The team, led by Catherine Murphy, also found that normal, healthy cells either slow down or speed up depending on the type of the nanoparticle they have vacuumed up, but that cancer cells always slow down.

In their experiments, the Illinois researchers placed live prostate carcinoma (PC3) and non-cancerous human dermal fibroblast (HDF) cells on a substrate and then added gold nanoparticles to the liquid placed above the cells. After the particles had settled, they imaged the cells using a simple technique called dark-field microscopy (which can pick up light scattered by the nanoparticles).

“The particles look like faint little stars on a black background, but the cells themselves are difficult to see initially because they are not stained with any dyes,” explained Murphy. “However, over time, the cells become brighter and brighter as they take up the nanoparticles and leave behind dark trails where the particles once were. Certain cells are ‘full’ of nanoparticles, while their nuclei remain ‘empty’ – appearing as a large black hole in the centre of each cell.”

Different speeds

Dark-field images were taken at five-minute intervals for at least eight hours. The cells were still alive at this time. By analysing movies of these experiments, Murphy and colleagues observed that the non-cancerous and cancerous cells moved at different speeds. The non-cancerous cells also appeared to slow down overall after taking up gold nanorods, but appeared to speed up after taking up gold nanospheres.

Biological cells take up nanoparticles from their surroundings. A number of cellular processes are involved in this phenomenon, says Murphy, and while many of the particles remain on the surface of the cells, many others end up inside the cells.

“In future experiments, we would like to figure out the exact mechanisms behind the nanoparticle uptake. As far as we know, this is the first time that anyone has done experiments such as these – most previous research has looked at the toxicity of gold particles, and did not measure nanoparticle uptake in real time or monitor cellular speeds.”

Anti-cancer treatment?

According to the team, the fact that nanoparticles influence cellular behaviour is important and might one day be used to exploit cellular function. “For example, cancer cells could be made to slow down thanks to nanoparticle uptake, so that they do not metastasize,” Murphy told

“Current treatments to remove tumours involve cutting out a huge amount of healthy issue at the same time to reduce cancer metastasis,” added team member Jie An Yang. “Being able to control cancer-cell function with nanoparticles may be a way of avoiding this and reducing the probability of patient relapse.”

The team is now busy looking into how generally applicable its results are. “We have thus far only tried two types of cell (HDF and PCF) and a few types of gold nanoparticles (including gold nanospheres and long gold nanorods),” added Murphy.

The current work is detailed in Nano Letters.