/5.0251048 .